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



Feeding mechanism Type 2 



The second feeding mechanism is typical of the majority of 

 'lower' turrids and the terebrid Hastula bacillus, which pos- 

 sess a well developed radular membrane and lack a radular 

 caecum. The characteristic feature of this mechanism is the 

 use of separate marginal teeth at the proboscis tip for 

 stabbing the prey, whilst the radula is also used as a whole 

 organ for different purposes (Sysoev & Kantor, 1986, 1989). 



The use of single marginal teeth at the proboscis tip by 

 turrids having radulas with well developed subradular mem- 

 branes has been demonstrated in representatives of all 7 

 subfamilies of 'lower' Turridae (excepting the Pseudome- 

 latominae) and also the terebrid Hastula bacillus (Kantor & 

 Taylor, 1991). 



According to the position of the buccal mass this type may 

 be divided into two sub-types. Gastropods of the first sub- 

 type have the buccal mass situated at the proboscis base. 

 These include species of Drilliinae, Cochlespirinae, Turrinae 

 and many Crassispirinae. In these gastropods, the solid or 

 wishbone marginal teeth, which become detached from the 

 membrane during its degeneration in the sublingual pouch, 

 are used at the proboscis tip for stabbing the prey. It should 

 be noted, that separate teeth were not found in the sublingual 

 pouch, therefore it does not serve for the storage of teeth. 

 Meanwhile, the radula as a whole organ probably has a 

 different function within the buccal cavity. This is most likely 

 for the transport of food from the cavity to the oesophagus. 

 Some evidence for this comes from the observations of Maes 

 (1981), who noted the presence of intact sipunculans in the 

 posterior part of the oesophagus of Drillia cydia (Drillinae). 

 Although at first sight, it might be thought that the large, 

 pectinate, lateral teeth found in this species might serve for 

 tearing or rasping the prey. 



A characteristic feature of the proboscis is the presence of 

 the sac-like enlargement of the anterior part of the buccal 

 tube and a well-developed, distal sphincter(s). Gastropods of 

 this group lack a radular caecum, so they can use only teeth 

 which are sporadically detached from the membrane. Either 

 the marginal teeth are not used in every feeding act, or, the 

 teeth are held at the proboscis tip for a long time. That is, 

 from the moment of their detachment from the subradular 

 membrane to the next feeding act. We have found teeth at 

 the proboscis tip in sections of 'lower' turrids much more 

 frequently, than in the 'higher' turrids. Moreover, in Splen- 

 drillia chathamensis , in addition to the normal buccal sphinc- 

 ters of the buccal tube, teeth are attached by their base to a 

 'mat' of epithelial cells in the enlargement of the buccal tube 

 (Kantor, 1990, fig. 3). Such a mechanism of tooth fixation 

 confirms the long-term presence of the tooth at the proboscis 

 tip. Thus, the enlargement of the anterior part of the buccal 

 tube, could be considered as a functional analogue of the 

 radular caecum. 



The use of marginal teeth at the proboscis tip, in turrids 

 with a well-developed radular membrane, explains how hol- 

 low, marginal teeth might have evolved independently in 

 different groups possessing the radular membrane and odon- 

 tophore. For example, Imaclava (Drillinae) (Shimek & 

 Kohn, 1981), has hollow teeth and most probably uses these 

 at the proboscis tip for stabbing the prey in a manner similar 

 to that of higher Conoidea. 



The second feeding sub-type is seen in Funa latisinuata 

 (Crassispirinae), which feeds upon nemerteans. From dissec- 

 tion of relaxed animals, Miller (1989, fig 6f) showed that in 



the everted position, the buccal mass with the radula is 

 protruded through the mouth opening (Fig. 14a). In sections 

 of animals with a contracted proboscis, the buccal mass lies 

 towards the base. It is known that this species uses the 

 marginal teeth at the proboscis tip (Kantor & Taylor, 1991). 

 Thus, the mode of feeding may be reconstructed as follows. 

 After stabbing the prey, the gastropod everts the buccal 

 mass, with the walls of the buccal tube, through the mouth 

 opening and picks up the prey with the protruded radula. 

 With retraction of the buccal mass, the prey is pulled into the 

 proboscis. Correlated with this feeding mechanism, is the 

 elongation of the anterior oesophagus between the buccal 

 mass and the circum-oral nerve ring. During protraction of 

 the buccal mass, the oesophagus should be pulled through the 

 nerve ring. But, as the nerve ring in Conoidea is highly 

 concentrated, and usually tightly attached to the oesophagus, 

 the only possibility is the elongation of the oesophagus itself 

 anterior to the nerve ring, forming a loop, which is straight- 

 ened during eversion of the buccal mass (Fig. 14b). 



In addition to Funa latisinuata, this elongation of the 

 oesophagus between the buccal mass and the nerve ring has 

 been found in species from several different subfamilies of 

 Turridae-Pseudomelatominae, all Clavatulinae, Pilsbryspira 

 nympha (Zonulispirinae), Vexitomina (Crassispirinae), Tur- 

 ricula nelliae spurius (Cochlespirinae), the radulate terebrids, 

 Hastula bacillus, and Pervicacia tristis (Pervicaciidae). It is 

 likely, that the turrid species at least have a feeding mecha- 

 nism similar to that of F. latisinuata. The elongation of the 

 anterior oesophagus is usually associated with the permanent 

 shifting of the buccal mass towards the distal end of the 

 proboscis. This is well demonstrated in the Clavatulinae and 

 probably facilitates the eversion of the buccal mass through 

 the mouth. 



In all species possessing an elongated oesophagus (except 

 Pseudomelatoma), there is a change in the histology of the 

 ante-rior part of the venom gland after its passage through 

 the nerve ring. However, such a change occurs in two species 

 (Lophiotoma leucotropis and Inquisitor sp.) which lack the 

 elongated oesophagus. The anterior part of the gland is 

 ciliated and duct-like, with no secretory granules. This indi- 

 cates, that the differentiation of the gland is connected with 

 the elongation of the oesophagus and thus, the latter is a 

 secondary feature. 



Feeding mechanism Type 3 



The majority of Conoidea possess the third type of feeding 

 mechanism, in which separate marginal teeth are used at the 

 proboscis tip for stabbing prey, and the radula not used as a 

 whole organ. 



The very specialized radular morphology is the most 

 remarkable and well-known feature of the toxoglossan diges- 

 tive system. It is characterized by a marked tendency towards 

 a reduction in the strength of the subradular membrane, 

 leading to its complete absence in many species of Turridae, 

 the majority of Terebridae and all Conidae. Species without a 

 subradular membrane, have a radula consisting only of 

 complex, hollow, marginal teeth. They are known for the 

 highly specialized feeding mechanism, in which individual 

 teeth are used at the proboscis tip for stabbing and killing 

 prey with secretions of peptide neurotoxins produced by the 

 venom gland (Oliviera et al. 1990). 



Despite the similarities with the previous feeding mecha- 

 nism, those 'higher' conoideans with hollow teeth and no 



