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A new genus and species of rhinatrematid caecilian, Amazops amazops gen. et sp. nov., is described based on a single specimen from Orellana, Ecuador collected in 1990. Among other features the new taxon differs from all other rhinatrematid caecilians in having less than four annular grooves interrupted in the region of the vent and in the squamosal contributing to the bony margin of the orbit. A consideration of its distinctive morphology suggests that it is plausible that the new taxon is the sister taxon of all other rhinatrematid caecilians. That the genus is known from a single specimen, and that this is the first new rhinatrematid species from the Andes described for more than 50 years, highlights the poor sampling (collecting) of rhinatrematid caecilians and limited knowledge of their diversity.

Information on even the most basic biological aspects is often missing for many species and even higher taxa of caecilians. As in other amphibians, development is plesiomorphically biphasic and aquatic larvae are present in Rhinatrematidae, Ichthyophiidae, and some Indotyphlidae. However, only very little information on larval morphology and ecology is available. Here I describe a series of Epicrionops bicolor larvae and metamorphs from Peru and provide details on the development of the annulation pattern, colouration, external gills, lateral line system, and other morphological characters and discuss the taxonomic value of lateral line characters. Specimens were collected at two different times of the year, allowing inferences of a few key demographic characteristics. Hatching probably occurs around August and September at a size of approximately 55 to 65 mm. Larval development takes about 1 year to complete and metamorphosis occurs at around 180–190 mm total length.

Caecilians (order Gymnophiona) are elongate, limbless, snake-like amphibians that are the sister-group (closest relatives) of all other recent amphibians (frogs and salamanders). Little is known of their cardiovascular anatomy and physiology, but one nearly century old study suggests that Hypogeophis (family Indotyphlidae), commonly relied upon as a representative caecilian species, has atrial septation in the frontal plane and more than one septum. In contrast, in other vertebrates there generally is one atrial septum in the sagittal plane. We studied the adult heart of Idiocranium (also Indotyphlidae) using immunohistochemistry and confirm that the interatrial septum is close to the frontal plane. Additionally, a parallel right atrial septum divides three-fourths of the right atrial cavity of this species. Idiocranium embryos in the Hill collection reveal that atrial septation initiates in the sagittal plane as in other tetrapods. Late developmental stages, however, see a left-ward shift of visceral organs and a concordant rotation of the atria that reorients the atrial septa towards the frontal plane. The gross anatomies of species from six other caecilian families reveal that (i) the right atrial septum developed early in caecilian evolution (only absent in Rhinatrematidae) and that (ii) rotation of the atria evolved later and its degree varies between families. In most vertebrates a prominent atrial trabeculation associates with the sinuatrial valve, the so-called septum spurium, and the right atrial septum seems homologous to this trabeculation but much more developed. The right atrial septum does not appear to be a consequence of body elongation because it is absent in some caecilians and in snakes. The interatrial septum of caecilians shares multiple characters with the atrial septum of lungfishes, salamanders and the embryonic septum primum of amniotes. In conclusion, atrial septation in caecilians is based on evolutionarily conserved structures but possibly exhibits greater variation than in any other vertebrate order.

The reduction in the visual system of the Gymnophiona has been noted by many authors. Adult caecilian amphibians eyes are small, covered by skin and sometimes bone, with retinal cells that contain only rod opsins and co-option of structures usually associated with the visual system used for novel sensory structures and functions. Here, we provide a description of the eye of Rhinatrema bivittatum, the first of any rhinatrematid caecilian, and consider its significance for our understanding of the nature of the eye in the last common ancestor of living caecilians. Characters discovered include zonule fibres, an aqueous humour and the remnants of an attachment that could be a protractor lentis muscle.

Caecilians are wormlike amphibians that occur worldwide in the tropics, except for Madagascar and Oceania. Only 189 species are known, distributed among 35 genera and 10 families. Most caecilians are fossorial, living in moist soils usually adjacent to streams, lakes, and swamps; a few species are aquatic. Conservation status of caecilians is summarized. An up-to-date phylogeny details approximate time periods during which divergences occurred during the evolutionary history of caecilians and shows evolutionary relationships among the families as we now know them. Taxonomic accounts provide information on generic content, distribution, characteristics, and biology of each family.

