146 



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



**" ***■. ' *H 



*%'^K - - 



*Si " 







Fig. 24 Venom gland of Clavus sp. Guam. a. section through critical-point dried venom gland showing venom granules. Scale bar = 10 \im 

 b. enlargement of single venom granule. Scale bar = 1 um. 



five main and several sub-types of feeding mechanism. Some 

 of these have already been described (Kantor & Sysoev, 

 1990; Kantor, 1990), but are here partially revised and 

 corrected. 



I. Venom gland present 



Feeding mechanism Type 1 



The first functional type of digestive system and feeding 

 mechanism, that in which the radula is used only as a whole 

 organ in conjunction with the venom apparatus is found 

 among species of Pseudomelatominae and in Toxiclionella 

 twnida (Clavatulinae) and can be subdivided into two sub- 

 types. 



The first sub-type is characteristic of the Pseudomelatomi- 

 nae, an endemic subfamily from western central America, 

 which includes 3 genera and several species (McLean in 

 Keen, 1971). The anatomy of two species Pseudomelatoma 

 penicillata and Hormospira maculosa indicates the isolated 

 position of the group among Conoidea (Kantor, 1988). This is 

 particularly clear, from the radular morphology, which con- 

 sists of a large and well developed central tooth, flanked by 

 large, scythe-like, but solid, marginal teeth. 



The buccal mass is situated either at the proboscis base and 

 far ahead the nerve ring in Pseudomelatoma penicillata, or in 

 front of the nerve ring and distant from the proboscis base in 

 Hormospira maculosa. The anterior part of the digestive tract 

 forms a long curve, either by the elongation of that part of the 

 oesophagus between the nerve ring and the buccal mass (P. 

 penicillata), or by the elongation of the posterior part of the 

 buccal tube (H. maculosa). 



Both species have a well-developed venom gland and 

 although the diet of Pseudomelatominae is unknown, the 

 presence of the large venom gland indicates the predatory 

 mode of feeding. The gastropods also have a muscular 

 proboscis with a wide oral opening but without a sphincter. 

 The absence of the oral sphincter, which is usually used for 

 holding single radular teeth at the proboscis tip (Kantor & 

 Taylor, 1990), coupled with the curved form of the marginal 

 teeth, indicate that the gastropods do not use separate teeth 

 for stabbing the prey. Kantor (1988) supposed that prey 

 capture occurs with the aid of the proboscis tip and is 

 facilitated by the wide and highly extensible oral opening. If 

 this is so, then envenomation of the prey should occur within 

 the anterior part of the proboscis. This facilitates the trans- 

 port of prey into the buccal cavity, by the peristaltic move- 

 ments of well-developed circular muscles of the buccal tube. 



However, the presence of the elongated part of the 

 oesophagus between the buccal mass and nerve ring in P. 

 penicillata may indicate another mode of prey capture. In 

 some turrids (e.g. Funa latisinuata. Fig. 14), the presence of 

 such an elongation of the oesophagus is connected with the 

 ability to evert the buccal mass, with the radula, through the 

 proboscis and mouth. It is possible, that P. penicillata can 

 evert the buccal mass through the mouth and use the radula 

 directly in prey capture. Envenomation would in this case 

 occur through the damage to the prey made by the radular 

 teeth. Also the very large odontophore (the largest of all the 

 turrids studied) suggests that the radula may also tear the 

 prey. 



The morphology of Hormospira differs from that of 

 Pseudomelatoma, in that the curve is formed by the posterior 

 part of the buccal tube and elongated buccal mass. The 



