Himerometra, A. H. CLARK, 1907

HIMEROMETRA A.H. CLARK, 1907 View in CoL

Diagnosis: Himerometridae with proximal pinnules much larger and thicker than those following; proximalmost pinnule [P II on IIBr2 of IIBr4(3 + 4)] largest and the following decreasing in size; cirrals with or without aboral spines; centrodorsal low hemispherical to discoidal with concave to deeply depressed aboral apex; brachitaxes aborally rounded and well separated (A.H. Clark, 1909b, 1941; Hess & Messing, 2011).

Type species: Antedon crassipinna Hartlaub, 1890 (a junior synonym of Actinometra robustipinna ).

Distribution: Often abundant on shallow coral reefs from southern Japan southward through mainland southeast Asia, Philippines, island Malaysia, Indonesia and Papua New Guinea to tropical Australia, and westward to the Persian Gulf (A.H. Clark, 1941; Bradbury et al., 1987; Messing, 1998).

Remarks: Feather stars now attributable to Himerometra have a confused taxonomic history. A.H. Clark’s (1907) initial description of the genus included 52 species formerly in Antedon Fréminville, 1811 , the majority of which he subsequently distributed among three families ( Colobometridae , Himerometridae and Mariametridae ) and numerous genera (e.g. Amphimetra , Cenometra , Heterometra , Dichrometra , Lamprometra , Liparometra and Stephanometra ). He did not include what has proved to be the senior name, Actinometra robustipinna Carpenter (1881) , based on a mutilated specimen placed among what are now treated as Comatulidae (formerly Comasteridae ). A.H. Clark (1912b) finally recognized its true affinities but considered its identity uncertain within Himerometra , only treating it as distinct (and senior) in the paper that first recognized the six extant species accepted until the current study (A.H. Clark, 1913).

Himerometra View in CoL as construed herein includes two extant taxa: H. robustipinna View in CoL and H. sol View in CoL . Four fossil species have been attributed to the genus: Himerometra bassleri Gislén, 1934 , H. grippae Anderson, 1967 , H. caldwellensis Strimple & Mapes, 1984 and H. louisianensis Strimple & Mapes, 1984 . Of these, only H. bassleri is known from a centrodorsal, radial circlet and disassociated plates. All four are unlikely candidates for inclusion in the genus, chiefly because their radial articular facets differ strongly from those of H. robustipinna View in CoL , as illustrated by Clark (1921: 26, as H. martensi View in CoL , treated here as a junior synonym of H. robustipinna View in CoL – see the following). In particular, the portion of the facet adoral to the transverse ridge in H. robustipinna View in CoL is parallel to the oral-aboral axis of the radial circlet and includes a pair of large, squarish interarticular ligament fossae, and an extremely thin adoral muscle fossa. In contrast, the entire radial facet in the fossil species slopes inward, especially strongly in H. caldwellensis , H. louisianensis and H. grippae ; the interarticular ligament fossae are triangular or aborally rounded, and wider than tall, and, in H. grippae , the muscle fossae are triangular. All four appear to have a much larger central cavity within the radial circlet than H. robustipinna View in CoL . In addition, the adoral surface of the centrodorsal of H. bassleri (the only fossil species in which this feature is visible) lacks the radiating coelomic grooves characteristic of extant Himerometra ( Clark, 1915: 253) View in CoL and other himerometroids ( Hess & Messing, 2011). Finally, Gislén (1934) considered H. bassleri as most closely related to Himerometra persica View in CoL , which we remove from this genus herein. We consider the fossil taxa as Himerometroidea incertae sedis.