The Biology of Hastula inconstans (Hinds, 1844) and a Discussion of Life History Similarities among other Hastulas of Similar Proboscis Type

Miller, Bruce A.
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University of Hawaii Press
Terebrid gastropods of the genus Hastula are found in great abundance on fine-sand beaches throughout the tropics. Hastula inconstans, a species common to surf beaches in the Hawaiian Islands, is the first hastula for which a complete life history is known. Hastula inconstans is a primary carnivore, preying exclusively on Dispio magna, a tube-dwelling, depositfeeding spionid polychaete. The gastropod lives just beyond the surf zone and exhibits well-developed adaptations that permit survival in this habitat. The broad, fleshy foot, used in anchoring the snail in the sand and in rapid reburrowing, is also highly modified as a "sail" which carries H. inconstans up and down the beach with the passage of waves. A highly specialized foregut contains long retractile labial and buccal tubes, which, combined with a poison bulb and radular teeth, rapidly sting, immobilize, and ingest prey. The snail lies buried in the sand when not feeding, but emerges when prey are detected by distance chemoreception. Nearby prey are reached by rapidly crawling over the sand surface, and prey at a distance are reached by using the foot to "sail" to their location. In either case, contact with the prey is first made by the propodium of the foot, rapidly followed by proboscis eversion. After contact is made, the prey is stabbed by a radular tooth held by the buccal tube, poison is injected into the wound, and engulfing of the worm begins. This entire sequence occurs between the passage of waves, and the snail usually reburrows to continue feeding before the next wave arrives. The sexes in Hastula inconstans are separate. Mating takes place above the sand while the animals are coupled and rolling freely in the surf, and approximately 40 spherical eggs are later deposited in a capsule covering a small piece of basalt. Larvae metamorphose when they are less than 1 mm in length and reach 3-5 mm in length by late spring. Individuals grow between 0.5 and 0.8 mm per month, reaching a maximum size of 34 mm, which suggests an average life-span of 3-4 years. Other hastulas with a proboscis nearly identical in structure to that of H. inconstans exhibit similar life history aspects, including habitat choice and prey specificity. It is suggested that feeding types may not only be useful as a diagnostic characteristic, but also in predicting basic life history aspects throughout the family.
Miller BA. 1979. The biology of Hastula inconstans (Hinds, 1844) and a discussion of life history similarities among other Hastulas of similar proboscis type. Pac Sci 33(3): 289-306.
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