BUFONIDAE

Candioti, M. Florencia Vera, 2007, Anatomy of anuran tadpoles from lentic water bodies: systematic relevance and correlation with feeding habits, Zootaxa 1600, pp. 1-175 : 13-26

BUFONIDAE

Chaunus arenarum . Previous literature on the skeleton and musculature of this species includes Fabrezi and Vera (1997) and Haas (2003); the oral apparatus was described in Fiorito de López and Echeverría (1984; 1989). Lajmanovich (1998) studied the qualitative composition of the diet.

Chondrocranium and hyobranchial skeleton (N = 5, stages 33–36. Fig. 4). The chondrocranium of these larvae represents 43% of the body length. The maximum width is at the level of posterior part of the subocular bar. The suprarostral cartilage has a single, U-shaped corpus that is fused dorsally to the alae. The alae are well-defined, ventrally rounded, and bear a well-developed processus dorsalis posterior. The trabecular horns are long (24% of the total length of the chondrocranium) and narrow, and diverge from the ethmoid plate. They show relatively straight anterior margins, and on the lateroventral margin, the processus lateralis trabeculae is slightly outlined. The cranial floor is completely cartilaginous, with thin cartilage in the central area. The carotid and craniopalatine foramina are not clearly identifiable because of the light chondrification of the intertrabecular plate. In the posterior margin of the cranial floor, the notochordal canal reaches 20% of the chondrocranium length. The lateral walls of the chondrocranium are formed by the orbital cartilages. The chondrocranium is open dorsally, and the frontoparietal fenestra is bordered on both sides by the taeniae tecti marginales. The otic capsules are ovoid, occupy nearly 29% of the chondrocranium total length, and bear an acute anterolateral process. A large fenestra ovalis (45% of capsule length) is located ventrolaterally on each otic capsule. The otic capsules are dorsally joined by the tectum synoticum. The palatoquadrate is long and relatively narrow. It has a long, thin articular process, and a wide, dorsally rounded muscular process. The subocular bar has a smooth margin and it is posterolaterally rounded. The palatoquadrate attaches to the braincase via three points: the quadratocranial commissure, the quadratoorbital commissure, and the ascending process. The quadratocranial commissure is thin and bears a well-developed, triangular quadratoethmoid process. The ascending process attaches to the braincase ventral and posterior to the oculomotor foramen (low attachment). The lower jaw includes the Meckel’s and infrarostral cartilages joined by a cartilaginous intermandibular commissure. Meckel’s cartilages are sigmoid, with dorsomedial and ventromedial processes, and articulate with the articular process via the retroarticular process. The infrarostral cartilages are short, rectangular and independent. In the hyobranchial skeleton, the ceratohyals are long and have a tall anterior process, a rounded anterolateral process, an acute lateral process, and a large and wide posterior process; the articular condyle is a rounded, robust projection visible from a dorsal view. The ceratohyals are joined medially by the pars reu- niens that is shorter than the basibranchial. The basihyal is small, visible as a narrow sliver of cartilage, and the basibranchial is long and bears a short urobranchial process (18% of the basibranchial length). The hypobranchial plates are flat and triangular, and they articulate medially leaving a posterior ovoid gap. The ceratobranchials are long, thin, and have numerous lateral projections. They are distally joined by terminal commissures. Four cartilaginous spicules arise dorsally from each ceratobranchial.

Musculature (N = 5, stages 33–36. Table 2 and Fig. 5). Thirty-one muscles are present in this species.

