424 



PHYLUM MOLLUSC A. 



ClaSS II. SOLENOGASTRES 



The members of this class are worm-like animals, in which the 

 mantle envelops the whole body and bears numerous spicules, but no 

 shell. It is somewhat doubtful if they are Molluscs at all. There are 

 two families Neomeniidse and Chaetodermidse. 



Of Neomeniidae, six genera are known, e.g. Neomenia and Pro- 

 neomenia. They have a longitudinal 

 pedal groove, an intestine without 

 distinct digestive gland, two neph- 

 ridia with a common aperture, and 

 hermaphrodite reproductive organs. 

 The Chaetodermidse, represented by 

 one genus Chatoderma y are cylin- 

 drical in form, without a pedal groove, 

 with a radula bearing one tooth, with 

 a distinct digestive gland, and with 

 two nephridia opening separately into 

 a posterior cavity, which also contains 

 two gills. The sexes are separate. 



Class III. SCAPHOPODA 



Very different in many respects from 

 Gasteropoda are the Scaphopoda, of 

 which Dentalium (Elephant s tooth- 

 shell) is the commonest genus. They 

 are apparently related to the Zeugo- 

 branchiate Gasteropods, and also to 

 the simplest Bivalves. They burrow 

 in the sand at considerable depth off 

 the coasts of many countries. The 

 mantle has originally two folds, which 

 fuse ventrally, and the shell becomes 

 cylindrical, like an elephant's tusk. 

 FIG. m.Proneomenia. Ner- Jt is .P en at bot j ^nds. T *? e . lar er 

 voussystem.-FromHubrecht. P e ^ m g (directed downwards m the 



sand) is anterior, the concave side of 

 the shell is dorsal. The mouth opens 

 posterior vis- at the end of a short buccal tube, 

 at the base of which is a circle of 

 c ili ate d tentacles. The foot is long, 



thr . ee sma11 terminal lobes - 



is used in slow creeping, and is pro- 

 truded at the anterior opening. There are cerebral and pleural ganglia 

 near one another in the head, pedal ganglia in the foot, and a long 

 untwisted visceral loop with olfactory ganglia near the posterior anus. 

 Sense organs are represented by otocysts beside the pedal ganglia. 

 There is an odontophore with a simple radula. The food consists of 

 minute animals. There is a much reduced heart, and colourless blood 

 circulates in the body cavity. There are two nephridial apertures, one 



terior pedal; 

 cerals; si., sublingual connectives; 

 ., cerebro-pedal connective; *., 



' "*" 



