%VATEH FOLLUriON CONTROL RESEARCH SERIES ♦ 18050 ELD05/72 BIOTA OF FRESHWATER ECOSYSTEMS HentJlic&tioa Manual 17 1 FRESHWATER (ASELLIDAE) OF NORTH U.S. ENVIROIM^^mi PROXKCTION AGENCY i 1^ ' m • _□ MBL/WHO Hi n- □- CD □ CD ==^ m a CD WOODS HOLE OCEAMOGl-RAPK'O IMCTITUTION WOODS HOLE, MASSACHUStiiS 02543 ^ i\S Biota of Freshwater Ecosystems Identification Manual No. 7 FRESHWATER ISOPODS (ASELLIDAE) OF NORTH AMERICA _ MARINE BiOl-CGlCAL LABORATORY LIBRARY by i~~ ■ — 1 vVGQOS HOLE, fMSS. | W. D. Williams f V^. H. 0. L \ Department of Zoology, Monash University ' Clayton, Victoria 3168 Australia for the ENVIRONMENTAL PROTECTION AGENCY Project # 18050 ELD Contract # 14-12-894 May 1972 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 ■ Price $2.50 Stock Number 5501-0390 EPA Review Notice This report has been reviewed by the Environ- mental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the EPA, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. WATER POLLUTION CONTROL RESEARCH SERIES The Water Pollution Control Research Series describes the results and progress in the control and abatement of pollution in our Nation's waters. They provide a central source of information on the research, development, and demonstration activities in the water research program of the Environmental Protection Agency, through inhouse research and grants and contracts vjith Federal, State, and local agencies, research institutions, and industrial organizations. Inquiries pertaining to Water Pollution Control Research Reports should be directed to the Chief, Publications Branch (Water), Research Information Division, RSM, Environmental Protection Agency, Washington, DC 20460. 11 FOREWORD "Freshwater Isopods (Asellidae) of North America" is the seventh of a series of identification manuals for selected taxa of invertebrates occurring in freshwater systems. These documents, prepared by the Oceanography and Limnology Program, Smithsonian Institution for the Environmental Protection Agency will contribute toward improving the quality of the data upon which environmental decisions are based. Additional manuals will include but not necessarily be lim- ited to, freshwater representatives of the following groups: amphipod crustaceans (Gammaridae) , branchiuran crustaceans (^Argulus) , decapod crayfish crustaceans (Astacidae) , leeches (Hirudinea) , polychaete worms (Polychaeta) , freshwater plan- arians (Turbellaria) , aquatic dryopoid beetles (Dryopoidea) and freshwater clams (Sphaeriacea) . XIX ABSTRACT A key is given to the North American genera {Asellus and Liroeus) of asellid isopods. Another key is provided for the surface- living species of Asellus but lack of clear, published morphological distinctions in the genus Liroeus prevents the construction of a key for that genus. Notes on ecology, collection, preservation and identification are also included. CONTENTS Section Page I Introduction 1 Collecting and Preservation 3 Identification 4 II Species List and Distribution 13 III Key to Genera of North American Freshwater Asellidae 17 IV Key to North American Surface-living Species of Asellus 19 V References 43 VI Index of Scientific Names 45 Vll FIGURES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 Dorsal view of male Aseltus communis and Lirceus sp. Anterior head appendages of A. communis Posterior head appendages of A. communis Peraeopod 1 oi A. communis Peraeopods 2-7 of A. communis Pleopods 1 and 2 of i4. communis Pleopods 3-5, uropod and telson of A. communis Dorsal view of head of Lirceus sp. and Aseltus sp. Pleopod 3 of Lirceus sp. and Aseltus sp. of A. of A. occidentatis A. occidentatis taticccudatus taticaudatus communis intermedins racovitzai racovitzai A. racovitzai racovitzai Various appendages of A Endopod of pleopod 2 of Various appendages of A Endopod of pleopod 2 Endopod of pleopod 2 Various appendages of A Endopod of pleopod 2 of ^4. intermedins Various appendages of A. attenuatus Various appendages of A Endopod of pleopod 2 of Pleopod 1 of A. racovitzai racovitzai Various appendages of A. racovitzai australis Endopod of pleopod 2 of A. racovitzai australis Various appendages of A. forbesi Endopod of pleopod 2 of A. forbesi Endopod of pleopod 2 of ^. forbesi Peraeopod 1 of i4. obtusus Various appendages of A. obtusus Endopod of pleopod 2 of A. obtusus Various appendages of A. montanus Various appendages of A. nodulus Various appendages of A. dentadaotytns Various appendages of A. brevicauda brevicauda Pleopod 2 of A. brevicauda brevicauda Various appendages of A. scrupntosus Endopod of pleopod 2 of i4. scrupulosus Various appendages of A. kenki Page 4 5 6 7 8 9 10 17 17 18 20 21 22 22 23 24 25 26 27 28 29 30 31 32 32 32 33 34 35 36 38 39 40 41 41 42 vxii TABLES Page 1 Differences between Asellus racovitzai raoovitzai and A. raoovitzai australis 28 2 Differences between Asellus forbesi and A. obtusus 34 3 Differences between Asellus breviaauda brevioauda and A. brevioauda bivittatus 40 XX SECTION I INTRODUCTION The Asellidae are the most important surface- living freshwater isopods in North America. The other isopod families which occur in North Ameri- ca, Bopyridae, Sphaeromatidae (formerly Sphaeromidae) , and Cirolanidae, are much less important. The Bopyridae are parasitic forms, and the Cirolanidae are spring or underground forms occurring in Mexico, areas immediately to its north, and Virginia. The Sphaeromatidae, otherwise a predominantly marine family, includes several species found in fresh to brackish waters near the coast and in hot springs. Sphaeromatids and cirolanids are easily recognised by their uropods which are attached anterolaterally to the abdomen, and not, as in asellids, posteriorly or posterolaterally. None of these additional isopod families, all of whose representatives are only rarely or occasionally encountered in sur- face fresh waters of North America, is considered further in this publi- cation. The North American fauna of the Asellidae is not well-known, but Williams (1970) has revised the systematics of the surface- living species of AselluSj the principal genus, and the ecology of some asellids of known identity has also been studied recently (e.g. Ellis, 1961, 1971; Clifford, 1966; Styron, 1968; Seidenberg, 1969). For the purposes of this report. North American asellids are considered to be represented by two genera, Liraeus and Aseltus. Other generic names that have been applied include Asellopsis ^ Mancaseltus , and Caeoidotea. All species of these are now regarded as either species of Liraeus {=Asettopsis ^ Manaasellus) or Aseltus (= Caeoidotea) . It has re- cently been proposed (Henry and Magniez, 1968, 1970) that North American Aseltus species be divided between the genera Conaseltus^ Aseltus (of restricted definition) , and Pseudobaioalasetlus . Of these, the first two represent the elevation of former 'subgenera' to generic rank, and the latter a newly proposed genus. It may well be that North American