Oral apparatus and buccopharyngeal cavity (N = 2, stage 35. Fig. 6). The width of the oral disc represents nearly 22% of the body length, and gape width reaches 22% of the body length. The oral disc is emarginate, with a simple papillar margin interrupted in wide dorsal and ventral gaps; there are a few submarginal papillae in the commissural region. Papillae are conical, with smooth, rounded tips. The rostrodonts are welldeveloped and keratinized. The keratodonts are arranged in five rows, two upper (anterior) and three lower (posterior), resulting in a labial tooth row formula –LTRF– 2(2)/3. Row A2 is interrupted by a wide, median gap, and P3 is slightly shorter than the other rows. In the buccal roof, the prenarial arena has a quadrangular, short and wide ridge. The choanae are large, obliquely arranged at an angle of 40º from the transversal line. The anterior margin has small prenarial papillae, and the narial valve is visible. In the postnarial arena there are four pairs of conical postnarial papillae, the two most anterior pairs smaller and closer to each other. The lateral ridge papillae are well-developed and trifid, with pustulate tips. The median ridge is triangular, high, wider at the base, and with an irregular free margin. The buccal roof arena is delimited on both sides by 4–5 tall, conical marginal papillae; numerous pustules are scattered among the papillae. The secretory pits are arranged in a V-shaped display located near the posterior margin of the dorsal velum. The dorsal velum is short and it has a smooth margin, without projections. In the buccal floor, posteriorly to the infrarostrodonts, there is a pair of small, non-keratinized spurs, medially directed. The infralabial papillae are tall, bifid, and with tips of unequal development, and they do not overlap each other in the middle line. On the tongue anlage, there are four lingual papillae; they are tall, conical, and transversally aligned, and the medial pair is slightly shorter than the lateral one. The prepocket region, on the lateral portion of the ceratohyals, shows numerous pustules and one pair of prepocket papillae. The buccal floor arena is delimited on both sides by 12–14 tall papillae accompanied by numerous pustules and small papillae. The buccal pockets are elongate and transversally arranged. The ventral velum is semicircular and supported by spicules. Three main marginal projections appear on each side, over each filter plates; the median notch is absent, and secretory pits appear on the edge of the velum.

Gut content (N = 8, stages 34–36. Tables 21 and 22). The most frequent food items were diatoms (41.39%), followed by ciliates and oligochaete remnants. Regarding food sizes, the highest percentages ranged from below 1-2% of the tadpole body length. The abundance of sand-grains in the gut contents suggests bottom feeding.

Chaunus spinulosus . Ulloa Kreisel (2003) described the buccopharyngeal cavity of this species; the remaining data are unpublished.

Chondrocranium and hyobranchial skeleton (N = 5, stages 34 and 36. Fig. 7). The chondrocranium of these larvae represents 57% of the body length. The maximum width is at the level of posterior part of the subocular bar. The suprarostral cartilage has a single, U-shaped corpus dorsally fused to the alae. The alae are well-defined, ventrally rounded, and bear an acute processus dorsalis posterior. The trabecular horns correspond to nearly 23% of the total length of the chondrocranium and diverge from the ethmoid plate. They have relatively straight anterior margins, and on the lateroventral margin, the processus lateralis trabeculae is slightly outlined. The cranial floor is completely cartilaginous with thin cartilage in the central area. The carotid foramen is visible, but the craniopalatine foramen is not clearly identifiable, because of light chondrification of the intertrabecular plate. On the posterior margin of the cranial floor, the notochordal canal extends 19% of the chondrocranium length. The lateral walls of the chondrocranium are formed by the orbital cartilages. The optic foramen, posteroinferiorly placed, the oculomotor foramen, slightly smaller, and the trochlear foramen, small and dorsally placed, are visible on the posterior part of the orbital cartilage. The chondrocranium is dorsally open through the frontoparietal fenestra lined on both sides by the taeniae tecti marginales. In the stages analyzed, the taenia tectis transversalis and the taenia tectis medialis are also present. The otic capsules are ovoid, occupy nearly 27% of the chondrocranium total length, and bear an acute anterolateral process. A large fenestra ovalis (44% of the capsule length) is located ventrolaterally on each otic capsule. The otic capsules are dorsally joined by the tectum synoticum. The palatoquadrate is long and relatively narrow. It has a long and thin articular process, and a wide, dorsally rounded muscular process. The subocular bar has a smooth margin, and it is posterolaterally wider and rounded. The palatoquadrate attaches to the braincase via three points: the quadratocranial commissure, the quadratoorbital commissure, and the ascending process. The quadratocranial commissure is thin and bears a well-developed, triangular quadratoethmoid process. The ascending process attaches to the braincase ventrally and posteriorly to the oculomotor foramen (low attachment). The lower jaw includes Meckel’s and infrarostral cartilages, joined by a cartilaginous intermandibular commissure. Meckel’s cartilages are sigmoid in shape and show well-developed ventromedial and retroarticular processes. The infrarostral cartilages are short, rectangular and independent. In the hyobranchial skeleton, the ceratohyals are long and have a tall, triangular anterior process, a small, rounded anterolateral process, a short and acute lateral process, and a large and wide posterior process; the articular condyle is a rounded, robust projection visible from a dorsal view. The ceratohyals are joined medially by the pars reuniens nearly as long as the basibranchial. The basihyal is small, visible as a narrow sliver of cartilage, and the basibranchial is short and bears a short, quadrangular urobranchial process (23% of basibranchial length). The basibranchial is fused to the hyobranchial plates. The hypobranchial plates are flat and triangular, and they articulate medially with a posterior triangular, narrow gap remaining. The ceratobranchials are long, thin, and have numerous lateral projections. They are distally joined by terminal commissures. Four cartilaginous spicules arise dorsally from each ceratobranchial, the third one being reduced.

