No. 83 RECORDS OF THE QUEEN VICTORIA MUSEUM LAUNCESTON Edited by C. B. TASSELL Director of the Museum the Gastropods assiminea and hydrococcus in Tasmania (MOLLUSCA: GASTROPODA) R. C. Kershaw Honorary Research Associate, Queen Victoria Museum and Art Gallery Honorary Associate in Invertebrate Zoology, National Museum of Victoria Manuscript received: 1 /7/1982 Published 27/7/83 The saline marsh species Assiminea tasmanica Tenison-Woods and the intertidal flat species Hydrococcus brazieri (Tenison-Woods) are redescribed. The external morphology of the species is compared and differences demonstrated. Assiminea australis Petterd is recognised as the gerontic form of Hydrococcus brazieri. Statistical analysis of Tasmanian and southern Australian forms reveals greater variation within than between these gastropod species. INTRODUCTION Species of the Mesogastropod families Hydrococcidae and Assimineidae have been confused within the genus Assiminea in Tasmania. The question of an ecomorphic relationship between the forms observed has also caused taxonomic confusion requiring further comparitive study. The species Assiminea tasmanica Tenison-Woods, 1876 and Hydrococcus brazieri (Tenison-Woods, 1876) originally assigned to the genus Rissoina are now recognised and redescribed. The anatomy of these species has been studied by Dr. Winston Ponder (in press, 1981) and will not be considered here. The two species have certain common morphologic features and similar patterns of variation. The apparent resemblances together with possible habitat overlap called specific identity into question. The recognition by McMichael (1967) of the Hydrococcidae as inclusive of "a single monotypic genus from south-western Australia" raised the question of correct placement of Rissoina brazieri from Western Australia, McMichael's dissimilar operculum and freshwater habitat suggested further study of Tasmanian material. Records of the Queen Victoria Museum No. 83. 2 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) Fig. 1 Map of south-east Australia showing localities mentioned in the text. THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) 3 Comparison with Western Australian shells has again been made using fresh material provided by the Western Australian Museum. This established the presence of Hydrococcus as distinct from Assiminea in Tasmania. Type material of Rissoina braz/er/Tenison-WoodsintheTasmanianMuseum is unmistakable allowing immediate recognition of the original author’s concept of his species. The probable holotype (in the Tasmanian Museum) of Assiminea lasmanica Tenison- Woods is a corroded specimen from Sorell, southern Tasmania. Fresh live material from the type locality collected by Tasmanian Museum staff has clearly established the species as described. Pending this investigation, Smith and Kershaw (1979, 1981) retained the senior taxon Assiminea tasmanica Tenison-Woods. This species does not belong in the Hydrococcidae as placed by these authors. Their figured shell is a Victorian Assiminea species not applicable to the Tasmanian Hydrococcus brazieri (Tenison-Woods). MATERIAL STUDIED The bulk of the material here listed is in the Tasmanian Museum or the Queen Victoria Museum. The number of specimens for each locality is given together with the collector and date. Hydrococcus brazieri (Tenison-Woods, 1876) Locality Number Collection Tasmania: Kelly Basin 2 South Arm Neck 104 Taroona 4 Parsons Bay 5 Pipe Clay Lagoon 2 Midway Point 18 Pittwater 34 Pittwater 206 Saltwater River 2 White Beach 13 North Oyster Bay 36 Kelso 44 Kelso 87 Greens Beach area 226 Greens Beach - Tamar mouth 35 Welcome River mouth 240 Whitemark, Flinders Island 93 Victoria: Corio Bay, Port Phillip 278 Western Australia: Albany 3 Bunbury 6 Swan River 4 Shark Bay 3 Total 1 442 E. Smith January 1953 A. P. Andrews 13 March 1980 Tasmanian Museum staff May 1966 Mrs. Fenton 20 March 1967 B. J. Nielsen 1 September 1957 E. Aves 9 August 1967 Tasmanian Museum staff 13 April 1965 E. Turner and A. P. Andrews 10 October 1980 A. J. Dartnall 22 May 1966 A. J. Dartnall October 1967 J. Thwaites September 1967 R. C. Kershaw September 1949 R. C. Kershaw and I. S. Norton 2 October 1980 R. C. Kershaw 1950 R. C. Kershaw August 1953 B. C. Mollison 27 October 1964 R. C. Kershaw August 1957 R. Burn October 1980 4 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) Assiminea tasmanica Tenison-Woods, 1876 Locality Number Collection Tasmania : Margate 6 South Port Lagoon 16 Frogmore Beach 28 Penna 51 Pittwater 1 Crayfish Creek 6 Kelso Bay 20 West Arm (Tamar River) 44 Rosevears (Tamar River) 14 Lone Pine Point (Tamar River) 251 Port Sorell 1 Tasmania 2 Victoria: Corio Bay Port Phillip 51 Cardinia Creek Western Port 36 Total 537 E. Aves 19 April 1967 A. J. Dartnall 28 September 1974 (old label) E. Turner and A. P. Andrews