The escape of veligers from the egg capsules of Nassarius obsoletus and Nassarius trivittatus (gastropoda, prosobranchia)
The escape of veligers from the egg capsules of Nassarius obsoletus and Nassarius trivittatus (gastropoda, prosobranchia)
Date
1975-06
Authors
Pechenik, Jan A.
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DOI
10.1575/1912/4823
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Prosobranchia
Abstract
Many species of prosobranch gastropod deposit their eggs in tough
capsules affixed to hard substrates. Generally, there is a small opening
near the top of such capsules, occluded by a firm plug (operculum) which
must be removed before the veligers can escape. Although the removal of
the operculum is generally attributed to embryonic secretion of enzymes,
there is little experimental support for this sugsestion. In the limited
experiments which have been reported, all dealing with species that
emerge as juvenile snails, no attempt was made to determine the properties
of the hatching substance, or the timing of its production.
My research has dealt with the escape of veligers from the egg capsules
of two related species, Nassarius obsoletus and N. trivittatus. Their
egg capsules are quite similar in size, number of eggs contained, general
morphology, and the thickness of the material plugging the opening at the
top. Both hatch as swimming veligers, after about one week of encapsulated.
development.
By adding fresh plug material to small volumes of sea-water containing
veligers obtained prior to, or at known times after their normal hatching,
I have demonstrated conclusively the essentially chemical nature of
operculum removal for these two species. In addition, the hatching substance
was found to be produced in a short pulse, to be functionally short-lived,
and to be species-specific in its action for the two species considered.
There is no evidence that the secretion of the hatching substance
is stimulated by short pulses of light or increased temperature; the
capsules of N. obsoletus contain many more embryos than are needed to
successfully remove the plug, so that complete synchrony of hatching
substance production by all individuals within a capsule is probably
not necessary.
Lastly, the observed rates at which N. obsoletus veligers leave
their egg capsules were compared with those predicted from an equation
assuming random movement of individuals. A close agreement was found,
the capsules losing 98% of their residents within 45 to 55 minutes of
the first escape. Thus, the location of the exit by an individual is
probably by chance.
Description
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology [and the Woods Hole Oceanographic Institution] June 1975
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Citation
Pechenik, J. A. (1975). The escape of veligers from the egg capsules of Nassarius obsoletus and Nassarius trivittatus (gastropoda, prosobranchia) [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server. https://doi.org/10.1575/1912/4823