asellids will prove to be a group that should legitimately be regarded as representing several genera, but as the proposals of Henry and Magniez were published before adequate taxonomic consideration had been given surface-living species of North American asellids, and before systematic knowledge of surface-living and underground species has been integrated, such proposals seem decidedly premature to the present author. In order not to perpetuate at generic level the sort of confusion that has exis- ted in part at 'subgeneric' level in North American asellids {see Williams, 1970, p. 2), the most practical procedure for the moment is to regard all North American species as referable to two genera only, Aseltus as defined by Birstein (1951, p. 51), and Liraeus. The former contains both surface-living and underground species; species of the latter typically live in surface waters only. Livoeus was revised taxonomically by Hubricht and Mackin (1949) who in- cluded a key, but the revision is not entirely satisfactory in that con- siderable emphasis was placed upon a number of apparently diagnostic characters which in fact are subject to great variation and intergrada- tion between species (Styron, 1969). The genus, according to Hubricht and Mackin (1949) , lacks the sort of singular characters provided for Asellus by the structure of the male sexual pleopods (see below) , and species recognition is based upon the evaluation of many characters. In the interests of providing some useful indications of the ecological and geographical distributions of Liraeus species as described, a summary of relevant data, abstracted mainly from Hubricht and Mackin (1949) , has been compiled and is given following the similar summary for Asellus com- piled from Williams (1970) (see Species List and Distribution below), but no attempt is made to provide a key for their identification here. The ecological status of Asellus in North America is not clear. In most of Europe, Asellus (as A. aquaticus L.) is characteristically present within given sections of organically polluted rivers. Kolkwitz and Mar- sson (1909) noted that it is one of the organisms abundant in the so- called a -mesosaprobic polluted zone in particular but also occurs in the 3-mesosaprobic zone (the 'a- and 3-mesosaprobic zone' proposed by Kolkwitz and Marsson (1909) may be regarded as roughly equivalent to the 'recovery zone' of several American water pollution biologists), and Hynes (1960) noted that Asellus is a member (with tubificids and chiron- omids) of the 'pollution fauna' in the badly polluted zone of rivers affected by organic wastes. Many investigators of North American pollu- ted rivers make no reference to the genus in published accounts of results, whereas others do indicate its occurrence in organically polluted rivers; Bartsch (1948) and Bartsch and Ingram (1959), for example, indicated that it is characteristic of the 'zone of recovery'. In part, some of this ecological uncertainty may be a reflection of the formerly unclear syste- matic position of surface- living forms. Because this key to Asellus has been prepared for use by biologists con- cerned with investigating pollution of inland waters, only surface- living forms are discussed. Neither this key nor the more detailed account of Williams (1970) should be regarded as definitive; undoubtedly much re- mains to be discovered concerning the systematics of North American asel- lids. It is felt, nevertheless, that the key does deal with those species that are most likely to be encountered. North American species alone are considered, i.e. species occurring in the United States and Canada. Asellids are known from Mexico (Cole and Minckley, 1968), but are not considered here. COLLECTING AND PRESERVATION A variety of methods may be used to collect specimens for qualitative purposes. None requires elaborate apparatus or an involved technique; freshwater asellids are easily-seen, macroscopic animals that are rela- tively slow-moving, do not swim, and dwell amongst submerged vegetation and bottom detritus. They are not conspicuous burrowers, although they may often occur on the undersurfaces of submerged stones. The most straightforward method is the direct removal by the investiga- tor of small amounts of submerged vegetation or bottom material either by hand or using a fine-meshed (scrim) dipnet or pondnet followed by the searching of this material for specimens. If asellids occur they may be handled by gripping the middle of their body with a pair of blunt forceps held at right-angles to the long axis of the body. Searching may be facilitated by placing the vegetation or other material to be examined into a white, shallow dish or tray containing water to a depth of about one inch. A tray normally used by the author measures 8 x 10 x 3 inches. If the material is slightly teased apart after being placed in the tray and is then undisturbed for a minute or so, specimens often become con- spicuous by their slow movements amongst the material or by their move- ment from the material towards clear areas of water in the tray. Such specimens may also be removed by forceps, but a better, less damaging method is to suck them gently with some water into a glass tube (diameter about 3/8 inch) in which suction is maintained by a rubber bulb attached to one end. A little practice on the part of the operator is required with this tube method of handling specimens for satisfactory performance. Asellids may also often be collected by removal of submerged stones and the examination of their lower surfaces. Specimens are best killed and preserved by directly placing them in 70- 80% ethyl alcohol. Transference to fresh alcohol after a few days is re- commended. Care should be exercised to ensure that crowding of preserved specimens does not occur, and that tubes are adequately labelled. The maintenance of live specimens is not required for species identification. It should be stressed that reasonably large collections are necessary for adequate systematic examination since species identification (for both Asellus and Lirceus) is based on adult males only, and more than one species may occur in the same collection. Liraeus and Asellus may also occur together. It is suggested that 25 specimens be regarded as the min- imal adequate number for one collection, although, of course, smaller collections will often be useful also. IDENTIFICATION For generic separation of Liraeus and Asellus and for species identifica- tion of Asellus it will be necessary in using this publication to be familiar with the conformation of and the terminology applied to at least certain parts of the external structure of asellids. For confirmation of species identity by reference to the original description or to a complete description given elsewhere, a similar familiarity will be required with regard to most of the remaining body parts. Before discussing the actual technique of specimen examination, it is appropriate therefore to describe briefly the morphology of a typical species. Asellus aommunis has been selected for this purpose. Fig. 1. A, dorsal view of male Asellus communis; B, dorsal view of male Liraeus sp. Drawn from preserved specimens. Original, a. = abdomen, h.