Table of Contents
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    MOLLUSCA

    ( GASTROPODA )

    Thais (formerly Purpura or Nucella) lapillus

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    Both adults and egg-capsules of this species are common on rocks in shallow water. They may be easily collected at low tide at Cuttyhunk or at Plymouth, Mass., where they are abundant. The sexes are separate.

    The limits of the breeding season have not been determined for the Woods Hole region, but there is evidence that the animals breed in early summer. At Plymouth, England, spawning occurs throughout the year, but the egg-capsules are most abundant in early summer.

    A. Care of Adults: Only animals with a thick, toothed lip on the shell aperture should be selected for breeding purposes; individuals with a thin lip are immature (Moore, 1936). They can be kept in flowing sea water in an aquarium with a right-angled edge, or with a wire-screen top, to prevent their escape. Barnacles should be supplied regularly for food.

    B. Procuring Fertilized Ova: Oviposition in the laboratory has been reported by Wilson (1900), but Portmann (1931) was unsuccessful in his attempts to obtain eggs in captivity. He recommends the use of capsules collected from their natural habitat.

    C. Preparation of Cultures: Open the capsules by clipping off one end with a pair of fine scissors. If the capsules are now everted, the eggs will drop out of the cut end. Since the young embryos do not seem to develop normally unless they are associated with the yolk mass, it is doubtful whether they could be cultured outside the capsule. However, the veligers may be reared in fingerbowls of filtered sea water.

    A. The Ovum: The mature ovum measures approximately 180 microns in diameter (Selenka, 1872), and is enclosed within a very delicate membrane. Individual egg-capsules are not formed, but 500 to 1000 ova are deposited with a clear gelatinous material in a long, slender vase-shaped capsule (8-9 mm. high, and 2 mm. across). The capsules are attached to the substrate by a short stalk with an expanded base.

    B. Fertilization and Cleavage: Fertilization is internal and no membrane is elevated. Only a very few of the eggs (12 to 30, according to Carpenter, 1857) develop into normal embryos. The remainder never complete the maturation divisions, but instead, they fuse to form a column of yolk in the middle of the capsule, which is eventually consumed by the normal embryos. In normally fertilized eggs, cleavage is total, unequal and spiral with prominent polar lobes formed. Gastrulation is by epiboly. Further details can be found in papers by Selenka (1872) and Pelseneer (1911).

    C. Rate of Development: Development of this species is slow. The compact yolk mass is formed by the time gastrulation is completed, which is between four and eight days after fertilization. The embryos become attached to the developing yolk mass, which is usually absorbed by the tenth day. The young snails hatch from the capsules in about four months.

    D. Later Stages of Development and Metamorphosis: The embryo, which attaches to the yolk mass, has a round, sparsely ciliated velum, a shell gland, a small foot, a pair of larval kidneys, and a large stomodeum and oesophagus. The intestine is short or lacking. Organogenesis ceases during the parasitic period, but after the yolk has been stored in the intestine, the embryo transforms into a typical veliger, with a well-formed velum, whorled shell, otocysts, eyespots, and a complex digestive tract. As metamorphosis approaches, the early larval heart and kidneys are replaced by adult organs. Tentacles appear and the velum slowly regresses. The metamorphosed larva, which emerges from the top of the capsule, is a miniature of the adult snail.

    CARPENTER, W. B., 1855. On the development of the embryo of Purpura lapillus. Trans. Micr. Soc., London, 3: 17-30.

    CARPENTER, W. B., 1857. Remarks on MM. Koren and Danielssen's researches on the development of Purpura lapillus. Ann. and Mag. Nat. Hist., ser. 2, 20: 16-21.

    KOREN, J., AND D. C. DANIELSSEN, 1857a. Researches on the development of the Pectinibranchiata. Ann. and Mag. Nat. Hist., ser. 2, 19: 353-366.

    KOREN, J., AND D. C. DANIELSSEN, 1857b. Researches on the development of the Pectinibranchiata. Ann. and Mag. Nat. Hist., ser. 2, 19: 433-442.

    McMURRICH J. P., 1886. A contribution to the embryology of the prosobranch gasteropods. Stud. Biol. Lab., Johns Hopkins Univ., 3: 403-450.

    MOORE, H. B., 1936. The biology of Purpura lapillus. I. Shell variation in relation to environment. J. Mar. Biol. Assoc., 21: 61-89.

    MOORE, H. B., 1938. The biology of Purpura lapillus. III. Life history and relation to environmental factors. J. Mar. Biol. Assoc., 23: 67-74.

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

    PORTMANN, A., 1925. Der Einfluss der Nahreier auf die Larvenentwicklung von Buccinum undPurpura. Zeitschr. f. Morph. u. Okol. Tiere, 3: 526-541.

    PORTMANN, A., 1931. Die Entstehung der Nahreier bei Purpura lapillus durch atypische Befruchtung. Zeitschr. f. Zellforsch. u. miter. Anat., 12: 167-178.

    SELENRA, E., 1872. Die Anlage der Keimblatter bei Purpura lapillus. Niederland. Arch. f. Zool., 1: 211-218, WILSON, H. V., 1900. Marine biology at Beaufort Amer. Nat., 34: 339-360.