File:American malacological bulletin (1986) (18152775452).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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178 AMER. MALAC. BULL. 4(2) (1986)
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Fig. 5. Diagramatic view of a single egg capsule of a typical calyp- traeid gastropod. ing young, depending on the species. The crawling young of the Calyptraeidae have evidence of shell coiling but have lost the operculum. However, the newly-hatched crawling young of Hipponix grayanus of Costa Rica were observed to still have an operculum. The capsule of Crepidula protea from southern Brasil differs from all others of the family. Twenty-five brooding females dredged off Barra, Rio Grande do Sul, in 25-30 m of water, were found to have embryos embedded in a gelatinous matrix in which they did not move freely (Hoagland, 1983). It is not known if the matrix has a nutritive or a protec- tive function. The egg capsule of calyptraeids are brooded beneath a gill enlarged for filter-feeding (Fig. 4). Therefore strong water currents carry oxygen to the permeable sacs and can remove wastes. However, the broods may interfere with respiration and/or feeding of the adult, or otherwise cause stress. To test this possibility, I examined the survivorship of females of Crepidula fornicata with and without broods when subjected to near starvation and to low oxygen. Survivorship under near- starvation conditions was better when larvae were not pre- sent (Table 2). Six of the 10 brooding females lifted the shell vigorously and were observed to bend the head and neck as if the broods were at the stage of hatching; the broods were expelled prematurely. Similar results were obtained when 10 pairs of test animals were subjected to unaerated seawater, except that mortality was higher in animals both with and without broods. All broods were expelled prior to death of the females (Table 2). Survivorship of broods artificially removed from the parent and placed in aerated artificial seawater was poor. Of 25 broods of Crepidula fornicata removed at various stages of development, only 4 survived to hatching, and these were already at a stage possessing eye spots when removed. No broods survived when placed in natural seawater; all were consumed by ciliated protozoans. No individuals removed from the capsule survived for more than 2 days. Table 2. Effect of starvation and low oxygen on broods and adult Crepidula fornicata at 24 + 2°C. % Adult Mean No. % Mann-Whit- Survival Days Brood ney U test: N at 14 Survived Survival probability of days signif. diff. Fed controls: Females 10 100 21 Brooding Females 10 100 21 90 Starved, aerated: Females 10 40 13.8 Brooding P<.02 * Females 10 20 10.8 20 Fed, unaerated' Females 10 10 6.5 Brooding .05<p<.10 Females 10 0 4.6 0 'signif. difference CAPSULE AND EGG SIZE AND NUMBER, AND NUTRITION OF EMBRYOS The size of the calyptraeid egg sac, number of sacs, and number of eggs per sac are all variable within species, populations, and even within individuals. Nonetheless, there are species-level differences in these values (Table 3). Egg size is far more stable within species and can also be used as a species character. Smaller species tend to have larger, fewer, yolkier eggs and fewer egg sacs than larger species. The larger eggs hatch later in development, omitting the free- swimming veliger stage of the smaller eggs, although the em- bryos pass through a veliger stage in the egg capsule. The size of the egg sac is proportional to the number of eggs per sac, a factor related not only to species but to the size of the female as well. The number of eggs per sac also varies within a single brood; examples are given in Table 3. Control of the packaging of eggs into capsules is probably related to rate of release from the gonad and passage through the posterior pallial oviduct. No data are available to check this assumption. The average number of young released from a brood is often substantially lower than the number of eggs laid per brood. Observations on the three North Atlantic species of Crepidula revealed that damaged embryos or those with ab- normal development were ingested by the healthy embryos

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