GENERIC RESUSCITATION AND REDESCRIPTION OF ACTINOTRYX SANCTITHOMAE DUCHASSAING DE FOMBRESSIN AND MICHELOTTI, 1860

(CNIDARIA: ANTHOZOA: CORALLIMORPHARIA)

Harim ChaDepartment of Ecology and Evolutionary Biology, Natural History Museum and Biodiversity Research Center

The University of Kansas, Lawrence, KS 66045, USA (harim@ku.edu)

• Type species of genus Actinotryx • Type specimens: no longer exist• Type locality: St. Thomas, US Virgin Islands• Where does this species belong?

Genus ActinotryxGenus OriniaGenus DiscosomaGenus 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 2004. 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 supportedby NSF PEET DEB99-78106 to Dr. Daphne Fautin

Is Actinotryx sanctithomae a species of genus Discosoma?

Family Discosomatidae

Nominal genera

ActinodiscusActinotryxAmplexidiscusDiscosomaMetarhodactisOriniaParadiscosomaPhialactisRhodactis

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 ofActinotryx sanctithomae

Type species

Characters

Actinotryx sanctithomae

Oriniatorpida

(SMNH type-71 syntype)

Discosomanummiforme

(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 Papilliform Nummiform Branched

Tentacle-free zone on oral disc

Yes Yes No 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 Weak - diffuse Absent or weak Weak- diffuse

Endosymbionts Yes Yes Yes Yes

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.

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