FOREGUT ANATOMY AND CLASSIFICATION OF CONOIDEA 



133 



Fig. 10 Eucithara stromboides; longitudinal section through the 

 anterior end of the proboscis showing the buccal tube introvert. 

 Abbreviations: i, introvert; is, intermediate sphincter; m, mouth. 



The buccal cavity and radular apparatus 



From the true mouth, the buccal tube leads to a well-defined 

 chamber, the buccal cavity, which is surrounded by thick 

 walls of circular muscle. The radular diverticulum usually 

 opens ventrally into the buccal cavity. It consists of the 

 radular sac within which the radular teeth are formed, and in 

 less-derived turrids, an odontophore and sublingual pouch 

 (Fig. 15). The latter is the site where degeneration of the 

 radular teeth and ribbon occurs. The buccal sac is defined 

 (Shimek, 1976), as that part of the radular diverticulum that 

 lies between the buccal cavity and the entrance of the salivary 

 ducts. 



In higher turrids without a radular membrane and odonto- 

 phore, the sublingual pouch is transformed into a caecum for 

 the storage of radular teeth prior to their use at the proboscis 

 tip. 



Fig. 11 Turricula nelliae spurius; extended proboscis, showing the 

 inner ring of the protrusive lips. Scale bar = 100 um. 



of the buccal lips from a short tube to long proboscis-like 

 structures, are seen in species of the subfamily Mangeliinae. 

 Sections of Mangelia nebula (Sheridan et al. , 1973; Delaunois 

 & Sheridan, 1989) show that the buccal lips can be inverted 

 into the buccal cavity (Fig. 9b). In the genus Aforia (Cochle- 

 spirinae), some species have well developed buccal lips, but 

 in others they are absent (Sysoev & Kantor, 1987). 



In some conoideans lacking a proboscis and radula (e.g. 

 Terebra gouldi (Miller, 1975)), the buccal lips are enlarged 

 and consist only of circular muscles. They have the appear- 

 ance of, and may be confused with, the true proboscis. 



Radula caecum (often called short arm of the radula 

 sac) 



This is a diverticulum which branches off the anterior end of 

 the radular sac, in which detached radular teeth are stored 

 prior to their use at the proboscis tip (Fig. 15). We regard this 

 structure as a homologue of the sublingual pouch found in 

 other gastropods with a radular ribbon. A radular caecum is 

 present in higher turrids, for example the subfamilies Man- 

 geliidae, Daphnellinae, and Borsoniinae and also in Conidae 

 and some Terebridae. 



Shimek (1976) showed that the caecum in Oenopota lev- 

 idensis is divided longitudinally by a septum. We have seen 

 this structure only in Micantapex parengonius (Borsoniinae). 



Radular membrane 



In general, the 'lower' turrids have a robust radular mem- 

 brane, whilst in 'higher' turrids, it is thin or absent. However, 

 even in 'lower' turrids, the strength of the membrane varies 

 considerably between taxa and we recognise only the pres- 

 ence or absence of the membrane as a functionally important 

 character. 



A radular membrane is absent in the subfamilies Borsonii- 

 nae, Mangeliinae, Daphnellinae, Conorbinae, Clathurelli- 

 nae, Taraniinae, Conidae and most Terebridae. 



Odontophore 



An odontophore with cartilages is present in many lower 

 turrids (Drilliinae, Pseudomelatominae, Strictispirinae, Clav- 

 atulinae, Turrinae, Cochlespirinae, Crassispirinae), the Per- 

 vicaciidae, and a few species of Hastula (Terebridae), but is 

 absent in higher turrids, Conidae and most other Terebridae. 

 If an odontophore is present, then the cartilages may be 

 either fused, or separated at the anterior end. If the cartilages 

 are separated, they are joined by a muscular connection. We 

 have seen fused odontophoral cartilages in Lophiotoma, 

 Pseudomelatominae, Splendrillia, Clavus sp., Inquisitor and 

 Funa spp., Toxiclionella and some Aforia species. Two 

 separate cartilages are usually present in species of Clavatuli- 

 nae (except Toxiclionella), Strictispira paxillus (Strictispiri- 

 nae) (Fig. 13). In Aforia lepta (Cochlespirinae), only the 

 muscle is present, over which the radular membrane bends 

 (Sysoev & Kantor, 1988). 