October 1980 Tasmanian Museum staff 13 April 1965 B. C. Mollison 27 July 1963 R. C. Kershaw October 1954 R. C. Kershaw September 1965 R. C, Kershaw 1950 R. C. Kershaw and I. S. Norton 2 October 1980 J. F. Greenhill 15 January 1964 W. F. Petterd R. Burn October 1980 R. C. Kershaw March 1977 All the material studied was measured using a micrometer scale. The means, standard deviation and variation coefficient for each population was determined using recognised methods (Runyon & Haber, 1975, Parker, 1976). For statistical comparisons material of both species collected in south Tasmania prior to 1980 has been treated as a single population in each case. (Copies of graphical data not presented in this paper may be obtained from the Queen Victoria Museum on request.) TAXONOMY Hydrococcus brazieri (Tenison-Woods, 1876) Plate 1 1876 Rissoina (Setea) brazieri Tenison-Woods, p. 14. 1877 Ampullarina minuta Tenison-Woods, p. 155. 1887 Rissoa brazieri (Tenison-Woods): Tryon, p. 335, pi. 71, fig. 97. 1889 Assiminea australis Petterd, p. 77, pi. 3, fig. 10. 1901 Assiminea brazieri (Tenison-Woods); Tate & May, p. 395. 1901 Assiminea australis (Petterd); Tate & May, p. 395. 1903 Rissoa brazieri (Tenison-Woods); May, p. 112 1903 Ampullarina minuta (Tenison-Woods); May p. 113 1905 Assiminea brazieri (Tenison-Woods); Gatliff, p. 15. 1921 Syncera brazieri (Tenison-Woods); May p. 55. 1923 Assiminea brazieri (Tenison-Woods); May, pi. 25, fig. 24. 1938 Assiminea brazieri (Tenison-Woods); Cotton & Godfrey, p. 12 1942 Assiminea brazieri (Tenison-Woods); Cotton, p. 127. 1955 Assiminea brazieri (Tenison-Woods); Kershaw, p. 309 1958 Assiminea brazieri (Tenison-Woods); Kershaw, p. 84 1958 Assiminea brazieri (Tenison-Woods); Macpherson in May, pi. 25, fig. 24. 1959 Assiminea brazieri (Tenison-Woods); Cotton, p. 356. 1962 Assiminea brazieri (Tenison-Woods); Macpherson & Gabriel, p. 95 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) 5 Plate 1 Figs. 1-6 Hydrococcus brazieri, adult shells from Kelso, Tamar River, x 1.2. Figs. 7-9 Hydrococcus brazieri, gerontic shells from Welcome River, north-western Tasmania, x 13.7. Figs. 10-14 Hydrococcus brazieri (Tenison-Woods), syntype series Tasmanian Museum. Photos N. R. Kemp. 6 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) DESCRIPTION: Shell of less than six somewhat convex whorls, conically turbinate, typically abruptly angled at periphery with flatly sloping base, body whorl flattened supraperipherally, sloping distinctly near and into suture. Apex obtuse, protoconch about 214 whorls, glassy pale orange, surface pitted, diameter 0.5mm, Aperture rounded, slightly peaked above, outer lip convex or angular, adult basal lip produced, columellar margin partly reflected over variable umbillical chink, adult with thin distinct callus deposit to apex Operculum horny, transparent, dished, rounded with a weak riblet coiling from columellar margin in at least four spirals to central or sub-central nucleus (Figs. 2e, 2f). Adult aperture distinctly less than half shell length, proportionately larger in juvenile. Colour white, off white, cream or yellow, speckled brown or occasionally wholly brown but typically with a broad pale brown band overlapping peripheral angle. Tasmanian shells usually smooth but may possess growth lines. EXTERNAL ANIMAL MORPHOLOGY: Proboscis narrow roundly ovate elongate usually protruding no more than 0.5mm from shell lip, dorsally marked with transverse very close very dark grey, brownish-tinted, lines: ventrally pale transparent. The 1,5mm long foot and sole is pale translucent, somewhat sharply bilobate in front. The lobes are very flexible and have a probing function. Tentacles three, of which two are pale elongate with swollen white bases bearing laterally situate slightly raised small black eyes. Third tentacle more robust elongate, protrudes from the pallium on right side adjacent the shell suture. The animal is active, constantly probing the substrate with the foot lobes. Absorbed food particles can be readily seen rolling into the gullet with the convulsive radula-feeding action. Food particles are dislodged by the probing foot. The tentacles and foot lobes have a combined apparent sensory function. GROWN PATTERN AND VARIATION: First 3 to 3'/? whorls globose, convex, uniform bright brown: whorls four and five slightly flattened, variably angular at the periphery with a colour band commonly present. Subsequent angularity is reduced in the gerontic stage to a keel-like process which may be just apparent at aperture margin or absent. Consequently gerontic shells are of seemingly different form, and are commonly corroded without colour bands. Assiminea australis Petterd. 