. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. PREMETAMORPHIC SHELL MINERALIZATION 225. FIGURES 16-19. Shells of newly hatched veligers of the opisthobranch Hennissenda crassicornis. FIGURE 16. Right lateral view of control larva under polarized light, demonstrating birefringence of shell and statocysts (arrowheads). A large portion of the birefringent shell appears dark due to the maltese cross pattern. FIGURES 17-19. Scanning electron micrographs of air-dried shells. FIGURE 17. Shells of control larvae. The shells are calcified and show no signs of deformation on air d
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. PREMETAMORPHIC SHELL MINERALIZATION 225. FIGURES 16-19. Shells of newly hatched veligers of the opisthobranch Hennissenda crassicornis. FIGURE 16. Right lateral view of control larva under polarized light, demonstrating birefringence of shell and statocysts (arrowheads). A large portion of the birefringent shell appears dark due to the maltese cross pattern. FIGURES 17-19. Scanning electron micrographs of air-dried shells. FIGURE 17. Shells of control larvae. The shells are calcified and show no signs of deformation on air drying. The only shell sculpturing present is a series of raised lines near the aperture. The two spherical structures (arrowheads) visible inside the shell are the statocysts. FIGURES 18-19. Shells of larvae incubated in calcium-free seawater for 24 h. Shells of swimming larvae were birefringent but deformed during air drying due to partial decalcification (Fig. 18); shells of larvae stuck in the water surface were nonbirefringent, totally decalcified, and collapsed during air drying (Fig. 19). Statocysts (arrowheads) were still birefringent. in the juvenile shell (Kapur and Gibson, 1967, 1968). In contrast, A. S. M. Saleuddin (pers. comm.) has observed prehatch shell calcification in H. duryi. Coryphella sal- monacea, a nudibranch gastropod with benthic prejuvenile development, never calcifies its shell (Eyster, 1985); although an organic shell is formed it is not subsequently calcified. Since all nudibranch gastropods shed their shells at metamorphosis, lack of shell calcification by C. salmonacea may reflect adaptation to a non-planktonic ex- istence. According to Fretter and Pilkington (1971), the shells of Crepidula fornicata (and of several other prosobranch species) are fibrous, flexible, and do not significantly calcify until metamorphosis. In contrast, the shells of C. fornicata veligers observed in the present study were birefringent, shattered under pressure, exhibit
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