Morphology, Larval Development, and Distribution of Bathypera feminalba n. sp. (Ascidiacea: Pyuridae), a Deep-Water Ascidian from the Fjords and Sounds of British Columbia

Abstract

A new species of the ascidian genus Bathypera (Ascidiacea: Pyuridae), B. feminalba, is described from deep-water habitats of Saanich Inlet and Barkley Sound, British Columbia, Canada, with data on the depth distribution, substratum use, reproduction, embryology, and larval development. The species is characterized by hourglass-shaped spicules topped with a single large spine and several smaller spines, a branchial sac with 7 folds per side, and irregular and curved stigmata. B. feminalba spawned in response to light following dark adaptation during the month of June. Development was similar to that of other pyurids. The tadpole larva, the first to be described in this genus, has the same sensory organs found in shallow-water relatives: an ocellus, a statocyst, and 3 large conical adhesive papillae. The ocellus is sensitive to monochromatic light between 475 and 600 nm with peak sensitivity in the blue region of the spectrum. This species occurs below 20-30 m depth, where it occupies vertical cliffs, the sides of boulders, and also smaller cobbles. It shares this habitat with a characteristic assemblage of ascidians, brachiopods, serpulid polychaetes, and sponges, few of which are found in shallow water. On a small scale, the distribution of B. feminalba is aggregated, with the pattern suggesting gregarious larval settlement. At the upper end of its depth range, this species appears to be excluded from surfaces with coralline algae; competition with algae or interactions with some organism associated with the coralline algal community may determine its upper limit. The coast of the northeastern Pacific between southern Alaska and central California has a diverse ascidian fauna of more than 80 known species (Austin 1985). Many species occurring in the intertidal and shallow subtidal zones have been studied extensively; indeed, some species from this region are among the best-known ascidians anywhere. However, the biology of ascidians living beyond scuba depths in this region remains virtually unknown. Between 1978 and 1984 we examined the ascidians of Saanich Inlet and Barkley Sound fjords, using a manned submersible, dredges, and scuba. We found a relatively sharp faunal transition: below about 30 m depth, most but not all of the shallow-water ascidians are replaced by a distinct ascidian assemblage with several previously undescribed or recently described species. This assemblage includes, besides the pyurid Bathypera feminalba n. sp. described in this paper, the pyurid Boltenia polyplacoderma recently described from 91-117 m depth off central California (Lambert 1993); an ascidiid, Rhopalaea cloneyi n. sp. (Vazquez & Young, unpubl.); the corellid Chelyosoma columbianum, which lives in deep water throughout the north Pacific; and the ascidiid Ascidia ceratodes, which defies the pattern predicted by equatorial submergence by living in shallower water in California than in British Columbia. A few species of ascidians characteristic of shallow subtidal habitats, notably Halocynthia igaboja, Styela coriacea, and Ascidia paratropa, also extend into deep water in British Columbia. Ascidians share the deep fjordic habitats with a fauna dominated by brachiopods (Tunnicliffe & Wilson 1988), galatheid crabs (Burd & Brinkhurst 1984), hexactinellid sponges, serpulid polychaetes, and cup corals (reviewed by Levings et al. 1983). The physical and biological factors that impose the upper limit of these organisms remain unknown, though low oxygen levels may determine their lower depth limit in fjords (Tunnicliffe 1981; Burd & Brinkhurst 1984). Ascidians of the genus Bathypera Michaelsen, 1904 are beautiful animals that resemble old-fashioned beaded purses. The beads are minute papillae arranged in a regular pattern and each containing a spiky calcareous spicule (Lowenstam 1989), often shaped like the acanthus-leaf decorations found atop Corinthian columns in ancient Greek architecture (Van Name 1945). The branchial sac has more than 4 plications on each side, and the stigmata are normally This content downloaded from 207.46.13.111 on Tue, 09 Aug 2016 04:49:15 UTC All use subject to http://about.jstor.org/terms