UNI HARVARD UNIVERSITY Library of the Museum of Comparative Zoology —/ auj ^^^CC /.v.us. COMP. zoou. ^/ . — I LIBRARY OCCASIONAL PAPERS APR 1 4 1976 ^ ,, HARVARD OI the UNIVERSITY MUSEUM OF NATURAL HISTORY The University of Kansas Lawrence, Kansas NUMBER 48, PAGES 1-23 MARCH 25, 1976 ORAL MORPHOLOGY OF ANURAN LARVAE: TERMLNOLOGY AND GENERAL DESGRIPTION By Richard J. VVassersug^ This paper is an introduction to certain morphological features in the mouths of tadpoles. It was undertaken as part of a com- parative investigation on the evolution of anuran larvae and the systematics of frogs. The first use of larval morphology in anuran systematics was by Lataste (1879), who in 1888 proposed that frogs could be divided into two groups based on the spiracle position of their larvae. Many herpetologists since have used larval features in their systematic studies. The literature prior to mid-century has been ably reviewed by Orton (1944), whose own studies constitute a major contribu- tion to our understanding of the superfamilial relationships of the Anura. Orton (1953, 1957) proposed a classification of frog families based on four larval types. Her Type 1 includes the Pipidae and Rhinophrynidae, with tadpoles that have paired spiracles and lack keratinized mouth parts. Type 2 consists solely of the Microhylidae, with tadpoles lacking keratinized mouth parts and having a single, medial spiracle. Type 3 includes the families Ascaphidae and Discoglossidae, with keratinized larval mouth parts and a medial spiracle. Type 4 includes all the remaining families; their tadpoles have keratinized mouth parts and a sinistral spiracle. Although a few scientists object to use of any larval features in systematic stud- ies (Griffiths and Carvalho, 1965), Orton's superfamilial groups have 1 Department of Anatomy and Committee on Evolutionary Biology, Uni- versity of Chicago, Chicago, Illinois 60637. 2 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY been accepted by most herpetologists. Starrett (1973) has gone so far as to replace Orton's numbers with names, giving formal tax- onomic recognition to these groups. The value of this has been questioned by Sokol ( 1975 ) , who objects to the phyletic implica- tions of this move. For the purposes of this introductory study, I recognize Orton's groups without Starrett's names. There is much disagreement among students of anuran system- atics as to whether Orton's groups represent a linear evolutionary sequence (see Griffiths, 1963; Hecht, 1963; Tihen, 1965; Inger, 1967; Nevo, 1968; Starrett, 1968, 1973; Kluge and Farris, 1969; Spinar, 1972; Lynch, 1973; Savage, 1973; Sokol, 1975). The arguments all rest on the determination of primitive features in tadpoles and what weight can be given the two larval characters used in Orton's classification. With so few characters, the chance of convergence between the families is necessarily high. To determine whether cer- tain families appear similar because of common ancestory or be- cause of convergence is a major problem. One way to attack such a problem is to find additional diagnostic characters. My study began with a search for new characters. For two reasons I chose to look at feeding structures. The first reason is one of convenience, in that a large proportion of tadpole tissue is in- volved in ingestion; consequently, feeding structures are relatively easy to examine. The second reason for studying feeding struc- tures is that in nutrient acquisition an organism comes in direct contact with the environment. Thus, feeding structures are centers for evolutionary action that may be highly adaptive. The adaptive significance of the larval stage for anurans in general may be tied directly to the feeding mechanism of the tadpoles (Wassersug, 1975). The present study is limited to surface features in the oral cavity of tadpoles that are visible with a dissecting microscope; the emphasis here is on organs that are directly in contact with the water or with food in the water. A preliminary examination of the inside of the oral cavity of a variety of tadpoles (Wassersug, 1973) revealed many morpholog- ical difl^erences among tadpoles of various families, genera and spe- cies. A literature survey further demonstrated much diversity in the oral structures of anuran larvae. Descriptions or figures of struc- tures in the oral cavity are available for the tadpoles of Ascaphus truei (Gradwell, 1971a, 1973), Bombina igneus (=bombina) (Goette, 1875), Alytes obstetricans (Magnin, 1959), Rana pipiens (Parker, 1881, Plate 1), Rana agilis {=dalmatina) Kratochwill, 1933), Rana teniporaria (Savage, 1952; Dejongh, 1968), Rana catesbeiana (Gradwell, 1970, 1972a), Rana fuscigula (Gradwell, ORAL MORPHOLOGY OF ANURAN LARVAE 3 1972c), Pelobates fuscus (Schulze, 1870, 1892), Biifo bufo (Savage, 1952), Phijllomediisa trinitatis (Kenny, 1969a), Hijla geographica (Kenny, 1969b), Pseudis paradoxa (Parker, 1881), Xenopus laevis (Weisz, 1945; Sterba, 1950; Ueck, 1967; Gradwell, 1971, 1975), Hymenochirus boettgeri (Sokol, 1962; Ueck, 1967), Pipa carvalhoi (Sokol, in manuscript), CaUueUa gutttilata, Glyphoglossus molossus, Chaperina fusca (Savage, 1952), Hypopachus aguae (Savage, 1955; Nelson and Cuellar, 1968), Hypopachus variolostis, Gastrophryne oUvacea, Gastrophryne iista (Nelson and Cuellar, 1968) and Phrynomenis annectens (Gradwell, 1974). Unfortunately, the ter- minology used in these papers is inconsistent. Few of the descrip- tions or figures are complete, and many drawings tend to be stylized in a manner that does not inspire confidence in fine detail. Many oral structures have received two or three names; in some cases the names imply functions that are speculative at best. Other structures have been repeatedly ignored by anatomists. I have not referred to one major study (Severtzov, 1969) because the author claims a de- gree of morphological similarity in the larvae that he examined that I could not verify in my own material of the same genera and families. As a prelude to a comparative study of tadpole oral structures (Wassersug, in manuscript) I present here a general description of the oral features of tadpoles. Old terms are redefined and some new ones are introduced. I have selected terminology that is most applicable to Orton's Type 4 tadpoles because these are the most common type of larvae. The description is relevant to tadpoles be- tween stages 26-39 ( Gosner, 1960 ) . Ontogenetic variation is treated in a separate work (Wassersug, 1976). In most cases I follow Kratochwill's terminology ( 1933 ) with English translations. All terms pertaining to the inside of the oral cavity are printed in bold- face capitals as they are introduced. Major features are illustrated in