1889 is an example. A growth increment range of up to 0.6mm in width for a 0.1 mm height increase was found in the study material. This maximum was found about 2.5mm to 2.7mm shell height. The maximum variation usually found was 0.5mm probably because of limited material. The largest shell measured was 4.4mm height, 3.0mm width at 5 !h whorls. A relationship between growth pattern and whorl number could not be established. Aperture change is rapid in early growth and reduces to minimal in adult shells. An average adult aperture is 1.3mm height by 1,6mm wide. SHAPE AND COLOUR VARIATION: Globose shell morphology varies with the degree of peripheral angling. Generally a proportion of shells exhibit a reduction in angling. Less often the body whorl is convex. Convexity is always distinct above the aperture. The apex is variably flattened, frequently corroded and may lose the first whorl increasing the obtuse appearance. Colour banding may be very distinct, indistinct or partly or wholly hidden by brown speckling. Brown is much more common than pale brown. The solidity of the shell apparently increases with exposure. THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) 7 a b Fig. 2a Assiminea tasmanica operculum external surface, Rosevears, Tamar River, Tasmania. Fig. 2b Assiminea tasmanica operculum internal surface, West Arm, Tamar River, Tasmania. Fig. 2c Assiminea tasmanica operculum, Corio Bay, Victoria. Fig. 2d Assiminea tasmanica operculum, Cardinia Creek, Victoria. Fig. 2e Hydrococcus brazieri operculum, Corio Bay, Victoria. Fig. 2f Hydrococcus brazieri operculum, Welcome River, north-west Tasmania. 8 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) Plate 2 Zostera meadow, intertidal flats at Kelso, Tamar River. Plate 3 Hydrococcus brazieri on Zostera leaves, Kelso Tamar River. THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) 9 Victorian shells studied are distinctly more globose and have a peripheral keel-like angle. The distinct angling of Tasmanian shells appears absent and the shells are not as solid. In the Victorian material colour varies from white to cream or pale yellow with usually distinct variably broad pale or dark brown bands. The shell may be uniform cream, brown or horny. Gerontic shells, usually of more than five whorls are mottled or unicoloured and lack a keel. Growth lines are present. Western Australian shells studied are more distinctly globose with angled whorls less common. The four localities from which specimens came, give a wide coverage although of small samples. Shells are pale, cream, pale yellow to pale brown with occasional pale very narrow brown banding. The operculum of the Shark Bay shell has five to six spirals while Bunbury shells had several more. Generally the umbilical chink varied widely and degree of globosity varies. Clear growth lines are present. Compared to Tasmanian shells, the Western Australian material has a smaller protoconch, an operculum with more spirals, the nucleus above centre rather than below and slight keeling instead of strong peripheral angling. Formerly known as Hydrococcus granilormis Thiele the morph is now known to be H. brazieri (Tenison-Woods) (Wells & Threlfall, 1981). HABITAT: Data on the habitat in which the species occurs is presented by Kershaw (1958) and Wells & Threlfall (1981). In Tasmania it is most common in the mid-littoral zone of sand or muddy-sand flats, usually within Zostera meadows (Plates 2, 3) at or near the mouths of estuaries (such as the Tamar River, Welcome River), deep bays, inlets or sheltered waters such as the extensive flats north from Whitemark, Flinders Island. It is accidental to higher tide levels. It is an animal of semi-sheltered to sheltered marine or estuarine environments. All the apparent marine tidal localities have reduced exposure where the species occurs. Despite being recorded from Greens Beach at the Tamar mouth it has not been found alive there. Although probably subject to salinity variation. H. brazieri is not a freshwater species. The suggestion that it occurred in freshwater in Western Australia may have been due to past confusion as to the nature of the Swan Estuary according to Mrs. Slack-Smith of the Western Australian Museum (pers. comm.). She has not found the species outside its normal habitat. DISTRIBUTION: It is found widely in Tasmania and Bass Strait. Recorded from Victoria, South Australia and Western Australia to Shark Bay. TYPE MATERIAL: Syntype material: Five shells Tasmanian Museum Reg. no. E466/7807, (TM5481). Rissoina brazieri Tenison-Woods. Isthmus Bay, Bruny Island, south Tasmania Syntype material: Three shells Tasmanian Museum Reg. No. (TM5629). Ampullarina minuta Tenison-Woods. Circular Head, north-west Tasmania. DISCUSSION. The Isthmus Bay type is representative of the species. The description of the shell by Tenison-Woods enables recognition but his operculum is incorrectly described, probably because the spirals are commonly difficult to see. The form Ampullarina minuta has caused doubt. May (1903) thought it could be juvenile Salinator iragilis. But study of a range of juveniles suggests that Tenison-Woods would not have confused S. Iragilis. The poorly figured Assiminea australis Petterd, based on a Tate MS name, was collected by Beddome at Kelso where H. brazieri is plentiful. It is an apparent gerontic H. brazieri and the described habitat is identical to that of H. brazieri at Kelso. 