Internal Oral Morphology of Tadpoles of Dermatonotus muelleri and Elachistocleis bicolor

Abstract

-The internal oral morphology of tadpoles of Dermatonotus muelleri and Elachistocleis bicolor were analyzed using scanning electron and stereoscopic microscopy. Similarities between these larvae include the architecture of the buccal roof and floor: wide and almost flattened surfaces; unperforated internal nares appearing as circular depressions; absence of infralabial and lingual papillae; presence of massive, triangular postnarial papillae; and absence of other papillae posterior to the median ridge. Differences include a raised glottis placed in the center of the buccal floor arena in D. muelleri, and the number of the lateral papillae positioned at each side of the prenarial arena. We suggest that the oral flaps and the roof papillae play a significant role in the capture of food particles by establishing the inflow of alimentary water, and aggregating food particles and mucus inside the buccopharyngeal cavity. Microhylid tadpoles have a stable pattern of body size and shape, and oral and buccopharyngeal features, which may reflect ecological and functional constraints relative to the morphology of other suspension feeding anuran larvae. Although there is some information on the interal oral morphology of larvae of several species of the extremely diverse Microhylidae (over 280 species distributed in 10 subfamilies; Duellman, 1993), there are only eight descriptions of the oral cavity (e.g., Wassersug, 1980; Inger, 1985; Wassersug and Pybur, 1987; Chou and Lin, 1997). There is only one such description for a neotropical representative of this family, namely the peculiar tadpoles of Otophryne robusta (Wassersug and Pyburn, 1987). Our investigation focused on the two southernmost species of neotropical microhylids, Dermatonotus muelleri and Elachistocleis bicolor, whose larvae have received attention by many authors. Both species have lentic, suspension feeding, Type II tadpoles (Altig and Johnston, 1989). The external larval morphology of D. muelleri was characterized by Vizotto (1967) and Lavilla (1992), who also described the structure of the chondrocranium and visceral skeleton. The tadpole of E. bicolor was described by Williams and Gudynas (1987). Lavilla and Langone (1991, 1995) analyzed the ontogenetical peculiarities of the proctodeal tube and spiraculum of this species, as well as the structure of the cephalic skeleton. Wild (1995) reported a phylogenetic analysis of all New World microhylid genera which included tadpole features of the genera Dermatonotus and Elachistocleis, but nothing concerning internal oral morphology. Herein we present descriptions of the internal oral features of the tadpoles of Dermatonotus muelleri and Elachistocleis bicolor MATERIALS AND METHODS All tadpoles were captured from the wild and preserved in 10% formalin. Oral and buccopharyngeal features were observed using stereoscopic and scanning electron microscopy (SEM) following the techniques proposed by Wassersug (1976) and Echeverria (1992). Once dissected, buccal structures were critical-point dried and coated with gold-palladium for SEM. Video records of some of the SEM are kept at the VIDEO collection in the research laboratory of DDE. Drawings of the buccal surface were made with a camera lucida, after staining structures with 2-3 drops of Carazzi's hematoxylin. Terminology is that of Viertel (1982) for the buccopharyngeal cavity and Gosner (1960) for tadpole stages. Portions of the anterior gut of two individuals of each species were dissected for qualitative examination of their contents. For light microscopy (LM) observation, the gut was dehydrated, cleared, and embedded in paraffin (56-58 C); longitudinal and transverse sections (4 ,um) were stained with PAS or a modified version of Masson's trichrome (Martoja and Martoja-Pierson, 1970). Tadpoles were deposited in the personal collection of DDE, Department of Biological Sciences of Facultad de Ciencias Exactas y Naturales (FCEN).