144 



D.J. GOWER AND M. WILKINSON 



large — 

 intestine 



cloaca 



-urodeum- 



. phallodeum — 



- anterior— +*- posterior-^ 



vent 



- phallus 



Fig. 1 Schematic sagittal section through the posterior of a male 

 caecilian showing (a) main divisions of the uneverted cloaca, and (b) 

 the everted phallus with the internal, lumenal surface of the phallodeum 

 on its exterior surface, and the urodeum forming its core. 



34 caecilian species, including representatives of 20 currently recog- 

 nised genera and all six of the currently recognised families. Exbrayat 

 ( 1991) compared cloacae of single species from four genera in three 

 families. Wake (1998) provided comparative data on the cloacal 

 spines and spicules of the three nominate species of Scolecomorphus 

 Boulenger, 1883. 



Species limits in caecilians are poorly understood and the tax- 

 onomy within many genera is best viewed as uncertain and potentially 

 unstable (Nussbaum and Wilkinson, 1989). The inadequate state of 

 current knowledge has been attributed to the group's tropical distri- 

 bution, largely fossorial and secretive lifestyle, under-representation 

 in museum collections, lack of detailed study, and a relative paucity 

 of obvious external morphological features in association with their 

 limbless bodies, reduced or absent tails, and reduced head features 

 (e.g. Nussbaum & Wilkinson, 1989). Some 34 years after the 

 publication of Taylor's ( 1968) taxonomic monograph, species level 

 caecilian systematics is still dominated by counts of annuli, verte- 

 brae, and teeth. Of the phallus, Taylor ( 1968: 31) was 'certain that 

 most genera and many species could be identified by the characters 

 of this organ alone' and Wake ( 1972: 353) stated that 'the arrange- 

 ment of musculature and cloacal accessory structures is 

 species-specific in males.' If correct, male cloacal morphology, with 

 its complex structure and many variations, should provide a much 

 needed tool for investigating species limits in and phylogenetic 

 relationships among caecilians. However, not much has changed 

 since Largen etal. (1972: 187) pointed out that 'The value of penis 

 structure as a taxonomic character has yet to be fully investigated'. 



We have made observations of the cloacal morphology of a broad 

 range of caecilian species. Without assembling a thorough synthesis 

 of these observations, we draw upon them here to provide a descrip- 

 tion of the male cloaca that emphasises some features that can be 

 homologised across taxa, and that indicates the kind of variation that 

 occurs. It is hoped that this contribution will clarify some points of 

 confusion in the literature and be a stimulus to future research. Our 

 focus here is on the male cloaca only. 



Abbreviations 



UMMZ: 



University of Michigan, Museum of 



Figures 





a.ll 



anterior tuberosity of 1.1 



a.md 



anterior tuberosity of md 



ap 



anterior part of phallodeum 



a.rdl 



anterior tuberosity of r.dl 



a.rvl 



anterior tuberosity of r.vl 



b 



bladder 



bp 



blind pit 



bs 



blind sac 



c 



colliculus 



cl 



copulator loop 



c.md 



central tuberosity of md 



cs 



cloacal sheath 



ebs 



entrance to blind sac 



eu 



entrance to urodeum 



i 



intestine 



l.bs 



left blind sac 



l.dl 



left dorsolateral longitudinal ridge 



1.1 



left lateral longitudinal ridge 



l.vl 



left ventrolateral longitudinal ridge 



md 



mid-dorsal longitudinal ridge 



P 



phallodeum 



p.lvl 



posterior tuberosity of l.vl 



p.md 



posterior tuberosity of md 



PP 



posterior part of phallodeum 



p.rdl 



posterior tuberosity of r.dl 



p.rl 



posterior tuberosity of r.l 



p.rvl 



posterior tuberosity of r.vl 



r.bs 



right blind sac 



r.dl 



right dorsolateral longitudinal ridge 



r.l 



right lateral longitudinal ridge 



rm 



retractor muscle 



r.vl 



right ventrolateral longitudinal ridge 



s 



sulcus 



sph 



sphincter 



u 



urodeum 



ud 



urogenital duct 



umd 



mid-dorsal ridge of urodeum 



V 



small additional ventral tuberosity 



vd 



vent denticulations 



vp 



vascular plexus 



MORPHOLOGY 



Disposition of the cloaca. The cloaca of male caecilians is 

 essentially a tube that extends between the posterior end of the 

 intestines and the vent, and that may or may not have paired dorsal 

 diverticula or blind sacs. The intestines, the paired urogenital ducts 



