Search

Caymanostellidae is a group of rarely collected and morphologically unusual sea stars that have been exclusively encountered on wood falls in the deep sea. There are currently three genera and seven species described, occurring in the Atlantic, Pacific and Indian Oceans with a depth range between 418 and 6780 m. Three new species are here described from specimens collected from wood falls in multiple localities across the Pacific margin of Costa Rica and near the Gulf of California (Mexico): Caymanostella scrippscognaticausa sp. nov., Caymanostella davidalani sp. nov. and Caymanostella loresae sp. nov. These records expand the known geographical distribution of caymanostellids and constitute their first report from wood falls found at methane seeps. This study also includes the first descriptions of early-stage juvenile caymanostellids and reveals that traits previously considered useful for diagnosis might represent intraspecific and ontogenetic variability, with important consequences for caymanostellid taxonomy.

Background: Numerous deep-sea invertebrates, at both hydrothermal vents and methane seeps, have formed symbiotic associations with internal chemosynthetic bacteria in order to harness inorganic energy sources typically unavailable to animals. Despite success in nearly all marine habitats and their well-known associations with photosynthetic symbionts, Cnidaria remain one of the only phyla present in the deep-sea without a clearly documented example of dependence on chemosynthetic symbionts., Results: A new chemosynthetic symbiosis between the sea anemone Ostiactis pearseae and intracellular bacteria was discovered at ~ 3700 m deep hydrothermal vents in the southern Pescadero Basin, Gulf of California. Unlike most sea anemones observed from chemically reduced habitats, this species was observed in and amongst vigorously venting fluids, side-by-side with the chemosynthetic tubeworm Oasisia aff. alvinae. Individuals of O. pearseae displayed carbon, nitrogen, and sulfur tissue isotope values suggestive of a nutritional strategy distinct from the suspension feeding or prey capture conventionally employed by sea anemones. Molecular and microscopic evidence confirmed the presence of intracellular SUP05-related bacteria housed in the tentacle epidermis of O. pearseae specimens collected from 5 hydrothermally active structures within two vent fields ~ 2 km apart. SUP05 bacteria (Thioglobaceae) dominated the O. pearseae bacterial community, but were not recovered from other nearby anemones, and were generally rare in the surrounding water. Further, the specific Ostiactis-associated SUP05 phylotypes were not detected in the environment, indicating a specific association. Two unusual candidate bacterial phyla (the OD1 and BD1-5 groups) appear to associate exclusively with O. pearseae and may play a role in symbiont sulfur cycling., Conclusion: The Cnidarian Ostiactis pearseae maintains a physical and nutritional alliance with chemosynthetic bacteria. The mixotrophic nature of this symbiosis is consistent with what is known about other cnidarians and the SUP05 bacterial group, in that they both form dynamic relationships to succeed in nature. The advantages gained by appropriating metabolic and structural resources from each other presumably contribute to their striking abundance in the Pescadero Basin, at the deepest known hydrothermal vents in the Pacific Ocean.

The formerly monotypic taxon, Hyalopale bispinosa Perkins 1985 (Chrysopetalinae), is comprised of a cryptic species complex from predominantly tropical embayments and island reefs of the Western Atlantic and Indo-Pacific Oceans. Hyalopale species are of meiofaunal size (length: 1-2.8mm), but considered non-interstitial, with the majority of species inhabiting a singular habitat of shallow littoral zones among algae and epifauna overlying sediments in rubble. Hyalopale adults exhibit notochaetal fans characterized by the presence of lateral and midline notochaetal spines. Species of Hyalopale can be distinguished by the shape of glass-like notochaetal paleae and the number of densely stacked ribs. Hyalopale bispinosa forms a western and eastern Atlantic species complex, comprising the type species, Hyalopale bispinosa s.s., a comparatively larger form with the highest number of notochaetal paleael ribs from Florida, and Hyalopale cf. bispinosa, from the western and eastern Mediterranean, a smaller form with a similar notochaetal morphology to the latter. Unfortunately, no molecular sequence data is available for Hyalopale bispinosa s.s. Five new species are described, with molecular sequence data provided for three: Hyalopale leslieae sp. nov., a small form with a comparatively low number of paleal ribs, found from the Florida Keys to Belize, Caribbean Sea, H. zerofskii sp. nov. from southern California and Mexico, eastern Pacific and H. sapphiriglancyorum sp. nov., a distinctive species with the lowest number of paleael ribs, from Raja Ampat, Indonesia and the Great Barrier Reef, Queensland, western Pacific. Two other species are described from morphology alone: H. angeliensis sp. nov. from Dampier, Western Australia and Seychelle Islands, eastern Indian Ocean and H. furfuricula sp. nov. from the Red Sea and Mozambique, western Indian Ocean, possessing a unique paleal brow shape. While well supported as a clade, support for relationships within Hyalopale is low. Hyalopale cf. bispinosa (Mediterranean) was recovered as sister group to the remaining Hyalopale, with H. leslieae sp. nov. as sister to the Hyalopale Pacific clade, comprising H. zerofskii sp. nov. (eastern Pacific) and H. sapphiriglancyorum sp. nov. (western Pacific). Within Chrysopetalinae, Hyalopale and Paleanotus formed a clade that was the sister group to the other paleate chrysopetalids under maximum likelihood, though Paleanotus grouped with the other paleate forms under maximum parsimony. The adult morphology of Hyalopale species is compared with that exhibited in the larvae of Paleanotus species; based on these results, including possession of a shared notochaetal character, Hyalopale is considered to contain paedomorphic taxa.