=head, t.= thorax. There are three major body regions, the head, thorax, and abdomen (Fig. 1) The head and abdomen appear unsegmented, whereas the thorax is divided into seven segments. Each region bears a number of appendages projecting either anteriorly, posteriorly, ventrally or laterally. r— r— . * I r^i-^ ^ I i \ l\ ll ,11 It Fig. 2. A. communis: A, first antenna; B, second antenna; C, upper lip; D, lower lip. From Williams (1970). Anteriorly, the head bears a pair of short antennae (first antennae or antennules) and a pair of much longer ones (second antennae or, simply, antennae) (Fig. 2A, B) . Ventrally the head bears a mouth which has an upper (or anterior) lip or flap and a bilobed, lower (or posterior) lip (Fig. 2C, D) . Posterior to the mouth is a paired series of small appendages used in feeding; from front to back these are respectively the mandibles, first maxillae (or maxillules) , second maxillae (or, simply, maxillae), and maxillipeds (Fig. 3A-F) . In addition the head has a pair of small eyes; these occur dorsal ly, one on each side (Figs lA, 8B). Each segment of the thorax is dorsoventrally flattened and bears lat- erally a leg or peraeopod (pereiopod or pereopod) ; in all there are seven pairs (Fig. lA) . There are some differences in structure between each pair of legs, but these are not great, and only the structure of the first pair of legs of adult males is distinctly different in that the two most distal leg segments are expanded to form a claw-like appa- ratus (Figs 4A,B; 5A-F) . The palm of this usually bears near its mid- point a prominent triangular projection and proximally a few tooth-like setae (Fig. 4A) . Each leg consists of six apparent segments, termed respectively the dactylus, propodus, carpus, merus, ischium and basis of which the dactylus is the most distal. A seventh leg segment, the Fig. 3. A. communis: A, left mandible; B, right mandible; C, first maxilla; D, distal margin of outer plate of first maxilla; E, second maxilla (dorsal surface); F, maxilliped. From Williams (1970). Fig. 4. A. oomrmmis: A, dactylus and palm of first peraeopod; B, first peraeopod. From Williams (1970). coxa, is not distinct from the thorax. Dorsally, the thorax is covered by a tergal plate, which in the second to seventh segments is expanded to a small lobe at each anterolateral angle. Breeding females bear ventral ly a series of flaps, oostegites, which arise from near the in- side of the base of the anterior legs and form a brood-pouch or marsu- pium. In non-breeding females, their place is taken by small, club- shaped structures. In males, a pair of tube-like penes arise from the posterior, ventral margin of the last thoracic segment; the penes pro- ject backwards. The abdomen is conspicuously dorsoventrally flattened. In males, five pairs of pleopods are borne ventrally, of which the anterior two pairs are small and serve a sexual function (Fig. 6A, B) . The remaining pleo- pod pairs (3-5, Fig. 7A-C) are large, plate-like, and serve a respira- tory function; each of these pleopods consists of a larger, more robust and variously setose lower plate (exopod) , and a smaller, fragile, non- setose upper (or inner) plate (endopod) . In females, only four pairs of pleopods occur (the true first pair are always absent) of which the most anterior pair consists of small and simple triangular plates, whilst the remaining three pairs are similar to those in males. Of greatest importance in the identification of Asellus species is the structure of the first and second male pleopods, and of critical impor- tance is the conformation and shape of the tip of the endopod of the second pleopod; especially marked variation between species is dis- played in the structure of the endopod tip. It is for this reason that these appendages are discussed further below firstly for A. aommunis in particular, and secondly, with respect to the conformation of the tip of the endopod of the second pleopod alone, for all North American species of Asellus in general. Fig. 5. A. communis, peraeopods: A, second; B, third; C, fourth; D, fifth; E, sixth; F, seventh. From Williams (1970). The first pleopod of the male (Fig. 6A) consists of two segments, a basal sympod and a distal segment. The second pleopod (Fig. 6B) consists of a large sympod bearing distal ly a two-segmented exopod (outermost structure) and an unsegmented endopod (innermost structure) (Fig. 6C) . The endopod has two laterally projecting lobes basal ly, inner and outer apophyses. From near the distal tip of the endopod (Fig. 6D, E) projects a tube-like cannula, whilst the distal edge of the endopod itself gives rise to a rounded lobe, the caudal process. This conformation of endopod tip is unique to A. oommunis. It, and that for other North American species of Fig. 6. A. oommunis: A, first pleopod; B, second pleopod; C, dorsal surface of endopod of second pleopod; D,E, respectively dorsal and ventral surfaces of tip of endopod of second pleopod. (After Williams, 1970). can.=cannula, c.p.=caudal process, v.g.=ventral groove. Fig. 7. A. aommunis: A, third pleopod; B, fourth pleopod; C, fifth pleopod; D, uropod; E, uropod and telson. From Williams (1970). 10 Asellus, appears to be derivable from a structure consisting in principle of a terminal ventral groove associated with which are four terminal ele- ments: a mesial process arising from the medial edge of the ventral groove; a cannula, essentially a tubular prolongation of the ventral groove; a lateral process arising from the lateral edge of the groove; and a terminal caudal process. Loss or modification '^^ these elements, it has been suggested, can produce the conformation unique for each species of Asellus. A final pair of abdominal appendages project backwards from the posterior border of the abdomen; these appendages are the uropods. Each (Fig. 7D) consists of a basal segment, the peduncle, and two distal segments or rami, an inner one, the endopod, and an outer one, the exopod. The upper sur- face of the region referred to here as the abdomen in effect constitutes the telson, also referred to as the pleotelson (Fig. 7E) . EXAMINATION TECHNIQUE. A stereoscopic and a compound microscope, a pair of fine forceps, a mounted needle, a petri-dish (or similar container) and microscope slides and coverslips are equipment needed for species identifi- cation. Preliminary examination and dissection should be made using the stereoscopic microscope with the specimens immersed in 70-80% ethyl alcohol and illuminated by reflected light against a dark background. Further identification is carried out by removing appropriate appendages or body parts, mounting these on a microscope slide in a small amount of the alco- hol from which they were withdrawn, and examining by transmitted or re- flected light as appropriate. Such preparations are temporary; more per- manent ones may be made using one of several mounting reagents now com- mercially available which do not require passage of specimen material through a series of other reagents. The author uses "Euparol" (George Gurr Ltd., U.K.). Readers are warned, however, that many such mounting reagents also include clearing agents and if their action is too severe distortion and contraction of mounted material (particularly of the endopod tip of the second pleopod of male Asellus specimens) may occur. It is important that this does not happen. Readers are also warned that endopod tips of the second pleopod of male Asellus specimens should be viewed in a variety of positions so that a better appreciation of the arrangement of terminal parts is gained. 