Figs. 1 to 3. Appended is an outline for the description of tad- pole oral surface features. Acknowledgments This paper is an extension of a doctoral thesis submitted to The University of Chicago, where James Hopson, Robert Inger, George Rabb, David Wake and Rainer Zangerl patiently provided advice and encouragement. I thank them and especially Inger and Wake, who co-chaired my doctoral committee. For logistical support I thank the directors and department heads of the following institu- tions: The Committee on Evolutionary Biology and the Depart- 4 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY ment of Anatomy, The University of Chicago; The Center for Graduate Studies and the Division of Reptiles, Field Museum of Natural History, Chicago; The Museum of Natural History, The University of Kansas. Financial support was provided by a fellow- ship from the Center for Graduate Studies, Field Museum of Nat- ural History, and grants from the Hinds Fund of The University of Chicago and the Ecology Program of the National Science Foun- dation. I sincerely thank the many people who aided directly in the preparation of the manuscript. Samuel Grove and Mrs. Alonzo Davis executed drawings. Mrs. Use Hecht assisted in the translation of several foreign language papers. Christine McNamara, Linda Throckmorton, Judy Hamilton and Karen Rosenberg typed the many manuscript drafts. Various versions of this paper have been read and criticized by William Duellman, Robert Inger and Otto Sokol. For moral sup- port I thank Marilyn Belka, Martha Crump, James L. Edwards, Karel Liem, R. Eric Lombard, Hymen Marx and Everett C. Olson. Materials and Methods The description presented here is based on a review of the liter- ature, the detailed study of 26 species from six families (Ascaphidae, Discoglossidae, Rhinophrynidae, Microhylidae, Hylidae and Pelo- batidae; Wassersug, 1973), and a cursory examination of an assort- ment of species from three additional families ( Bufonidae, Ranidae, Leptodactylidae). Figs. 1 and 2 were made with a camera lucida from a Hyla reii,iUo tadpole. This species was the most extensively studied and its larval oral structures are described in fuller detail elsewhere (Wassersug, 1976). The tadpoles that I dissected were washed briefly in tap water to remove superficial preservatives. All dissections were made with assistance of a stereoscopic microscope. Observations and measure- ments were taken on tadpoles pinned under water in a depression carved in a black-stained paraffin block. Dissections were made by carefully inserting the blade of a scissors into the left corner of the mouth between the upper and lower beaks and cutting back to the posterodorsal corner of the pharynx. The scissors were then gently worked transversely and the mouth cut to the opposite, postero- dorsal corner. Oral surface could then be exposed by simply open- ing the mouth from the side. As the mouth was opened, the inter- meshing nature of dorsal and ventral features could be assessed. A longitudinal cut was made along the side of the mouth, freeing the ORAL MORPHOLOGY OF ANURAN LARVAE 5 roof from the floor. This cut separated the ceratohyal on the right side from the palatoquadrate bar. Externally it was not always pos- sible to determine exactly the position of the posterodorsal corner of the pharynx; in such cases the initial cut was made relatively high. This procedure assured the retention of intact gill filters but at the expense of damage to the pressure cushions and ciliary groove. In tadpoles lacking extensive pigmentation of the buccal and pharyngeal epithelia, surface features are transparent and difficult to discern. Therefore, these tadpoles were stained with either a methyl blue or crystal violet solution after they had been dissected. Because of the mucin specificity of methyl blue, secretory tissues were specifically accentuated. Gross Features In tadpoles the forelimbs and gills are covered by a flap of skin, the operculum. The elongate intestine is tightly cofled. The oral orifice is small due to the short Meckel's cartilage. Structures pe- culiar to tadpoles, infralabial and supralabial cartilages, serve as the functional jaws. The most remarkable feature of tadpoles in com- parison to other tetrapods is the greatly elongate palatoquadrate, which is rotated anteriorly so that it parallels the trabeculae cranii. At metamorphosis this suspension is largely rebuilt. The quad- rate rotates down and backwards into a more typically vertical posi- tion and Meckel's cartilage elongates. The forelimbs emerge, and the tail and gills are absorbed. Free-swimming Type 3 and 4 larvae have externally visible keratinized mouth parts surrounding the mouth opening. The major elements are the upper and lower beaks, which sheath the supra- labial and infralabial cartilages. Rows of keratinized denticles or teeth ("odontoids" of Sokol, 1975) are arranged in characteristic patterns above and below the beaks on the oral disc. The denticle rows may be continuous or medially divided. Denticle patterns have been much used in diagnosis of tadpoles; the notational schemes for denticle patterns have been reviewed by Lynch ( 1971). By the simplest scheme, that of giving the upper and lower row counts divided by a slash, the 2/3 pattern is the commonest. The margins of the oral disc are lined with various pustulations and short, blunt papillae. Their form and pattern have also been used extensively in tadpole identification (Altig, 1970; Duellman, 1970; van Dijk, 1966). By definition, Orton's Type 1 and 2 tadpoles lack keratinized mouth parts, but may have elaborate structures on the OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY BUCCAL POCKET PREPOCKET PAPILLA -i BFA PAPILLAE -1 LINGUAL PAPILLAEn INFRALABIAL PAPILLA n .