430 MOLLUSC A SUB-KINGDOM vi 



Class 2. SCAPHOPODA. Bronn. 1 



(Cirrhobranchiata, Blainville ; Solenoc&nchia, Lacaze-Duthiers ; 

 Prosopocephala, Stoliczka.) 



Aquatic, marine, bilaterally symmetrical Mollusks, protected by an external, 

 tubular, somewhat curved and tapering shell, open at both ends, the concave side 

 of which is dorsal ; the shell secreted by a mantle of the same shape, the larger, 

 anterior opening of which is provided with a circular muscular thickening, the smaller 

 opening serving as outlet for organic waste and genital products. Mouth furnished 

 with a radida, borne on a cylindrical snout, and surrounded by a rosette of leaf -like 

 appendages ; a cluster of numerous exsertile filaments (captacula) springing from its 

 base. Otoci/sts present, but no eyes or tentacles. Foot rather long, conical, with 

 lateral lobes, and adjacent to the snout ventrally. 



Gills are wanting, the general surface assuming respiratory functions. Liver 

 large, bilateral ; intestine, strongly folded, the anus ventral and rather anterior, and 

 kidney orifices adjacent to it. Heart rudimentary, with a. single chamber. Nervous 

 system with well-developed ganglia united by commissures. Reproduction without 

 copulation, the sexual products voided through the right kidney. 



Scaphopods are without exception marine, and for the most part inhabit 

 deep water. There are no littoral species. They live embedded in mud or 

 sand, with only the smaller end of the shell projecting above the surface. 

 Their food consists chiefly of Foraminifera and similar organisms, captured 

 by the filamentary captacula. 



The tubular, curved shell, open at both ends, is characteristic of the class, 

 the tubular shells of certain Gastropods and Cephalopods being invariably 

 closed at the smaller end. Some tubicolous Worms (Serpulidae) form a similar 

 shell, but it is composed of two layers only, instead of three 

 as in Scaphopods, the growth is more irregular, and its micro- 

 scopic structure very different. 



The shell of Scaphopods increases by successive increments 

 at the larger end, and at the same time loses by wear and 

 absorption at the smaller end. The posterior slits or notches 

 occurring in some species are therefore formed by reabsorption 

 of the previously solid shell wall, and have a genesis wholly 

 different from the slits or fissures of Pleurotomaria, Fissurella, 

 (y) and other Gastropods. 



Various genera described as Scaphopods have since been 

 p r cndonMowt f un d to belong to the Serpulidae. Such are Pyrgopolon, Montf. 

 Montf. upper ere- (Fig. 788), from the Maestricht of Belgium, also known as 

 Entalium, Defr., and Pharetrium, Konig; and Hamulus, Morton 

 (Falcula, Conrad), of the American Cretaceous. The Cambrian genus Spiro- 

 dentalium, Walcott, in which the shell has spiral striae, is at present too 



1 Literature (see also, under the head of Mollusca, pp. 344, 345) : 

 Deshayes, G. P., Anatomic et Monographic du Genre Dentale (Mem. Soc. Hist. Nat., Paris, vol. II. 



pp. 321-378), 1825. 

 Lacaze-Duthiers, 11. de, Histoire de 1'organisation et du developpment du Dentale (Ann. des Sci. 



Nat. [4], vols. VI. -VIII.), 1856-57. 