11 SECTION II SPECIES LIST AND DISTRIBUTION It is stressed that our knowledge of species distributions is still in- complete so that the notes below on this subject are to be regarded as summaries of known distributions not actual distributions. Genus Asellus Asellus attenuatus Richardson, 1900. Known only from one locality. Dismal Swamp, Virginia (see Richardson, 1901). Asellus hvevioauda breviaauda Forbes, 1876. Springs and spring-fed streams in large but relatively restricted area of east-central United States: Arkansas, Illinois, Kentucky, Missouri. Asellus hvevioauda bivittatus Walker, 1961. Known only from one locality. Doe Run, a spring- fed creek in Kentucky. Asellus aommunis Say, 1818. Creeks, rivers, ponds, lakes, reser- voirs, occasionally in swamps. Not present in the Great Lakes. Mainly distributed in northeastern United States and south- eastern Canada, but has also been recorded from Colorado and Washington, Complete list of States and Provinces: Colorado, Maine, Maryland, Massachusetts, New Jersey, Pennsylvania, Vermont, Washington, West Virginia; Nova Scotia, Ontario. Asellus dentadaotylus Mackin and Hubricht, 1938. Small creeks in Arkansas and Louisiana. Asellus forbesi Williams, 1970. Typically in temporary ponds, flood pools, and sloughs, but also in marshes, small creeks, and occasionally lakes. Has been collected from Lake Huron at a depth of 15 meters. Distributed over very large area of east- central United States and in southern Ontario. Complete list of States and Provinces: District of Columbia, Indiana, Iowa, Kentucky, Maryland, Michigan, Missouri, North Carolina, Ohio, South Carolina, Virginia, West Virginia, Ontario. Asellus intermedius Forbes, 1876. Typically in running waters (creeks, streams and rivers), but also in springs, ditches, ponds, lakes. Large area of east-central United States and southern Ontario: Illinois, Indiana, Iowa, Kentucky, Michigan, Missouri, Wisconsin; Ontario. Asellus kenki Bowman, 1967. Springs and spring-fed creeks (not in large streams and ponds) in small area near Washington, D. C: District of Columbia, Maryland, Pennsylvania, Virginia. Asellus latiaaudatus Williams, 1970. Small creeks and ponds in south- eastern United States: Kentucky, Louisiana. Asellus montanus Mackin and Hubricht, 1938. Creeks, streams, sloughs in Arkansas and Oklahoma. Asellus nodulus Williams, 1970. Swamps, roadside ditches, streams, and spring outlets in Maryland. 13 Asellus obtusus Williams, 1970. Swamps, roadside ditches, temporary ponds, rivers, small streams in small region of southeastern United States: Florida, Georgia, Louisiana. Asellus ooaidentalis Williams, 1970. Spring-brooks, streams, rivers, marshy edges of lakes in far northwestern United States and extreme southwestern Canada: Oregon, Washington; British Columbia. Asellus racovitzai vaaovitzai Williams, 1970. Creeks, rivers, ponds, swamps, small lakes, and great Lakes down to 42 meters. Mainly dis- tributed in northeastern United States and southeastern Canada, but has also been recorded from Washington. Complete list of States and Procinces: District of Columbia, Indiana, Maryland, Massachusetts, Michigan, Vermont, Washington; Ontario, Quebec. It is the dominant Great Lakes species except for Lake Michigan from where it is still unrecorded {see Racovitza, 1920) Asellus racovitzai australis Williams, 1970. Creeks and rivers in south- eastern United States: Florida, Georgia. Asellus scruipulosus Williams, 1970. Vernal and woodland pools in West Vir- ginia. Genus Liraeus Liroeus aldbccmae Hubricht and Mackin, 1949. Seeps and springs in Alabama, Liroeus biauspidatus Hubricht and Mackin, 1949. Springs, seeps, creeks, and streams in Arkansas. Liroeus bidentatus Hubricht and Mackin, 1949. Known only from a seep in Arkansas. Liroeus braohyuvus (Harger, 1876). Springs and small streams of Atlan- tic drainage from northeastern Pennsylvania to northern Virginia: Pennsylvania, Virginia. Liroeus fontinalis Rafinesque, 1820. Typically in springs but also in drain outlets, seeps and streams: Georgia, Illinois, Indiana, Ken- tucky, Ohio, Tennessee. Liroeus garmani Hubricht and Mackin, 1949. Springs, seeps, creeks, streams (sometimes temporary) and ponds (also sometimes temporary) in Arkansas, Kansas, Missouri, Oklahoma. Liroeus hargeri Hubricht and Mackin, 1949. Springs in Tennessee and Virginia. Liroeus hoppinae hoppinae (Faxon, 1889) . Springs in Missouri {see Carman, 1889). Liroeus hoppinae ozarkensis Hubricht and Mackin, 1949. Springs and sometimes streams in Missouri and northern Arkansas. Liroeus hoppinae ouaohitaensis (Mackin and Hubricht, 1938). River tri- butaries in Oklahoma. Liroeus lineatus (Say, 1818). Rivers, creeks, sloughs, swamps, lakes including Great Lakes. Distributed in Great Lakes region and southeastern United States from Virginia to Florida and Alabama. Complete list of States and Provinces: Alabama, Florida, Georgia, Illinois, Indiana, Michigan, New York, South Carolina, Tennessee, Virginia; Ontario. 14 Livoeus louis ianae (Mackin and Hubricht, 1938). Spring-fed marshes, temporary pools, sloughs, roadside ditches, small streams, seeps: Arkansas, Illinois, Louisiana, Missouri. Liraeus megapodus Hubricht and Mackin, 1949. Springs in Missouri. Lirceus riahavdsonae Hubricht and Mackin, 1949. Known only from a drain outlet in Ohio. Lirceus trilobus Hubricht and Mackin, 1949. Knovm only from woodland pools in Oklahoma. 15 SECTION III KEY TO GENERA OF NORTH AMERICAN FRESHWATER ASELLIDAE Lateral margin of head produced to form thin plate covering or over- hanging base of mandible, this plate frequently but not always incised (Fig. 8A) . Anterior margin of head with pointed median protuberance (carina) between bases of antennules (Fig. 8A) . Distal segment of exopod of pleopod 3 (outer gill operculum) approximately hemispherical in shape, with division between it and proximal segment running obliquely backwards from inner distal angle (Fig. 9A) : Liraeus Rafinesque (species not identified here; see Introduction) Lateral margin of head not produced to cover or overhang base of man- dible (Fig. 8B) . Anterior margin of head without a median protu- berance between bases of antennules (Fig. SB). Distal segment of exopod of pleopod 3 (outer gill operculum) sub-quadrangular in shape, division between it and proximal segment running approxi- mately at right-angles to long axis of specimen and commencing well anterior to inner distal angle of appendage (Fig. 93): Asellus St. Hilaire (page 19) Fig. 8. Dorsal view of head: A, Liraeus sp.; B, Asellus sp. Original ca.