Actiniaria of the southwestern Atlantic Ocean. II. Sagartiidae and Metridiidae.

On the biogeography of the southwest Atlantic with special reference to the sea anemones (Coelenterata: Actiniaria).

The Porcupine Abyssal Plain in the north-eastern Atlantic Ocean is subject to periodical deposition of phytodetritus and has a highly diverse benthic fauna dependent on this source of organic matter. Among the most abundant species from the northern study site of the Institute of Oceanographic Sciences Deacon Laboratory (IOSDL) at ~48°50′N 16°30′W, 4850 m, is Iosactis vagabunda gen. nov., sp. nov. (Cnidaria: Actiniaria, Iosactiidae fam. nov.), a small endomyarian sea anemone. The fact that this species is a burrower, with a smooth, unspecialized column, and a rounded aboral end provided with a central pit, makes it stand out from the other families of endomyarian anemones and prompted the establishment of the new family Iosactiidae. There is evidence that the closest relatives of the new family are the ‘deep water actiniids’ (e.g. Bolocera, Liponema, Leipsiceras), and the Andresiidae. Long-term in situ time-lapse photographs indicate a unique behaviour of this anemone in that it moves out of its hole at times, presumably exhibiting a hemisessile lifestyle in this peculiar abyssal habitat.

The new species Saccactis coliumensis is described with an emendation of genus Saccactis Lager, 1911 (family Actiniidae). The taxonomic relations of the genus are discussed giving additional information on Isoulactis chilensis Carlgren, 1959 and Isocradactis magna sensu Carlgren, 1924. The terms "verrucae", "vesicles" and "acrorhagi" are discussed and taxonomically valuated.The anemone S. coliumensis hves in eutrophicated sediments on the central Chilean shelf that is at least temporarily under the impact of deoxygenated waters from the Peru-Chile-SubsurfaceCurrent. The most conspicuous features of the new species (the ruff of dehcate, gill-hke vesicles beneath the tentacles and its thick pedal disc ectoderm with small, fragile spirocysts and ciha-hke structures) may be considered adaptive in this peculiar habitat.

The Arctic abyssal anemone Bathyphellia margaritacea, type species of the genus and of the family Bathyphelliidae is redescribed. Acontia in this species are highly variable both in quantity and in cnidome characteristics, implying that this genus is one of the links between acontiate and nonacontiate mesomyarian actiniarians, and has to be considered a ‘late’ mesomyarian according to the scheme proposed by Schmidt (1972b, 1974). By contrast, the new abyssal species Daontesia porcupina has normally developed acontia, a cuticle consisting of multistratified sheets and a more archaic and diverse cnidome, suggesting its systematic allocation within the ‘early’ mesomyarians. The allocation of the genus Daontesia to the family Bathyphelliidae is questionable.

Forschungsinstitut Senckenberg (Zentrum fur Biodiversitatsforschung) postal address: Alfred-Wegener-Institut fur Polar-und Meeresforschung, D-275 15 Bremerhaven, Germany. With 7 figuresKey words: Actiniaria, sea anemones, free-living and pelagic forms, post-metamorphic juveniles, behavioural ecology. dispersal.Abstract. There is scattered information in the literature that sea anemones are not always sedentary but instead may temporarily or permanently live loosely attached, detached or even pelagically. This is the first attempt to summarize and assess these observations and their probable ecological significance for the life cycles of the respective species. According to current knowledge there are no truly pelagic species of sea anemones; thus, the 'Minyadidae' (sensu CARLGREN, 1949) have to be abolished as a taxonomic group. Instead, there are indications that there are phases and stages within the life course of many anemone species which are liable to lead a free life in response to abiotic and biotic environmental factors. Juvenile, post-metamorphic stages seem to be of major significance in these respects and may be subjected to long distance dispersal. It is speculated that some of these free-living stages may represent morphologically and/or ecologically diffetent stages between larvae and adults. The newly discovered lifestyle of 'straying predator' is described from sublittoral habitats off South Africa.

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