The morphology of the tectum mesencephali and the medial pallium is studied in species representing the six families of caecilians (Amphibia: Gymnophiona) in order to determine whether differences in brain morphology are related to function, phylogenetic history, or life history strategies. In general, the caecilian tectum is characterized by simplification in having little to no lamination and few migrated cells. The degree of morphological complexity differs between species and between brain regions. Our data suggest that changes in brain morphology are due to a mosaic of different influences. We did not find a strict correlation between visual system reduction and tectal morphologies. However, phylogenetic effects exist. The greatest degree of morphological complexity is found in members of the Rhinatrematidae, a family that is considered basal to the lineage. Thus, simplification of brain morphology in caecilians must be considered a secondary or derived rather than a primitive feature. Direct development and miniaturization are correlated with the greatest simplification in the tectum mesencephali and medial pallium. There is a relationship between differences in brain morphology and heterochrony in caecilians, as in other amphibians. J. Morphol. 231:11-27, 1997. © 1997 Wiley-Liss, Inc.

Previous studies have shown there to be considerable inter-specific variation in the cardiovascular anatomy of five of the six families of caecilians. Observations on the previously unstudied Rhinatrematidae reveal this family to be characterized by a number of cardiovascular features that are unique within the Gymnophiona. These include a poorly developed sinus venosus sinistra, a short truncus arteriosus, separate carotid and systemic arches and the right atrium larger than the left. Character analysis indicates that these unique features are primitive within the Gymnophiona and they provide considerable additional support for the hypothesis that the Rhinatrematidae are the sister-group to all other caecilians. This hypothesis appears to be among the best supported hypotheses of relationships within the Gymnophiona. Caecilian cardiovascular variation provides a useful source of evidence for phylogeny reconstruction that should be integrated into phylogenetic studies of the group.

Based on examination of 622 specimens of Gymnophiona, 15 species are recognized for Brazilian Amazonia. Geographical variation in characters is low and is mainly restricted to the number of annuli. One new species is described, Microcaecilia rochai sp. nov. New distribution data and maps for most species are provided. A key to the identification of caecilians of Brazilian Amazonia is presented.

Publisher Summary Caecilians are amphibians that look like earthworms. They have blunt, bullet-shaped heads, cylindrical, limbless bodies, and short tails. In some taxa, the primary annuli are further divided into secondary and even tertiary annuli by additional encircling grooves. Most caecilians are fossorial, living inmoist soils usually adjacent to streams, lakes, and swamps; a few species are aquatic. Because of their secretive nature, their biology is largely unknown, and much of the knowledge comes from observations made during capture and captive or museum specimens. All caecilians have internal fertilization. The male copulatory organ, the phallodeum, is an eversible part of the posterior cloaca. Offspring develop internally or externally, depending upon species. If externally, development is indirect or direct; developmental mode is invariable within each species. This chapter describes six families—namely, caeciliidae, ichthyophiidae, rhinatrematidae, scolecomorphidae, typhlonectidae, and uraeotyphlidae of amphibians separately.

A new species of rhinatrematid caecilian, Rhinatrema ron sp. nov., is described based on a single specimen from the state of Amazonas in Brazil. The new species differs from other Rhinatrema in several features, including its larger size, different colouration, and distinctively plicate oral mucosa.

The first new species of rhinatrematid caecilian in more than 50 years, Rhinatrema shiv sp. nov., is described from Guyana. The type series of 10 specimens differs from the only other species in the genus, R. bivittatum, in having a longer tail, different colour pattern, more acuminate and relatively shorter head, and in several features of the skull and mandible including dentition. Sequence data for 1572 aligned base pairs of mitochondrial DNA are > 15% different between the two species. Rhinatrema shiv is known only from Guyana, and R. bivittatum from French Guiana and far northeastern Brazil. The only reported specimen of the genus from Suriname is not clearly referable to either of the named species.