=carina, e.=eye. Fig. 9. Third pleopod: A, Liraeus sp.; B, Asellus sp. Original. 17 Fig. 10. A. OGoidentalis . A, dactylus and propodus of first peraeo- pod; B, first pleopod; C, second pleopod; D, E, respectively dor- sal and ventral surfaces of tip of endopod of second pleopod; F, uropod; G, uropod and telson. (After Williams, 1970). can.= cannula, l.p.= lateral process, v.g.= ventral groove. 18 SECTION IV KEY TO NORTH AMERICAN SURFACE-LIVING SPECIES OF ASELLUS The following key is of use only for adult male specimens; as indicated in the text above, it is the males which in Asellus provide the diagnos- tic characters for the species separation. Females cannot be identified at present. In the key, the terms mesial process, lateral process, caudal process, ventral groove, and cannula refer to structures at the tip of the endopod of the second pleopod. All drawings of the first and second pleopods, unless contraindicated, are of right pleopods. With respect to the surface of these, ventral=anterior, and dorsal=posterior. All principal distinguishing characters have been used in compiling the key, and are illustrated in the accompanying figures (no direct refer- ence may be made to such characters in the final part of the couplet for each species). In certain cases, to aid identification some quantitative data are given in tabular form. 1 Palm of propodus of peraeopod 1 lacking triangular process near midpoint, but with 3-5 teeth- like spines variously arranged (Fig. lOA) . Pleopod 1 distinctly longer than pleopod 2, dis- tal segment with numerous long plumose setae (Fig. lOB) . Pleo- pod 2 with mesial and caudal processes not developed, but lat- eral process large, projecting beyond cannula, and distally recurved (Figs lOD, E, llA-E); endopod shape and relative pro- portions of segments as in Fig. IOC. Both exopod and endopod of uropod longer than peduncle (Fig. lOF, G) : A. ocoidentdlis Palm of propodus of peraeopod 1 usually (not always) with both a large triangular process near midpoint and some teeth-like spines variously arranged. Pleopod 1 either longer than pleopod 2 and distal segment with numerous long plumose setae, or shorter to subequal in length to pleopod 2 and lacking distal plumose setae. Lateral process of pleopod 2 either absent or developed in conjunction with mesial process (i. e. not as shown in Figs lOD, E, llA-H); endopod shape and relative proportions of segments more or less dissimilar to those shown in Fig. IOC. Exopod of uropod typically shorter than peduncle, endopod usually subequal in length to peduncle (but sometimes longer) 2 2(1) Pleopod 1 usually subequal in length to pleopod 2 or distinctly shorter, distal segment subovate to subrectangular without long plumose setae on distal margin but with few to numerous short simple setae. Pleopod 2 with prominent cannula, often wide, never hidden ventral ly by lateral or mesial processes 3 Pleopod 1 usually distinctly longer than pleopod 2, distal segment usually subovate, often curved outward, and with few to numerous long plumose setae on distal margin. Pleopod 2 with small, narrow cannula sometimes hidden ventrally by lateral or mesial processes 10 19 Fig. 11. A. ocoidentalis . Variation in morphology of tip of endopod of second pleopod. A-E, ventral views; F-H, dorsal views. From Williams (1970). 3(2) Pleopod 2 with neither mesial nor caudal processes developed, only cannula projects distally from endopod tip (Figs 12D, E, 13A-F) ; dorsal surface of distal end of endopod with numerous minute comb-like structures (Fig. 12D) ; endopod shape and proportion of segments as in Fig. 12C. Both rami of uropod always flat, lanceolate and broad (Fig. 12F, G) : A . latiaaudatus Caudal process of pleopod 2 always more or less developed, mesial process either developed or not, cannula never only process to project distally from endopod tip; dorsal surface of dis- tal end of endopod usually lacking minute comb- like struc- ture (if present, these extend on to caudal process); endo- pod shape and proportions of segments more or less dissimilar to drawings of Fig. 12C. Rami of uropod either flat, lance- olate and broad or linear and narrow 4 4(3) Mesial process of pleopod 2 scarcely or not present 5 Mesial process of pleopod 2 present and well-developed 6 5(4) Inner and outer basal apophyses of endopod of pleopod 2 distinct (Fig. 6B, C) ; caudal process usually broadly rounded, cannula long and narrow (Figs 6D, E, 14A-M) ; shape of endopod and proportions of segments as in Fig. 68: A. communis Inner basal angle of endopod of pleopod 2 obtuse, sharply angled, or produced into small, acutely pointed apophysis, outer basal apophysis not distinct (Fig. 15C) ; caudal process often with acutely pointed apex, cannula short and wide (Figs 15D, 16A- H) ; shape of endopod and proportions of segments as in Fig. 15C: A. intermedius 6(4) Cannula of pleopod 2 long and narrow or triangular 7 Cannula of pleopod 2 relatively short and wide 9 20 Fig. 12. A. taticaudatus . A, dactylus and propodus of first perae- opod; B, first pleopod; C, second pleopod; D, E, respectively dor- sal and ventral surfaces of endopod of second pleopod; F, uropod; G, uropod and telson. (After Williams, 1970). can.= cannula. 21 Fig. 13. A. latiaaudatus . endopod of second pleopod. Variation in morphology of tip of A-F, ventral views. From Williams (1970) Fig. 14. A. communis. Variation in morphology of tip of endopod of second pleopod. A-M, ventral views; A-K, specimens from eastern States and southeastern Canada; L, specimen from Washington; M, specimen from Colorado, From Williams (1970). 22 Fig, 15. A. intermedius . A, dactylus and propodus of first perae- opod; B, first pleopod; C, second pleopod; D, E, respectively dor- sal and ventral surfaces of tip of endopod of second pleopod, (After Williams, 1970). can.= cannula, c.p.= caudal process, v.g.= ventral groove. 23 Fig. 16. A. intermedius . Variation in morphology of tip of endo- pod of second pleopod. A-H, ventral views. From Williams (1970). 