Reproduction and Larval Development of the West Indian Topshell, Cittarium Pica (Trochidae), in the Bahamas
The reproduction and larval development of the West Indian topshell, Cittarium pica (Linnaeus), was studied in the southern Exuma Cays, Bahamas, between June 1990 and June 1991. Topshells held in outdoor water tables spawned unpredictably, possibly in response to simulated low and high tides and the moon phase. Eight of nine spontaneous spawnings occurred within 4 days of either the full or new moon between 20 June and 4 November. Larvae of C. pica were lecithotrophic with a relatively short larval life of 3.5–4.5 d, when reared at 26.5–27.5°C. Emergence from the egg membrane occurred at the trochophore stage. At this stage the larval shell covered about two-thirds to three-fourths of the posterior end of the larvae, with the velum not yet developed. Settlement could be induced by providing a bacterial/algal film substratum. Oocyte diameters from histological slides of ovaries were used to determine reproductive seasonality. Females began to mature in July. A gradual increase in oocyte diameters occurred over the summer until they peaked in late September and early October, followed by a significant decline. Oocyte size was variable between October and January, after which the mean size was consistently small with little variability. The data suggest a natural spawning period in early October. Mean oocyte diameter was highly correlated with seawater temperature. An influx of juvenile C. pica (1–2 mm shell width) was observed in January. Using growth rates of laboratory-reared juvenile C. pica, a spawning date corresponding to the significant decline in oocyte diameter in early October was extrapolated.
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Document Type: Research Article
Publication date: 1992-09-01
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