This species burrows on muddy bottoms and can sometimes be obtained by dredging in Hadley Harbor or the Fisheries Basin at Woods Hole, Mass. It is not very commonly found at present. The sexes are separate and cannot be distinguished externally.

Another member of this genus, N. delphinodonta, is found in the localities mentioned above, but it is smaller than N. proxima, and usually inhabits shallower waters. Various sub-species of N. proxima occur at intervals along the Atlantic Coast. The eggs of N. delphinodonta are retained in a brood-pouch attached to the shell, until the embryos have undergone metamorphosis. Neither eggs nor larvae of this species will develop outside the brood-pouch.

Although it has not been investigated in the Woods Hole region, Drew (1901) indicated that in Maine waters, this species spawns during the summer.

A. Care of Adults: Adults may be kept in large fingerbowls supplied with running sea water.

B. Procuring Gametes: It is not known whether eggs removed from the gonads can be successfully fertilized. Drew (1901) reported that in the laboratory, the animals will shed in fingerbowls of sea water, but he did not describe his methods in detail.

C. Preparation of Cultures: Naturally-inseminated eggs have been cultured through metamorphosis by Drew (1901). The larvae are well supplied with yolk, and do not require any special feeding.

A. The Unfertilized Ovum: The mature ovum is yolky, and measures 90 microns in diameter. There is some evidence that maturation is completed in sea water, even if the egg is not inseminated.

B. Cleavage: Cleavage is total and spiral, but has not been described in detail. If the cleavage pattern resembles that of N. delphinodonta, it is unequal, and polar lobes are formed before both the maturation divisions and first cleavage. Gastrulation is probably by epiboly (Drew, 1899).

C. Rate of Development: Development is very rapid. By 25 hours, the larvae are swimming and possess a well-marked shell gland and intestine. Metamorphosis occurs at about 60 hours.

D. Later Stages of Development and Metamorphosis: The free-swimming larva is similar to that of Yoldia, but is smaller and rounder in shape. The embryo develops within an external test, formed of five rather indistinctly arranged rows of ciliated ectodermal cells. As in Yoldia, the cilia of three of these rows are long and concentrated into bands; there are indications occasionally of a fourth banded row, which is not characteristic of Yoldia. There is a prominent apical tuft and a well-marked stomodeum, leading into an elongate midgut. Close to the stomodeal opening on the dorsal side, there is an opening in the test which probably represents a region where the test failed to grow over the shell gland. At metamorphosis, the test is cast away, and the embryos lie helpless for several days while the foot develops. Diagrams of the larvae may be found in the papers by Drew (1899, 1901).

DREW, G. A., 1899. Some observations on the habits, anatomy, and embryology of members of the Protobranchia. Anat. Anz., 15: 493-519.

DREW, G. A., 1901. The life-history of Nucula delphinodonta (Mighels). Quart. J. Micr. Sci, 44: 313-391.