>— -w LOWER BEAK n FILTER ROW ^ •ESOPHAGEAL FUNNEL l-MEDIAN NOTCH ABOVE GLOTTIS '-BUCCAL FLOOR ARENA VENTRAL VELUM-" Fig. 1. — The floor of the mouth of a typical Type 4 tadpole (Orton, 1953, 1957). The illustration is based on a stage 37 HyJa regilla larvae (max. \\ddth of pharynx = 6.1 mm). The filter folds are schematically drawn. oral disc or lips. Examples include the "funnel mouth" in certain microhylids such as Microhyla heijmonsi (Parker, 1934) and the tentacles in Xenopus and Rhinophrynus. The oral orifice opens anteriorly or anteroventrally. The orifice is usually less than a quarter the width of the mouth, rarely larger. Internally, the mouth or oral cavity widens posteriorly and then abruptly constricts along the posterior walls of the pharynx into the ORAL MORPHOLOGY OF ANUK\N LARVAE 7 esophagus. The oral cavity thus is roughly triangular in shape in the horizontal plane and dorsoventrally compressed (Figs. 1 and 2). The oral cavity can be divided into two major regions: an anterior, BUCCAL CAVITY and a posterior, PHARYNGEAL CAVITY. These cavities are separated on both structural and func- tional grounds by a distinctive, movable but non-muscular flap, which is essentially continuous across the floor and roof of the mouth. It should be noted that by using this prominent ring of tis- sue as the boundary between the two regions, the first gill pouch resides in the buccal, rather than the pharyngeal, cavity. The terms buccal and pharyngeal are therefore not strictly homologous to the same terms used for other vertebrates. The ventral portion of the dividing flap is supported by posteriorly projecting, cartilaginous spicules on the posterodorsal margin of the hypobranchial plate. In the few tadpoles (viz. Pipidae) that lack this flap there is a com- mon buccopharyngeal cavity. Viewed from above, the ventral por- tion of the flap is a continuation of the buccal floor. Its posterior margin, grossly a posteriorly directed "U" or "V", is free and un- supported. This trailing edge may be slightly thickened and bears large, paired crenulations or short caudad projections on each side of the midline. These projections often appear in one to one asso- ciation with the individual gill pouches that they partially cover. A MEDIAN NOTCH lies in the middle of the ventral portion of the flap. The lower surface of the ventral portion of the flap op- poses the gill filters and the anterior portion of the pharyngeal cavity. The ventral portion of the flap has been called either the VEN- TRAL VELUM or the ANTERIOR FILTER VALVE (Kenny, 1969a; Sokol, 1975) in the literature of the last forty years (reviewed by Gradwell, 1970). While convincingly demonstrating a valvular function for the organ in Rana catesheiana, Gradwell chose to use the term "velum", with the realization that the structure may, in part, serve an auxfliary role of redirecting water currents. He also followed Savage in claiming historical priority for the term "velum", credited to Goette (1875). In fact, Schulze in 1870, first named this stmcture the "gill cover plate" {Kiemendeckpiatte) , but for brevity, I will use the shortest accurate term, ventral velum. The lower surface of the ventral velum has some unique histological features, which will be discussed in more detail below. The continuation of the velum on the roof of the mouth is more posterior than the trailing edge of the ventral portion. It has been called both the DORSAL VELUM and the POSTERIOR FILTER VALVE. Both Gradwell (1970, 1973, 1974) and Dejongh (1968) OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY I- BUCCAL ROOF ARENA LATERAL RIDGE PAPILLA POSTNARIAL PAPILLA NARIAL VALVE PROJECTION— I PRENARIAL PAPILLAE- UPPER BEAK— I CILIARY GROOVE-" ■PRESSURE CUSHION DORSAL VELUM-" GLANDULAR ZONE BRA PAPILLAE-" MEDIAN RIDGE-' Fig. 2. — The roof of the mouth of a typical Type 4 tadpole (Orton, 1953, 1957). The illustration is based on the same stage 37 Hijla regilla larvae seen in Fig. 1. and, to a certain extent, Kratochwill ( 1933 ) have suggested a true velar function for this structure. The dorsal velum is deepest di- rectly above the second and third ceratobranchials and shallowest or absent on the midline in front of the esophagus. Thus, it has sometimes been considered a paired structure symmetrical about the midline. The dorsal velum is a liner, more delicate epithelial fold lacking both the cartilaginous spicules and the extensive con- nective tissue support of the ventral velum. It does not project directly ventrad but tends to curl forward in fixed specimens. ORAL MORPHOLOGY OF ANURAN LARVAE 9 Features of the Buccal Cavity The floor of the buccal cavity has several distinctive topographic features, though from the posterior margin of the short Meckel's cartilage to the margin of the velum it is generally flat. The most anterior projections of the epithelium within the buccal cavity are called INFRALABIAL PAPILLAE, because they lie over the infra- labial cartilage and its articulation with Meckel's cartilage. The infralabial papillae, as with other major papillae in the oral cavity, may be single, multiple, attenuate, blunt, bifurcate, multiple- branching, compressed, pointed, conical, pustulate, curved, re- curved, finger-like, etc. PAPILLAE are here defined simply as any projection with a circular or elliptical base and a height twice the diameter of the base. Smaller projections are called PUSTU- LATIONS. In all glossal frogs the TONGUE develops medially, just behind the infralabial cartilages at the front of the ceratohyals. It is an anteriorly convex, raised ridge in the beginning of its ontogeny. Later it expands posteriorly into a roundish pad. Its development has been reviewed most recently by Hammerman (1969). Premeta- morphic lingual papillae, which degenerate with development of the tongue, have been studied by Rieck (1932), Hammerman (1964, 1965), Helff and Mellicker (1941),' and Schulze (1870). Kenny (1969a) calls these sensory papillae. They arise medially near the anterior base of the tongue and are normally paired, being symmetrically arranged about the midline. I call these structures LINGUAL PAPILLAE restricting the term to premetamorphic structures. Most papillae on the buccal floor posterior to the tongue anlage are arranged with the larger ones more or less evenly spaced and forming two rows aligned from front to back. At the edge of the hypobranchial plate these papillate rows begin to converge toward the midline and may parallel the edge of the ventral velum. The papillae, if large enough, often curve anteromesiad and circum- scribe the area in the center of the buccal floor. This area is called the BUCCAL FLOOR ARENA (BFA). The papillae which define this area are therefore BUCCAL FLOOR ARENA PAPILLAE or BFA PAPILLAE. Various minor papillae and pustulations may occur within or about the arena. The epithelium of the buccal floor descends into the lateral spaces between the posterolateral margin of the ceratohyals and the anterior margins of the first ceratobranchials, forming deep pockets on each side. These pockets may be visibly perforated in certain tadpoles, thus forming the first true gill slits which lead to 10 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY the ATRIAL (OPERCULAR) CHAMBER. These shts serve as m- dependent connections from the buccal cavity to the atrial chamber and a functional bypass of the pharynx (at least in Rana catesbei- ana; Gradwell and Pasztor, 1968 — "gill cleft :^r'="pharyngeal by-pass"). There is no filter epithelium lining these pockets. For convenience they can be called BUCCAL POCKETS or BUCCAL SLITS for their topographic position, anterior to the edge of the velum