FOREGUT ANATOMY OF CRASSISPIRINE GASTROPODS 



69 



Glands 



The salivary glands are large, paired and acinous. The venom gland 

 changes in histology after passing anteriorly through the nerve ring. 

 The duct is very narrow, ciliated, coiled, and opens at the border 

 between the buccal mass and oesophagus. The muscular bulb is 

 large, with the wall formed of two equal layers of longitudinal 

 muscle fibres, divided by a connective tissue layer, with an inner- 

 most, thin layer of circular muscle. 



Odontophore and radula 



The odontophore is rather large and protrudes into the buccal cavity. 

 It has paired, unfused cartilages, formed by single layer of cells. The 

 radula (Fig. 14c) consists of marginal teeth of the wishbone type, 

 each tooth with a large major limb with a pointed tip, the middle part 

 of the tooth broad and concavo/convex and narrowing towards the 

 base. The secondary limb is thin at the distal end broadening towards 

 the base. The marginal tooth is 172pm in length (1.1% of SL, 4.2% 

 AL) 



Haedropleura septangularis (Montagu, 1803) 



(Figs 14d, 15) 



The specimen sectioned was rather similar to the illustration in 

 Sheridan et al. (1973, fig. 6) and differs only in some details. 



Rhynchodeum and proboscis 



The rhynchodeal sphincter is small and anteriorly located. The 

 epithelium of the anterior half of rhynchodeum wall is tall, glandular 

 and folded. Posteriorly, it is replaced abruptly with a low, non- 

 glandular, cubic epithelium continuous with that of the proboscis 

 wall. 



The whole rhynchocoel is rather short and the thick proboscis, 

 although not long, occupies nearly the entire cavity. The ratio 

 between the proboscis length and its diameter is about 1.3. The 

 proboscis tapers toward the tip, which is slightly invaginated at the 

 mouth opening. The proboscis walls are medium-thick and compose 

 about 16% of the proboscis diameter at its base. The mouth opening 

 is very narrow. The muscles of the proboscis wall are equally 

 developed along the length, and only in the inverted part are they 

 somewhat thinner. The proboscis retractor muscles are very large 

 and occupy the whole inner lumen. A large anterior buccal tube 

 sphincter is present, situated somewhat posterior to the proboscis 

 tip. The distance between the sphincter and the uninverted part of the 

 proboscis tip is equivalent to the length of a single radular tooth. A 

 sac-like enlargement of the distal part of the buccal tube is present, 

 but poorly defined. This is lined with loose, tall, ciliated epithelium, 

 while the remaining part of the tube is lined with extremely low. 



Fig. 15 Haedropleura septangularis (Montagu, 1803). Longitudinal 

 section of the proboscis (radular sac not shown). 



inconspicuous, epithelial cells. There is no intermediate sphincter. 

 The buccal tube has thin walls. 



Buccal mass and oesophagus 



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

 rather long, equivalent to about two thirds of the proboscis length. It 

 has thick walls and a narrow inner cavity, which is uncurved. Long, 

 extensible, buccal lips are present (not shown by Sheridan et al., 

 1973). The oesophagus shows no elongation between the buccal 

 mass and nerve ring. 



Glands 



The salivary glands are paired, large, tubular and coiled. Their 

 diameter is much larger than illustrated by Sheridan et al. ( 1 973 ) and 

 only 2-3 times smaller than that of the venom gland. The salivary 

 ducts are very short, narrower than the glands and ciliated. There is 

 no change in the histology of the venom gland to the anterior of the 

 nerve ring, and it opens into posterior part of the buccal cavity at the 

 boundary with the oesophagus. The venom gland is very large, 

 highly coiled and occupies most of the body haemocoel.The muscu- 

 lar bulb is very large and elongate; longer and thicker in fact than the 

 proboscis. Its wall is formed of two subequal layers of longitudinal 

 muscle fibres, divided by a connective tissue layer, with a very thin 

 innermost layer of circular fibres. 



Odontophore and radula 



The odontophore is medium-sized, with paired, unfused, 

 odontophoral cartilages. The radula consists of marginal teeth, 

 which are of the wishbone type (Fig. 14d), but with the major 

 element having a large, spathulate, pointed, distal end and a narrow 

 shaft. The minor element is thinner and attaches distally to the broad 

 blade of the major element and to the radula ribbon at the base. The 

 marginal tooth is long, ca. 145pm (1.7% of SL, 4.0% AL). 



Nquma scalpta Kilburn, 1988 

 (Figs 16, 17a, 30a) 



Rhynchodeum and proboscis 



The rhynchodeal sphincter is large and anteriorly situated. The 

 epithelium of the anterior two thirds of the ventral rhynchodeum 

 wall and three quarters of the dorsal wall is tall, glandular, folded and 

 formed of large cells. The epithelium of the posterior rhynchodeum 

 is formed of low, non-glandular, cubic cells continuous with that of 

 the proboscis wall. 



The proboscis is long, slightly longer than the rhynchocoel and 

 with the tip not infolded. The proboscis walls are medium-thick, 

 comprising about 13% of the proboscis diameter in its central part. 

 The mouth opening is extremely narrow. The muscles of the probos- 

 cis wall are equally developed along its posterior part, but are absent 

 near the distal tip of the proboscis. There is no anterior sphincter of 

 the buccal tube. The distal end of the buccal tube possesses a sac-like 

 enlargement which is lined in the anterior part with very tall and 

 narrow columnar cells where there is also an epithelial pad. The base 

 of a marginal radular tooth was seen attached to the pad. Posterior to 

 the pad, the epithelium is very low, similar to that of the remaining 

 part of the buccal tube, but becomes tall and probably glandular just 

 in front of the large intermediate sphincter, which lies close, about 

 two marginal tooth lengths, distant from the proboscis tip. The 

 buccal tube has rather thin walls. 



Buccal mass and oesophagus 



The buccal mass is long, equivalent to about 2/3 of the proboscis 

 length and lies at the proboscis base, projecting a long way to the 