Musculature (N = 5, stages 34 and 36. Table 3 and Fig. 8). Thirty-two muscles appear in this species.

Oral apparatus and buccopharyngeal cavity (N = 2, stages 31 and 33. Figs. 9 and 10). The oral disc width represents nearly 24% of the body length, and gape width reaches 23% of the body length. The lateral margins have deep indentations in the commissural region. The papillar margin is simple with wide dorsal and ventral gaps; scarce submarginal papillae appear in the commissures. Papillae are large and conical, with smooth, rounded tips. The rostrodonts are well-developed and keratinized. The serrations are triangular with sharp points. The keratodonts are arranged in five rows, two upper (anterior) and three lower (posterior), resulting in a LTRF 2(2)/3. The row A2 is interrupted by a wide, median gap, and P3 is slightly shorter than the other rows. The keratodonts have an elongate and convex head with 10–12 cusps and a sheath shorter and wider than the head. In the buccal roof, the prenarial arena shows a small, quadrangular ridge accompanied by pustules. The choanae are large, obliquely arranged at an angle of 37º from the transversal line. The anterior margin has small prenarial papillae, and the narial valve is scarcely visible. In the postnarial arena there are four pairs of conical or slightly bifid postnarial papillae. The lateral ridge papillae are well-developed, with three or four pustulate tips. The median ridge is rectangular, twice as long as wide, and with an irregular free margin. The buccal roof arena is delimited on both sides by 3–4 tall, conical marginal papillae. Some pustules appear anteriorly and posteriorly to the papillae. The secretory pits are arranged in a V-shaped array, located near the posterior margin of the buccal roof. The dorsal velum is smooth and short. In the buccal floor, poste- rior to the infrarostrodonts, there is a pair of small non-keratinized spurs. The infralabial papillae are tall, bifid, with points of unequal development, and they do not overlap to each other. On the tongue anlage, there are four tall, conical, transversally arranged lingual papillae. The prepocket region, on the lateral portion of the ceratohyal, has numerous pustules and 1–2 prepocket papillae. The buccal floor arena is delimited on both sides by 4–5 peripheral, tall, conical papillae accompanied by pustules and small papillae. The buccal pockets are elongate and transversally arranged. The ventral velum is long and supported by spicules; it has three main pronounced marginal projections on each filter plate, and two small ones on each side of the middle line; the median notch is absent, and secretory pits appear on the posterior edge of the velum.

Gut content (N = 10, stages 31–36. Tables 21 and 22). The preponderant food-category was diatoms

(99.33%) with a size range of 1–2% of the tadpole body length.