axus^nsz-/ 



Bull. not. Hist. Mus. Loud. (Zool.) 68(2): 143-154 



Issued 28 November 2002 



Phallus morphology in caecilians (Amphibia, 

 Gymnophiona) and its systematic utility 



DAVID J. GOWER AND MARK WILKINSON 



Department of Zoology, The Natural History- Museum, London SW7 5BD, UK. 

 email addresses: davig@nhm.ac.uk, marw@nhm.ac.uk 



CONTENTS 



Introduction 143 



Abbreviation used in text 144 



Abbreviations used in figures 144 



Morphology 144 



Disposition of the cloaca 144 



Divisions of the cloaca 146 



Urodeum 146 



Blind sacs 146 



Anterior phallodeum 147 



Posterior phallodeum 148 



Phallodeal ornamentation 148 



Composition of phallodeal structures 148 



Relationship between the uneverted cloaca and the phallus 149 



Systematics 149 



Is phallus morphology species specific? 149 



Species differentiation and generic identity 152 



Discussion 152 



Acknowledgements 153 



References 153 



Synopsis. The cloaca of male caecilian amphibians (Gymnophiona) is a tube that comprises an anterior urodeum and a posterior 

 phallodeum. The phallodeum everts (with the urodeum lying inside it) to form a phallus used for direct sperm transfer in 

 copulation. Phallodeal morphology is rich in detail and variation, and has therefore been considered a potentially useful and much 

 needed tool for caecilian phylogenetics and species-level taxonomy. Despite this, it has been almost entirely ignored in caecilian 

 systematics. there is confusion regarding some aspects of morphology, and variation within and among species is poorly 

 understood. A short review and reconsideration of phallus morphology is presented, and the systematic potential assessed. The 

 anterior part of the phallodeum appears to offer the most obvious systematic potential, and the morphology of longitudinal ridges 

 and their ornamentation here seem to have diagnostic and/or phylogenetic value for some taxa. Although there is evidence of 

 intraspecific variation, at least some of which is associated with ontogeny and reproductive condition, individuals of the same 

 species generally have a common pattern of phallodeal ridges and ornamentation, and congeners often share a similar pattern. 

 However, these patterns are not universally species specific, at least among uraeotyphlids. Although variation needs to be better 

 understood, the male cloaca offers great potential for caecilian systematics. 



INTRODUCTION 



As in other amphibians, caecilians (Gymnophiona) possess a cloaca, 

 a chamber that opens to the exterior via the vent and into which open 

 the large intestine, the urogenital (Wolffian and Miillerian) ducts, 

 and the bladder. In contrast to other amphibians, the cloaca of male 

 caecilians can be everted through the vent (Fig. 1) to serve as an 

 intromittant organ, or phallus, used in copulation to effect direct 

 sperm transfer (e.g. Himstedt, 1996). It has long been recognised 

 that the external surface of the caecilian phallus and the correspond- 

 ing internal surface of the uneverted cloaca may bear distinctive 

 ridges and grooves, tuberosities and even spines (e.g. Duvernoy. 

 1849;Gunther. 1864;Spengel, 1876; Noble, 1931). There is consid- 

 erable interspecific variation in the complex patterns of these features, 

 but there have been few comparative studies. 



Spengel ( 1 876) compared cloacal features in males of six species 

 in what are now recognised as six genera from three families, and 

 aspects of cloacal morphology were compared further in some of 

 these species by Wiedersheim (1879). Tonutti (1931) provided a 

 very detailed documentation of the uneverted and everted cloaca of 

 the caeciliid Hypogeophis rostratus (Cuvier, 1829) and compared it 

 with the uneverted cloaca of the ichthyophiid Ichthyophis glutinosus 

 (Linnaeus, 1758) and of the caeciliid Spihonops annulatus (Mikan, 

 1820). Tonutti (1933) expanded the comparative aspect of his study 

 of the caecilian phallus by incorporating detailed data on a further 

 six species, including representatives of Scolecomorphidae and 

 Typhlonectidae. Tonutti's work remains the most detailed to date. 

 Taylor ( 1968 and references therein) figured (though without labels 

 or orientation ) everted phallodea and in situ dissections of 1 2 species 

 in eight genera and four families. The broadest comparative study of 

 the male cloaca was presented by Wake (1972), who examined 



© The Natural History Museum, 2002 



