LARVAL AND JUVENILE SHELLS OF 4 NORTH-ATLANTIC SCAPHOPOD SPECIES

Ontogenetically early shells of four North Atlantic scaphopod species, Antalis occidentalis Stimpson, 1851, Entalina quinquangularis (Forbes , 1844), Pulsellum lofotensis (M. Sars, 1865), and Cadulus subfusiform is (M. Sars, 1865) were examined by SEM. The larval shell of previousl y described scaphopods can be divided into the bulbous protoconch A an d the more or less elongated protoconch B. In A. occidentalis and E. q uinquangularis, a smooth teleoconch A is distinguished from the ribbed teleoconch B. The protoconch of A. occidentalis matches previous repo rts on A. tarentinum (Lamarck, 1818) (type 1). E, quinquangularis and P. lofotensis have a protoconch with a marked constriction, but withou t annulations (type 2). In C. subfusifomis, only teleoconchs A and B w ere found, hut no distinct protoconchs. Teleoconch A of this species r esembles a juvenile Pulsellum, before it forms a constriction separati ng it from the rapidly expanding teleoconch B, In addition to shell mo rphometrics, the microstructure is described for each species. The res ults are compared to earlier descriptions of Recent and fossil scaphop od protoconchs: type 1 is restricted to the Dentaliida, type 2 typical for Cadilida except for the presumably derived condition in C. subfus iformis.