7(6) Antenna 2 slightly longer than body. Pleopod 1 distinctly shorter than pleopod 2, division of distal and proximal segments incomplete (Fig. 17B) . Caudal process of pleopod 2 rounded, not well -developed (but clearly present), and lacking associated hooks and setae; cannula and subequal mesial process extending beyond caudal process (Fig. 17D, E) ; shape of endopod and proportions of segments as in Fig. 17C. Rami of uropod linear, narrow and subequal in length to each other (endopod only slightly longer) (Fig. 17F) : A. attenuatus Antenna 2 usually shorter than body but sometimes subequal. Pleopod 1 subequal in length to or slightly longer than pleopod 2, division between distal and proximal segments more or less complete (Figs 18B, 20A-H, 21B) . Caudal pro- cess of pleopod 2 distinctly developed, large, terminating in prominent apex, usually with several fine comb-like struc- tures on dorsal surface and some lateral setose processes; cannula and mesial process usually not extending distally beyond caudal process (Figs 18D, E, 19A-J, 21D, E, 22A-F); shape of endopod and proportions of segments more or less dissimilar to Fig. 17C. At least endopod of uropod lanceo- late, distinctly longer than exopod (Figs 18F, 21F) A. raoovitzai 8 24 ^^CCHCt.- Fig. 17. A. attenuatus. A, dactylus and propodus of first peraeopod; B, first pleopod; C, second pleopod; D, E, respectively dorsal and ventral surfaces of tip of second pleopod; F, uropod. (After Williams, 1970). can.= cannula, m.p.= mesial process, v.g.= ventral groove. 25 Fig. 18. A. vaoovitzai vaoovitzai. A, dactylus and propodus of first peraeopod; B, first pleopod; C, second pleopod; D, E, respectively dorsal and ventral surfaces of tip of endopod of second pleopod; F, uropod. (After Williams, 1970). can.= cannula, c.p.= caudal process, m.p.= mesial process, v.g.= ventral groove. 26 8(7) Distal segment of pleopod 1 more or less subrectangular (Fig. 18B) . Cannula of pleopod 2 triangular in shape, not markedly thickened on outer margin (Figs 18D, E, 19A-J) ; shape of end- opod and proportions of segments as in Fig, 18C. (Table 1): A. vacovitzai raoovitsai Distal segment of pleopod 1 more or less subovate (Fig. 20A-H) . Cannula of pleopod 2 not conspicuously triangular in shape, and outer margin thickened (Figs 21D, E, 22A-F) ; shape of endopod and proportions of segments as in Fig. 21C. (Table 1) : A. vacovitzai australis Fig. 19. A. vacovitzai vacovitzai. Variation in morphology of tip of endopod of second pleopod. A-J, ventral views; A-H, J, specimens from eastern States and southeastern Canada; 1, specimen from Washing- ton. From Williams (1970). 27 Fig. 20. A. raoovitzai vaoovitzai. Variation in shape of first pleopod. TABLE 1 SOME DIFFERENCES BETWEEN TWO SUBSPECIES OF ASELLUS RACOVITZAI (males only) (From Williams 1970, Table 4) A. raoovitzai vaoovitzai A. vaoovitzai austvalis length of antenna 2 body length Range M* + S.D. 0.44-0.80 0.60 0.08 0.67-1.00 0.80 0.09 Pleopod 2 length of endopod Range M* + S.D. 1.05-1.89 1.34 0.18 0.72-1.20 0.96 length of distal segment of exopod 0.11 Pleopod 2-distal segment of exopod length width Range M* + S.D. 0.96-2.00 1.45 0.20 1.48-2.47 1.78 0.25 Pleopod 2-endopod length width Range M* + S.D. 2.34-3.20 2.78 0.24 2.15-2.80 2.49 0.17 * difference between means highly significant in all comparisons (by "t" test, P =<0.001) 28 Fig. 21. A. vaeovitzai australis. A, dactylus and propodus of first peraeopod; B, first pleopod; C, second pleopod; D, E, respectively- dorsal and ventral surfaces of tip of endopod of second pleopod; F, uropod. (After Williams, 1970). can.= cannula, c.p.= caudal process, m.p,= mesial process, v.g.= ventral groove. Fig. 22. A. vaaovitzai austratis. Variation in morphology of tip of endopod of second pleopod. A-F, ventral views. From Williams (1970) . 9(6) Antenna 2 usually shorter than body length. Proximal pro- jection on palm of propodus of peraeopod 1 typically with tooth-like seta (Fig. 23A) . Mesial process of pleopod 2 usually long and not very wide; cannula of moderate width (Figs 23D, E, 24A-G) ; endopod shape and/or proportions of segments as in Figs 23C, 25A-J; proximal segment of exopod frequently with marginal setae (Fig. 23C) . Uropods mostly subequal in length to telson. Both telson and uropods only moderately setose laterally (Fig. 23F, G) (Table 2): A. fovbesi Antenna 2 usually subequal in length to body. Proximal pro- jection on palm of propodus of peraeopod 1 with long stout seta (never a tooth-like seta) (Fig. 26). Mesial process of pleopod 2 usually short and wide, cannula very wide with recurved outer lip (Figs 27C, D, 28A-H) ; endopod shape and proportions of segments as in Fig. 27B; proximal segment of exopod without marginal setae (Fig. 278). Uropods distinct- ly longer than telson and both telson and uropods very setose laterally (Fig. 27E) (Table 2): A. obtusus 10(2) Body of endopod and associated terminal processes of pleopod 2 arranged in spiral fashion so that 'ventral' groove actually lies dorsally (Fig. 29C, D, E) ; cannula not visible; endopod shape and proportions of segments as in Fig. 29C. Endopod of uropod shorter than peduncle (Fig. 29F) : A. montanus Body of endopod of pleopod 2 not spirally arranged although some torsion may be displayed by terminal processes (i.e. not as indicated in Fig. 29C, D, E) ; cannula (at least tip) visible from ventral or dorsal view; endopod shape and proportions of segments more or less dissimilar to Fig. 29C. Endopod of uropod typically longer than or subequal in length to peduncle 11 30 Fig. 23. A. forbesi. A, dactylus and propodus of first peraeopod; B, first pleopod; C, second pleopod; D, E, respectively dorsal and ventral surface of tip of endopod of second pleopod; F, uropod; G, uropod and telson. (After Williams, 1970). can.= cannula, c.p.= caudal process, m.p.= mesial process, v.g.= ventral groove. 31 Fig. 24. A. forbesi. Variation in morphology of tip of endopod of second pleopod. A-H, ventral views. From Williams (1970). Fig. 25. A. forbesi. Variation in shape of endopod of second pleopod. From Williams (1970). Fig. 26. A. obtusus. Distal segments of first peraeopod with dactylus and palm of propodus shown in greater de- tail. From Williams (1970). 32 Fig. 27. A. obtusus. A, first pleopod; B, second pleopod; C, D, respectively dorsal and ventral surfaces of endopod of second pleopod; E, uropod and telson. (After Williams, 1970). can.= cannula, c.p.= caudal process, m.p.= mesial process, v.g.= ventral groove. 33 Fig. 28. A. obtusus. Variation in morphology of tip of endopod of second pleopod. A-H, ventral views. From Williams (1970). TABLE 2 SOME DIFFERENCES BETWEEN TWO SPECIES OF ASELLUS (males only) (From Williams 1970, Table 5) A. forbesi A. obtusus Maximum body length (mm) 18.5 12.5 length of antenna 2 Range body length M* + S.D. 0.5-1.0 0.75 0.12 0.8-1.5 1.03 0.19 Pleopod 2-proximal segment of exopod Number of marginal setae 0-4 0 Pleopod 2-endopod Range length M* width + S.D. 1.65-2.64 2.05 0.22 1.39-1.84 1.63 0.15 uropod length Range telson length M* + S.D. 0.67-1.5 1.16 0.20 1.0-2.0 1.48 0.32 * difference between means highly significant in all comparisons (by "t" test, P =<0.001) 34 Fig. 29. A. montanus.- A, dactylus and propodus of first peraeopod; B, first pleopod; C, second pleopod; D, E, respectively dorsal and ventral surfaces of tip of endopod of second pleopod; F, uropod. (After Williams, 1970). 