''Ophiothrix'' is a large genus of
brittle star
Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...
s (Ophiuroidea) found in oceans worldwide from tropics to Arctic and Antarctic regions. At present a total of 93 Ophiothrix
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
have been recognized. It is considered as one of the most interesting genera because of the presence of its brilliant colors and associations with
coral
Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...
and sponges as well. This genus has been labelled particularly difficult with respect to
taxonomy
image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy
Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...
, due to a high degree of variability in characters that are described is a
morphological aspect.
Evolution
The fossil record of brittle stars can be traced back around 500 million years to Early
Ordovician
The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...
period. Despite the fact there have been a considerable number of fossils reported from
Paleozoic
The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...
,
Mesozoic
The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...
and
Cenozoic
The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...
periods, a startlingly little amount is known about the evolutionary history of the group. Paleozoic ophiuroids bear an uncanny resemblance to the modern relatives with respect to
ambulacral
Ambulacral is a term typically used in the context of anatomical parts of the phylum Echinodermata or class Asteroidea and Edrioasteroidea. Echinoderms can have ambulacral parts that include ossicles, plates, spines, and suckers. For example, sea ...
plate pairs which have been fused firmly into their vertebrae and ambulacral groove which their
ventral
Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
arm plates cover. They also have the presence of ventrally lateral arm plates.
Systematics and phylogeny
''Ophiothrix'' is a large genus that is currently divided into the following three subgenera: ''Acanthophiothrix'', ''Ophiothrix'' and ''Theophiothrix. Extant species include:
References
{{Ophiuroidea-stub