Rhodactis - Natural History Museum

Corallimorpharians of Oman,
with discussion of the generic
circumscription of Rhodactis
Ha-Rim Cha
Division of Invertebrate Zoology
KU Natural History Museum and
Biodiversity Research Center
Harim anemone Kirkendale, 2004

Corallimorpharians of Oman,
with discussion of the generic
circumscription of Rhodactis
Ha-Rim Cha
Division of Invertebrate Zoology
KU Natural History Museum and
Biodiversity Research Center

Cnidaria: Anthozoa: Hexacorallia
Actiniaria
Corallimorpharia
Scleractinia
Zoanthidea
Ceriantharia
Antipatharia

Corallimorpharia
• Cnidaria
– 2 layered, organ-less body, with
stinging nematocysts
• Anthozoa
– Polyp form only in life cycle
• Corallimorpharia
– Skeleton-less, solitary or clonal
(not colonial)

Why study corallimorpharians
• Diverse in habitat,
biology, life history
• Relatively unknown
• Understand evolution of
colonies and skeletons
among Anthozoa

Habitat
• Attached to rocks or
coral skeletons
• Tropical to polar areas
• Intertidal to deep sea

Shallow tropical
• Family
Discosomatidae
• Family
Ricordeidae
1 cm
1 cm
10 cm
Dunn D. F. and Hamner W. M.,
1980, Page 30 , fig. 1

Shallow
tropical and temperate
• Family Corallimorphidae
Genus Corynactis
Genus Pseudocorynactis
1cm

Deep water
• Family Corallimorphidae
Genus Corallimorphus
• Family Sideractiidae
Moseley H.
N., 1877,
Plate XLV ,
fig. 7
Zamponi M. O., 1976, Page 131 , fig. 1

How can we interpret and
understand this diversity
TAXONOMY and SYSTEMATICS

What is it
Process of identification
• Find specimen
• Compare multiple specimens
• Develop sense of range of
variation in color & morphology

Is it the same
Process of comparison
• Color, size, shape, behavior
& habitat
• Arrangement and
morphology of mesenteries
& muscles
• Size, shape & distribution of
nematocysts

Oman
• May 7 ~ 30, 2004
• Survey of Actiniaria and Corallimorpharia
in Oman
• Participants: Meg Daly, Adorian Ardelean
and Ha-Rim Cha
• Collaborator: Dr. Michel Claereboudt,
Department of Marine Science and
Fisheries, Sultan Qaboos University
(SQU), Muscat, Oman

The Gulf of Oman
• The area is strongly
influenced by seasonal
monsoon cycles associated
with upwelling and algal
blooms
• The coast of Oman includes
three distinct habitats: muddy
and sandy shores, rocky
shores, and coral
communities (Coles 1996)

Distribution of Corallimorpharia

Oman

Underwater Oman

Underwater Oman

Diversity in Oman
• 12 species of actiniarians
• 3 species of corallimorpharians
Edwardsiidae n. sp.1 Edwardsiidae n. sp.2 Discosoma n. sp.

Actiniarians in Oman
• ● Components of the tropical Indo-
Pacific fauna
• New species
(possibly endemic)
• Lacking
representatives
of Acontiaria

Corallimorpharians of Oman
Genus Discosoma

Corallimorpharians of Oman
Genus Rhodactis
Rhodactis rhodostoma

Family Discosomatidae
Rhodactis Milne Edwards and Haime, 1851
• Problem 1
The original description of the type species
of Rhodactis (Metridium rhodostomum
Hemprich and Ehrenberg in Ehrenberg,
1834) contains few diagnostic characters.
• Problem 2
Most generic characters are not consistently
used among authors.

What are the characters of
Rhodactis rhodostoma (Hemprich and
Ehrenberg in Ehrenberg, 1834)
• Type specimens: no longer extant
• Type locality: Tor, the Red Sea
• Material examined: Oman -- KUNHM
002077 (x3), KUNHM 002093 (x5)

What are the characters of
Rhodactis rhodostoma (Hemprich and
Ehrenberg in Ehrenberg, 1834)
• Column: short, smooth, mesenterial
insertions visible
• Oral disc: densely covered with tentacles.
30~50 mm diameter in life, preserved
specimens 15~25 mm. No tentacle-free
zone.
• Pedal disc: about half as wide as oral disc
• Color: greenish purple to purple

What are the characters of
Rhodactis rhodostoma (Hemprich and
Ehrenberg in Ehrenberg, 1834)
• Tentacle: Two kinds of tentacles; digitate and
branched. No distinction between marginal and
discal tentacles. Peripheral tentacles and those
around the mouth digitate; most intermediate
tentacles branched. In life to 5 mm long.

What are the characters of
Rhodactis rhodostoma (Hemprich and
Ehrenberg in Ehrenberg, 1834)
• Nematocyst size and distribution
• Musculature: no sphincter muscle; weak
retractor muscles
• Habitat: live in patches on dead coral or rocks;
3~10 m deep
• Behavior: Feeding by envelopment. Mesenterial
filaments extruded when disturbed
• Symbionts: zooxanthellae (size 8~9.5 µm in
diameter)

Characters of Rhodactis based on
the examination of type species
Nature of tentacles: DIGITATE and BRANCHED tentacles
Distinction between marginal and discal tentacles: NONE
Tentacle-free zone on oral disc: NO
Nematocyst composition:
holotrichs (large and small), microbasic p-
mastigophores, microbasic b-mastigophores
Sphincter muscle: NO
Behavior: Feeding by ENVELOPMENT
Symbionts: YES

Species composition
Before
After
Rhodactis bryoides
R. howesii
R. inchoata
R. indosinensis
R. musciformis
R. rhodostoma
R. mussoides

Revise the family Discosomatidae
• Family Discosomatidae
Genus Rhodactis
Discosoma
Paradiscosoma
Metarhodactis
Actinotryx
Orinia
Phialactis
Amplexidiscus

Caribbean

Trip to St. Thomas,
US Virgin Islands

Purposes of the trip
• Survey of corallimorpharians of St.
Thomas
• Revision of corallimorpharian genera
described from the Virgin Islands

Species sanctithomae
• Type specimens: no longer exist
• Type locality: St. Thomas, Virgin Islands
• Where does this species belong
Genus Actinotryx
Genus Orinia
Genus Discosoma
Genus Rhodactis

Collecting Sites

What I saw
in St. Thomas…

Corallimorpharians
collected from St. Thomas
Discosoma sp.
Ricordea florida

Corallimorpharians
collected from St. Thomas
Duchassaing de Fonbressin P. and
Michelotti G., 1860, Plate VII , fig. 2
sanctithomae

Future directions
• Gathering data from
type specimens of
species of genera
in family
Discosomatidae
• Molecular data will be
added for the genus
and order level
phylogenies
Corallimorpharia I
Corallimorpharia II
Scleractinia
Actiniaria
Ceriantharia

Acknowledgments
• Michel Clareboudt, staff & faculty of
Marine Sciences, SQU
• Dr. Daphne Fautin (KU)
Dr. Meg Daly (OSU)
Dr. Adorian Ardelean (West
University of Timisoara, Romania)
Matthew Kost (KU)
• American Association for the
Advancement of Science, National
Science Foundation, KU Natural History
Museum & Biodiversity Research Center