Molgula pacifica (Huntsman) is a recently rediscovered ascidian that occupies shallow subtidal rocks on wave-swept coasts of British Columbia. Individuals occur most abundantly at sites with intermediate exposure at or near 4 m depth. On a scale of centimeters, they are highly aggregated. Molgula pacifica is hermaphroditic, self-fertile, and oviparous. Embryos develop on the bottom without passing through a typical tadpole stage. Each of the egg follicle cells contains a single large adhesive vacuole that occupies most of the cell volume. Shortly after spawning these vacuoles rupture, causing the follicle cells to secrete a sticky mucus coat that adheres the egg to the substratum. Juveniles hatch and move away from the chorion using epidermal ampullae, as reported for other anural molgulids. Adhesive eggs may be an adaptation that permits anural development in high-energy hard-bottom habitats. Egg adhesion may also explain the small-scale distribution of the species.

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On the central coast of Victoria, Australia, the dimorphic ascidian Pyura stolonifera (Heller, 1878) harbors three endosymbionts: the nemertean Gononemertes australiensis Gibson, 1974, the copepod Doropygus pulex (Thorell, 1859), and the amphipod ParaIeucothoe novaehollandiae (Haswell, 1880). The specificities of these symbionts to two host colour morphs were studied during 1989 to 1991 as part of a multidisciplinary investigation aimed at determining whether the two morphs are genetically distinct. Distributional surveys revealed that nemerteans and copepods occur only in yellow and brown ascidians, respectively, and that amphipods live in both forms. These specificities held true not only when the two morphs were in allopatry, but also in sympatry. These observations, especially the sympatric data, suggest that the two host morphs might be genetically distinct. For example, the two morphs might have different genetically encoded internal milieus that favour the survival of nemerteans in yellow ascidians, and copepods in brown hosts. In transplant experiments, which involved moving ascidian morphs within and between habitats, the "wrong" symbionts never colonised the "wrong hosts". These results, although consistent with the hypothesis of genetic maintenance of specificity, were deemed inconclusive because of the difficulty of establishing reliable controls (i.e. vacant hosts). The relationships between symbiont prevalences and several factors (season, year, site within host, host individual, host habitat, host size/age, host breeding condition, and co-occurrence of other symbiont Department of Biology, Carnegie Science Hall, Bates College, 44 Campus Avenue, Lewiston, Maine 04240-6084, USA species) were also analysed. Both simple (e.g. greater prevalences for large hosts) and complex (e.g. prevalence x season x gonad state of host) interactions were detected for all three symbiont species. These are among the very few quantitative analyses of factors affecting prevalences of ascidicolous nemerteans and amphipods. The present report identifies one of very few definite nemertean-ascidian symbioses. Since no differences in gross condition were ever noticed between occupied and vacant hosts, it is suggested that all three symbionts are commensals rather than parasites or mutuals.

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1985. Behavioral interactions between the actinian Tealia piscivora (Anthozoa: Actiniaria) and the asteroid Dermasterias imbricata. Can. J . Zoo1 . 63: 192 1 -1929. Interactions between the sea anemone Tealia piscivora and the sea star Dermasterias imbricata have been studied in the laboratory and in subtidal habitats. Dermasterias causes the release of the pedal disk of smaller T. piscivora. The response is specific. Nineteen other sea stars did not cause release; four other species of Tealia did not respond to Dermasterias. The response is size dependent; unfailing and quick in small T. piscivora, less frequent and slow in those of intermediate size, it did not occur at all in large specimens. Unrestrained T. piscivora generally survived interactions with Dermasterias but when prevented from detaching, most of the small anemones were devoured. Tealia piscivora have been observed to detach and engulf small Dermasterias. Most small anemones were found at greater depths; most large anemones were found at lesser depths where Dermasterias were most abundant. It is suggested that by releasing the pedal disk, small T. piscivora eventually end up in deeper water where there are few Dermasterias and thus the anemones escape predation. ELLIOTT-, J., J. DALBY, JR., R. COHEN et D. M. Ross. 1985. Behavioral interactions between the actinian Tealia piscivora (Anthozoa: Actiniaria) and the asteroid Dermasterias imbricata. Can. J. Zoo1 . 63: 192 1 -1929.On a ktudik les interactions entre I'ankmone de mer Tealia piscivora et I'ktoile de mer Dermasterias imbricata au laboratoire et dans la zone des markes. Dermasterias provoque le dktachement du disque pkdieux chez T. piscivora de petite taille. Cette rkponse est spkcifique. Dix-neuf autres Ctoiles de mer n'ont pu provoquer ce dktachement; quatre autres espkces de Tealia n'ont pas rkagi a la prksence de Dermasterias. La rkponse dkpend de la taille: elle est rapide et infaillible chez les T. piscivora de petite taille, moins frkquentes et lente chez les sujets de taille intermkdiaire, et absente chez tous les individus de forte taille. Les sujets libres de s'kchapper ont gknkralement survkcu aux attaques de Dermasterias, mais non ceux que I'on emflchait de se dktacher: la plupart des sujets de petite taille furent alors dkvorks. On a observe des T. piscivora en train de dktacher et de consommer de petites Dermasterias. La plupart des ankmones de petite taille ont kt6 trouvkes en zones plus profondes, tandis que les sujets de forte taille ktaient concentrks plut6t en eau peu profonde oh les Dermasterias abondent. Nous croyons qu'en rellchant leur disque pkdieux, les T. piscivora de petite taille aboutissent kventuellement en eau plus profonde oh il y a peu de Dermasterias; elles kchappent ainsi ce prkdateur. IntroductionSeveral actinian species from the northeast Pacific release their pedal disks when brought into contact with certain sea stars. The behavioral physiology of these interactions has been studied in three species: in the "swimming anemones," Stomphia coccinea and S...