LEIGHTON: EARLY GROWTH OF THE ABALONE 



continued growth the asjTiimetry is reduced and 

 the shell form, as viewed from above, is almost 

 circular until the "notch stage" is reached. For- 

 mation of the first respiratory aperture is ini- 

 tiated by separation of two portions of the mantle 

 at the right anterior margin interrupting other- 

 wise uniform marginal shell deposition. The 

 "notch" so formed is a convenient growth mark, 

 reached by the most rapidly growing H. soren- 

 seni at an age of 55 days and a shell length of 

 2.0 or 2.1 mm (Figure 5). 



In the juvenile H. sorenseni observed, shell 

 pigmentation was a pale violet-pink becoming 

 more vivid as the notch stage was approached. 

 In most cases a cyan-blue flare spread from the 

 apex to the right shell margin. After comple- 

 tion of the first respiratory pore, a dichotomy 

 in pigment pattern emerged. Although all ju- 

 veniles developed from eggs of a single female, 

 fertilized by a single male, approximately 40% 

 developed an even red-violet shade throughout 

 the greater extent of the shell while the majority 

 became increasingly bicolored with growth. The 

 bicolored pattern consisted of a rich red zone 

 along the left edge of the shell (extending to the 

 aperture row) and pigmentation of blue, green, 

 and yellow over the broader surface right of 

 the aperture row. In individuals of both color- 

 ation patterns, a conspicuous ivory-white patch 

 remained at the position of attachment of the 

 right shell muscle until obscured by nacre depo- 

 sition at about 8 mm. The apex, in turn, became 

 increasingly white. 



Elevated apertures, typical of the species, ap- 

 pear even in first-pore individuals. More con- 

 spicuous is the ridge bordering the left shell 

 margin. It is this ridge that forms the sharp 

 corner and relatively straight left anterior mar- 

 gin (Figure 6). 



DISCUSSION 



Establishment of specific characteristics by 

 which larvae and juveniles of the seven cooccur- 

 ring California species of Haliotis may be dis- 

 tinguished must await results of studies of fine 

 structure of larval shells. Examination by scan- 

 ning electron microscope has revealed sufficient 

 detail of fine crystalline and basement structure 



Figure 5. — Juvenile Haliotis sorenseni at "notch" stage 

 (2.0 mm, 55 days). Shell is still slightly transparent 

 and prominent anatomical features are readily seen from 

 the dorsal aspect, a. cephalic tentacle, b. mouth, c. in- 

 dentation at point of formation of first respiratory pore 

 ("notch"), d. right shell muscle, e. intestine, f. digestive 

 gland, g. epipodial tentacle. 



of larval shells in certain other prosobranchs 

 (Fretter and Pilkington, 1971). Gross shell 

 morphology alone is inadequate to differentiate 

 larvae of even distantly related species. Pig- 

 mentation of velar and visceral portions may 

 provide distinctive features for recognition of 

 some species. 



Pigments derived from parental yolk appear 

 to be retained by trochophore and veliger larvae 

 of Haliotis. Among California species, ovarian 

 tissue is dark green in H. rufescens, H. crach- 

 erodii, H. walallensis, and H. kamtschatkana 

 assimilis. Correspondingly, larvae of these spe- 

 cies are conspicuously green. The remaining 

 three species found locally, H. fulgens, H. corru- 

 gata, and H. sorenseni, produce eggs of brown, 

 olive, and beige color, respectively. Their larvae 



377 