10 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) Plate 4 Figs. 1-2 Assiminea tasmanica Tenison-Woods, possible holotype Tasmanian Museum E468/7809, Figs. 3-7 Assiminea tasmanica typical shells from Kelso Bay, Tamar River, x 13.6. Figs. 8-9 Assiminea tasmanica adult shells from Corio Bay, Victoria, x 15. THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) 11 Assiminea tasmanica Tenison-Woods 1876 Plate 4 1876 Assiminea tasmanica Tenison-Woods, p. 79. 1877 Rissoa (Letia) siennae Tenison-Woods, p. 153. 1887 Assiminea siennae (Tenison-Woods); Boettger, p. 203, pi. 6, fig. 8. 1889 Assiminea bicincta Petterd, p. 77, pi. 2, fig. 4. 1901 Assiminea bicincta (Petterd); Tate & May, p. 395. 1901Assiminea tasmanica (Tenison-Woods); Tate & May, p. 395. 1903 Rissoa siennae (Tenison-Woods); May, p. 112. 1905 Assiminea tasmanica (Tenison-Woods); Gatliff, p. 15. 1906 Assiminea tasmanica (Tenison-Woods); Hedley, p. 527, pi. 32, figs. 27-29. 1921 Syncera tasmanica (Tenison-Woods); May, p. 55. 1923 Assiminea tasmanica (Tenison-Woods); May, pi. 25, fig. 25. 1927 Assiminea (Melassiminea) australis Thiele, p. 131, pi. 1, fig. 6. 1938 Assiminea tasmanica (Tenison-Woods); Cotton & Godfrey, p. 12. 1942 Assiminea tasmanica (Tenison-Woods); Cotton, p. 127. 1955 Assiminea tasmanica (Tenison-Woods); Kershaw, p. 309. 1958 Assiminea australis (Thiele); Abbott, p. 238. 1958 Assiminea bicincta (Petterd); Abbott, p. 265. 1958 Assiminea sienae (Tenison-Woods); Abbott, p. 273. 1958 Assiminea siennae (Tenison-Woods); Abbott, p. 273. 1958 Assiminea tasmanica (Tenison-Woods); Abbott, p. 274 1958 Assiminea tasmanica (Tenison-Woods); Macpherson in May, pi. 25, fig. 25. 1959 Assiminea tasmanica (Tenison-Woods); Cotton, p. 356. 1962 Assiminea tasmanica (Tenison-Woods); Macpherson & Gabriel, p. 95. 1979 Hydrococcus tasmanicus (Tenison-Woods); Smith & Kershaw, p. 56. 1981 Hydrococcus tasmanicus (Tenison-Woods); Smith & Kershaw, P. 50. DESCRIPTION: Shell turbinately conical, of six subconvex whorls moderately flattened, often with a weak peripheral keel, sutures clear, apex acute. Protoconch about two whorls marked with close minute pustules which become spirally aligned on second whorl often ending at a fine line. Adult ornament minute pustules commonly with weak to clear growth lines developing. Aperture pyriform, broadly expanded, peaked at apex, adult margin entire, barely expanded basally, columella expanded and continuous as a thin to thickened callus deposit; a minute umbilical chink may be present. Operculum horny translucent sculptured with curved close radiating lines, nucleus submarginal surrounded by distinct impressed ring, internally with a curved sloping ridge ending in a distinct raised peg behind the nucleus (Figs. 2a-2d). The adult aperture approximates one-half to more than one-half shell length. Colour light brown, yellowish or faintly orange sometimes with pale or off-white weak bands or darker brown base, apex pale brown. Live specimens have a dark greyish brown epidermis while the operculum may appear black EXTERNAL AJsllMAL MORPHOLOGY: Proboscis pale yellow with very fine, very close velvety dark brown or purplish brown transverse lines which are also present on mantle and flanking proboscis. Bright pink internal organs are weakly visible between and anterior to tentacles. Occasional animals without pigment or with greyish speckled transverse lines, occur, Foot and sole very pale pinkish purple. Proboscis thin relatively broad, capable of considerable extension and expansion, somewhat bilobate. Tentacles short, broader than high, glassy whitish with black eyes centrally situated, capable of forward to lateral movement but not very active. 