508 MOLLUSCA phylum vi 



Class 2. SCAPHOPODA Bronn.i 



(Cirrhobranchiata Blainville ; Solenoconchia Lacaze-Duthiers • 

 Prosopocephala Stoliczka.) 



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

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

 of tvhich 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 smuller 

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

 with a radula, 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. Otocysts 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 emus ventral and rather anterior, 

 genital and kidney orifices adjacent to it. Heart rudimentary, vjith a single chamber. 

 Nervous system with well-developed ganglia united by commissures. Beproduction 

 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 few 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 microscopic structure very different. 



The shell of Scaphopods inci'eases 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 occiirring in some 



species are therefore formed by resorption of the previously 



solid shell wall, and have a genesis wholly different from the 



slits or fissures of Pleurotomaria, Fissurella, and other Gastropods. 



Various genera described as Scaphopods have since been 



found to belong to the Serpulidae. Such are Pyrgopolon Montf. 



(Fig. 837), from the Maestricht of Belgium, also known as 



Entalium Defr., and Pharetrium Kopig ; and Hamulus Morton 



{Falcula Conrad), of the American Cretaceous. The Cambrian 



Fig. S37. genus Spirodentalium Walcott, in which the shell has spiral 



PyrgopoionmoMti Striae, is at present too imperfectly known to justify its refer- 



taceous; Boigiunt 6nce to the Scaphopods, or even to the Mollusca. 



^ Literature (see also, under the liead of Molliisea, anleu) : Leshayes, (i. I'., Anatomie et 

 monogra]iliie du genre Dentale. Mem. Soc. Hist. Nat. Paris, 1825, vol. iii. — Lacaze-Dvthiers, II. de, 

 Histoire del'organisation et du developpement du Deutale. Ann. des Sci. Nat., 1856-5'/, ser. 4, vols, 

 vi. , viii. — Sars, M., Om Siphonodeutalium vitreum, en ny Slaegt af Dentalidernes Faniilie. 

 Universitets-Program, Christiania, 1861. — Stoliczka, F., Palaenntologia Iiidica. Cretaceous Fauna 

 of Soutliern India, vol. ii., 1867-68. — Gardner, J. S., On the Cretaceous Dentaliidae. Quar. 

 Journ. Geol. Soc. Loudon, 1878, vol. xxxiv. — Kovalersky, A., llltude sur I'embryogeuie, etc., du 

 Dentale. Ann. Mus. Hist. Nat. Marseille, 1882-83. Zoologie, Mem. No. \.— Plate, L., tiher 



