FOREGUT ANATOMY AND CLASSIFICATION OF CONOIDEA 



129 



0-1 mm 



ovg 



cis, when withdrawn, lies behind the septum, with the 

 retracted introvert lying to the anterior. A probably homolo- 

 gous septum is also found at the extreme posterior and 

 ventral end of the rhynchocoel in Thatcheria and Pontio- 

 thauma (Pace, 1901). A thin septum is also found in the 

 posterior part of the rhynchocoel in Pervicacia tristis (not 

 reported by Rudman (1969)) and in Duplicaria kieneri (Tay- 

 lor, unpublished). 



The function of the septum is unknown, but it appears 

 better developed in species with a long proboscis and where 

 the proboscis withdraws behind the septum. 



Accessory proboscis structure 



This is an extensible muscular structure which arises from the 

 left hand wall of the rhynchocoel. It has been found only a 

 few species of Terebridae and Pervicaciidae. It is long and 

 branched in Hastula bacillus (Taylor & Miller, 1990), shorter 

 and club-like in Terebra affinis (Miller, 1971), 'Hastula' 

 colorata and D. kieneri and a curved, club-shape in Terebra 

 imitatrix (Auffenberg & Lee, 1988). In H. bacillus the 

 accessory proboscis is covered in possible chemosensory 

 structures (Taylor & Miller (1990). 



Snout gland 



This is a subspherical gland which opens into the right-hand 

 posterior end of the rhynchocoel in a number of Conns 

 species (Marsh, 1971). The gland consists of folded glandular 

 epithelium (Fig. 7) and is surrounded by a muscular sheath of 

 circular muscles. From histochemical tests. Marsh (1971) 

 concluded that the gland secretes mucus. The gland has been 

 reported in 18 species of Conus, all but one of which are 

 known to be vermivorous (Marsh, 1971). 



Fig. 4 Daphnella reeveana; A, longitudinal section through the 

 foregut; B, Enlargement of the mouth area showing the short 

 proboscis lying behind the septum. Abbreviations: bm, buccal 

 mass; cm, columellar muscle; con, circum-oral nerve ring; in, 

 rhynchodeal introvert; oe, oesophagus; ors, opening of radular 

 sac; ovg, opening of venom gland; p, proboscis;s, rhynchostomal 

 sphincter; spt, septum; vg, venom gland. 



glandular (Fig. 6C), but in the posterior half the epithelium is 

 low, cuticularized and similar in morphology to that of the 

 outer surface of the proboscis. This feature indicates that the 

 posterior part of the rhynchodeum can be extended outwards 

 when the proboscis is protruded through the rhynchostome. 

 We have observed this condition of the rhynchocoel epithe- 

 lium in Clavatula, and Clionella (Clavatulinae), Vexitomina 

 (Crassispirinae), Turricula nelliae spurius (Cochlespirinae), 

 Pilsbryspira nympha (Zonulispirinae). and Anarithma metula 

 (Borsoniinae). 



In 'lower' turrids, excepting Vexitomina, this feature seems 

 to associated with those species in which the buccal mass lies 

 in a distal position within the proboscis (see below). Its 

 presence may be connected with the mechanism by which the 

 buccal mass is everted from the proboscis tip. 



Septum in rhynchodeum 



A thin, slightly muscular septum, pierced by a circular orifice, 

 and dividing the rhynchodeal cavity into two parts is known in 

 Daphnella reeveana (Fig. 4), Philbertia purpurea (Sheridan et 

 al., 1973) and Terebra subulata (Taylor, 1990). The probos- 



The proboscis and its structures 



An extensible proboscis arising from the posterior of the 

 rhynchocoel is present in the Drilliinae (formerly Clavinae; 

 ICZN decision pending on further name change to Clavusi- 

 nae) and all the radulate turrids examined, excepting Gymno- 

 bela emertoni, where the radula is vestigial. A proboscis is 

 present in all species of Conus, in Hastula, and in other 

 radulate Terebridae, such as T. subulata, and T. babylonia 

 (Taylor, 1990). The distal opening to the proboscis forms the 

 true mouth as in all probosciferous gastropods. Shimek 

 (1975) referred to the opening of the buccal cavity as being 

 the true mouth. 



A proboscis is absent in the radula-less Turridae such as 

 Teretiopsis, Taranis (Kantor & Sysoev, 1989), Philbertia 

 leufroyi boothi, P. linearis (Smith, 1967, Sheridan et al., 1973) 

 and the radulate Gymnobela emertoni. A proboscis is also 

 absent in species of Duplicaria and Pervicacia, which are 

 radulate forms of the Pervicaciidae (Taylor, 1990), and in the 

 many species of Terebridae which lack a radula, such as 

 Terebra maculata, T. gouldi, T. dimidiata, and T. affinis 

 (Miller, 1970, 1975; Taylor, 1990). 



In Duplicaria spectabilis and Gymnobela emertoni we have 

 observed a low cylinder of muscular tissue surrounding the 

 opening to the buccal cavity (Fig. 8) (Taylor (1990, Fig. 2). 

 We think that this may represent the remnant of a much 

 reduced proboscis. A similar reduced structure found in 

 Cenodagreutes spp. and Philbertia linearis, was described by 

 Smith (1976) as the muscular sheath. 



