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J.D. TAYLOR, Y.I. KANTOR AND A.V. SYSOEV 



MOMBBn 



Fig. 5 Duplicaria spectabilis; relaxed, critical-point dried specimen. A, Section of the rhynchodeal wall showing the transverse muscles 

 joining the inner and outer walls. Scale bar = 100 urn. B, Detail of junction of transverse muscles joining the inner wall of the 

 rhynchodaeum. Scale bar = 20 um. 



Buccal tube 



The buccal tube is that portion of the alimentary canal lying 

 between the buccal cavity and the true mouth, which is 

 situated at the distal end of the proboscis. The buccal tube is 

 present in all toxoglossans with a proboscis and is absent only 

 in those species where that organ is lost. It is very short in 

 Strictispira paxillus where the buccal mass lies at the extreme 

 anterior end of the proboscis. 



In the Mangeliinae the epithelium of the buccal tube is very 

 thin (Fig. 9), but much thicker in species of other subfami-lies 

 such as the Drilliinae and Clavatulinae (Fig. 6). Shimek 

 (1975) refered to the buccal lips (see below) as the buccal 

 tube, and he called the true buccal tube, the inner proboscis 

 wall. 



Buccal tube sphincters 



In most toxoglossans, one or more annular sphincters may be 

 found in various positions within the proboscis. 



a) Distal sphincter(s) 



In most species with a proboscis, there is a distal sphincter 

 around the true mouth. Frequently, there is a second sphinc- 

 ter also near the proboscis tip, but located just to the 

 posterior of the first (Fig. 6). In 'lower' turrids such as the 

 Drilliinae Cochlespirinae and Clavatulinae, the sphincter(s) 

 grip the solid, radular teeth whilst they are held at the 

 proboscis tip (Sysoev & Kantor, 1989; Kantor & Taylor, 

 1991). 



b) Intermediate sphincter 



A small muscular sphincter, situated about halfway along the 

 length of the proboscis is found in Splendrillia (Kantor & 

 Sysoev, 1989, fig. 3c). Species of Conus also have a sphincter 

 situated some distance posterior to the proboscis tip (Greene 

 & Kohn, 1989) which we classify as an intermediate sphinc- 

 ter. 



c) Basal sphincter 



A sphincter located near the base of the proboscis has been 

 described for Mangelia nebula (Sheridan et al., 1973). 

 Recently, Delaunois & Sheridan (1989) have illustrated a 

 section through the buccal area of M. nebula, showing a 

 single radular tooth held in the buccal tube. The tooth is 

 gripped at the anterior end by the buccal tube introvert (see 

 below), and the posterior end by the basal sphincter (Fig. 9). 



Buccal tube introvert 



This is a muscular, flap-like structure found towards the distal 

 end of the buccal tube of Mangelia nebula (Fig. 9) and called 

 a valve (valvule) by Sheridan et al. (1973). Eucithara strom- 

 boides has a longer, but apparently homologous structure 

 (Fig. 10). Delaunois & Sheridan (1989) showed that one of 

 the functions of this structure is to grip the radular tooth in 

 the buccal tube, but in Eucithara where the structure is very 

 long (Fig. 10), it may possibly be used to transport teeth to the 

 proboscis tip. 