and independent of the remaining gill slits in the pharynx. Papillae and pustulations are often present in front of the buccal pockets on the buccal floor above the lateral arms of the ceratohyal. Large and distinctive papillae arranged in a line along the edge of the pocket are called PREPOCKET PAPILLAE. In general the buccal roof is level. The rostral area, however, may curve sharply ventrad. Topographic features allow a conven- ient division of most of the buccal roof into three major sections. The most anterior section is the PRENARIAL ARENA. It is en- closed by the supralabial cartilages anteriorly and internal nares posteriorly. Pustulations, papillae, or ridges are often present in the prenarial arena; when present, these structures generally show symmetry about the midline. The second section, the POST- NARIAL ARENA, is a small, but structurally complex area be- tw^een the nares anteriorly and a transverse median ridge or flap posteriorly. The transverse flap, here called the MEDIAN RIDGE (the "Gaumenquerklappe" = "palatal transverse flap" of Schulze, 1870; "transverse fold" of Dejongh, 1968; "sensory papillae" of Kenny, 1969b), is an important landmark usually about halfway back on the buccal roof. The last section of the buccal roof is the BUCCAL ROOF ARENA (BRA), a faintly defined area which corre- sponds to the buccal floor arena ventrally. The buccal roof arena begins behind the median ridge and is bound laterally by papillae. The prenarial and postnarial arenas are generally smaller than the BRA and together make up a third or less of the total surface area on the buccal roof. The INTERNAL NARES or choanae are a major feature on the buccal roof. They project down from the rostral surface, and are slit-like, with an oblique to transverse orientation. The fold of mucosa that makes up the narial wall on each side starts at the anterolateral corner of the nares, where the nare does not project noticeably because of the natural curvature of the rostrum. Small, sometimes paired, posteriorly directed papillae occur in certain spe- cies at this anterolateral corner and project over a portion of the narial opening. While these are not properly shaped or positioned to act as valves, they were originally called '^vordere Choanenklap- ORAL MORPHOLOGY OF ANURAN LARVAE 11 pen" by Schiilze (1870). I will refer to them as ANTERIOR NARIAL PAPILLAE or PRENARIAL PAPILLAE. Posteriorly, the flap of mucosa which constitutes the narial wall tucks into a lateral pocket on each side rather than abutting directly on the rostral surface. The posterior narial wall thus forms an extensive free flap, the NARIAL VALVES. As is consistent with an undisputed valvu- lar function for this posterior wall (e.g., Gradwell and Pasztor, 1968), the posterior narial rim is always thinner and more freely movable than the anterior narial wall. Single, tall tongues of the narial valves are called NARIAL VALVE PROJECTIONS. When present, they are usually on the medial end of the narial valve. Within the narial arena, between the internal nares and the median ridge, there may be short, distinct rows of papillae. When present, these rows are usually oriented obliquely, anteromediad to posterodorsad. These papillae are usually positioned directly be- hind each narial valve and will be called posterior narial papillae or POSTNARIAL PAPILLAE. These postnarial papillae do not structurally parallel the prenarial papillae (that is, they are not asso- ciated with the narial walls); nevertheless, I accept the term be- cause of its simplicity. In certain species there are POSTERIOR NARIAL RIDGES instead of papillae within the narial arena. At about the middle of the buccal roof, the median ridge arises as a transverse fold. It is a free, thin epithelial flap, the edge of which points anteroventrad and may be papillate and have a me- dial notch. Subsidiary LATERAL RIDGE PAPILLAE ("sensory papillae," Kenny, 1969b), usually one on each side of the median ridge, may be present. In certain species the lateral ridge papillae are the most conspicuous feature on the buccal roof. A secondary papillary zone or fringe may develop on the anterior surface of the median ridge. Secondary papillae, likewise, can occur on the an- terior surface of lateral ridge papillae. Papillae are common on the buccal roof proper, posterior to the median ridge. They are never as numerous as on the corresponding central region of the buccal floor. Papillae of the buccal roof proper are arranged into two symmetrical regions. Larger papillae form rows aligned in an approximately anterior to posterior direc- tion, roughly halfway between the lateral margins of the mouth and the midline. These are the BRA PAPILLAE that serve to de- fine the lateral limits of the buccal roof arena. LATERAL ROOF PAPILLAE, ah^'ays smaller in size and usually fewer in number, sometimes occur in clusters or short rows far lateral on the buccal roof. The posterior limit of the buccal roof behind the buccal roof 12 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY arena is lined with a transverse crescentic band, which was first identified as a mucous membrane ("Schleimhaut") by Schulze (1870). Under low magnification this tissue has a buffed texture and was called the glandular zone ("Driisenzone') by Kratochwill (1933). In most species definite SECRETORY PITS can be seen with SOX or higher magnification. While Kenny (1969a) felt that this was a major region of food collection, and referred to the zone as the "dorsal food traps," I am not convinced of the function im- plied in this term and choose to retain Dejongh's simple, descrip- tive term GLANDULAR ZONE. This secretory zone often extends posteriorly and laterally onto the dorsum velum. Identical secretory pits line the posterior edge of the ventral velum in many species. Features of the Pharyngeal Cavity Surfaces exposed behind the dorsal and ventral vela, but in front of the esophagus and internal to the gill slits, are pharyngeal. Viewed from above, the major and most conspicuous features in the pharynx are the GILL FILTERS. These are ruffled epithelial organs associated with the posterior surfaces of ceratobranchial 1 (cb. 1), the anterior surface of ceratobranchial 4 (cb. 4), and both the anterior and posterior surfaces of ceratobranchials 2 (cb. 2) and 3 (cb. 3). They project outward from dorsomesad projecting plates of connective tissue, the FILTER PLATES. The filter plates are oriented parallel to the gill slits in an anteromeso-posterolateral direction surrounding the FILTER CHAMBERS. The plates originate anteriorly, from the posterior margin of the hypobranchial plate, where the ceratobranchials be- gin. The ventral velum also originates here, and for a short