Chthonerpeton Indistinctum Research Articles

Morphology and postnatal ontogeny of the dentition of Chthonerpeton indistinctum (Gymnophiona: Typhlonectidae)

Abstract The gross morphology, histology and postnatal ontogeny of the dentition of the viviparous and direct-developing typhlonectid Chthonerpeton indistinctum were described and compared with other caecilian species. C. indistinctum exhibited the typical pedicellated condition present in lissamphibians, with a conical monocuspid crown. Our histological analysis demonstrated that the tissue joining crown and pedicel was formed by two bands (internal and external), whereas the external band circumvented the complete periphery of the tooth junction. Likely this condition was not described for another gymnophionan species. In viviparous and some oviparous caecilians, dentition changes radically during ontogeny. Thus, there is a foetal dentition arranged in multiple rows of teeth (i.e. tooth patch), which is replaced by single tooth rows in neonate or juvenile individuals. Details of dentition in the lower jaw of neonate specimens are firstly reported for C. indistinctum herein, adding another member of Typhlonectidae. In some slightly larger specimens the foetal tooth patch on the lower jaw coexisted with a lingual row of the adult-type teeth, indicating that replacement of foetal dentition in the lower jaw did not take place just after birth. The number of teeth, a character widely employed among caecilian species descriptions, varies during postnatal ontogeny. Hence, we concluded that at least for typhlonectid caecilians, tooth number should not be considered as a character with a strong taxonomic value without considering the intraspecific ontogenetic variation. An extensive survey exploring the relationship between body length and tooth count becomes necessary to test the usefulness of tooth counts in species diagnosis.

A new species of Chthonerpeton (Amphibia: Gymnophiona: Typhlonectidae) from Bahia, Brazil

A new species of the Chthonerpeton indistinctum group is described from Brazil based on fourteen specimens collected in the Municipality of Conde, State of Bahia. The new species is characterized by 94–103 primary annuli, 100–108 vertebrae, tentacular aperture closer to nares than to eyes, umpigmented cloacal disk and narial plug areas, and by the number of vomeropalatine and dentary teeth that is smaller than that of the other species in the group. The new species is aquatic and fossorial, and can be found swimming actively at night or borrowed in mud in places near the river.

Estimating Juvenile Abundance in a Population of the Semiaquatic Caecilian, Chthonerpeton indistinctum (Amphibia: Gymnophiona: Typhlonectidae), in Southern Brazil

Chthonerpeton indistinctum is nontropical, and reports suggest a distinct breeding season, allowing the potential for estimation of reproductive success. A total of 67 juvenile (and four adult) C. indistinctum were captured over five visits to a site in Rio Grande do Sul, Brazil, during Winter 2001. All individuals were marked and released, and the seven juveniles recaptured allowed a Schnabel estimate of 161.0 (95% confidence limits 81.9-343.1), the first quantitive estimate of juvenile caecilian abundance. How- ever, the large size range of juveniles caught suggests that growth rates of individuals are highly variable or that C. indistinctum does not have a distinct breeding period in this region.

The Spermatogenic Cycle of Dermophis mexicanus (Amphibia: Gymnophiona)

The general notion that amphibian reproduction in the tropics is non-cyclic and aseasonal (cf. Duellman and Trueb, 1986) is countered by the spermatogenic cycles of caecilians. In fact, for virtually all caecilians investigated, spermatogenic cycles (and particularly sperm release, fertilization, and hatching or birth) are synchronous and seasonal. Spermatogenesis has been described for members of four of the five currently recognized families of caecilians. Seshachar, in a series of papers, carefully described spermatogenesis in the ichthyophiid Ichthyophis glutinosus (1936, 1937, 1943), the uraeotyphlid Uraeotyphlus narayani (1939, 1945), and the caeciliaids Siphonops annulatus and Schistometopum (then Dermophis) gregorii (1942), and Gegeneophis carnosus (1945). Exbrayat (1986) and Exbrayat and Sentis (1982) examined the cycle of the typhlonectine Typhlonectes compressicaudus, and de Sa and Berois (1986) described that of the typhlonectine Chthonerpeton indistinctum. Wake (1968) discussed spermatogenesis in the caeciliaid Gymnopis multiplicata, that of a number of other species in less detail. She considered active spermatogenesis to be the entire period of spermatocyte production, maturation, and sperm release, because multiple stages of development of sperm are present in the testis much of the time.

