FOREGUT ANATOMY OF CRASSISPIRINE GASTROPODS 



79 



the proboscis wall are equally developed along its length. The mouth 

 is narrow. The proboscis is covered with ciliated epithelium with 

 long cilia, which is replaced by non-ciliated epithelium with a rather 

 thick cuticle at its base. 



A small, anterior, buccal tube sphincter lies in front of the sac-like 

 enlargement of the buccal tube, close to mouth opening. The epithe- 

 lium, lining the enlargement is tall, forming pads on both walls (Fig. 

 30d). A second larger sphincter lies at the base of the enlargement at 

 the distance slightly longer than one tooth length and therefore 

 should be considered as anterior. The walls of the buccal tube are 

 thin in the anterior part, but become rather thick (about 10% of 

 proboscis diameter) after the second sphincter. 



Buccal mass and oesophagus 



The buccal mass lies at the proboscis base and is short in comparison 

 to the proboscis. It is thick-walled, with a broad lumen and curved. 

 There are very large, extensible buccal lips. The oesophagus is 

 greatly elongated between buccal mass and nerve ring and forms a 

 long loop. There is no buccal sac. The opening of the radular 

 diverticulum is narrow and relatively long. The salivary ducts open 

 into the buccal cavity on both sides of the opening of the radular 

 diverticulum. 



Glands 



The salivary glands are medium-sized, paired and acinous. The 

 venom gland changes markedly in histology after passing through 

 the nerve ring. The duct is very narrow, unciliated and opens at the 

 border between the buccal mass and oesophagus. The muscular bulb 

 is medium-sized, with the wall formed from two layers of longitudi- 

 nal muscle fibres (the outer about twice as thick as the inner), 

 divided by a connective tissue layer, with a thin, innermost layer of 

 circular muscle. 



Odontophore and radula 



The odontophore is rather large, with paired, unfused cartilages. The 

 radula consist of marginal teeth (Fig. 26d), which are long and 

 harpoon-like in form, but concavo-convex (gutter-shaped) in profile. 

 The distal end of the tooth is sharply pointed with a pronounced 

 barb, whilst the shaft is more or less straight-sided, with just a slight 

 enlargement at the base. A very thin secondary limb lies along the 

 edge of the shaft (Fig. 26d). The marginal tooth is very long, ca. 

 320pm ( 1 .3% of SL, 4.0% AL). 



Cheungbeia robusta (Hinds, 1843) 



(Figs 25, 26a-c) 



See also Taylor (1994, plates li, 6c; figs 16-17) 



Rhynchodeum and proboscis 



The rhynchodeal sphincter is large and located slightly to the 

 posterior. The epithelium of nearly the whole wall of the rhynchodeal 

 cavity is glandular, whilst only a small posterior portion is non- 

 glandular and continuous with that of the proboscis wall. The 

 rhynchostome is rather wide. 



The proboscis is very long, longer than the rhynchocoel and 

 coiled within it. It is relatively wide at the base and narrows towards 

 the tip. The walls of the proboscis are thin and highly folded, 

 forming about 10% of the proboscis diameter. Muscles of the 

 proboscis wall are equally developed along its length. The mouth is 

 narrow. The anterior, buccal tube sphincter is very small and lies 

 close to the mouth opening, in front of the short, only slightly 

 differentiated, sac-like enlargement of the buccal tube The epithe- 

 lium lining this enlargement is tall, forming pads on both walls. A 



second, larger sphincter lies at the base of the enlargement at slightly 

 more than one radular tooth length from the mouth and therefore 

 should be considered as an anterior sphincter. The buccal tube is 

 narrow anteriorly, but expands greatly posterior to the sac-like 

 enlargement and occupies nearly the whole proboscis lumen. Never- 

 theless, its walls are thin and form only about 5% of the proboscis 

 diameter at its base. 



Buccal mass and oesophagus 



The buccal mass is long, thick-walled with broad lumen, curved, and 

 lies at the proboscis base. The boundary between the posterior 

 buccal tube and the buccal mass is not well defined. The buccal lips 

 are very short. The oesophagus is greatly elongated between buccal 

 mass and nerve ring and forms a long loop, which is narrow when 

 leaving the buccal cavity and expands posteriorly. There is no buccal 

 sac. The opening of the radular diverticulum is rather narrow and 

 moderately long. The thick and long salivary ducts open in the 

 buccal cavity on both sides of the opening of the radular diverticu- 

 lum. 



Glands 



The salivary glands are medium-sized, paired, and of the modified 

 acinous type. The venom gland changes abruptly in histology after 

 passing through the nerve ring. The duct is very narrow, unciliated 

 and opens at the border between the buccal mass and oesophagus. 

 The muscular bulb is large, with the wall mainly formed of two 

 layers of circular muscle fibres (the outer being about twice the 

 thickness of the inner), divided by a connective tissue layer, with a 

 thin, innermost layer of circular muscle. 



Odontophore and radula 



The odontophore is small, with paired, unfused cartilages. The 

 radula consist of marginal teeth only (Figs 26a-c) which are har- 

 poon-like and very similar to those of Cheungbeia mindanensis 

 (Fig. 26d). These have long shafts which are concavo-convex (gutter 

 shaped) in profile. The distal end of the tooth is sharply pointed with 

 a pronounced barb, whilst the shaft is more or less straight-sided, 

 with just a slight enlargement at the base. A very thin secondary limb 

 lies along the edge of the shaft (Fig. 26c). 



Antiguraleus morganus (Barnard, 1958) 

 (Figs 27, 28a) 



Rhynchodeum and proboscis 



The rhynchodeal sphincter is medium-sized and anteriorly located. 

 The epithelium of the anterior half of the rhynchodeal cavity is tall, 

 glandular, folded and formed of large cells, while that of the poste- 

 rior half of the rhynchodeum is non-glandular and continuous with 

 that of the proboscis wall. This posterior part of the rhynchodeum is 

 attached by numerous muscle fibres to the body wall and probably 

 cannot be everted. The rhynchostome is narrow. 



The proboscis is very long, more than twice as long as the 

 rhynchodeal cavity, rather thin and coiled. The proboscis walls 

 comprise about 15% of the proboscis diameter. The mouth is very 

 narrow. The muscles of the proboscis wall are equally developed 

 along its length. The anterior buccal tube sphincter is small, and 

 lies in front of a very broad sac-like enlargement of the buccal 

 tube. The epithelium, lining the enlargement is similar to that of 

 the rest of the buccal tube. Additionally, there is large intermediate 

 sphincter, situated approximately half-way along the proboscis. 

 The buccal tube has rather thin walls, forming about 8% of probos- 

 cis diameter. 