distance posteriorly, the velum is attached to the dorsal edge of the filter plate, before it becomes a completely free flap. The filter plates are rarely perpendicular to the buccal floor, but are usually imbricated to varying degrees, with their dorsal edges posterior and medial to their ventral supporting ceratobranchial cartilages. The plates are not necessarily fixed in this position in life; they are rather flexible and could become more erect with depression of the branchial basket during the regular oral pumping cycle. The height of the filter plate reflects the size and depth of the branchial baskets. The filter chambers or cavities are spaces in the pharyngeal cavity above the gill slits, between whole filter plates on opposing arches. There are three filter cavities on each side. The first is between the filter plates of cb. 1 and 2, the second between cb. 2 and 3, and the last between cb. 3 and 4. The second filter cavity is the largest. ORAL MORPHOLOGY OF ANURAN LARVAE 13 The gill filters arise as epithelial folds on the filter plates. The filters have been termed "gills", "internal gills", and "gill rakers" in the older literature, but should not be confused with the true gills that arise from the distal edges of the interbranchial septa. The essential structure of the filters was described by Naue (LSTO), who reported no major differences between the filters of Peloljates fusciis, Rmm. tempomria, and Rona esculenta. Kratochwill (1933) made a detailed description of the filter apparatus in Rana agilis {^dal- matina) and Kenny (1969a) described the filters of Phyllomediisa trinitatis. Gradwell (1972a) described the filters of Rana catesbei- arm. The filter epithelium is convoluted into FILTER RUFFLES CFilterkrause:' Kratochwill, 1933) or FILTER FOLDS (Kenny, 1969a), that run in parallel rows down the filter plates from dorso- posteromedial to ventroanterolateral. Full filter rows run the length of the filter plates and are usually a bit wider near their ventral margin on the plates than near their dorsal margin. In species with dense filter surfaces, partial folds form triangular wedges that pro- ject down the filter plate. These partial rows fill spaces between full rows along the dorsal margins of the filter plates. These fea- tures of filter anatomv are illustrated in Fig. 3. Unlike the true gill filaments, which are often elongate, the filter ruffies appear short and truncate in section. In some ways they resemble abutting, overly trimmed garden hedges in that they are widest away from their substrate attachment, in this case, the sur- face of the filter plate. This results in the formation of partially to fully covered passages between neighboring folds called FILTER CANALS. The short and stout ruffied appearance of the filters is caused by the sequence of folding on each rufHe. The MAIN FOLD (^middle fold of Kratochwill, 1933 and Kenny, 1969a) of each ruffle is low and broad. The SECONDARY, TERTIARY and occasionally higher order SIDE FOLDS that follow are increasingly shorter. The spaces between any two neighboring branches of one filter ruffle are FILTER CREVICES (Kenny, 1969a). The open, multi-sided spaces that form between the secondary and tertiary filter folds have been called the FILTER NICHES by Kratochwill and by Kenny. The GLOTTIS lies on the midline between the anterior portions of the fourth ceratobranchials. It is a simple longitudinal slit in the middle of a circle that indicates the presence of the trachea below. It may have distinct lips. The circular outline of the trachea is identifiable as a LARYNGEAL DISC. The laryngeal disc, the glot- tis, or both, are often slightly elevated on an elliptical dome. The glottis increases in prominence with metamorphosis. Before meta- 14 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY rFILTER CREVICE r FILTER NICHE r FILTER, CANAL r DORSAL MARGIN hFULL FILTER ROW h PARTIAL FILTER ROW TERTIARY FOLD SECONDARY FOLD MAIN FOLD Fig. 3. — Greatly enlarged segment of a single filter plate showing details of the filter folds. This drawing was based on a low magnifieation scanning electron micrograph of the second filter plate in a Rana pipiens larva. Because of drying artifacts the filter density is not quite as great as it may have been in life. morphosis it is most distinct in the species whose larvae have lungs that begin to function earliest (Wassersug and Seibert, 1975). Viewed from above, the trailing edge of the ventral velum partially or fully obscures the glottis. A short distance behind the glottis is the ESOPHAGEAL FUN- NEL, where the pharynx narrows into the esophagus. The profile of the funnel is determined by both the width of the esophagus and the width of the pharynx. If the pharynx is narrow and the esoph- agus slender, the tadpole will appear to have a small, narrow fun- nel. With a broad esophagus and wide pharynx the funnel may appear both larger and broader. Essentially the esophagus is an extension of the CILIARY ORAL MORPHOLOGY OF ANURAN LARVAE 15 GROOVE, the most posterior and lateral feature on each side of the pharynx. The ciliary groove runs in the horizontal plane at the margin of the roof of the pharynx. It starts on each side at the anterolateral corner of the ventral velum, where the velum is abruptly reflected dorsally and posteriorly. The groove continues behind the dorsal velum around the wall of the pharynx, first pos- teriorly, then more medially, and finally directly into the esophageal funnel. The ciliary groove varies from being open and rather shal- low posteriorly to being more inset and trough-like laterally. The groove {"Flimmeninne") was first identified by Kratochwill (1933) and seems to be an invariant feature of all microphagous larvae. Obviously, cilia are not visible in gross dissection of the ciliary groove. Food particles however compacted in mucous cords, often mark the ciliary groove in specimens that were eating extensively before they were fixed. The anterior limit of the ciliary groove is in the immediate vicinity of the lateral limit of the SECRETORY RIDGES. These secretory ridges are on the ventral surface of the ventral velum and appear as fine parallel striations when stained with methyl blue. Near the margin of the velum the ridges parallel the velar edge. More anteriorly the ridges tend to follow the posteriorly concave arches formed by the adjoining filter plates and the hypobranchial plate. The ridges maintain an orientation at right angles to the long axis of the filter plates. The collection of ridges between each arch have been called BRANCHIAL FOOD TRAPS by Kenny (1969a) and have been numbered to correspond with each filter chamber. Anteriorly, in each filter chamber the food traps may ex- tend