12 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) The active animal extends the proboscis in front of the foot with a continuous flexibile sampling or grazing movement over the substrate, apparently performing the major sensory function in this respect. A normal proboscis extension of 1 mm from the shell lip has an observed further extension of 2mm. b a c Fig. 3a Assiminea lasmanica operculum external surface, West Arm, Tamar River, Tasmania. Fig. 3b Assiminea tasmanica operculum internal surface, West Arm, Tamar River, Tasmania. Fig. 3c Assiminea tasmanica operculum lateral view, West Arm, Tamar River, Tasmania. GROWTH PATTERN AND VARIATION: The obvious feature is a progressive increase in width per unit length, up to 0.5mm increase per 0.1mm increase in length increment at widely separate stages. No relationship between keeling and growth was observed in studied material. The columella normally shows increased callus deposit with maturity. Gerontic shells are usually but variably corroded depending on the environment. Largest specimen measured: 5.5mm long, 3.3mm wide. A six whorl Port Sorell specimen had an aperture height 2.4mm, width 1,9mm. An average aperture (4mm shell) is 2.1 mm high, 1.1 mm wide. SHAPE AND COLOUR VARIATION: While normally convex a weak keel on the body whorl is noticeable but not common. A very small umbilical chink may occur and variation is present in the columellar callosity. Frequently seen colour variation ranges from pale to distinctly brown. Colour bands are variably weak, but one type locality example possessed a light brown base, a narrow peripheral cream band, a narrow brown band with a cream band to the suture. The shell also has slight angling and, without the animal, could be confused with Hydrococcus. Colour variation differs with locality and may be related to environment. Greenish staining can occur. THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) 13 Plate 5 Rocky shore near Rosevears, west bank Tamar River. Plate 6 Small creek entering Kelso Bay through marsh environment. 14 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) Plate 7 Saltmarsh near Anderson's Creek, West Arm, Tamar River. Plate 8 Assiminea lasmanica on small stone in saltmarsh, West Arm, Tamar River. THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) 15 Victorian shells appear larger than Tasmanian, 614 whorls being found in a 4.3mm shell, the protoconch 2% whorls. Corio Bay shells are brown, often with distinct growth lines, the animal being very dark grey or black in appearance. Western Port Bay material has greyer colouration and the operculum has many almost transverse lightly curved lines, the nucleus outlined by two fine lines. HABITAT: This species is found near high tide level, occasionally above in suitably moist situations. It occurs on and under rocks of rocky shores, as at Penna and at Rosevears (Plate 5), near the mouths of creeks flowing into estuaries as at Kelso Bay (Plate 6) and in saltmarsh as at West Arm (Plates 7, 8). It is most common in the sheltered estuarine and marsh environment. It is not an animal of the sheltered intertidal environment described for Hydrococcus brazieri. In the Tamar Estuary it is most plentiful at inland localities. A large number is easily obtained at Rosevears as the tide withdraws from the rocky shore. In the West Arm by comparison it is sparsely distributed about the slightly raised tussocks of the saltmarsh and not apparently amongst the Salicornia plants. DISTRIBUTION: It is recorded from south-east and northern Tasmania but not yet from eastern or western localities. The nature of relationship to South Australian, Victorian and New South Wales morphs is beyond the scope of this work. TYPE MATERIAL: Holotype: One shell Tasmanian Museum Reg. No. E468/7809, (C369), pi. 4, figs. 1-2. Assiminea tasmanica Tenison-Woods. Sorell, south Tasmania. Syntypes: Six shells Tasmanian Museum Reg No. E467/7808, (TM5496), Rissoa siennae Tenison-Woods. North coast, Tasmania. DISCUSSION: The corroded holotype in the Tasmanian Museum measures 4mm long by 2.6mm wide (E. Turner pers. comm.) and fits within the normal observed variation. It is not possible to establish the precise type locality at Sorell, south-east Tasmania. But live material collected by Mrs. Turner and Mr. Andrews (Tasmanian Museum, 1980) is evidence that Penna may be regarded as very close to the type locality. As Rissoa siennae Tenison-Woods, 1877 can be included without difficulty the north coast type locality need not be further defined. The somewhat confusing Assiminea bicincta Petterd, 1889 has been studied in relation to the actual and described habitat and observed morphs. This habitat is not that of Hydrococcus. Assiminea australis Petterd is rejected from the genus but the name has been used invalidly. Syncera is rejected for Tasmanian shells as Assiminea is in common use in the literature (Abbott, 1958). Victorian shells are considered probably conspecific for comparitive purposes although difference can be seen between the operculum of Corio Bay specimens and those collected at Cardinia Creek, Western Port Bay (Fig. 2c, 2d). COMPARISONS As the.two species have been distinguished on an anatomical basis (W. J. Ponder pers. comm.), certain comparative morphological features only are required for field identification. Those discussed are summarised in Table 1. 