508 MOLLUSCA phylum vi 



Class 2. SCAPHOPODA Bronn.i 



(Cirrhohranchiata Blainville ; Solenoconchia Lacaze-Duthiers ; 

 Prosopocephala Stoliczka.) 



Aquatic, marine^ hilaterally sijmmetrical moUusks, profeded hy an external, 

 tubulär, somewhat curved and fapering 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- circidar muscidar thicJcening, the smaller 

 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 düster of numerous exsertile filaments (captacula) sprhiging from its 

 base. Otocysts present, but no eyes or tentacles. Foot rather long, conical, with 

 lateral lobes, and adjacent to the snout ventrally. 



GUIs are wanting, the gener al surface assuming respiratory fundions. Liver 

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

 genital and kidney orifices adjacent to it. Heart rudimentary, with a single Chamber. 

 Nervous System with well-developed ganglia united by commissures. Reprodudion 

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



the tubulär 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 irregulär, and its microscopic 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 resorption of the previously 



solid shell wall, and have a genesis whoUy 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 



/g\ Entalium Defr., and Pharetrium König ; and Hamulus Morton 



\>J^ {Falcula Conrad), of the American Cretaceous. The Cambrian 



Fig. 837. geuus Spirodentolium Walcott, in which the shell has spiral 



Pyrgopolon mosat Striae, is at present too imperfectlv known to lustify its refer- 



Montf. UppsrCre- i.j.i.cii ^ iT»«-n 



taceous; Belgium. ence to the bcaphopods, or even to the Mollusca. 



1 Literature (see also, .linder the head of Mollusca, antea) : Deshayes, G. 1\, Anatomie et 

 monographie du genre Dentale. Mem. Soc. Hist. Nat. Paris, 1825, vol. in.— Lacaze-Duthiers, H. de, 

 Histoire de l'organisation et du doveloppement du Dentale. Ann. des Sei. Nat., 1856-57, ser. 4, vols. 

 vi., wm.—Sars, M., Om Siphonodentalium vitreiim, en ny Slaegt af Dentalidernes Familie. 

 Universitets-Prograra, Christiania, 1861. —Stoliczka, F., Palaeontologia Indica. Cretaceous Fauna 

 of Southern India, vol. ii., 18Q7-Q8.— Gardner, J. S., Ou the ^Cretaceous Dentaliidae. Quar. 

 Journ. Geol. Soc. London, 1878, vol. xxxiv. — Kovalevsky, A., I^tude sur rembryogenie, etc., dn 

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