Histology of the Ovaries and Fat Bodies of Chthonerpeton indistinctum

Histological analysis revealed three different stages in the development of ovarian follicles of Chthonerpeton indistinctum. These stages are identified by (1) location of the oocyte in the ovary wall, (2) oocyte morphology and staining characteristics, (3) development of the zona pellucida, and (4) orga- nization of the follicular layer. Atretic follicles and corpora lutea also were found. Fat bodies are composed of well-developed adipose tissue. The caecilian family Typhlonectidae in- cludes 19 aquatic, viviparous species. Aside from Taylor's monograph on Gymno- phiona (1968) and the work done on Typh- lonectes compressicauda by Exbrayat (1983), Exbrayat and Collenot (1983), Exbrayat et al. (1981, 1982) and Delsol et al. (1981), little information is available on the re- productive biology of this family. Lieber- man (1939) and Barrio (1969) described some aspects of the reproductive behavior of Chthonerpeton indistinctum (Reinhardt and Lutken, 1862). Histological aspects of the oviducts of this species were studied by Welsch et al. (1977), and de Sa and Berois (1986) studied the spermatogenesis. Ovar- ian morphology and histology were de- scribed by Wake (1968, 1977) for several species of caecilians, but histological data for Chthonerpeton were not included. Clas- sification of ovarian eggs in caecilians has been based on egg sizes (Wake, 1977; Ex- brayat and Collenot, 1983). Review papers dealing with the ovary of nonmammalian vertebrates, such as those in the volume by Jones (1978) and Wallace (1983), base their presentations on the am- phibian ovary from work done on anurans or urodeles only. In this paper, we present a histological analysis of the ovary and fat bodies of C. indistinctum. It was found that

Spermatogenesis and Histology of the Testes of the Caecilian, Chthonerpeton indistinctum

Macroscopically, the testes of Chthonerpeton indistinctum consist of a series of oval lobes. The number and size of lobes is variable in Chthonerpeton indistinctum. Histologically, the testes are divided into structural units, locules separated by septa of connective tissue. Inside of each locule spermatogenesis takes place in cysts of germinal cells that divide synchronically. Sper- miogenesis is divided chronologically into four stages of development based on the shape of the nuclei of the spermatids and their arrangement in the cyst: (1) round, (2) kidney shaped, (3) atten- uate, and (4) bouquet arrangement.

The Southernmost Population of a Caecilian, Chthonerpeton indistinctum, in Uruguay

The Southernmost Population of a Caecilian, Chthonerpeton indistinctum, in Uruguay

Early Development of Caecilian Skin with Special Reference to the Epidermis

The early developing skin of two species of caecilians, a uterine Chthonerpeton indistinctum and a free-living Ichthyophis kohtaoensis, has been described using electronmicros- copy. On the whole caecilian skin is typical of amphibians in its fine structure and in the Ichthyophis larva it includes most of the components recognized in premetamorphic larvae of other amphibian groups. The epidermis of Chthonerpeton, in terms of skin development relatively younger than that of Ichthyophis, has 3 types of epithelial cells and a highly microvillar surface, which may be related to its viviparity. As yet the epidermis of Chthonerpeton does not possess other cell components recognized in the better differentiated skin of the Ichthyophis larva. The presence of Merkel cells and the ultrastructure of Leydig cells, reported for the first time in the epidermis of a larval Ichthyophis, have morphological properties which conform to those al- ready described for similar cells in other amphibian larvae. Merkel cells of Ichthyophis originate early in ontogeny and it is known that they are present in adults. Leydig cells presumably disappear at metamorphosis, as in urodeles, for they do not occur in adults. From examination of numerous specimen cells in different regions of the body of the larval Ichthyophis, it appears that Leydig cells develop from a granular type cell originating in the basal layer of the epidermis.

