The adults are very abundant on fronds of Ascophyllum and Fucus in the Woods Hole, Mass., region. They can be shaken from the vegetation into a scrim dip-net. The animals are smaller than L. Iittorea and larger than L. saxatilis. The shell is almost without striations, and is compressed so that the spire seems to be lacking.

This form has not been studied at Woods Hole. European workers (Pelseneer, 1911; Delsman, 1914) report that it breeds during the spring and summer months in European waters.

PROCURING AND HANDLING MATERIAL

A. Care of Adults: The animals may be kept in aquaria supplied with running sea water; they should be furnished with a supply of sea-weed which must be renewed from time to time.

B. Obtaining Gametes: The egg-masses are deposited daily on the sea-weed (apparently never on the sides of the aquarium). If the masses are kept in running sea water, the eggs develop readily.

NORMAL DEVELOPMENT

A. Egg Characteristics: The eggs are laid in oval or kidney-shaped gelatinous masses on sea-weed. The gelatinous material is transparent and faintly yellow in color. An egg-mass measures, on the average, 7 by 3 mm. (See the paper by Hertling and Ankel, 1927, for a diagram of the egg-mass.) The eggs are contained in a capsule and surrounded by an albuminous fluid; they are deposited in the germinal vesicle stage, but this lasts only a short time before the vesicle breaks down. Measurements of the egg diameter vary from 205 microns (Delsman, 1914) to 250 microns (Lebour, 1937). Fertilization apparently takes place before the eggs are laid.

B. Cleavage and Gastrulation: Cleavage is total, equal and spiral, with micromeres larger than those of L. Iittorea or L. saxatilis. Gastrulation is by epiboly and invagination.

C. Rate of Development: Development is said to be slow; at 13-14û C., the embryos hatch in three weeks, having passed the veliger stage within the capsule.

D. Later Stages of Development: Although the veliger stage is spent within the capsule, a well-formed velum is present. The veligers have a foot, operculum, single-whorled shell, kidney, ganglia, and a complex gut. At the time of emergence from the capsule, the larvae are fully-formed, crawling snails. See the papers by Delsman (1914) and Pelseneer (1911) for diagrams.

SPECIAL COMMENTS:

This species of Littorina is moderately common at Woods Hole, although L. Iittorea is found in greater abundance. The eggs of L. Iittorea, however, are laid in transparent capsules (with from one to nine eggs per capsule, according to Bequaert, 1943), and are planktonic, so that they are somewhat difficult to obtain and to study. The ova of L. obtusata are plentiful and relatively easy to study.

BEQUAERT, J. C., 1943. The genus Littorina in the western Atlantic. Johnsonia, no.. 7, pp.

DELSMAN, H. C., 1914. Entwicklungsgeschichte von Littorina obtusata. Tijdschr. Nederl Dierkundige Vereeniging, ser. 2 13: 170-340

HERTLING, H., AND W. E. ANKEL 1927. Bemerkungen über Laich und Jugendformen von Littorina und Lacuna. Wiss. Meeres. Komm. Unt. Deutsch. Meere, N. F., Abt. Helgoland,

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

LINKE, O., 1935. Der Laiche von Littorina (Melaraphe) neritoides L. Zool. Anz., 112:

PELSENEER, P., 1911. Recherches sur l'embryologie des Gastropodes. Mem. Acad. Roy Belgique ser. 2, 3: 1-167.