GENERIC RESUSCITATION AND REDESCRIPTION OF ACTINOTRYX SANCTITHOMAE DUCHASSAING DE FOMBRESSIN AND MICHELOTTI, 1860 (CNIDARIA: ANTHOZOA: CORALLIMORPHARIA) Harim Cha Department of Ecology and Evolutionary Biology, Natural History Museum and Biodiversity Research Center The University of Kansas, Lawrence, KS 66045, USA Type species of genus Actinotryx Type specimens: no longer exist Type locality: St. Thomas, US Virgin Islands Where does this species belong? Genus Actinotryx Genus Orinia Genus Discosoma Genus Rhodactis Actinotryx sanctithomae Duchassaing de Fombressin and Michelotti, 1860 is the only species of genus Actinotryx, which belongs to family Discosomatidae. The Actinotryx has been confused with and is in partial synonymy with most genera in the family Discosomatidae; it is important to clearly circumscribe Actinotryx to resolve nomenclatural ambiguity at the genus level. Type specimens of A. sanctithomae are not extant and specimens of the type were collected from type locality, St. Thomas, US Virgin Islands in August The specimens were examined and identified as A. sanctithomae based on the original description containing an illustration including several critical morphological features for recognition of A. sanctithomae. The morphological characters are distinct from the ones of other type species of genera in the family Discosomatidae. I redescribe Actinotryx sanctithomae and propose resuscitation of the genus Actinotryx in this study. ABSTRACT Actinotryx santithomae Duchassaing de Fombressin and Michelotti, 1860 Illustration in the original description Duchassaing de Fonbressin P. and Michelotti G., 1860, Plate VII, fig. 2 This research is supported by NSF PEET DEB to Dr. Daphne Fautin Is Actinotryx sanctithomae a species of genus Discosoma? Family Discosomatidae Nominal genera Actinodiscus Actinotryx Amplexidiscus Discosoma Metarhodactis Orinia Paradiscosoma Phialactis Rhodactis den Hartog (1980) Classification Discosoma Major features distinguishing genera in the family Discosomatidae Shape of marginal tentacles Shape of distal tentacles Tentacle-free zone on oral disc ACKNOWLEDGMENTS  Dr. Daphne Fautin, Dr. Sandra Romano, Matt Kost  National Science Foundation  KU Natural History Museum & Biodiversity Research Center  University of the Virgin Islands Comparisons of type species of each genus Distinctive features of Actinotryx sanctithomae Type species Characters Actinotryx sanctithomae Orinia torpida (SMNH type-71 syntype) Discosoma nummiforme (SMNH type-1156 syntype) Rhodactis rhodostoma Shape of marginal tentacle Digitiform (length: 3-4 mm in preservative) Digitiform (length: 2-3 mm in preservative) Reduced digitiform (length: very short) Digitiform (length: 4-5 mm in preservative) Shape of discal tentacles Papilliform NummiformBranched Tentacle-free zone on oral disc Yes No Nematocyst composition Holotrichs up to 250 µm long in mesenterial filaments Microbasic p-mastigophore Microbasic b-mastigophore Type specimen has been severely damaged: impossible to measure nematocysts. Holotrichs up to 160 µm long in mesenterial filaments Microbasic p-mastigophore Microbasic b-mastigophore Holotrichs up to 180 µm long in mesenterial filaments Microbasic p-mastigophore Microbasic b-mastigophore Sphincter muscle development Weak - diffuse Absent or weakWeak- diffuse EndosymbiontsYes Whole specimen Nematocyst composition Endosymbionts Digitiform marginal tentacles Papilliform discal tentacles Tentacle-free zone between marginal and discal tentacles No distinct sphincter muscle Holotrichs in mesenterial filaments up to 250 um long Weak mesogleal development Conclusion Actinotryx is distinguished from Discosoma with which it has been synonymized: its two most distinctive characters are a tentacle-free zone on the oral disc and size of holotrichs in the mesenterial filaments. Actinotryx sanctithomae is the type species of genus Actinotryx: neotype designation is required. Orinia torpida, type species of genus Orinia, is a junior synonym of Actinotryx sanctithomae. 1 cm