16 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) Table 1 Summary of comparative features. Shell: H. brazieri A. tasmanica adult whorl No. Observed length range at 6 whorls maximum 6 more than 6 4.0 - 5.5mm Observed length range at 5.5 whorls Observed length range at 5 whorls 3.9 - 4.4mm 2.3 - 3.6mm 2.7 - 3.8mm maximum length 4.4mm 5.5mm apex obtuse acute supra-peripheral outline moderately convex slightly flattened peripheral outline commonly angular may have weak keel gerontic outline convex convex aperture rounded pyriform columellar margin callus very thin callus clear to very distinct umbilical niche small to very small minute if present operculum nucleus central nucleus sub-marginal Animal: tentacles elongate short broad proboscis narrow sub-rounded broad flattened Habitat: mid-littoral upper littoral substrate semi-sheltered flats sheltered to marshy shelter on sea grass, excluding rocks among marsh plants including rocks In Tasmanian populations H. brazieri can be expected to have an angled body whorl with a distinct colour band. A. tasmanica will have a greyish-brown shell usually with no colour band. Gerontic shells of both species will be corroded with convex whorls possibly with a weak keel. I n life these may be distinguished by apertural features but principally by the difference in habitat and the head of the animal. Both species exhibit considerable variation. Statistical comparisons have produced limited results. An attempt to relate whorl number to growth patterns has proved beyond the scope of this work. Initial statistical analyses did not demonstrate significant differences between the species. It is possible to demonstrate a difference using the presence and absence of the clear peripheral angling which is not seen in A. tasmanica. But this feature proves to be inconsistent over the southern Australian range of H. brazieri. It is further, confused by the presence of more or less convex gerontic shells which resemble A. tasmanica. Samplings from the Welcome River population for example indicated that more than 10% may have this form. Apertural variation reduced the effectiveness of the feature. The aperture in A tasmanica apparently increases more uniformly in size with growth and may be slightly more or slightly less than half the adult height. The H. brazieri aperture may exhibit uniform height over a range of shell height but many measurements were required to demonstrate this. THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) ' 17 Table 2 Hydrococcus brazieri. Shell height. Locality Mean Standard Deviation Tamar Mouth 2.8 0.57 Kelso 2.7 0.54 Combined Tamar 2.8 0.57 Welcome River 2.2 0.73 Whitemark 2.2 0.39 South-east Tasmania 2.3 0.59 Pittwater Combined south 2.8 0.40 Tasmania 2.5 0.50 South Arm Neck 2.9 0.39 Oyster Bay 2.7 0.55 Corio Bay (Victoria) 2.2 0.31 Western Australia 2.6 0.47 Table 3 Hydrococcus brazieri. Height/diameter Locality Mean Standard Deviation Tamar Mouth 1.30 0.10 Kelso 1.32 0.08 Combined Tamar 1.30 0.09 Welcome River 1.31 0.13 Whitemark 1.24 0.08 South-east T asmania 1.32 0.11 Pittwater Combined south 1.33 0.08 Tasmania 1.32 0.09 South Arm Neck 1.33 0.13 Oyster Bay 1.38 0.11 Corio Bay (Victoria) 1.16 0.07 Western Australia 1.30 0.07 Range Variation Coefficient Sample No. 4.4 -1.2 20.4 261 4.0 - 1.4 20.0 131 4.4 - 1.2 20.4 392 4.3 - 0.5 33.2 240 3.0 - 1.4 17.7 93 3.7 -0.9 25.7 77 4.0 -1.8 14.3 203 4.0-0.9 20.4 384 4.0-1.9 13.4 104 3.6 -1.6 20.4 39 3.4 -1.4 14.1 278 3.7 -1.7 18.1 16 Range Variation Coefficient Sample No. .55 -1.00 7.6 261 .53-1.12 6.4 131 .55 -1.00 7.2 392 .64 - 0.83 10.2 240 .46 -1.07 6.5 93 .57 -1.07 8.3 77 .59 -1.12 6.0 203 .59 -1.07 6.7 384 .59 -1.09 9.6 104 .64 -1.14 7.6 39 .33 - 0.93 6.0 278 .42 -1.17 1.3 16 ratio. 1 1 1 1 1 1 1 1 1 1 1 1 18 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) Table 4 Assiminea tasmanica. Shell height. Locality Mean Standard Deviation Range Variation Coefficient Sample No. Rosevears 2.5 0.51 3.7 -1.3 20.4 265 West Arm 3.0 0.35 4.0 - 2.3 11.7 44 Kelso Bay 2.9 0.56 4.0-1.8 19.3 20 Combined Tamar 2.6 0.54 4.0-1.3 20.8 329 South Tasmania 3.4 0.60 5.5 -1.9 17.6 111 Corio Bay 4.1 0.24 5.1 - 4.1 5.8 51 Cardinia Creek 2.8 0.38 3.6 -1.6 13.6 36 Combined Victoria 3.4 0.59 5.1 -1.6 17.4 87 Table 5 Assiminea tasmanica. Height/diameter ratio. Locality Mean Standard Deviation Range Variation Coefficient Sample No. Rosevears 1.33 0.09 1.69- 1.07 6.9 265 West Arm 1.37 0.07 1.60 - 1.23 5.1 44 Kelso Bay 1.41 0.13 1.65- 1.12 9.1 20 Combined Tamar 1.36 0.10 1.69- 1.07 7.6 329 South Tasmania 1.37 0.11 1.67- 1.00 7.7 111 Corio Bay 1.42 0.05 1.48- 1.28 3.5 51 Cardinia Creek 1.46 0.08 1.65- 1.29 5.1 36 Combined Victoria 1.44 0.07 1.65 - 1.29 4.5 87 Table 6 Analysis of variation coefficient. Tamar South Tasmania Victoria Mean A. tasmanica H/D 7.6 7.7 4.5 6.6 H. brazieri H/D 7.2 6.7 6.0 6.6 mean H/D 7.4 7.2 5.25 A. tasmanica Height 20.8 17.6 17.4 18.6 H. brazieri Height 20.4 20.4 14.1 18.3 mean Height 20.6 19.0 15.75 