Histological, immuno- and enzyme-histochemical investigations on the adenohypophysis of the urodeles, Mertensiella caucasica and Triturus cristatus and the caecilian, Chthonerpeton indistinctum

The pituitary glands of two urodelan species (Mertensiella caucasica, Triturus cristatus) and one one caecilian species (Chthonerpeton indistinctum) were examined with histological (Alcian blue, Brookes' trichrome stain), enzyme histochemical (acid phosphatase, alpha-naphthylacetate-esterase, acetylcholinesterase) and immunofluorescence techniques (anti-carp GTH, anti-ovine prolactin, anti-synthetic alpha-MSH). In the pituitary gland of Mertensiella and Triturus six chromophilic cell types could be distinguished. A strong fluorescence was observed in the MSH-, GTH- and TSH-cells. In the pituitary gland of Chthonerpeton only five chromophilic cell types could be distinguished: in the rostral part of the pituitary gland the B3-cell; in the basal region of the central area the B2-cell; dorsocaudally the B1-cell. The acidophilic cells were found in the central and caudal part of the pars distalis. The basophils of the pars intermedia could be observed in the dorsocaudal part of the pituitary gland surrounding the neurohypophysis. All acidophilic cells showed a strong immunofluorescence with anti-ovine prolactin (LTH).

Observations on the Breeding Habits of the Aquatic Caecilian Typhlonectes compressicaudus

Copulation in the aquatic caecilian Typhlonectes compressicaudus was observed and photographed. The period of copulation lasted over 3 hrs and the use of the male intromittent organ was documented. A summary of the methods used for maintenance of the specimens is presented. An analysis of the urogenital systems including a comparison of copulatory patterns between this species and Chthonerpeton indistinctum is undertaken.

Observations on the fine structure, enzyme histochemistry, and innervation of parathyroid gland and ultimobranchial body of Chthonerpeton indistinctum (Gymnophiona, Amphibia).

Fine structural and enzyme histochemical observations on ultimobranchial body and parathyroid gland of the caecilian Chthonerpeton are presented. The cell clusters and follicles of the ultimobranchial body consist mainly of granulated cells which are termed C-cells and obviously belong to the APUD cell series. In the larger follicles additional possibly exhausted degranulated cells and replacement cells occur. A rich supply of nerve fibres has been found in this gland. Frequently nerve terminals were observed to come into synaptic contact with the C-cells. Two categories of nerve fibres occur: a) fibres containing large polymorphic electron dense granules (probably purinergic fibres), b) fibres containing small electron transparent vesicles and a few electron dense granules (probably cholinergic fibres). The parathyroid gland consists of elongated cells (one cell type) poor in organelles and often containing fields of glycogen and lipid droplets. The cells are further characterized by fair amounts of lysosomal enzymes; they are interconnected by maculae adhaerentes and occludentes. No nerves and blood vessels have been found in the parathyroid gland of Chthonerpeton.

The Cytogenetics ofChthonerpeton Indistinctum(Amphibia: Gymnophiona)

SUMMARYThe cytogenetics of Chthonerpeton indistinctum was studied. The karyotype was composed of five pairs of metacentric chromosomes, four pairs of submetacentrics and one pair of telocentrics (diploid number 2n = 20).The meiotic behaviour revealed the existence of ring bivalents some of them with unter- minalized chiasmata at metaphase first, similar in structure to those found in Urodela and primitive Anura.Major spirals were present during meiotic prophase and metaphase suggesting that they are more related to Anura than to Urodela.The absence of microchromosomes and the low somatic number is markedly different with those presentend by the two only species of Apoda, I. glutinosus and U. narayani studied up to now. Furthermore, the fundamental number (FN) as well as the morphological and biological characteristics of the two mentioned species seem to be, in C. indistinctum less advanced from the evolutionary viewpoint.These considerations led us to conclude that the more advanced forms had undergone a chromosome reduction by structural rearrangements and microchromosome loss.Along the meiotic or mitotic cycles no morphological differentiation of chromosomes that may be interpreted as sex chromosomes could be found.