The morphology of the bony palate in larval and metamorphosed Epicrionops bicolor Boulenger and E. petersi Taylor (Rhinatrematidae) was studied to assess the extent of palatal change at metamorphosis. In larvae the maxilla is short; it abuts the dorsolateral process of the palatine at mid-choanal level. The pterygoid is long and straight; it runs anteromedially, close to the lateral edge of the parasphenoid. At metamorphosis the maxilla fuses with the palatine. The maxillary part of the maxillopalatine expands dorsally and caudally, surrounding the orbit and lacrimal ducts and completing the lateral border of the subtemporal fenestra. The anterior part of the pterygoid shifts laterally, broadening the interpterygoid vacuity, and separates from the posterior part of the pterygoid. The quadrate develops a rostrally directed quadratojugal process, overlapped by the maxilla and squamosal. A review of the literature shows that a similar pattern of palatal metamorphosis (except for the division of the pterygoid) is seen in other caecilian genera with free-living larvae: Ichthyophis (Ichthyophiidae), Grandisonia (Caeciliaidae), and probably Uraeotyphlus (Uraeotyphlidae) and Sylvacaecilia (Caeciliaidae). This implies that the shared pattern is plesiomorphic for caecilians. Features of palatal metamorphosis shared among caecilians, salamanders, and frogs support the hypothesis of lissamphibian monophyly. rnal of Herpetol gy, Vol. 30, No. 1, pp. 27-39, 1996 yright 19 6 Society for the Study of Amphibians and Reptiles latal Metamorphosis n Basal Caecilians phibia: Gymnophiona) as Evidence for sa phibian Monophyl Extant amphibians comprise three distinct, monophyletic groups: frogs (Anura), salamanders (Caudata), and caecilians (Gymnophiona) (Duellman and Trueb, 1986; Milner, 1988; Cannatella and Hillis, 1993). The relationship of each group to the others, and of these to fossil taxa, has been much debated. However, an emerging consensus-based on both morphological and molecular evidence-supports the hypothesis first explicitly proposed by Parsons and Williams (1962, 1963; see also Gadow, 1901; 1 Present Address: Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona 85721, USA. tant amphibians compris three distinct, onophyletic groups: frogs (Anura), salamaners (Caud ta), and caecilians (Gym ophiona) uellman and Trueb, 1986; Milner, 1988; Canatella and Hillis, 1993). The relationship of ch group to the others, and of the e to fossil Parker, 1956; Szarski, 1962): that the extant groups are a monophyletic unit, the Lissamphibia (e.g., Milner, 1988, 1993; Bolt, 1991; Trueb and Cloutier, 1991; Cannatella and Hillis, 1993; Hedges and Maxson, 1993). Since basal members of all three modern groups have a biphasic life cycle with a discrete metamorphosis from the larval to the juvenile form (Duellman and Trueb, 1986), we might expect to find common character transformations retained in the metamorphosis of each group. Such shared character transformations could serve as additional lissamphibian synapomorphies (cf. de Queiroz, 1985). Both frogs and salamanders undergo profound changes in skull structure at metamorphosis, especially in the palate and the hyoer, 1956; Szarski, 1962): hat the extant ps are a monophyletic unit, the Lissami ia (e.g., Milner, 1988, 1993; Bolt, 1991; Trueb 27 This content downloaded from 157.55.39.32 on Mon, 10 Oct 2016 04:24:55 UTC All use subject to http://about.jstor.org/terms

The classification and phylogeny of the caecilians has received much attention in the past decade, yet no consensus has been reached. We present new mitochondrial ribosomal gene sequence data from 13 caecilian species representing 10 genera from four of the six recognized families. Out of 1208 total sites, 890 were aligned, 475 were variable, and 329 were informative under the parsimony criterion. A phylogeny for these taxa supports the Caudata (as represented by Amphiuma) as the sister lineage to the Gymnophiona, the basal position of the Rhinatrematidae and Ichthyophiidae, the paraphyly of the Caeciliaidae, and the monophyly of the Seychellean caecilians. These sequence data support previous morphological studies suggesting that the typhlonectids were derived from Neotropical caeciliaids, and therefore the Typhlonectidae is synonymized within the family Caeciliaidae. Species previously placed in the Typhlonectidae are assigned to a separate subfamily (Typhlonectinae) of the Caeciliaidae. Resolution of relationships within the largest family, the Caeciliaidae, remains the major task of caecilian systematics.

Descriptions of the trunk musculature of six species representing sex genera and five families of caecilians reveal considerable variation, which may be useful in future systematic studies. The muscle units of the external muscular sheath (M. dorsalis trunci, M. subvertebralis) of caecilians are homologous with, and closely similar in position to, those of salamanders. The major difference in trunk musculature is the presence in caecilians of an additional muscle layer ventral to the M. subvertebralis. This muscle may be a neomorphic derivative from either the M. subvertebralis or the M. transversus. Unlike burrowing reptiles, which have ball-and-socket intervertebral joints, caecilians have retained the primitive amphicoelous centrum and compensate for stresses associated with burrowing by the presence of intercentral ligaments and interlocking basapophyses and subcentral keels. Association of Uraeotyphlus with the Ichthyophiidae and the validity of the Rhinatrematidae are supported by data from the trunk musculature.