HIPPASTERINAE, VERRILL, 1899

Mah, Christopher, Nizinski, Martha & Lundsten, Lonny, 2010, Phylogenetic revision of the Hippasterinae (Goniasteridae; Asteroidea): systematics of deep sea corallivores, including one new genus and three new species, Zoological Journal of the Linnean Society 160 (2), pp. 266-301 : 290-292

THE HIPPASTERINAE AND CORALLIVOROUS GONIASTERIDAE

Deep-sea corals form habitats that are host to a variety of associated fauna, including fishes and invertebrates. The importance of these habitats to fishes has been investigated in a number of regions ( Huesbo et al., 2002; Costello et al., 2005; Stone, 2006; Ross & Quattrini, 2007). However, habitat utilization by invertebrates is not fully understood. Several recent investigations conducted in both the eastern

OG: Mediaster aequalis Hippasteria californica OG : Cladaster analogus Washington to S. California OG: Peltaster placenta 110-2000 m Hippasteria Hippasterias 377 Alaska -454, m Aleutian spinosa heathi Islands Hippasteria Aleutian Islands to California 10-512 m Hippasteria phrygiana North & South Atlantic/Pacific 10-860 m Evoplsoma virgo NW Gulf of Mexico, 2060-2105 m Evoplsoma NE Davidson Rodriguez Evoplosoma Pacific Seamount, voratus Seamount 730 claguei -1842 n. sp m & n.. sp. Evoplosoma NE Pacific, 2669 m Evoplsoma scorpio N. Atlantic, Rockall Trough, 1600-1900 m Sthenaster emmae n. gen. n. sp. S. Carolina, tropical Atlantic 110-2000 m Cryptopeltaster lepidonotus Aleutian Islands to Chile, 360-1244 m Gilbertaster caribaea W. Tropical Atlantic 360-1244 m Gilbertaster 5 changes Gilbertaster anacanthus Hawaii to New Zealand 462-913 m

and western North Atlantic involving quantitative surveys of mega- and macroinvertebrates report diversity to be extremely high ( Jensen & Frederiksen, 1992; Mortensen et al., 1995, Jonsson et al., 2004, Reed et al., 2005, 2006; Henry & Roberts, 2007; Roberts et al., 2008). These recent surveys, however, often report only a fraction of the diversity associated with these habitats because sampling methods utilized target only a portion (either size- or taxonspecific) of the associated fauna, the interest of the investigators is limited to a few taxonomic groups, or the overall goals of the project are such that not all associated fauna are collected. As a result, many megafaunal taxa are often over-looked during collections or are under-sampled.

Asteroids are known from many deep-sea coral study sites but observations of these taxa have lacked taxonomic precision, precluding more precise ecological interpretations. Several papers provide vague entries (unidentified asteroid, Mortensen et al., 1995; Asteroidea, unid. sp., Reed, Weaver & Pomponi, 2006) or have identified individuals only to the generic level ( Mortensen et al., 1995; Jonsson et al., 2004). Few report species-level identifications (e.g. Jensen & Frederiksen, 1992; Henry & Roberts, 2007).

Much remains to be learned about the megafauna associated with deep-sea coral habitats. Large, prominent animals such as the Asteroidea have been shown to have ecologically complex relationships with cnidarians from shallow marine habitats (e.g. Birkeland, 1974; Birkeland & Lucas, 1990) and seem to be important to those living in deep-sea habitats as well (e.g. Chave & Malahoff, 1998; Krieger & Wing, 2002).

The in situ observations of Krieger & Wing (2002) documented Hippasteria as a main predator of deepsea coral. Subsequent observations have now shown that at least one species of every genus included in Hippasterinae (Goniasteridae) , except for Gilbertaster , has been reported to feed on deep-sea corals, mainly gorgonians, but also alcyonaceans, antipatharians, and other cnidarian species. Krieger & Wing (2002) reported H. heathi , in addition to other species, as the main predator on the gorgonian Primnoa sp. in the Gulf of Alaska. Hippasteria imperialis has been observed feeding on isidid corals in the Hawaiian Islands, off Kona (C. Mah, unpubl. observ.). Japanese researchers using submersibles have also observed an unidentified species of Evoplosoma feeding on deep-sea coral in Java ( Fujikura et al., 2008).

In the Pacific, submersibles from the Monterey Bay Aquarium Research Institute have documented several instances of hippasterines feeding on deep-sea cnidarians, including gorgonians ( Paragorgia ), bamboo corals ( Keratoisis and Lepidisis ) and sea whips ( Halipteris ) by Cryptopeltaster , Evoplosoma , and Hippasteria at Rodriguez and Davidson seamounts off the west coast of California.

Video observations of Sthenaster show the holotype hunched over colonies of the co-occurring gorgonian Eunicella modesta ( Verrill 1883) . Gut contents of the holotype of Sthenaster (USNM 1124468) included distinctive spicules belonging to the E. modesta ( Verrill, 1883) . These observations support the hypothesis of corallivory in Sthenaster , and suggests that dietary preferences would be similar to other known hippasterines. If Sthenaster is indeed a predator on gorgonians, this would be the first account of hippasterine predation on gorgonians in the Atlantic.

It is unclear how specific nutritional preferences are within the Hippasterinae . Feeding in the shallowwater Hippasteria suggests a feeding preference for many types of cnidarians but not to the exclusion of other food sources. The north-west Pacific species Hippasteria spinosa has been reported as a predator on the sea pen Ptilosarcus ( Mauzey, Birkeland & Dayton, 1968; Birkeland, 1974), the white-plumed sea anemone Metridium sp. , the zoanthid Epizoanthus scotinus ( Wood, 1958) , the tunicate Metandrocarpa sp. , the polychaete Nereis sp. , and eggs of the nudibranch Armina sp. ( Lambert, 2000) . Additionally, H. spinosa elicits an escape response in the sea anemone Stomphia sp. ( Lambert, 2000) . Similar to its northwest Pacific congener, H. phrygiana has been reported to incite swimming behaviour in the Atlantic sea anemone, Stomphia coccinea ( Müller, 1776) ( Robson, 1961) . Hippasteria phrygiana preys upon Metridium senile ( Linné, 1761) in Maine ( Harris, 1991) and has been reported feeding on ‘cnidarians’ ( Mercier & Hamel, 2008). Stomach contents from H. phrygiana have indicated that echinoderms, polychaetes, molluscs, and sediment are also incorporated in the diet of this species. In contrast, stomach contents from the deep-sea H. californica suggest that it is primarily a sediment/detrital feeder ( Carey, 1972). Sediments were also found in the gut of H. spinosa ( Birkeland, 1974) .

Other examples of presumed corallivory in nonhippasterine members of the Goniasteridae include the Hawaiian Calliaster pedicellaris ( Fisher, 1906) ( Chave & Malahoff, 1998) and Circeaster pullus ( Mah, 2006) , and the Atlantic Plinthaster dentatus ( Perrier, 1884) ( Halpern, 1970a, b) and Tessellaster nobilis ( Clark, 1941) .

This work represents a first step to further our understanding of the major taxonomic concepts within the neglected Hippasterinae . Future efforts would be best directed towards a complete investigation of Hippasteria , which occurs worldwide, is the most speciose of the Hippasterinae , and is one of the most frequently encountered asteroids observed feeding on deep-sea corals. Questions relating to dietary preferences/restrictions correlated to phylogeny could be important particularly with regard to management and conservation of these ecosystems.