Acta Zoologica (Stockholm) 80: 75±84 (January 1999) Structure of the caecilian Siphonops annulatus (Amphibia, Gymnophiona): general aspect of the body, disposition of the organs and structure of the mouth, oesophagus and stomach L. C. U. Junqueira1, C. Jared2 and M. M. Antoniazzi2 Abstract 1LaboratoÂrio de Biologia Celular Junqueira, L. C. U., Jared, C. and Antoniazzi, M. M. 1999. Structure of the Faculdade de Medicina caecilian Siphonops annulatus (Amphibia, Gymnophiona): general aspect of the Universidade de SaÄo Paulo, body, disposition of the organs and structure of the mouth, oesophagus and Sao Paulo, Brazil stomach. Ð Acta Zoologica (Stockholm) 80: 75±84 2LaboratoÂrio de Biologia Celular Instituto Butantan The caecilians (or Gymnophiona) constitute one of the least well known Av. Vital Brazil 1500 groups of terrestrial vertebrates because most species live underground, in CEP 05503900 quite unaccessible environments. Siphonops annulatus is an exclusively SaÄo Paulo, Brazil fossorial species and is the most extensively distributed caecilian in South Keywords: America. This work is the first of a series which intends to study the Gymnophiona, caecilian Siphonops, complete morphology of this species. It describes the general anatomy and general anatomy, digestive system the initial portion of the digestive system, from the mouth to the stomach. The general aspect of the body and the elongation of the organs seem to be Accepted for publication: related to adaptation to the fossorial environment. 10 August 1998 Carlos Jared, LaboratoÂrio de Biologia Celular, Instituto Butantan, Av. Vital Brazil 1500, CEP 05503900, SaÄo Paulo, Brazil. E-mail: [email protected] and colleagues, data about the morphology of these Introduction amphibians are still few. Caecilians (Gymnophiona) are amphibians restricted to Siphonops annulatus is an exclusively fossorial species the tropics that have a serpentiform and annulated body and is the most widely distributed caecilian in South and reduced eyes covered with skin. Extant species are America. Since it can adapt to different levels of humidity, limbless and have a pair of tentacles at the snout, an intro- it is found from quite dry regions (semiarid) to rain forests mittent copulatory organ (phallodeum) (Wiedersheim (Taylor 1968). This species is found in Brazil, mainly on 1879) and a unique dual jaw closing mechanism (Bemis the cacao plantations at the south of Bahia State and in et al. 1983; Nussbaum 1983). They are primarily adapted many other countries. to a fossorial life, although a few species are secondarily In the last 9 years, our group has maintained an adapted to the aquatic or semiaquatic environment interchange with the Cacao Research Center, in IlheÂus, (Nussbaum and Wilkinson 1989). Bahia State, Brazil. We have made 12 expeditions for Because of their distribution and the type of observation and collection of specimens of Siphonops environment in which they live, the caecilians constitute annulatus. During this time, we have also developed a one of the least well known groups of terrestrial methodology for maintenance of these animals in captivity. vertebrates. Information about physiology, ecology, natural This study primarily aims to describe the structure of history and behaviour of these animals is very scarce. Siphonops annulatus and intends to use these morphological Lawson (1963) noticed the low number of references data for assessing the behaviour of these animals. In this about the anatomy of individual species of caecilians; initial paper, we present the general aspect of the body, the despite the continuous and comprehensive efforts of such anatomy of its viscera and the histological structure of its authors as M.H. Wake and colleagues and J.-M. Exbrayat mouth, oesophagus, and stomach. q 1999 The Royal Swedish Academy of Sciences 75 Structure of the caecilian Siphonops . Junqueira, Jared and Antoniazzi Acta Zoologica (Stockholm) 80: 75±84 (January 1999) Materials and Methods Anatomy of the viscera Ten adult specimens of both sexes of S. annulatus Mikan The gross distribution of the viscera of S. annulatus is (1820), classified according to Taylor (1968) were captured presented in Fig. 2. at the Cacao Research Center (CEPEC CEPLAC) in the The digestive tube. The mouth presents short conical teeth region of Itabuna and llheÂus in the State of Bahia, Brazil. of various sizes forming a single row in the lower jaw and a After capture they were kept in a terrarium and periodically double row in the upper jaw (Fig. 3A,B). The tongue is a fed with minced meat and newborn mice. We therefore soft and short structure firmly linked to the lower jaw. The studied well fed animals weighing between 23 and 48 g and mouth communicates with a long, flattened and thin-walled measuring from 28 to 43 cm. oesophagus presenting an average diameter of 5 mm. At the Some of the specimens are deposited in the collection height of the heart the oesophagus