60 



Y.I. KANTOR, A. MEDINSKAYA AND J.D. TAYLOR 



Crassispira (Gibbaspira) dysoni (Reeve, 1 846) 

 (Figs 4c, 5) 



Rhynchodeum and proboscis 



The rhynchostomal sphincter is medium-sized and anteriorly lo- 

 cated. The epithelium of the anterior half of the rhynchodeal wall is 

 tall and glandular, while the posterior half is continuous with that of 

 the proboscis wall. The proboscis tip is not inverted. The proboscis 

 is short (about half of the rhynchocoel), not coiled, but slightly 

 folded and narrowing towards the tip. The muscles of the proboscis 

 wall are equally developed along its length. 



The anterior buccal tube sphincter is small, whilst the sac-like 

 enlargement of the buccal tube is long, with a long epithelial pad, 

 formed of large cubic cells with large nuclei. At the base of the 

 enlargement, there is an intermediate sphincter, which lies at a 

 distance of three radular tooth lengths from the mouth. The walls 

 of the sac-like enlargement are thicker than the rest of the buccal 

 tube and similar to those of C. (Crassiclava) spp. The buccal tube 

 is lined with ciliated epithelium. The proboscis wall is thin, form- 

 ing about 10% of the proboscis diameter, while the wall of the 

 buccal tube comprises about 7% of proboscis diameter. Buccal 

 lips are absent. 



Buccal mass and oesophagus 



The buccal mass lies to the posterior of the proboscis, and is small, 

 thin-walled and curved, and comprises less than one fifth of the 



proboscis length. The oesophagus is greatly elongated between the 

 buccal mass and nerve ring and forms a long loop. The epithelium 

 bears very long cilia, which occupy nearly the whole lumen. The 

 opening of the radular diverticulum into the buccal cavity is quite 

 narrow and bordered by a rather tall circular muscular fold, similar 

 to that seen in C. harfordiana. The salivary ducts open into the 

 radular sac at the base of this fold (Fig. 5). 



Glands 



The salivary glands are large and acinous, with ducts that are 

 thick, very long and highly coiled. The histology of the venom 

 gland changes after passing anteriorly through the nerve ring. The 

 duct of the gland is narrow, highly coiled and probably ciliated. 

 The gland itself is very long, thick, and occupies a large part of the 

 body haemocoel. The muscular bulb is large, with thick walls 

 formed of two equal layers of circular muscle fibres, divided by a 

 connective tissue layer. The lumen of the bulb is filled with venom 

 granules. 



Odontophore and radula 



The odontophore is small, consisting of paired, unfused, subradular 

 cartilages, formed by a single layer of cells. The radula consists of 

 marginal teeth (Fig. 4c) which are of the wishbone type, with a large, 

 solid, sharply pointed, major limb and a shorter, slender, secondary 

 limb. The marginal tooth is medium long, ca. 105pm (0.8% of SL, 

 1.8% AL). 



Fig. 5 Crassispira (Gibbaspira) dysoni (Reeve, 1846). A, semidiagrammatic longitudinal section of the foregut (salivary ducts not shown); B, longitudinal 

 section of the proboscis tip; C, section of the buccal mass showing the opening of the radular sac. 