'v.g.'= 'ventral' groove. 35 Fig. 30. A. nodulus. A, dactylus and palm of first peraeopod; B, first peraeopod; C, first pleopod; D, second pleopod; E, F, respec- tively dorsal and ventral surfaces of tip of endopod of second pleopod; G, uropod; H, uropod and telson. (After Williams, 1970). 'd.p.'= dorsal process, 'v.p.'= ventral process. 36 11(10) Cannula of pleopod 2 completely enclosed between two promin- ent, heavily sclerotized, non-dentate, broadly rounded 'ventral' and 'dorsal' processes (Fig. 30E, F) ; distal end of endopod with small degree of torsion so that 'ventral' groove lies laterally; endopod shape and proportions of segments as in Fig. 30D. Endopod of uropod distinctly longer than peduncle (Fig. 30G, H) : A. nodulus Cannula of pleopod 2 not enclosed between two processes as des- cribed above (i.e. not as indicated in Fig. 30E, F) ; dis- tal end of endopod not displaying any obvious sign of torsion; ventral groove distinct; endopod shape and pro- portions of segments more or less dissimilar to drawing of Fig. 30D. Endopod of uropod typically only slightly longer than or subequal in length to peduncle 12 12(11) Cannula of pleopod 2 visible from ventral view, lateral pro- cess not (or only slightly) developed, mesial process prom- inent and bifid, caudal process wide and irregularly dentate (Fig. 31D, E) ; endopod shape and proportions of segments as in Fig. 3 IC: A. dentadactylus Cannula of pleopod 2 often hidden by lateral process in ventral view, lateral process well-developed, mesial process prom- inent but with either rounded or dentate distal margin (not bifid) , caudal process absent or rounded (not dentate) ; endopod shape and proportions of segments more or less dis- similar to Fig. 31C 13 13(12) Caudal process of pleopod 2 absent, distal dorsal surface of endopod with numerous minute setae, lateral process non- sclerotized with rounded margin, mesial process obtusely dentate (Fig. 32C, D) ; endopod shape and proportions of segments with some variation but typically as shown in Figs 32B, 33A-G. Uropods about half as long as telson (always < 0.7) , peduncle about as wide as long (Fig. 32E) : A. hvevicauda hvevioauda [Pending a further examination of specimens, two subspecies of A. hvevioauda have tentatively been proposed by Williams (1970), A, hvevioauda hvevioauda Forbes, 1876, and A. hvevi- oauda hivittatus Walker, 1961. The differences between them are small and mainly involve slight differences in setation, segment proportions, and number of segments in antennal fla- gella. Table 3 details the principal differences.] Distal endopodial processes of pleopod 2 (considered as a whole) of shape and arrangement other than as described for A. hvevioauda hvevioauda, distal dorsal surface of endopod lacks minute setae; endopod shape and proportions of segments more or less dissimilar to drawings of Figs 32B, 33A-G. Uropods subequal to or slightly longer than telson, peduncle always longer than wide 14 37 Fig. 31. A. dentadaatylus . A, dactylus and propodus o£ first perae- opod; B, first pleopod; C, second pleopod; D, E, respectively dor- sal and ventral surfaces of tip of endopod of second pleopod; F, uropod. (After Williams, 1970), can.= cannula, c.p.= caudal process, ni.p.= mesial process, v.g.= ventral groove. 38 Fig. 32. A. brevioauda brevioauda. A, first pleopod; B, second pleopod; C, D, respectively dorsal and ventral surfaces of tip of endopod of second pleopod; E, uropod. (After Williams, 1970). can.= cannula, l.p.= lateral process, m.p.= mesial process, v.g.= ventral groove. 14(13) Cannula of pleopod 2 small and narrow, lateral process pointed, mesial process obtusely dentate, caudal process absent (Figs 34D, E, 35A-G) ; endopod shape and proportions of segments as in Fig. 34C: A. sorupulosus Cannula of pleopod 2 not small and narrow, lateral process rounded, mesial process not dentate (but with rugose pos- terior lobe), caudal process present, broadly rounded with some rugosities (Fig. 36D, E) ; endopod shape and propor- tions of segments as in Fig. 36C: A. kenki 39 Fig. 33. A. brevicauda breviaauda. Variation in shape and pro- portions of segments of second pleopod. From Williams (1970). TABLE 3 PRINCIPAL DIFFERENCES BETWEEN TWO SUBSPECIES OF ASELLUS BREVICAUDA (males only) (From Williams 1970, Table 3) A. breviaauda brevicauda A. breviaauda bivittatus Maximum body length (mm) 17.0 5.5 Antenna 1 No. segments in flagellum 11-17 8-9 Antenna 2 No. segments in flagellum 60-124 31-44 Peraeopod 1 No. teeth-like setae on dactylus 6-14 5-6 Triangular process near mid- point of palm of propodus present absent No. coupling hooks on sympod 4-7 width Pleopod 1 length distal segment 0.40-0.50 No. plumose setae on distal segment 5-11 3-4 0.50-0.62 4-6 Pleopod 2 length width sympod 1.37-2.00 No. plumose setae on distal segment of exopod 12-17 1.25-1.60 5-10 uropod length telson length 0.48-0.68 0.36-0.44 40 Fig. 34. A. sarupulosus. A, dactylus and propodus of first peraeopod; B, first pleopod; C, second pleopod; D, E, respectively dorsal and ven- tral surfaces of tip of endopod of second pleopod; F, uropod. (After Williams, 1970). can.= cannula, l.p.= lateral process, m.p.= mesial process, v.g.= ventral groove. Fig. 35. A. sarupulosus. Variation in morphology of endopod tip of second pleopod. A-C, E, G, ventral views; D, F, dorsal views. From Williams (1970) . 41 Fig. 36. A. kenki. A, first pleopod; B, distal margin of first pleopod; C, second left pleopod; D, E, respectively dorsal and ventral surfaces of tip of endopod of second left pleopod. (After Bowman, 1967). can.= cannula, c.p.= caudal process, l.p.= lateral process, m.p.= mesial process, v.g.= ventral groove. 42 SECTION V REFERENCES Bartsch, A. F. 1948. Biological aspects of stream pollution. Sewage Works Journal^ 20:292-302. Bartsch, A. F. and W. M. Ingram, 1959. Stream life and the pollution environment. Public Works ^ 90:104-110. Birstein, Ya. A. 1951. Freshwater Isopods (Asellota) . Fauna S.S.S.E.^ 7(5), 148pp. [English translation by Israel Program for Scientific Translations, 1964] Bowman, T. E. 1967. Asellus kenki, a new isopod crustacean from springs in the eastern United States. Proceedings of the Biological Society of Washington, 80:131-140. [A. kenki described] Clifford, H. F. 1966. The ecology of invertebrates in an intermittent stream. Investigations of Indiana Lakes and Streams^ 7(2): 57-98. Cole, G. A. and W. L. Minckley, 1968. A new species of aquatic isopod crustacean (genus Asellus) from the Pueblo plateau, central Mexico. Proceedings of the Biological Society of Washington, 81: 775-60. Ellis, R. J. 1961. A life-history study of Asellus intermedins Forbes. Transactions of the Americop^ Microscopical Society, 80(1) : 80-102. 