The Biology of Hastula inconstans (Hinds, 1844) and a Discussion of Life History Similarities among other Hastulas of Similar Proboscis Type
The Biology of Hastula inconstans (Hinds, 1844) and a Discussion of Life History Similarities among other Hastulas of Similar Proboscis Type
Date
1979-07
Authors
Miller, Bruce A.
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University of Hawaii Press
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Abstract
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.
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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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