Standard error of means of localities p = 0.05 = 2.81. THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) 19 To study shell variation the simple statistics of shell height and maximum diameter were used. Diameter was found to vary with height increments in a similar pattern for both species. Height/diameter ratio was calculated for all shells measured. The mean, standard deviation and coefficient of variation were calculated for each population using shell length and height/diameter ratio. These data are listed in Tables 2, 3, 4, 5. As material of both species was not available for all localities analysis of varience has been made of the Tamar river, south-east Tasmania and Corio Bay (Victoria) populations for comparative purposes. A statistical difference could not be demonstrated between the species. But a statistical difference between the localities at probability exceeding 0.05 was demonstrated in shell height (Table 6). Comparison was made between the means of individual populations using Student’s “t” test with variances not assumed to be equal (Parker, 1976). Levels of significant difference in shell height are set out in Tables 7, 8,11,12. Results for south Tasmania, prior to 1980, and for Western Australia cannot be accepted as the material was insufficiently representative for this statistic. The Welcome River H. brazieri material includes a wide sampling of the population and hence differences exist between this and less effectively sampled populations. The range of height in Victorian A. lasmanica differs in Corio Bay and Cardinia Creek samplings. The significance indicated between these populations and between them and Tasmanian populations is due largely to this difference. A valid comparison is probably best achieved by combining the populations as has already been done for analysis of variance, into three groups. The results indicate that statistical differences do exist between populations (Tables 11,12). This suggests that shell height differences exist between Victorian and Tasmanian H. brazieri. For this statistic in A. tasmanica difference is apparent between south Tasmania and the Tamar River, north Tasmania in addition to Victoria. The results for shell height suggest that real differences may exist but must be looked at with caution in the absence of replicated random samplings. This comment must also apply to the statistic height/diameter ratio. But this statistic is believed to be less likely to be biased and can therefore be assumed to substantiate the validity of significant differences. On this basis H. brazieri from Corio Bay differ consistently from Tasmanian populations. The Whitemark (Flinders Island) and Oyster Bay (east Tasmania) populations also differ from other populations (Tables 9,10,13,14). Table 7 Probabilities of significant difference between populations of Hydrococcus brazieri: shell height. South Tasmania Pittwater South Arm Neck Oyster Bay Welcome River Tamar Mouth Kelso Whitemark W. Australia South Pitt- Tasmania water 0.001 0.001 NSD 0.05 NSD NSD 0.001 0.001 NSD 0.05 NSD NSD 0.001 NSD NSD South Arm Neck NSD 0.001 0.05 NSD NSD NSD NSD 0.001 0.01 NSD NSD Tamar River Mouth 0.001 0.01 NSD NSD 0.001 0.05 NSD Kelso White- mark 0.01 NSD 0.05 Corio Western Bay Australia NSD NSD 0.001 0.001 0.01 NSD 0.001 0.01 NSD 0.05 Oyster Welcome Bay River 20 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) Table 8 Probabilities of significant difference between populations of Assiminea tasmanica: shell height. Rosevears West Kelso Penna South Corio Cardinia Total Total Arm Bay Tasmania Bay Creek South Tasmania Tamar Rosevears 0.001 NSD West Arm 0.01 0.05 0.01 Kelso Bay 0.05 NSD 0.05 NSD Penna 0.01 NSD 0.05 NSD 0.001 South Tasmania 0.01 NSD NSD NSD NSD 0.001 Corio Bay 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Cardinia Creek NSD NSD NSD 0.01 0.05 0.001 0.001 NSD Total Victoria 0.001 0.05 0.05 NSD NSD 0.001 0.05 NSD 0.001 Total Tamar NSD 0.01 NSD 0.001 0.001 0.001 NSD 0.001 — Table 9 Probabliities of significant difference height/diameter ratio. Combined populations of Hydrococcus brazieri. Tamar River South Tasmania Victoria Tamar River South Tasmania NSD Victoria 0.01 0.01 Western Australia NSD NSD 0.01 Table 10 Probabilities of significant difference between Assiminea tasmanica and Hydrococcus brazieri. Height/diameter ratio, combined populations. A. tasmanica H. brazieri Tamar River South Tasmania Victoria Tamar River 0.01 NSD 0.001 South Tasmania 0.05 0.05 0.001 Victoria 0.001 0.001 0.001 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) 21 Table 11 Probabilities of significant difference between Assiminea tasmanica and Hydrococcus brazieri. Shell Height, combined populations. A. tasmanica H. brazieri Tamar River South Tasmania Victoria Tamar River NSD 0.01 0.001 South Tasmania NSD 0.001 0.001 Victoria 0.Q1 