1971. Notes on the biology of the isopod Asellus tomalensis Harford in an intermittent pond. Transactions of the American Microscopical Society, 90(1):51-61. [synonym of A. oocidentalis Williams, 1970] Forbes, S. A. 1876. List of Illinois Crustacea, with descriptions of new species. Bulletin of the Illinois Museum of Natural History, 1:3-25. [A. brevicauda brevicauda and A. intermedius described] Carman, S. 1889. Cave animals from southwestern Missouri. Bulletin of the Museum of Comparative Zoology at Harvard University, 17(6) : 225- 39. [L. hoppinae hoppinae described by Faxon] Harger, 0. 1876. Description of Mancasellus brachyurus, a new fresh- water isopod. American Journal of Science and Arts, ll(3):304-5. [L. brachyurus described] Henry, J. -P. and G. Magniez, 1968. Sur la systematique et la biogeo- graphique des Asellides. Comptes rendus des seances de I'Academie des Sciences, Paris, 267:87-9. 1970. Contribution a la systematique des Asellides (Crustacea Isopoda) . Annales de Speleologie, 25(2) :335-67. Hubricht, L. and J. G. Mackin, 1949. The freshwater isopods of the genus Liroeus (Asellota, Asellidae). American Midland Naturalist, 42(2) : 334-49. [L. hargeri, L. alabamae, L. richardsonae, L. megapodus, L. hoppinae ozarkensis, L. bidentatus, L. bicuspida- tus, L. garmani, L. trilobus described] Hynes, H. B. N. 1960. "The biology of Polluted Waters." Liverpool Uni- versity Press, Liverpool, 202 pp. Kolkwitz, R. and M. Marsson, 1909. Okologie der tierische Saprobien. Beitrage zur Lehre von der biologische Gewasserbeurteilung. Internationale Revue der gesampten Hydrobiologie und Hydrographie, 2:126-152. 43 Mackin, J. G. and L. Hubricht, 1938, Records of distribution of species of isopods in central and southern United States, with descriptions of four new species of Manaasellus and Asellus (Asellota, Asellidae) . Amerioan Midland Naturalist, 19:628-37. [^4. dentadactylus , A. mon- tanus, L. louisianae, L. hoppinae ouaahitaensis described] Racovitza, E. G. 1920. VII. Notes sur les isopodes. 6, Asellus Gommunis Say. 7, Les pleopodes I and II des Asellides; Morpholo- gie et development. Archives de Zoologie experimentale et generale. Notes et Revue, 58:79-115. Rafinesque, C. S. 1820. Annual synopsis of new genera and species of animals, plants etc. discovered in North America. Annals of Nature, 1:1-16. [L. fontinalis described] Richardson, H. 1900. Synopses of North American invertebrates. VIII. The Isopoda. Part II. Amerioan Naturalist, 34:295-309. 1901. Key to the isopods of the Atlantic coast of North America with descriptions of new and little known species. Proceedings of the United States National Museum, 23:494-579. [.4. attenuatus described] Say, T. 1818. An account of the Crustacea of the United States. Journal of the Academy of Natural Sciences of Philadelphia, 1:374-401, 423-33. {A. communis, L. lineatus described] Seidenberg, A. J. 1969. Studies on the biology of four species of fresh- water isopods (Crustacea, Isopoda, Asellidae) in east-central Illin- ois. Ph. D. dissertation. University of Illinois. Styron, C. E. 1968. Ecology of two populations of an aquatic isopod, Lirceus fontinalis Raf., Ecology, 49:629-36. 1969. Taxonomy of two populations of an aquatic isopod, Lirceus fontinalis Raf., American Midland Naturalist, 82:402-16. Walker, B. A. 1961. Studies on Doe Run, Meade County, Kentucky, IV. A new species of isopod crustacean (genus Asellus) from Kentucky. Transactions of the American Microscopical Society, 80:385-90. [A. brevicauda bivittatus described] Williams, W. D. 1970. A revision of North American epigean species of Asellus (Crustacea: Isopoda) . Smithsonian Contributions to Zoology, 49:1-80. [A. raaovitzai racovitzai, A. raoovitzai australis, A. forbesi, A. obtusus, A. laticaudatus , A. scrupulosus, A. nodulus, A. occidentalis described] 44 SECTION VI INDEX OF SCIENTIFIC NAMES aldbamae (Liraeus)^ 14 aquatiaus (Asellus) ^ 2 Asellidae, 1 AsellopsiSj 1 Asellus, 1,2,3,4,7,11,13,17 aquatiaus, 2 attenuatuSj 13,24,25 brevicauda bivittatus, 13,37,40 brevicauda, 13,37,39,40 communis, 4,5,6,7,8,9,10,13,20, 22 dentadactylus, 13,37,38 forbesi, 13,30,31,32 intermedius , 13,20,23,24 kenki, 13,40,42 laticaudatus , 13,20,21,22 montanus, 13,30,35 nodulus, 13,36,37 obtusus, 14,30,32,33,34 oooidentalis , 14,18,19,20 racovitzai australis, 14,27,28, 29,30 racovitzai, 14,26,27,28 scrupulosus, 14,40 attenuatus (Asellus) , 13,24,25 bicuspidatus (Liraeus) , 14 bidentatus (Lirceus) , 14 Bopyridae, 1 brachyurus (Lirceus) , 14 brevicauda bivittatus (Asellus) , 13, 37,40 brevicauda (Asellus) , 13,37,39, 40 Caecidotea, 1 Cirolanidae, 1 communis (Asellus) , 4,5,6,7,8,9,10, 13,20,22 Conasellus, 1 dentadactylus (Asellus) , 13,37,38 fontinalis (Lirceus) , 14 forbesi (Asellus) , 13,30,31,32 garmani (Lirceus), 14 hargeri (Lirceus) , 14 hoppinae hoppinae (Lirceus), 14 ouachitaensis (Lirceus), 14 ozarkensis (Lirceus) , 14 intermedius (Asellus) , 13,20,23,24 kenki (Asellus), 13,40,42 laticaudatus (Asellus), 13,20,21,22 lineatus (Lirceus), 14 Lirceus, 1,2,3,4,14,17 alabamae, 14 bicuspidatus, 14 bidentatus, 14 brachyurus, 14 fontinalis , 14 garmani, 14 hargeri, 14 hoppinae hoppinae, 14 ouachitaensis , 14 ozarkensis, 14 lineatus, 14 louisianae, 15 megapodus , 15 richardsonae , 15 trilobus, 15 louisianae (Lirceus), 15 Mancasellus, 1 megapodus (Lirceus ) , 15 montanus (Asellus) , 13,30,35 nodulus (Asellus) , 13,36,37 obtusus (Asellus), 14,30,32,33,34 occidentalis (Asellus), 14,18,19,20 Pseudobaicalasellus, 1 racovitzai australis (Asellus) , 13, 27,28,29,30 racovitzai (Asellus), 13,26,27, 28 richardsonae (Lirceus) , 15 scrupulosus (Asellus), 14,40,41 Sphaeromatidae, 1 Sphaeromidae, 1 trilobus (Lirceus) , 15 45 SELECTED WATER RESOURCES ABSTRACTS INPUT TRANSACTION FORM /. Report No. 3. Accession No. w 4. Title BIOTA OF FRESHWATER ECOSYSTEMS IDENTIFICATION MANUAL NO. 7. Freshwater Isopods (Asellidae) of North America, 7. Autbor(s) Williams, W. D. 5. Report Date 6. 8. Performing Organization Report No. 9. Organization Monash University, Clayton, Victoria, Australia 12. Sponsoring Organization IS. Supplementary Notes 10. Pro 'fSb^fr ELD //. Contract/Grant No. 14-12-894 13. Type of Report and Period Covered 16. Abstract A key is given to the North American genera (Asellus and Liraeus) of asellid isopods. Another key is provided for the surface-living species of Asellus but lack of clear, published morphological distinctions in the genus Li-raeus prevents the construction of a key for that genus. Notes on ecology, collection, preservation and identification are also included. 17a. Descriptors *Aquatic fauna, *Isopods, Distribution, Preservation, I7b.ldenti£ers * Identification Manual, *Illustrated key, *Asellidae, *North America, Species List, Collection, 17c. COWRR Field i Group j^q^ It. Availability 19. Security Class. (Report) 20. Security Class. (Page) Abstractor *> ■ °- WiHiams 21. No. of Pages 22. Price Send To: WATER RESOURCES SCIENTrFlC rNFORMATION CENTER US- DEPARTMENT OF THE INTERIOR WASHINGTON. D, C 20240 [institution Monash University, Victoria, Australia. WRSIC 102 (REV, JUNE 1971) » U. S. GOVERNMENT PRINTING OFFICE : 197J O - 46B-267