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Velvet shell, Velutina velutina (Müller, 1776), is a specialist predator of ascidians, like other members of the gastropod family Velutinidae. Globally, invasive ascidians have become problematic, ecologically and economically, yet ecological knowledge of velutinids remains limited. This study outlines the life history and feeding ecology of V. velutina in eastern Canada based on laboratory work complemented by field observations. The life history of V. velutina is closely linked with ascidians, which serve as prey and protection for their egg capsules. Egg capsules were embedded within tunics of Aplidium glabrum (Verrill, 1871) and Ascidia callosa Stimpson, 1852, with a preference for the latter. Seasonal behavioural shifts were consistent annually and corresponded with seawater temperature cycles. Feeding dominated during the coldest months (January–May), growth occurred as water temperature increased to the annual maximum (June and July), transitioning to mating during the warmest period (July–August), and egg capsule deposition dominated as water temperature declined (November–January). Larvae hatched between January and July after 2–4 months of development. Velutina velutina preyed on all ascidian species presented during this study, including golden star tunicate, Botryllus schlosseri (Pallas, 1766), and vase tunicate, Ciona intestinalis (Linnaeus, 1767), two non-indigenous species, although solitary species were preferred.

Sea anemones Allantactis parasitica Danielssen, 1890 (Actiniaria: Hormathiidae) living as epibionts on various gastropods were found at depths of ~725–1100 m off Labrador (eastern Canada). Live specimens collected with their hosts were studied in the laboratory to elucidate the role of the gastropod host in the reproductive and colonizing success of its actinian symbiont. Broadcast spawning occurred twice a year, in spring and late fall, in correlation with maximum phytoplankton or phytodetritus abundance, often during copulation of the gastropod hosts. The fully developed planula stage was reached after ~22 d. Settlement on the host’s shell generally occurred 40–44 d postfertilization, although some larvae delayed settlement for up to 22 weeks in the absence of a host. Independent and pairwise settlement trials showed that shells of live bathyal gastropods were highly favoured compared with shells of shallow-water gastropods, empty shells, pebbles, or sand. Juveniles developed 24 tentacles and reached ~10 mm in basal disk diameter and ~12 mm in stalk height after 21 months of growth. The estimated growth rates of A. parasitica suggest that symbiotic individuals would require 6–7 years to reach the mean maximum adult size (~35 mm, basal disk diameter), whereas asymbiotic individuals would need 11–12 years.

Combined laboratory and field experiments showed that sea cucumbers (Cucumaria frondosa) from the St. Lawrence estuary in eastern Canada have well-defined feeding cycles with marked seasonal and tidal variations. Typical feeding behaviour involved extension of the tentacles, which were then successively introduced into the oral cavity. Field observations and analysis of intestinal contents and indices demonstrated that C. frondosa fed mainly during spring and summer. Their diet comprised an abundance of phytoplanktonic cells (Coscinodiscus centralis, Chaetoceros debilis, Skeletonema costatum, and Thalassiosira gravida), with occasional ingestion of small crustaceans and a variety of eggs and larvae. Food types found in the digestive tract were closely related to the periodic abundance of plankton species in the water. Fewer individuals were observed feeding during fall and winter; they mostly ingested nonliving particles and the intestinal indices were low. In field populations, feeding rates were highest during ebb and rising tides, whereas under laboratory conditions without tidal variation, individuals showed no distinct feeding periods. However, individuals maintained under laboratory conditions and periodically provided with phytoplanktonic cells demonstrated a strong ability to detect the food in the water and react accordingly by extending their tentacles and beginning to feed. The results of the study suggest that food availability, rather than physical parameters such as temperature or current, best explains the cyclic feeding behaviour of C.\x11frondosa at seasonal and tidal scales.

Pycnogonids (Pigrogromitus timsanus) were discovered among a population of sea anemones (Bartholomea annulata) collected from the east coast of Florida. The predatory behavior of these sea spiders was investigated in the laboratory and its effects on the health of the sea anemones was detailed. In comparison with a reference group of noninfested sea anemones, the deterioration of the infested individuals was characterized by abundant mucus secretion, retraction of the tentacles, and difficulty in attaching to the substrate, eventually leading to death. As for the predators, they seemed undisturbed by the acontial filaments and nematocysts discharged by their prey. This is the first evidence of possible deleterious effects inflicted on actiniarians by pycnogonid predators.