ventrad from the velar surface proper. Posteriorly, the secre- tory ridges are often continuous from one filter cavity to the next under the free margin of the velum. In certain species the ridges cover the whole ventral surface of the velum and, consequently, the branchial food traps are not as disjunct as Kenny's coding would imply. Kenny homologized his branchial food traps with the struc- tures termed "crescentic organs" and "collecting organs" by Savage (1952 and 1955). Others, such as Kratochwill, Gradwell, and De- Jongh, have preferred to leave this tissue unnamed or simply refer to it descriptively as the secretory or glandular tissue of the ventral surface of the ventral velum. Kenny has given much attention to the comparative histology of this secretory tissue. The secretory ridges may vary in their size, density and uniformity. In certain species the secretory tissue in the branchial food traps is not well organized into ridges. Kenny 16 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY notes generic as well as possible familial differences in the micro- scopic patterns of these ridges. In Xenopiis the floor of the buccopharyngeal cavity is covered with secretory ridges forming v»'hat Weisz (1945) called the pharyngobranchial tract. Savage (1952) suggested the "pharyngeo -branchial tract" (Savage's modification) is identical to his ventral velum. This homology has been accepted by most authors. Accord- ing to Sokol (1975) the "pharyngeobranchial tract" (Sokol's modi- fication) in Xenopiis is a remnant of the ventral velum of non-pipid lai-vae, while to Gradwell (1975) the ventral velum of non-pipids is derived from the pipid configuration (specifically by a contra- lateral proliferation and spreading of squamous epithelium on the floor of the buccopharyngeal cavity). Without entering this con- troversy, I accept the homology of the secretory ridges of the pharyngobranchial tract with the secretory ridges of other tadpoles, but consider the Pipidae as lacking a true ventral velum. I am here restricting the term velum to a freely suspended epithelial flap and use the descriptive term, "secretory ridges," to refer to such ridges whether they occur under the velum or elsewhere in the oral cavity. The only remaining major oral features are the PRESSURE CUSHIONS or pads of Kenny (1969a). These have also been called "Druckpolsfer" (Kratochwill, 1933), "dorso-pharyngeal fold" (Weisz, 1945), "velar pads" (Gradwell, 1975, 1972a and earlier) and "lymph sacs" (Witschi, 1959). The pressure cushions are oblong bulges of epithelium that descend, two on each side, from the roof of the pharynx posterior to the dorsal velum. They are oriented with their long axes perpendicular to the margin of the dorsal velum and parallel to the filter cavities. The LATERAL PRESSURE CUSH- IONS fill the dorsal and posterior portions of the first filter cavities in undisturbed specimens. The MEDIAL PRESSURE CUSHIONS are aligned above the second filter cavities. There is only loose areolar tissue in association with the cushions, and, as noted by Kenny, they are often shrunken and distorted in fixed material. The lateral sides of the lateral pressure cushions make up the medial edge of the ciliary groove. Posterior portions of the medial pressure cushions contribute to the formation of the ciliary groove along the back of the pharynx. Summary A general description is presented of oral surface features in the mouths of tadpoles. Past terminology is reviewed and several previ- ously undescribed structures are identified and named. ORAL MORPHOLOGY OF ANURAN LARVAE 17 Except for the Pipidae, which have a common buccopharyngeal cavity, all tadpoles have their mouths partitioned into distinct an- terior, buccal, and posterior, pharyngeal, cavities. Epithelial flaps known as dorsal and ventral vela are the partitioning structures. By this separation the first pharyngeal gill clefts (the buccal pockets) technically lie in the buccal rather than pharyngeal cavity. The ventral velum is a functional valve. Typical features of the buccal floor include: anterior paired infralabial papillae; lingual papillae on the tongue anlage; pre- pocket papillae in front of the buccal pockets; a central field on the buccal floor termed the buccal floor arena (BFA) circumscribed by paired longitudinal rows of papillae, the BFA papillae. The buccal roof is characterized by: an anterior prenarial arena between the upper beak and the internal nares; a postnarial arena between the internal nares and a medial transverse fold called the median ridge; a buccal roof arena (BRA) dorsal to the BFA. Col- lections of papillae, termed the postnarial papillae and the BRA papillae, define the lateral boundaries of the postnarial and buccal roof arenas respectively. Other papillae on the buccal roof occur lateral to the median ridge (lateral ridge papillae) and in associ- ation with the narial valves (narial valve projections and prenarial papillae). The posterior margin of the buccal roof is lined by a secretory mucosa called the glandular zone. The shape of the buccal cavity and the number and arrange- ment of all major papillae and projections may differ among species. The number and shape of papillae and pustulations in the buccal cavity of tadpoles also varies intraspecifically. Patterns of pigmen- tation are extremely variable within any species. The ventral velum varies in its amount of attachment to the underlying filter plates and the extent of crenulation along its posterior margin. Dorsal and ventral vela vary in their integrity on the midline. The gill filters are the most conspicuous feature of the floor of the pharynx in tadpoles. They cover the filter plates on the 1st through 4th ceratobranchials. The posterior lateral margin of the pharynx is defined by a ciliary groove which runs posteriorly into the esophageal funnel. Anterior to the esophageal funnel lies the glottis on the laryngeal disc. These structures are partially or fully obscured from dorsal view by the free trailing edge of the dorsal velum in most tadpoles (Orton type 4). On the ventral surface of the ventral velum lies secretory tissue. This tissue is usually organized into distinct ridges. The collection of secretory tissue in each filter cavity is called branchial food traps. 