FOREGUT ANATOMY AND CLASSIFICATION OF CONOIDEA 



145 



more, the ducts from the accessory glands open near the tip 

 of the buccal tube, which is the homologous position to that 

 found in other neogastropods. 



Within the Turridae, we have observed accessory salivary 

 glands in only two subfamilies: the Borsoniinae (Scrinium 

 neozelanicum, Borsonia ochracea, and Micantapex parengo- 

 nius) and Cochlespirinae (Aforia hypomela, A. kupriyanovi, 

 A. abyssalis). In the Terebridae, we have seen accessory 

 glands in Hastula bacillus, Terebra babylonia, T. funiculata 

 and T. subulata (Taylor, 1990). Usually, only a single gland is 

 found, but two glands are present in Terebra subulata. 



Venom apparatus (venom gland and muscular bulb) 



The long, tubular, and convoluted venom gland is the most 

 conspicuous organ of the conoidean foregut. It always passes 

 through the nerve ring and always opens into the buccal 

 cavity immediately posterior to the opening of the radular sac 

 (Figs 1 & 7). The venom gland is present in most conoideans, 

 except the radulate Strictispira (Maes, 1983); Gymnobela 

 tincta, which has a vestigial radula; the radula-less turrids 

 from the subfamilies Daphnellinae and Taraninae (Smith 

 1967; Sheridan et al, 1973; Kantor & Sysoev, 1989), the 

 radula-less Terebridae (Miller 1975; Taylor, 1990) and the 

 radulate Pervicaciidae (Taylor, 1990). 



In some species, the histology of the venom gland changes 

 in the anterior portion of its length, after its passage through 

 the nerve ring. The posterior portion is packed with venom 

 granules (Fig. 24), but the anterior portion is duct-like and 

 ciliated (e.g. Clavatula, Clionella, Turricula, Lophiotoma and 

 Pilsbryspira). This change in histology is usually correlated 

 with the elongation of that part of the oesophagus lying 

 between the nerve ring and buccal mass. In other conoideans, 

 venom granules are present all the way along the length of the 

 gland, sometimes even into the buccal cavity. 



Extensive studies have been made of the composition and 

 pharmacology of the venom in a few Conus species (review 

 by Oliviera et al., 1990). The composition of the venom is 

 very complex and the results from these studies have a 

 potential utility in phylogenetic analysis. However, no com- 

 parable studies yet exist for the Turridae and Terebridae. 



Muscular bulb 



The muscular bulb (Figs 1 & 6) lies at the posterior end of the 

 venom gland and is present in all those species possessing the 

 gland. Differences between taxa are observed both in the 

 number, orientation and relative thickness of the various 

 muscular layers forming the wall of the bulb. The usual 

 condition is of an outer, circular-muscle layer, a thin, middle 

 connective tissue layer, with an inner longitudinal layer. We 

 have, however, observed other configurations of the muscle 

 layers. For example in Mangelia species and Eucithara, the 

 outer muscular layer is very thin, but the inner layer very 

 thick. Daphnella reeveana has only a single, thin muscle 

 layer, whilst Conus textile has four distinct alternating circular 

 and longitudinal muscle layers, three of them lying inside the 

 connective tissue layer. 



Additionally, Ponder (1970) mentions that he has observed 

 glandular cells in the epithelium lining the muscular bulb in 



Lucerapex (Turrinae) and Maoritomella albula (Borsonii- 

 nae). We have not observed the glandular cells in any turrid 

 we have examined. 



Summary of foregut anatomy 



From the foregoing discussion, it is clear that there is a great 

 variety of foregut anatomy present within the Conoidea and 

 considerable variation may be present even within species of 

 one subfamily. As a summary, twelve of the main types of 

 foregut configuration are shown diagramatically in Figs 25 & 

 26. It should be emphasized that only a relatively small 

 number of conoidean species have been investigated ana- 

 tomically and it is likely that further types of foregut remain 

 undiscovered. Nevertheless, there are several anatomical 

 characters which define the Conoidea and are present in most 

 representatives (and in all the least derived groups). These 

 are:- 



1. The presence of a venom gland. 



2. The buccal mass located at the base of the proboscis. 



3. The proboscis formed by the elongation of the buccal 

 tube. 



4. The presence of a permanent rhynchodeum. 



5. The tendency for the loss of central and lateral teeth from 

 the primary five toothed radular row. 



FUNCTIONAL MORPHOLOGY OF THE 

 DIGESTIVE SYSTEM AND FEEDING 

 MECHANISMS IN TOXOGLOSSA 



As has been outlined in the previous section, the morphology 

 of the digestive system of Conoidea and especially that of the 

 Turridae, is highly varied. These variations in morphology 

 probably reflect differences in feeding behaviour and diet. 

 Apart from Conus, conoidean diets are still very poorly 

 known. Indeed, for in excess of 4000 living species of 

 Turridae, feeding information is available for less than 30 

 species (reviewed by Miller, 1989). These data, derived 

 mainly from gut content analysis, show that turrids feed 

 mainly on errant and sedentary polychaetes and more rarely 

 on other phyla such as sipunculans, nemerteans, and mol- 

 luscs. Very few direct observations of the feeding process in 

 the Turridae have been made (Pearce, 1966; Shimek, 1883a, 

 b, c; Shimek & Kohn 1980; Miller, 1990). Because of this lack 

 of information, our conclusions concerning the feeding 

 mechanisms of Turridae are based upon analysis of the 

 morphology of the digestive tract and by comparison with 

 species whose feeding mechanism is known. 



Our classifications of feeding mechanisms is based upon 

 the following characters listed in order of priority: the 

 presence/absence of venom apparatus (used for immobilizing 

 or killing the prey); the mode of radula function ( which may 

 be used solely as a whole organ, as a whole organ with 

 simultaneous use of separate teeth, or as separate teeth only 

 at the proboscis tip); position of the buccal mass (either basal 

 or shifted anteriorly towards the proboscis tip). We recognize 



Fig. 23 Hypodermic-type marginal teeth with a large solid bases, a. Paramontana sp. Scale bar = 2 \im. b. Propebela rugulata. Scale bar = 

 10 urn. c. & d. Thatcheria mirabilis Scale bars = 20 um. e.& f. Mangelia powisiana. Scale bars = 5 \vm G. Eucithara stromboides . Scale bar 

 = 10 (im. 