ends and the stomach of the Zoological Museum of the University of SaÄo begins. This structure has a thicker wall and its diameter Paulo under numbers 71277, 71278 and 71279. They gradually increases to an average of 8 mm, ending at the were submitted to a temperature of 4 8C for 30 min and level of the lower portion of the liver. Both oesophagus and injected intraperitoneally with 4% paraformaldehyde stomach are elongated structures. The transition of the dissolved in 0.1 M phosphate buffered saline, dissected stomach to the small intestine is abrupt; the small intestine is andfurtherfixedinthesamesolution.Forlight much thinner and forms a series of irregular curved loops, microscopy tissues were embedded in Technovit 7100 constituting the only nonlinear portion of S. annulatus's resin (Heroeus, Wehrheim, Germany) and sectioned digestive tract. with glass knives at 1 and 2 mm. These sections were An elongated liver of dark colour is situated at the right stained with toluidin blue and fuchsin and mounted in of the stomach beginning just below the heart and Micromount (Surgipath Medical Industries, Richmond, extending as far as the end of the stomach. It is formed by IL, USA). Alternatively sections were stained with a the superposition of 20 leaflets of hepatic tissue linked variant of Romanowsky stain for haemopoetic tissues one to another by a thin structure at their central region. described by Rosenfeld (1947). The whole structure has an emarginated aspect. The gall To study the distribution of glycogen and neutral or bladder is found behind the lower caudal liver leaflets and acid polysaccharides associated with proteins the periodic communicates with the small intestine by a short and acid Schiff (PAS) and the Alcian blue methods were conspicuous bile duct. The spleen and pancreas appear applied according to Bancroft and Stevens (1990). Yellow bound to the dorsal region of the first intestinal loop. and green filters were used so as to increase photographic The large intestine is a much wider thin-walled structure contrast. that ends at the cloaca shortly before the anus. The Decalcification was performed in 5% EDTA diluted in elongated urinary bladder, inserted at the lower portion of isotonic saline containing 1% paraformaldehyde. As will the cloaca, is a very thin walled tube orientated toward the be seen thin sections of this material processed in our cranial region. From the caudal third of the cloaca a slim conditions produced figures with higher resolution when structure formed by smooth muscle, the musculus compared to paraffin embedded material. This permitted a retractor cloacae, emerges. This structure divides itself in better understanding of the function of the cells and the cranial direction assuming the form of an `Y'; its tissues studied (Junqueira 1995). terminal portions are bound to the lateral muscular wall of the body. The respiratory system. The trachea, an elongated and thin (1 mm) structure presenting superposed incomplete Results cartilage rings, begins immediately behind the tongue and ends near the heart, where it bifurcates. The right branch General aspect of the body gives rise to a long (2 mm) thin red lung situated between Figure 1(A) shows a dorsal view of Siphonops annulatus. the stomach and liver, which ends as a blind sac at the The body is cylindrical and serpentiform, head and tail level of the lower third of the liver. The left branch ends in presenting a similar diameter. The skin is shiny and a reduced lung with a length of 10% of the right lung. bluish-grey. The lighter colour of the annulae makes them The urinary system. The kidneys assume the form of a evident (Fig. 1A). The head is flattened dorso-ventrally red and long ribbon, which is flattened and continuous, and presents a pair of reduced eyes and a pair of white covering the dorsal midline of the animals inner surface. spots (Fig. 1B) that might correspond to the tentacles This ribbon is constituted in its central part by a large described for other caecilians (Billo and Wake 1987; Wake artery and vein bound laterally to the parenchyma of the 1992). The mouth has an antero-ventral position. The left and right kidneys. This organ begins just below the terminal cloaca is round and pleated and lacks pigmenta- heart level and proceeds caudally ending at the cloaca. In tion (Fig. 1C). the cranial region the ribbon is formed by segments 76 q 1999 The Royal Swedish Academy of Sciences Acta Zoologica (Stockholm) 80: 75±84 (January 1999) Junqueira, Jared and Antoniazzi . Structure of the caecilian Siphonops Fig. 1.ÐSiphonops annulatus.ÐA, Entire body. Ð B, Head. From left to right, the nostril is followed by a white spot (arrow) that corresponds to the region of the tentacle of other species and the eye (arrowhead). Ð C, Posterior end with anus (arrow). separated by constrictions; as it progresses caudally these region which corresponds to the large intestine and cloaca. constrictions disappear.