MOLLUSCA

( GASTROPODA )

Urosalpinx cinerea

The adults and vase-shaped egg-capsules of the oyster drill are found on rocks between tide levels. Near Woods Hole, Mass., they are abundant at Grassy Island (the Spindle) and at Sheep Pen Cove on Nonamessett Island. The sexes are separate. Males are easily recognized by the long, curved penis, which is located on the right side of the body behind the eye.

Federighi (1931) and Nelson (1931) both observed that breeding begins when the water temperature has remained for at least a week above 20û C. At Woods Hole, the season begins late in May (Bumpus, 1898), and probably continues throughout the summer.

A. Care of Adults: The adults should be kept in aquaria provided with running sea water, and will remain in good condition if fed occasionally with barnacles, small mussels or clams. Food debris should be removed before putrefaction sets in. A ten-gallon tank has been found adequate for as many as 300 drills if it is kept free of debris (Federighi, 1937).

B. Procuring Fertilized Ova: Copulation probably occurs at night. The female creeps to the upper levels of the tank to spawn, and does so only once per season. On the average, oviposition lasts about a week; between 28 (Federighi, 1931) and 50 capsules (Nelson, 1931) are produced. In 24 hours a female deposits approximately four egg-capsules, containing a varying number of eggs. The capsules are 4 12 mm. high, with an operculum at the free end; the outer of the two capsule layers can be peeled off readily, permitting better observation of the embryos (Hancock, 1956). Embryos in different stages of development are contained within the capsules. At hatching, the young drill is able to feed on young oyster spat or thin-shelled Crepidula.

NORMAL DEVELOPMENT

A. The Ovum: The fertilized, uncleaved egg is spherical, measuring approximately 240 microns in diameter (Lebour, 1937). It is white in color and opaque, and lacks a membrane. The eggs are deposited with an albuminous substance, which provides nourishment for the developing embryos, in a yellow, urn-shaped capsule. This has a short stem and an expanded base, and is laterally compressed. The latter feature distinguishes it from the somewhat similar capsule of Thais. (See the diagram by Federighi' 1937.)

B. Cleavage: Cleavage is unequal and spiral, with large polar lobes appearing during the first two divisions. Gastrulation is by epiboly. At about the time of gastrulation, a hatching enzyme apparently is produced within the capsule; this dissolves the operculum (Hancock, 1956).

C. Rate of Development: There seems to be no detailed information pertaining to the developmental rate. The average time from fertilization to hatching at temperatures varying between 18 and 32û C. is 40 days (Federighi, 1931). Hancock (1956) reports that at temperatures of 14-21û C., the veliger stage is reached in about 24 days.

D. Later Stages of Development: Embryonic development is similar to that of most gastropods. The veliger is formed at an early stage. The foot appears precociously, before closure of the blastopore; both velum and shell are well developed. The intestine and anus are late in appearing. The velum is lost before hatching, and the young animal emerges as a well-formed snail. Details of development and figures of the larvae can be found in a paper by Brooks (1879). Hancock (1956) presents diagrams of the egg-capsules.

BROOKS, W. K., 1879. Preliminary observations upon the development of the marine prosobranchiate gasteropods. Stud. Biol. Lab., Johns Hopkins Univ., 1: no. 5, pp. 121-142.

BUMPUS, H. C., 1898. The breeding of animals at Woods Holl during the month of May, 1898. Science, 8: 58-61.

CONKLIN, E. G., 1891. Preliminary note on the embryology of Crepidula fornicata and of Urosalpinx cinerea. Johns Hopkins Univ. Circ., 10: 89-90.

FEDERIGHI, H., 1931. Studies on the oyster drill ( Urosalpinx cinerea, Say). Bull. U. S. Burl Fish., 47. 85-115.

FEDERIGTTI, H., 1937. Culture methods for Urosalpinx cinerea. In: Culture Methods

for Invertebrate Animals, edit. by Galtsoff et al., Comstock, Ithaca, pp. 532-536.

HANCOCK, D. A., 1956. The structure of the capsule and the hatching process in Urosalpinx cinerea (Say). Proc. Zool. Soc., London, 127: 565-571.

LEBOUR, M. V., 1937. The eggs and larvae of the British prosobranchs with special reference to those living in the plankton. J. Mar. Biol. Assoc., 22: 105-166.

NELSON, J. R., 1931. Trapping the oyster drill. New Jersey Agric. Exp. Stat. Bull. no. 523.