File:American malacological bulletin (1986) (17535747323).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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D'ASARO: EGG CAPSULES OF SMALL MARINE PROSOBRANCHS 195
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Fig. 5. Views of prosobranch egg capsules prepared with reflected and transmitted light. Magnification bars = 0.2 mm. (a) Rissoella caribaea, side view, (b) Caecum nitidum capsule surrounded by a fecal layer with diatom frustules and three fecal pellets, (c) Marginella aureocincta, apical view, (d) M. aureocincta, side view, (e) Granulina ovuliformis, apical view, (f) G. ovuliformis, side view. specimens from Bimini in early March. Floridian specimens spawned in late March and April. Bahamian specimens deposited egg capsules in dense mats of Amphiroa sp. or in mats of epiphytes on Laurencia sp.. Floridian specimens used epiphytic mats on Laurencia sp.. Specimens from both locations cleared epiphytes from the site selected for oviposi- tion. No spawn was attached to seagrass leaves, calcium car- bonate substrata, or culture dishes. Egg capsules of Rissoella caribaea were elongate and laterally flattened ovoids with furrowed bases (Figs. 3b and 5a). These general features are known for R. diaphana and R. opalina (Fretter, 1948). When viewed by light microscopy, capsules appeared faintly cancellate, a character that was more obvious when electron microscopy was used (Fig. 3b). On the longitudinal axis, some cancellations were accented by deep furrows. In section, the primary capsule wall was composed of at least two laminae. The outer one had an op- tically dense outer surface that could constitute a third lamina (Fig. 4f). The dense surface formed the cancellated sculpture of the primary capsule wall. Primary capsules from Florida contained one or two embryos; those from the Bahamas had three or four embryos. Each yolky, yellowish embryo was sur- rounded by a thin secondary capsule, possibly the vitelline membrane, that also enclosed some fluid. Fretter (1948) iden- tified this fluid as albumen. Spherical secondary capsules were suspended in the thin fluid of the primary capsule. As development progressed, the inner spheres swelled to fill the lumen of the primary capsule. Embryos passed through a veliger stage, and after 18 days, hatched through a slit formed in a longitudinal furrow on the primary capsule as grayish- white, crawling juveniles. Capsular dimensions for a com- bined sample of Bahamian and Floridian specimens are presented in Table 3. Caecum nitidum Stimpson, 1851 (USNM 836985) Caecum nitidum released unattached, demersal egg capsules in the laboratory from January through May, 1985. After 24-hours acclimation during which few capsules were released, spawning progressed unabated in populations of adults provided with sufficient food (Table 2). Daily estimates of production were as high as six capsules per female. Released capsules sank rather quickly and became en- tangled and adhered to algae and detritus. In habitats with strong currents these capsules could be transported short distances. Egg capsules of C. nitidum, like those described for other caecids by Gbtze (1938), Marcus and Marcus (1963), and Bandel (1976a), were thin-walled spheres, probably ovarian in origin, enveloped in a nearly opaque coating, 0.02 to 0.04 mm thick, attached to the capsule by a thin matrix (Fig. 4g). The previously mentioned authorities believe the opaque material to be of fecal origin. Embedded in the coating were diatoms, spicules, and fragments of organic material that ap- peared identical to that found in fecal pellets (which, as shown in Figure 5b, were often longer than egg capsules.) Females frequently deposited capsules with little or no fecal layer. In section, early in development, embryos appeared to be at- tached to the capsular walls (Fig. 5b). The expanding inner lamina reported by Bandel (1976a) was not observed, but could have been present. Average capsular diameters (with and without the fecal layer) are given in Table 3. Planktotroph- ic veligers escaped from the capsules after two to three days. Marginella aureocincta Stearns, 1872 (USNM 836974) During April and May, 1985, Marginella aureocincta,

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