0.001 0.001 Table 12 Probabilities of significant difference: shell height. Combined populations of Hydrococcus brazieri. Tamar River Tamar River South Tasmania Victoria South Tasmania 0.05 - Victoria 0.001 0.05 - Western Australia NSD NSD 0.05 Table 13 Probabilities of significant difference between populations of Hydrococcus brazieri: height/diameter ratio. South Pitt¬ South Oyster Welcome Tamar Kelso White- Corio Western Tasmania water Arm Bay River River Mark Bay Australia Neck Mouth South Tasmania 0.01 NSD Pittwater NSD 0.01 South Arm Neck NSD NSD 0.01 Oyster Bay 0.05 NSD NSD 0.01 Welcome River NSD NSD NSD 0.05 0.05 Tamar Mouth NSD NSD NSD 0.01 NSD 0.01 Kelso NSD NSD NSD 0.05 NSD NSD 0.01 Whitemark 0.01 0.01 0.01 0.01 0.05 0.05 0.01 0.01 W. Australia NSD NSD NSD 0.01 NSD NSD NSD 0.05 0.01 22 THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) Table 14 Probabilities of significant difference between populations of Assiminea tasmanica: height/diameter ratio. Rosevears West Kelso Penna South Corio Cardinia Total Total Arm Bay Tasmania Bay Creek South Tamar Tasmania Rosevears NSD NSD West Arm 0.05 NSD NSD Kelso Bay 0.05 NSD NSD NSD Penna NSD NSD NSD NSD NSD South Tasmania 0.05 NSD NSD NSD NSD NSD Corio Bay 0.01 0.01 NSD 0.05 NSD 0.05 0.01 Cardinia Creek 0.01 0.01 NSD 0.01 0.01 NSD 0.01 0.01 Total Victoria 0.01 0.01 NSD 0.01 0.05 NSD NSD 0.01 0.01 Total Tamar NSD Significant difference between A. tasmanica populations is also essentially between Victoria and Tasmania (Table 8). In the case of the Tamar River Rosevears populations corrosion of the shell probably contributed to the difference between this and other Tasmanian localities. Hence in comparing these two species (Tables 10, 11) allowance must be made for uncontrolled and unmeasured factors affecting the populations. The presence and the absence of significant difference between the species must be discounted by an unknown factor. But, even in the absence of weighting the statistics used to compensate for features not included, real significant difference is apparent from the results. It is nevertheless evident for practical purposes that the species are most readily separated by certain minor morphologic features and by the difference in habitat. H. brazieri is clearly an intertidal species essentially estuarine but near the estuary mouth or similar sheltered situations. At Kelso in the Tamar River estuary it lives in the sea grass ( Zostera) zone. Assiminea is essentially a tidal marsh snail. In Victoria it occurs in Salicornia saltmarsh situations. R. Burn (pers. comm.) describes such an environment and I collected in such an area at Cardinia Creek. It may prefer greater shelter and occurs on the edge of marshy areas or under stones of the upper shore in Tasmania. In the Rosevears area of the Tamar River and at Penna in south-east Tasmania the habitat is stony. In the Tamar River localities of West Arm and Kelso Bay the habitat is at the landward edge of the very sparse Salicornia marsh (Plate 7). The difference in these situations and the intertidal habitat of H. brazieri; is fundamental. CONCLUSIONS Assiminea tasmanica Tenison-Woods and Hydrococcus brazieri (Tenison-Woods) are recognisably distinct species both in aspects of external morphology and habitat preferred. Probable confusion between the species could have arisen due to superficial resemblance between gerontic H. brazieri and A. tasmanica. The failure to separate H. brazieri generically for many years undoubtedly contributed to confusion. The two species reveal some parallel degree of variation so that in material studied consistent statistical difference was found only by combining populations on a regional basis. Statistical analysis demonstrates that more variation is present within the individual species than between the species. THE GASTROPODS Assiminea AND Hydrococcus IN TASMANIA (MOLLUSCA: GASTROPODA) 23 ACKNOWLEDGEMENTS The following people have loaned or collected material or have helped with discussion: Miss A. Green, Mrs. J. Greenhill, Mrs. E. Turner, Mr. A. P. Andrews (Hobart); Mr. I. S. Norton (Launceston); Mrs. S. M. Slack-Smith (Perth); Mr. R. Burn, Dr. B. J. Smith (Melbourne). Dr. W. F. Ponder kindly lent me his manuscript and provided valuable discussion. I wish to thank the Science and Industry Endowment Fund for support in my research. I thank the Queen Victoria Museum for arranging typing of the manuscript. Mr. N. R. Kemp photographed type material in the Tasmanian Museum for this investigation. Miss. R. Scott prepared the illustrations for Fig. 3. REFERENCES Abbott, R. T. 1958. The Gastropod Genus Assiminea in the Philippines. Proc. Acad. Nat. Sci. Philad. 110, 213-278, pis. 15-25. Boettger, 0. 1887. Aufzahlung der zur Gattung Assiminea Fleming gehorigen Aden. 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