FOREGUT ANATOMY OF CRASSISPIRINE GASTROPODS 



65 



about 25% of proboscis diameter, whilst the buccal tube walls are 

 highly folded, but thin, making up about 6% of the total diameter. 

 The mouth is narrow. The proboscis is highly folded, with the base 

 more muscular than the tip. Both the anterior buccal tube sphincter 

 and the epithelial pad are absent. The sac-like enlargement of the 

 buccal tube is long and lined with tall epithelium, but poorly 

 differentiated from the buccal tube. It has two unequal circular folds. 

 The anterior one is larger and directed anteriorly and lined with tall 

 epithelium. To the posterior of the second fold, the wall of the buccal 

 tube forms an invagination, where the base of the radular tooth is 

 situated. The intermediate sphincter of the buccal tube is rather 

 large. The buccal tube is lined with a low, loose epithelium and after 

 leaving the proboscis it expands slightly in diameter and forms two 

 small, poorly-muscularized lips which are directed anteriorly, simi- 

 lar to the 'valvule' seen in Mangeliinae (Sheridan etal., 1973). The 

 buccal lips are medium-sized, muscular, with the dorsal one inverted 

 inside the buccal cavity. 



Buccal mass and oesophagus 



The buccal mass is situated to the posterior of the proboscis, is rather 

 large and muscular, with a narrow lumen, and sharply curved. The 

 oesophagus is greatly elongated between the buccal mass and nerve 

 ring, forming a long loop. The buccal sac is long and narrow. 



Glands 



The salivary glands are medium-sized and acinous, with long, coiled 

 and rather thick ducts. The venom gland changes in histology after 

 passing through the nerve ring, but its diameter remains nearly the 

 same and there is no defined duct. The gland opens into the oesopha- 

 gus just posterior to the buccal cavity. The muscular bulb is large, 

 composed of two layers of longitudinal muscle fibres, divided by a 

 connective tissue layer, with an innermost, thin layer of circular 

 muscle fibres. 



Odontophore and radula 



The odontophore is medium-sized, with paired unfused cartilages 

 formed of one layer of cells. The radula illustrated by McLean 

 (1971, fig. 67) is composed of marginal teeth of the wishbone type, 

 with a robust and pointed major limb and a smaller, shorter, second- 

 ary limb. 



Crassispira (Crassiclava) turricula (Sowerby, 1834) 

 (Figs 10, Ilc-d) 



Rhynchodeum and proboscis 



The rhynchostomal sphincter is large and anteriorly situated. The 

 epithelium of the anterior one third of the rhynchodeal wall is 

 glandular, and arranged into high folds; whilst the posterior two 

 thirds is continuous with that of the proboscis wal 1 . The proboscis tip 

 is formed by the invagination of the outer proboscis wall into the 

 buccal tube. This is confirmed by the similar, low, cubic epithelia of 

 the outside of the proboscis and the anterior-most part of the buccal 

 tube. Posteriorly in the buccal tube the cubic epithelium is replaced 

 by one with columnar cells. 



The proboscis is of medium length (little more than half of the 

 rhynchocoel), uncoiled, but with telescopically folded walls. The 

 muscles of the proboscis wall are better developed at its base. 



An anterior buccal tube sphincter is present. The sac-like enlarge- 

 ment of the buccal tube is well-defined and lined with tall, glandular 

 epithelium. An intermediate sphincter is also present, situated at the 

 base of the sac-like enlargement. The walls of the buccal tube in the 

 area of the enlargement are much thicker and formed by relatively 



thicker circular muscle fibres, as if this part of the tube is capable of 

 strong contraction. The proboscis wall is thick, composing about 

 25% of proboscis diameter, whilst the wall of the buccal tube is 

 medium-thick, representing about 5% of proboscis diameter. Large 

 muscular buccal lips are present. 



Buccal mass and oesophagus 



The buccal mass lies mainly within the proboscis and is very long, 

 equivalent to about two thirds of the proboscis length. The oesopha- 

 gus is greatly elongated between the buccal mass and nerve ring and 

 forms a long loop. It is narrow and lined with an epithelium bearing 

 long cilia. The duct of the radular sac is broad and rather long. The 

 buccal sac is short. 



Glands 



The salivary glands are large, with the ramified tubular morphology. 

 The salivary ducts are very long, coiled, and thick. The histology of 

 the venom gland changes anterior to the nerve ring. The duct of the 

 venom gland is narrow and unciliated. The muscular bulb is ex- 

 tremely large, with thick walls mainly formed of two layers of 

 longitudinal muscle fibres, separated by a connective tissue layer, 

 with a much thinner, innermost layer of circular fibres. 



Odontophore and radula 



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

 cartilages, formed by a single layer of cells. The radula (Figs 1 lc-d) 

 consists of both lateral and marginal teeth. The lateral teeth ( use of 

 the term 'lateral' teeth here does not imply homology with the lateral 

 teeth of other neogastropods) are low and arcuate, sharply-curved 

 anteriorly towards the midline of the ribbon. In profile these teeth are 

 cuesta-like, with steep anterior faces and gentle posterior slopes. 

 The marginal teeth are of the robust wishbone form with a large, 

 pointed, major element and a thinner, shorter, minor element. The 

 marginal teeth are ca 200pm long (0.6 %SL; 2.0% AL) 



Crassispira (Crassiclava) apicata (Reeve, 1845) 

 (Fig. 12) 



The anatomy of the foregut is similar to the preceding species and 

 only the differences are mentioned. 



The anterior part of the rhynchodeum, which is lined with glandu- 

 lar epithelium is shorter than in C. turricula and comprises about 

 half the length of the rhynchodeum. The proboscis walls do not form 

 telescopic folds. Also, the proboscis is longer and occupies about 

 two thirds of the rhynchocoel. Only the anterior buccal tube sphinc- 

 ter is present and an epithelial pad is located within the sac-like 

 enlargement of the buccal tube. The enlargement itself is shorter 

 than in C. turricula. The proboscis walls are much thinner and 

 comprise only about 6% of its diameter. The salivary glands are very 

 large with the ramified tubular morphology. The radula (from Maes, 

 1983 figs 31 & 37) consists of both lateral and marginal teeth. The 

 lateral teeth have the arcuate form illustrated for C. turricula (Figs 

 llc-d), whilst the marginal teeth have the wishbone form with a 

 robust major limb and a shorter, thinner, minor limb. 



Hindsiclava andromeda (Dall 1919) 

 (Fig. 13) 



Rhynchodeum and proboscis 



The rhynchostomal sphincter is of medium size and located slightly 

 to the posterior. The epithelium of the anterior half of the rhynchodeal 

 wall is tall and glandular, whilst the posterior is low and cubic and 