18 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY Two oblong bulges of epithelium descend from dorsal velum into the filter cavities on each side of the pharynx. These are termed the medial and lateral pressure cushions and are the only major features of the typically small dorsal pharynx of tadpoles. There is much intraspecific variation in the size and shape of the pharynx in anuran larvae. Tadpoles differ in the folding pattern of their gill filters, the density of their filters, and the height and length of their filter plates. The premetamorphic size of the glottis, the distinctness of secretory ridges and the size of branchial food traps also show much variation among species. This study adds to our knowledge of the anatomical complexity of tadpoles. The structures described here all come in direct con- tact with the feeding currents of tadpoles. Interspecific variation in these structures is thus likely to reflect differences in the feeding ecology of tadpoles. All of the newly described features are relatively easy to exam- ine and may be applicable to studies of anuran systematics. An outline for description of oral surface features in tadpoles has been included as an appendix. Literature Cited Altig, R. 1970. A key to the tadpoles of the Continental United States and Canada. Herpetologica, 26:180-207. DeJongh, H. S. 1968. Functional morphology of the jaw apparatus of larval and metamorphosing Rana temporaiia L. Neth. Jour. Zool., 18(1):1- 103. VAN DijK, D. E. 1966. Systematic and field keys to the families, genera, and described species of Southern African anuran tadpoles. Ann. Natal Mus., 18(2):231-286. DuELLMAN, W. E. 1970. The Htjlid Frogs of Middle America. Monog. Mus. Nat. Hist., Univ. Kansas, 1. 753 pp. GoETTE, A. 1875. Atlas ztir Entivickhingsgeschicte der Unke. Verlag von Leopold Voss, Leipzig. GosNER, K. L. 1960. A simpliiied table for staging anuran embryos and larvae with notes on identification. Herpetologica, 16:183-190. Gradwell, N., Pasztor, V. M. 1968. Hydrostatic pressures during normal ventilation in tlie bullfrog tadpole. Can. Jour. Zool., 46:1169-1174. Gradwell, N. 1970. The function of the \entral \elum during irrigation in Rar^a catesheiana. Can. Jour. Zool., 48(6) :1179-1186. Gradwell, N. 1971a. Ascaphtis tadpole: experiments on the suction and gill irrigation mechanisms. Can. Jour. Zool., 49(3) :307-332. Gradwell, N. 1971b. Xenopus tadpole: on the water pumping mechanism. Herpetologica, 27:107-123. Gradwell, N. 1972a. Gill irrigation in Rana catesheiana. Part I. On the anatomical basis. Can. Jour. Zool., 50(5) :481-499. Gradwell, N. 1972b. Gill irrigation in Rana catesheiana. Part II. On the musculoskeletal mechanism. Can. Jour. Zool., 50(5) :501-521. Gradwell, N. 1972c. Comments on gill irrigation in Rana fiiscigula. Herpe- tologica, 28:122-125. ORAL MORPHOLOGY OF ANURAN LARVAE 19 Gradwell, N. 1973. On the functional morphology of the suction and gill irrigation in the tadpole of Ascaphus, and notes on hiberation. Herpe- tologica, 29:84-93. Gradwell, N. 1974. Description of the tadpole of Phnjnomems annectens, and comments on its gill irrigation mechanism. Herpetologica 30:53-62. Gradwell, N. 1975. The bearing of filter feeding on the water pumping of Xenoptis tadpoles (Anura: Pipidae). Acta Zoologica 56:119-128. Griffiths, I. 1963. The phylogeny of the Salientia. Biol. Rev., 38:241-292. Griffiths, I., de Carvalho, A. L., 1965. On the validity of employing larval characters as major phyletic indices in Amphibia, Salientia. Revista Brasileira de Biologia, 25 ( 2 ) : 1 13-121. Hammerman, D. L. 1964. Occurrence of premetamorpliic papillae in ranid tadpoles. Amer. Zool., 4(3):319. Hammerman, D. L. 1965. Development of the tongue of Rana damitans. Amer. Zool., 5(2) :250-251. Hammerman, D. L. 1969. The frog tongue: L General development and histogenesis of filiform papillae and mucous glands in Rana catesbeiana. Acta Zool., 50:11-23. Hecht, M. K. 1963. A reevaluation of the early history of the frogs. Part II. Syst. Zool., 12:20-35. Helff, 6. M., Mellicker, M. C. 1911. Studies on amphibian metamorphosis. XIX. Development of the tongue in Rana sijhatica, including histo- genesis of "premetamorphic" and filifomi papillae and the mucous glands. Amer. Jour. Anat., 68(3) :339-366. Inger, R. F. 1967. The de\'elopment of a phylogeny of frogs. Evolution, 21:369-384. Kenny, J. S. 1969a. Feeding mechanisms in anuran larvae. Jour. Zool., Lon- don, 157:225-246. Kenny, J. S. 1969b. Pharyngeal mucous secreting epithelia of anuran larvae. Acta Zool., 50:143-153. Kluge, a. G., Farris, J. S. 1969. Quantitatixe phyletics and the evolution of anurans. Syst. Zool., 18( 1 ) : 1-32. Kratochwill, K. 1933. Zur Morphologic und Physiologic der Nahmngsaufna- hue der Froschlarven. Zeit. wiss. Zool., 144(4) :509-572. Lataste, F. 1879. Etude sur la discoglosse. Actes Soc. Linn. Bordeaux., 33:275-341. Lynch, J. D. 1971. Evolutionary relationships, osteology, and zoogeography of Leptodactyloid frogs. Univ. Kansas Mus. Nat. Hist., Misc. Publ., 53:1-238. Lynch, J. D. 1973. The transition from archaic to advanced frogs. In Vial, J.L. (ed.). Evohitionanj Biology of the Anurans: Coniemporanj Re- search on Major Problems. Univ. Missouri Press, Columbia: 133-182. Magnin, E. 1959. Anatomic du tetard d'Ahjtes obsteiricans. Actes Soc. Linn. Bordeaux, 98:1-60. Naue, H. 1890. Uber bau und entwicklung der Kiemen der Froschlai-ven. Inaugural Dissertation, Leipzig. 1-48. Nelson, G. E., Cuellar, H. S. 1968. Anatomical comparison of tadpoles of the genera Hypopachiis and Gastrophryne (Microhylidae). Copeia, 1968 (2):423-424. Nevo, E. 1968. Pipid frogs from the early Cretaceous of Israel and pipid evolution. Bull. Mus. Gomp. Zool., 136(8) :255-318. Orton, G. L. 1944. Studies on the systematic and phylogenetic significance of certain larval characters in the Amphibia Salientia. Ph.D. dissertation, Univ. Michigan. Orton, G. L. 1953. The systemarics of vertebrate larvae. Syst. Zool., 2(2): 63-75. 20 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY Orton, G. L. 1957. The bearing of larval evolution on some problems in frog classification. Syst. Zool., 6:79-86. Parker, H. W. 1934. A Monograph of the Frogs of the Famihj Microhijhdae. British Mus., London. 208 pp. Parker, W. K. 1881. The structure and development of the skull in the Batrachia. Phil. Trans. Roy. Soc, 172:1-266. RiECK, W. 1932. Die Entwicklung des Mimdhohlenepithels der Anuren. Zool. Jahrb., Abthl. Anat. Ontog. Tiere, 55:603-646. Savage, J. M. 1973. The geographic distribution of frogs: patterns and pre- dictions, in Vial, J.L. (ed.). Evohitionanj Biology of the Anurans: Contemporary Research on Major Problems. Univ. Missouri Press, Co- lumbia: 351-445. Savage, R. M. 1952. Ecological, physiological and anatomical observations on some species of anuran tadpoles. Proc. Zool. Soc, London, 122:467-514. Savage, R. M. 1955. The ingestive, digestive and respiratory systems of the microhylid tadpole, Hypopachus aguae. Copeia, 1955 (2):120-127. ScHULZE, F. E. 1870. Die Geschmacksorgane der Froschlarven. Arch. mikr. Anat., 6:407-419. ScHULZE, F. E. 1892. Uber die inneren Kiemen der Batrachierlarven. II. Mittheilung. Skelet, Musculatur, Blutgefasse, Filterapparat, Respira- torische Anliange und Athmungsbewegungen erwachsener larven von Pelobates fuscus. Abhdl. der Konigl. Preuss. Akad. Wiss., Berlin, (l):l-66. Severtzov, a. S. 1969. Food seizing mechanism of Anura larvae. Dokl. Akad. Nauk SSSR, 187:211-214 (Trans.). SoKOL, O. M. 1962. The tadpole of Hymenochirus boettgeri. Copeia, 1962 (2):272-284. SoKOL, O. M. 1975. The phylogeny of anuran larvae: a new look. Copeia 1975(1 ):l-23. Spinar, Z. V. 1972. Tertiary frogs from Central Europe. Dr. W. Junk N.V., The Hague. 