A SURVEY OF THE SIPUNCULA OF THE INDIAN RIVER LAGOON

摘要

From 22 stations in the Indian River Lagoon, ranging from Haulover Canal in the north to St. Lucie Inlet in the south, 18 species of sipunculans are reported. Habitats include oyster beds, subtidal and intertidal sand, seagrass beds, and sea walls. The greatest number of species occurs near inlets: Sebastian, Fort Pierce, and St. Lucie. The most widely distributed sipun-culan in the Indian River Lagoon is Phascolion cryptum, averaging 3 cm in length. Usually buried in the upper 5 cm of sandy sediments associated with seagrass beds, it inhabits discarded gastropod shells in shallow waters throughout the lagoon. Development is direct, a crawling vermiform stage hatching from egg coverings within 2 days. The second most widely distributed sipunculan is Themiste lageniformis, attaining a maximum extended length of 4 cm. Occurring most commonly near the inlets of Fort Pierce and Saint Lucie, it is associated either with oyster beds, where it lives in and among the shells, or with the encrusting fauna on sea walls, among the vermetid snails, sponges, and tunicates. In oyster beds near Fort Pierce it occurs in densities as great as 2,100·m~2. This species is parthenogenic; its development includes a short-lived non-feeding pelagic larval stage. Other species, found mostly in relatively small numbers near the inlets, are characterized generally by developmental patterns with long-lived feeding pelagic larvae. Whether they establish breeding populations in the Indian River Lagoon has not been determined.