FOREGUT ANATOMY OF CRASSISPIRINE GASTROPODS 



57 



pt 



proboscis tip 



rh/rhc 



rhynchocoel 



rhs 



rhynchostomal sphincter 



rs 



radular sac 



rst 



rhynchostome 



rtsg 



anastomosing tubular salivary gland 



rw 



rhynchodeal wall 



rwg 



rhynchodeal wall glandular 



sd 



salivary duct 



se 



sac-like enlargement of buccal tube 



sg 



salivary gland 



stag 



single tube acinous salivary gland 



t 



radular tooth. 



tsg 



simple tubular salivary gland 



V 



valvule 



vg 



venom gland 



vga 



duct of venom gland 



In this section we describe and illustrate the foregut anatomy and 

 radulae of each of the species examined. The terminology of the 

 anatomical characters and organs largely follows Taylor et ai, 

 (1993). Most of the features are illustrated diagrammatically in 

 Fig. 1, with details of others given in the descriptions of individual 

 species. 



Crassispira (Crassispira) incrassata (Sowerby, 1834) 

 (Figs 2, 4a) 



Rhynchodeum and proboscis 



The rhynchostomal sphincter is large and located in a slightly 

 posterior position. The epithelium of the posterior rhynchodeal wall 



lmb 



Fig. 1 Composite diagram of the foregut of a hypothetical crassispirine 

 gastropod, showing the location of the major structures discussed in the 

 text. No single species has all these structures. 



is continuous with that of the proboscis wall for slightly more than 

 half the length of the rhynchodeum. Extremely large proboscis 

 retractor muscles are attached to the rhynchodeum at the border 

 between the two different epithelia and at the proximal ends to the 

 columellar muscle. 



The proboscis is long (more than half of the rhynchodeum), 

 slightly narrowing towards the tip. The proboscis tip is not inverted 

 inside. The muscles of the proboscis wall in the posterior two thirds 

 of the proboscis are significantly thicker than in the anterior section. 

 The proboscis lies coiled within the rhynchocoel (shown uncoiled in 

 drawing to illustrate relative proboscis length). There are two ante- 

 rior buccal tube sphincters. A sac-like enlargement of the buccal tube 

 is present, with the epithelium lining it taller than that of the rest of 

 the tube. An epithelial pad is also present. There is no intermediate 

 buccal tube sphincter. 



The proboscis walls and posterior part of the rhynchodeum are 

 highly folded, suggesting significant elongation of the proboscis 

 during protraction. The proboscis wall is thick, comprising about 

 10% of proboscis diameter in the posterior half. In the anterior one 

 third of the proboscis, the wall is thinner, but due to the decrease in 

 proboscis diameter the wall comprises about 12% of the total 

 diameter. The wall of the buccal tube is also thick, comprising about 

 7% of proboscis diameter in its posterior half. Small buccal lips are 

 present. 



Buccal mass and oesophagus 



The large and very long buccal mass is located entirely within the 

 proboscis, with a thick wall and is curved. The oesophagus is 

 elongated between the buccal mass and nerve ring. The buccal sac is 

 very short. 



Glands 



The salivary glands are very large and acinous, protruding nearly to 

 the anterior of the rhynchodeum. The histology of the venom gland 

 changes abruptly before passing through the nerve ring. The duct of 

 the venom gland is ciliated, and opens into the buccal cavity at the 

 posterior border with the oesophagus. The muscular bulb is large, 

 with thick walls formed from two equal layers of circular muscle 

 fibres separated by a connective tissue layer, with a third much 

 thinner innermost layer of larger circular fibres. 



Odontophore and radula 



The odontophore is medium-sized, consisting of a pair of unfused 

 cartilages, formed by single layer of cells. The radula (Fig. 4a) 

 consists of marginal teeth of the robust wishbone type, with a thick, 

 distally-pointed major limb and a shorter, thinner minor limb. The 

 marginal tooth is short, ca.l80|im (0.5% of SL (shell length),1.2% 

 AL (aperture length)). 



Crassispira (Crassispira) maura (Sowerby, 1834) 

 (Figs 3, 4b) 



Rhynchodeum and proboscis 



The rhynchodeal sphincter is medium-sized and anteriorly located. 

 The epithelium of the anterior two thirds of the rhynchodeum is 

 glandular, but posteriorly, it changes abruptly to low, cubic non- 

 glandular, epithelium, which is continuous with that of the proboscis 

 wall. The anterior rhynchodeum is narrow with high folds. 



The proboscis is short, occupying less than half the length of the 

 rhynchodeum, with the proboscis tip not inverted. The proboscis 

 walls are rather thick, forming about 20% of the proboscis diameter, 

 but the walls of the buccal tube are thin, composing about 4% of the 

 total diameter. The mouth is narrow. The muscles of the proboscis 