286 pp. Starrett, p. H. 1968. The phylogenetic significance of the jaw musculature in anuran ampliibians. Ph.D. disseration, Univ. Michigan. Starrett, P. H. 1973. Evolutionary patterns in ]ar\'al moiphology. in Vial, J.L. (ed. ). Evolutionary Biology of the Anurans: Contemporary Re- search on Major Problems. Univ. Missouri Press, Columbia: 252-271. Sterba, G. 1950. Uber die Morphologischen und Histogenetischen Thymus- probleme bei Xenopus lacvis Daudin nebst einigen Bermerkrmgen uber die Morphologie der Kaulquappen. Abh. Sachsischen Akad. Wiss. Leipzig Math, -naturwiss. Klasse, 44(l):l-54. TiHEN, J. A. 1965. Evolutionary trends in frogs. Amer. Zool. 5(2) :309-318. Ueck, M. 1967. Der Manicotto glandulare ("Drusenmagen") der Anurenlarve in Bau, Funktion und Beziehung zur Gesamtlange des Darmes. Eine mikroskopisch-anatomische, histochemische und elektronenoptische Studie an der omnivoren imd mikrophagen Lar\'e von Xenopus laevis und der carnivoren und makrophagen Larve \on Hymenochirus boettgeri (Anura, Pipidae). Zeit. wiss. Zool., 176(3/4): 173-270. Wassersug, R. J. 1973. Internal oral features of anuran larvae and the sig- nificance of the tadpole feeding mechanism to anuran evolution. Ph.D. Thesis. Univ. of Chicago. Wassersug, R. J. 1975. The adaptive significance of tire tadpole stage with comments on the maintenance of complex life cycles in anurans. Amer. Zool., 15:405-417. Wassersug, R. J., Seibert, E. A. 1975. Behavorial responses of amphibian larvae to variation in dissolved oxygen. Copeia (1):86-103. Wassersug, R. J. 1976. Internal oral features in Hyla regilla larvae: an ORAL MORPHOLOGY OF ANURAN LARVAE 21 ontogenetic study. Occas. Papers Mus. Nat. Hist. Univ. Kansas, 49: 1-24. Weisz, p. B. 1945. The development and morphology of the larva of the South African clawed toad, Xenopus laevis. Jour. Morph., 77:163-217. WiTSCHi, E. 1959. The bronchial cohnnella of the ear of larval Ranidae. Jour. Morph., 96:497-512. Appendix Outline for Description of Tadpole Oral Surface Features The following outline is used by Wassersug ( 1973, 1976 and in manuscript) for a comparative study of the oral features in the larvae of 26 species from six families. It emphasizes the features that are of most comparative value. The outline presents features in the order of ventral, anterior to posterior, then dorsal, anterior to posterior. This is a convenient seciuence for examination, but it contrasts with the functional organization (all buccal features fol- lowed by all pharyngeal features) used in the preceding descrip- tion. Not all features listed in this outline will be applicable to every species. I. General shape of floor of mouth; length to width ratio II. Ventral Buccal A. Infralabial papillae 1. Number 2. Position 3. Relative size 4. Presence and number of secondary projections or pustulations on papillae B. Lingual papillae 1. Number 2. Shape 3. Relative size C. Buccal floor arena (BFA) 1. General shape 2. BFA papillae a. number b. size — position of largest; uniformity in size c. number of bifurcations D. Prepocket papillae — number, general size E. Papillae and pustulations elsewhere on buccal floor 1. Numbers 2. Region of concentration F. Buccal pockets 1. Size; length to width ratio 2. Angle from transverse plane 3. Perforated or not perforated G. Free velar surface 1. Relative extent; area compared to rest of buccal floor 2. Spicules a. length b. stiffness 22 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY 3. Posterior margin a. shape b. size of peaks over filter cavities c. extent of emargination of middle portion; number of projections d. median notch; size 4. Secretory pits a. conspicuousness b. density c. distribution on posterior velar margin III. Ventral Pharynx A. Branchial baskets 1. Length to width ratio; general shape 2. Size compared to buccal area; depth 3. Relative size of filter cavities; prevalent orientation from midline B. Filter plates 1. Shape of dorsal edge 2. Length to height ratios; amount of imbrication 3. Number of filter rows on each plate C. Filter mesh 1. General density 2. Folding pattern of filter rows (e.g., presence of 3° folds, length of 2° folds, etc.) 3. Width of rows 4. Abutment of rows 5. Filter canals a. general size compared to filter rows b. covered or open D. Branchial food traps (collecting organs) 1. Relative area 2. Secretory ridges a. conspicuousness b. size c. uniformity E. Glottis 1. 7c \asible as viewed from above 2. Relative size 3. Thickness and height of lips 4. Size and conspicuousness of laryngeal disc F. Esophageal funnel 1. Profile 2. Size IV. General shape of roof of mouth; length to width ratio; relative position of nares and median ridge V. Dorsal Buccal A. Prenarial arena 1. Pustulations a. pattern b. numbers 2. Projections and other features a. shape b. size B. Nares 1. Relative size and internarial distance 2. Angle of orientation from transverse plane 3. Anterior wall a. height; thickness ORAL MORPHOLOGY OF ANURAN LARVAE 23 b. prenarial papillae 1 ) number 2 ) size, position 4. Posterior wall ( narial valve ) a. relative height to length b. narial valve projection — distinctiveness, height C. Postnarial arena 1. Postnarial papillae a. number b. size, shape c. position 2. Median ridge a. general shape b. presence and number of serrations or secondary papillae on ven- tral margin c. presence and size of pustulations or secondary ridge on anterior surface 3. Lateral ridge papillae a. size b. shape c. presence of secondary bifurcations D. Buccal roof arena (BRA) 1. General shape 2. BRA papillae a. number b. size — position of largest, uniformity in size c. number bifurcated E. Pustulations and papillae elsewhere on buccal roof 1. Numbers 2. Region of concentration F. Glandular zone 1. Secretory pits a. distinctiveness, size b. density 2. Conspicuousness of anterior margin 3. Relative length and unifonnity of length G. Dorsal velum 1. Length — maximum fully extended 2. Presence on the midline 3. Marginal papillation VL Dorsal Pharynx A. Pressure cushions 1. Distinctiveness 2. Size 3. Shape of lateral cushion 4. Shape of median cushion B. Giliary groove 1. Depth 2. 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