FOREGUT ANATOMY AND CLASSIFICATION OF CONOIDEA 



135 



Raclula 



The radula has been by far the most studied of the organs of 

 the foregut and there are many published illustrations of 

 conoidean radular teeth (e.g. Powell, 1966; McLean, 1971; 

 James, 1980; Bandel, 1984; Bogdanov, 1990; Nybakken, 1990 

 and Taylor, 1990). Shimek & Kohn (1981) classified turrid 

 radulae into a number of functional groups and attempted a 

 cladistic analysis of radular characters. However, amongst the 

 'lower' turrids there is little evidence from direct observations 

 to support their functional categories. Indeed, recent evi- 

 dence shows that even in the least-derived radulae which 

 possess a strong radular ribbon, the marginal teeth can be 

 held singly at the proboscis tip in a stabbing position (Kantor 

 & Taylor, 1991). 



A radula is present in most Turridae, all Conidae, possibly 

 all Pervicaciidae and some Terebridae. It is absent in some 

 species of Daphnellinae, Taraninae and many species of 

 Terebridae (Miller, 1970; Taylor, 1990). The phenomenon of 

 radula-loss in conoideans has recently been reviewed by 

 Kantor & Sysoev (1989). 



For the purposes of the present analysis, we have 

 attempted to recognise different morphological types of 

 radula, without any functional interpretation. 



The radula of the Drilliinae, which is usually regarded as 

 the least-derived condition within the Turridae, has five teeth 

 in each transverse row (Fig. 16a). These teeth are usually 

 refered to as central, lateral and marginal teeth respectively; 

 although there are different interpretations (Kantor, 1990; 

 Starobogatov, 1990). We consider the morphology of each of 

 these teeth in turn. 



1. Central tooth 



A central tooth is present in species of Drilliinae, Pseudome- 



latominae, Turrinae, Clavatulinae, and Cochlespirinae. It can 



be reduced and lost in some species of these subfamilies 

 except Pseudomelatominae. (i) In the Pseudomelatominae, 

 the central tooth is fairly robust and broad, with a large 

 curved central cusp and sometimes smaller cusps at either 

 edge (Fig. 17e & f). (ii) In the Drilliinae the central tooth is 

 robust, but small and narrow (Fig. 16b & d), usually with a 

 prominent central cusp and a number of subsidiary cusps, (iii) 

 In the Turrinae and Clavatulinae (Figs 18a-d, 19a & b), the 

 central tooth appears broad, but apart from a spine-like 

 central cusp is poorly defined. The central cusp appears 

 homologous with the central tooth of the Drilliinae, but the 

 insubstantial, lateral 'wings' may represent vestiges of lateral 

 teeth which have fused with the central tooth. Alternatively, 

 the whole tooth might be homologous with the central tooth 

 of the Pseudomelatominae, the central cusp remaining promi- 

 nent, but the lateral edges becoming less substantial. Study of 

 the ontogeny of the radula in these taxa might distinguish 

 between these alternative possibilities. 



2. Lateral teeth 



We recognise two types of lateral teeth, (i) In what is 

 considered to be the least-derived condition, most species of 

 Drilliinae have large, multicuspidate, comb-like, lateral teeth 

 (Fig. 16a, c,e). However, reduced teeth are found in some 

 drilliine species (Bandel, 1984, fig. 306). (ii) In Antiplanes 

 (Cochlespirinae), the radula folds along the middle of the 

 radular ribbon, suggesting that the poorly defined, plate-like 

 teeth are in fact laterals (Kantor, 1990; Kantor & Sysoev, 

 1991, figs 26-27, 30-32). These 'teeth' were not visible on 

 S.E.M. preparations. Similar, poorly defined, lateral 'teeth' 

 are also present in optical preparations of Crassispira and 

 Crassiclava of the Crassispirinae (Maes, 1983 fig. 31 & 37, p. 

 322; Kilburn, 1988, p. 239). 



In all other subfamilies of Turridae, Pervicaciidae, Tere- 

 bridae and Conidae. lateral teeth are absent. 



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Fig. 13 Strictispira paxillus; transverse section of the rhynchoel and the proboscis tip. a, mouth with distally-situated radula and virtually no 

 bucal tube. Scale bar = 100 urn. b, section of the proboscis slightly to the posterior of (a) showing the two large odontophoral cartilages. 

 Scale bar = 100 um. 



