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J.D. TAYLOR, Y.I. KANTOR AND A.V. SYSOEV 



Cenodagreutes (Smith, 1967) and Abyssobela atoxica (Kantor 

 & Sysoev, 1986), which lack the rhynchodeal introvert, there 

 is a vast rhynchocoel and well-developed cavity between the 

 rhynchodaeum and body walls. The walls of this cavity are 

 connected by numerous transverse muscles. Both the intro- 

 vert and cavity are lacking in the genus Taranis (Taraninae). 



A feeding mechanism for radula-less species is known for 

 some terebrids (Miller, 1970, 1975). Thus, Terebra gouldi 

 which has a relatively short introvert feeds upon the enterop- 

 neust Ptychodera flava, and Terebra maculata with a long 

 introvert feeds on polychaetes. Prey are caught with the aid 

 of the introvert. Turrids lacking the introvert, but with the 

 cavity between the rhynchodaeum and the body walls, prob- 

 ably engulf prey by contraction of the radial muscles in the 

 wall. This would cause negative pressure and an increase in 

 the inner volume of the rhynchocoel. 



The origin of the radula-less feeding mechanism can be 

 easily envisaged. It is known, that in some Conus species 

 hypodermic envenomation is not necessary in each feeding 

 attack (Kohn, 1959; Marsh, 1970; Sanders & Wolfson, 1961). 

 It is probable that some Turridae and Terebridae, especially 

 those with well-developed rhynchostomal lips or introvert, 

 also feed without stabbing the prey with radular teeth. Thus, 

 Daphnella reeveana, which possesses a venom gland, has a 

 very short proboscis and is probably unable to hold a tooth at 

 its tip (Fig. 4). As stabbing of the prey becomes unnecessary, 

 the proboscis, venom gland and radula disappear. An inter- 

 mediate stage is found in Gymnobela emertoni, in which the 

 proboscis and venom gland have disappeared, but there is 

 still a very short and reduced radular sac, opening to the 

 outer side of the buccal lip (Fig. 8). 



RELATIONSHIPS OF THE CONOIDEA 



Monophyly of the Conoidea 



There has been much discussion concerning the relationships 

 of the Conoidea to other prosobranch gastropods; some 

 considering them to be part of a monophyletic group with 

 other neogastropods (Ponder, 1973; Taylor & Morris, 1988), 

 whilst others suggest an origin entirely independent of the 

 neogastropods (Sheridan et al. 1973; Shimek & Kohn, 1981; 

 Kantor, 1990). 



In this section we briefly review some of the evidence for 

 the relationships of the Conoidea with other prosobranchs. 

 Some of this evidence has been discussed in some detail by 

 Kantor (1990) and only the principal arguments are presented 

 here. 



The location of the buccal mass at the base of the proboscis 

 as found in most conoideans, is different from the situation 

 seen in most neogastropods, where the buccal mass is found 

 at the distal end of the proboscis. The proboscis in most 

 conoideans is formed by the elongation of the buccal tube, 

 whilst in neogastropods it originates from the elongation of 

 the anterior oesophagus (Ponder, 1973). However, a basal 

 buccal mass is now known for the neogastropod Benthobia 

 (Pseudolividae) which also exhibits a number of other primi- 

 tive characters, and in Amalda (Olividae) (Kantor, 1991). 

 Additionally, in Benthobia, the radular retractor muscle 

 passes through the nerve ring and is connected to the 

 columellar muscle (Kantor, 1991 fig. 15a). This condition is 

 seen species of the turrid subfamily Drilliinae, and in most 



lower caenogastropods, but is absent in probosciform caeno- 

 gastropods. 



A key autapomorphy of the Conoidea is the possession of 

 the venom apparatus, comprising the venom gland and 

 muscular bulb. There has been much discussion concerning 

 the homology of this gland. But, Ponder (1970; 1973) 

 showed, that in the neogastropod family Marginellidae a long 

 coiled gland, similar in general appearance to the conoidean 

 venom gland is formed by the stripping off of glandular folds 

 from the oesophagus. In some marginellids the gland termi- 

 nates at the posterior in a muscular bulb which is homologous 

 with the gland of Leiblein. The venom gland of conoideans 

 may have been derived in a similar way and is probably 

 homologous with the glandular folds of the oesophagus and 

 the gland of Leiblein in other neogastropods. 



The possession of tubular, accessory salivary glands is also 

 considered to be an apomorphy of the Neogastropoda (Pon- 

 der, 1973). These glands are patchily distributed amongst 

 conoideans, but are known in some Turridae, Conidae and 

 Terebridae. Both the histology of the glands (Schultz, 1983; 

 Andrews, 1991) and the position of the opening of the ducts, 

 confirms their homology in the Conoidea and in other 

 neogastropods. The primitive Benthobia also has a large 

 accessory salivary gland (Kantor, 1991). 



A radula with five teeth in each row, as is found in the 

 turrid subfamily Drilliinae, has been considered as evidence 

 for a separate origin of the Conoidea and Neogastropoda, the 

 latter normally have three or less teeth in each row. (Shimek 

 & Kohn, 1981). However, it is now known that some Olivella 

 and Nassariidae have five teeth in each row (Bandel, 1984; 

 Kantor, 1991). All this suggests is that the common ancestor 

 of the Conoidea and the other neogastropods possessed five 

 or more teeth in each row. 



In conclusion, conoideans share a number of characters 

 with the neogastropods which suggest a common ancestry. 

 Nevertheless, the evidence both from the position of the 

 buccal mass and the formation of the proboscis, suggests an 

 early divergence of the two groups. An evolutionary scheme 

 for the derivation of the conoidean intraembolic proboscis 

 from the acrembolic type, typical of many mesogastropods, 

 has been developed by Kantor (1990). His arguments cor- 

 roborate and elaborate Ponder's (1973) hypothesis that the 

 Conoidea diverged from the other neogastropods before the 

 formation of the proboscis. Ontogenetic studies of proboscis 

 and foregut development in the Conoidea and other neogas- 

 tropods might provide corroborative evidence. 



Relationships within the Conoidea 



Phylogenetic analysis 



We attempted to determine relationships within the 

 Conoidea using cladistic analysis of many of the foregut 

 characters described in the first part of this paper, combined 

 with a few shell characters. 



Taxa used 



We have included 40 species in the analysis, with at least one 

 from all the currently-recognised, subfamilies. In a few cases 

 we have used previously published work. The species studied 

 represent only a small proportion of living species from any of 

 the subfamilies. Some of these subfamilies are very diverse 

 and morphologically disparate and our sample is certainly 



