FOREGUT ANATOMY OF CRASSISPIRINE GASTROPODS 



83 



The proboscis is long and thick, and occupies about two thirds of 

 the rhynchodeal cavity. The proboscis walls are thick and comprise 

 about 20% of the total diameter. The mouth is narrow in the 

 preserved condition, but appears capable of great enlargement. The 

 ventral side of the anterior part of the proboscis wall is invaginated. 

 The muscles of the proboscis wall are equally developed along its 

 length. Both anterior and intermediate buccal tube sphincters are 

 absent, as is also the distal sac-like enlargement of the buccal tube. 



Buccal mass and oesophagus 



The buccal mass is situated to the posterior of the base of the 

 proboscis. It is long, equivalent to about half of the proboscis length, 

 with thick walls and a rather narrow inner cavity, which is not 

 curved. Extensible buccal lips are absent. The oesophagus is elon- 

 gated between the buccal mass and nerve ring, forming a short loop. 



Glands 



The salivary glands large and acinous. The venom gland shows a 

 change in histology after passing anteriorly through the nerve ring. 

 The duct of the gland is narrow, ciliated and opens into the posterior 

 part of the buccal cavity. The muscular bulb is long with the wall 

 formed of two layers of equal thickness composed of longitudinal 

 fibres, divided by a connective tissue layer. 



Odontophore and radula 



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

 odontophoral cartilages formed of one layer of cells. The radula 

 comprises marginal teeth, which are of the robust, wishbone form, 

 with a long solid, distally pointed major limb and a thinner second- 

 ary limb, which attaches near the tip of the major limb. The marginal 

 teeth are short, ca. 165um (0.5% of SL, 1.4% AL). 



Vexitomina garrardi (Laseron, 1954) 

 (Figs 23b, 30b) 



Rhynchodeum and proboscis 



The rhynchodeal sphincter is large, long and situated slightly to- 

 wards the posterior. The epithelium of the anterior two thirds of the 

 rhynchodeum is glandular, forming tall folds, whilst the epithelium 

 of the posterior one third of the rhynchodeum is non-glandular and 

 continuous with that of the proboscis wall. The rhynchostome is 

 wide. The proboscis is short, cone-shaped, and occupies about half 

 the rhynchocoel.The proboscis walls form about 20% of the probos- 

 cis diameter. The muscles of the proboscis walls are equally developed 

 along its length. The mouth is very narrow. 



The anterior buccal tube sphincter is small, and lies close to the 

 mouth, opening in front of the long sac-like enlargement of the 

 buccal tube. A tall epithelium lines the enlargement. A second, larger 

 sphincter lies at the base of the enlargement, at a distance slightly 

 longer than one tooth length and therefore should be considered as 

 anterior. A tooth was seen in the buccal tube posterior to the latter 

 sphincter. The buccal tube walls are rather thin (about 8% of 

 proboscis diameter) and highly folded. In the posteriormost part the 

 tube forms a very long, but narrow, circular fold. 



Buccal mass and oesophagus 



The buccal mass is large in comparison with the proboscis, equiva- 

 lent to about two thirds of its length, with thick, folded walls and a 

 narrow lumen. It lies posterior to the proboscis base. The buccal lips 

 are small. The oesophagus is elongated between the buccal mass and 

 nerve ring and forms a short loop. After leaving the buccal cavity, the 



oesophagus is very narrow, but then expands greatly after passage 

 through the nerve ring. The buccal sac is very short. 



Glands 



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

 venom gland changes sharply in histology after passing anteriorly 

 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 of two 

 layers of longitudinal muscle fibres (the outer being twice as thick as 

 the inner), divided by a connective tissue layer and innermost thin 

 layer of circular muscle. 



Odontophore and radula 



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

 The radula consists of marginal teeth (Fig. 23b) which are long, with 

 a blade-like distal portion, which is sharply pointed with a small 

 barb. The shaft is long and tapers gradually towards the base. The 

 teeth are slightly concavo-convex in profile and a very thin splint- 

 like secondary limb lies along the edge of the shaft. 



Turridrupa bijubata (Reeve, 1843) 



Rhynchodeum and proboscis 



The rhynchodeal sphincter is medium-sized and posteriorly located. 

 The anterior half of the rhynchodeum has a highly folded, tall, 

 glandular epithelium whilst the posterior half has a low cubic 

 epithelium similar to that of the proboscis wall. The proboscis is 

 short and occupies about half of the rhynchodeum, the tip is thin, 

 while the base is thicker and muscular. There is a very small anterior 

 buccal tube sphincter, lying at the distal end of a small sac-like 

 enlargement containing a single radular tooth. A larger intermediate 

 sphincter lies at a distance of about 10 tooth lengths from the 

 proboscis tip. 



Buccal mass and oesophagus 



The buccal mass is long and curved and lies to the posterior of the 

 proboscis. The walls of the buccal mass are long and muscular 

 anterior to the entrance of the radular sac and the buccal lips small 

 and not invertible. The oesophagus is not elongated between the 

 buccal sac and nerve ring. 



Glands 



The salivary glands are large, paired and acinous, with large ciliated 

 ducts. The venom gland changes abruptly in histology after passing 

 anteriorly through the nerve ring and the duct opens into the oesopha- 

 gus just posterior to the buccal mass. The muscular bulb is large and 

 comprises two layers of circular muscle separated by a connective 

 tissue layer. The outer layer is about twice as thick as the inner. There 

 is no thin, innermost, muscular layer. 



Odontophore and radula 



The odontophore is large with two large unfused cartilages .The radula 

 consist of both central and marginal teeth (Kilburn, 1 988, fig. 40).The 

 central tooth comprises a square plate with a prominent spine-like 

 cusp. The marginal teeth are of the robust wishbone type with the 

 bifurcating proximal end, similar to Epidirona gabensis (Fig. 1 8a). 



Outgroup 



This species from the family Turrinae, was chosen as the outgroup. 

 The anatomy and radula is described and illustrated in Taylor (1994) 

 and further details are given below. 



