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Synoptic Keys to the Genera of Ophiuroidea

Historical Review

Historical Review

The bizarre form and tree-like branching arms of Gorgonocephalids attracted the attention of several pre-Linnean naturalists. The earliest reference seems to be the "Stella arborescens" of Rondelet (1554). Winthrop, a New England naturalist of Stuart times, made two communications to the Royal Society on "The Basket Fish" (Phil. Trans for 1670 and 1671). "Astrophyton" was illustrated and described by Linck in 1733; the species concerned, or one allied to it, now carries the name Gorgonocephalus linckii (M. & T.)

All star-shaped echinoderms known to Linné in 1758 were included in his genus Asterias. Certain species of ophiuroids were among the assemblage. Three of them are notable as becoming the types of genera subsequently erected:—Asterias caputmedusae, Asterias ophiura, and Asterias aculeata. Pennant (1777) added Asterias pentaphylla; Retzius (1783) Asterias euryale; Pallas (1788) Asterias oligactes; and Abildgaard (1789) Asterias nigra. These species are now placed in widely differing families of ophiuroids, and their incongruous association with Asterias serves to point the transitory character of taxonomic assemblages.

Realizing that Asterias comprized at least two main types of radiate animals, Lamarck in 1801 limited the content of the genus to asteroids and euryalids: the simple-armed ophiuroids were referred to a second genus Ophiura. The latter was, of course, based upon the Linnean species of that name, which is thus the type species and genus for all ophiuroids. However, Montagu (1804), Retzius (1805) and others continued to refer new species of ophiuroids to Asterias L., including some species which later became types of ophiuroid genera.

Fragmentation of the unmanageable genus Asterias was resumed in 1815 when, independently, Oken proposed Euryale, and Leach Gorgonocephalus—to include the forms with branching arms. These genera were originally synonymous but, thanks to restricted definitions proposed by Lyman in 1882, both names have survived as independent genera, as well as the pre-Linnean Astrophyton, revived by Mueller and Troschel in 1842. Meantime, Lamarck in 1816 further restricted Asterias, referring the forms with branching arms to Euryale, as Oken had proposed the previous year. Asterias thus ceased to have any connection with ophiuroids.

Three new genera were added by Louis Agassiz in 1835: Ophiocoma, Trichaster and Ophiurella. The first was based on Ophiura echinata Lmk., the second on Euryale palmiferum Lmk., but the identity of the third is not now clear.

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A landmark was the publication of Mueller and Troschel's paper on the genera of ophiuroids (1840), followed two years later by their "System der Asteriden". In the 1840 paper seven new genera were proposed—Ophiothrix, Ophiolepsis, Ophionyx, Ophioderma, Ophiomyxa, Ophiopholis and Ophiocnemis. Six further genera were proposed by them in 1842, and Forbes (1843) added three more (including the well-known Amphiura and Pectinura). By the mid-century a total of 22 recognisable genera had been established.

During the next twenty years Lütken added thirteen more genera, every one beginning with either Ophi(o)- or Ast(e)ro- Unfortunately this convention has been followed too faithfully by later naturalists, with the result that about 200 of the generic names are so tediously uniform as to make them extremely difficult to remember. Through slips of the pen variant spellings continually arise to confound the synonymy.

During the second half of the nineteenth century some 125 new genera were proposed, as follows: Lyman (45, 18 of which stem from the Challenger), Verrill (26), Lütken (13), Ljungman (10), Koehler (5)—the remainder by less prolific authors. During this period the Challenger report by Lyman (1882) provided the first (and so far, only) monograph on ophiuroids.

The first half of the twentieth century saw the publication of notable descriptive works, especially those of Koehler, including his Siboga Reports (1904–5). Important systematic contributions have been those of Matsumoto (1915–17) and Doederlein (1911, 1927, 1930). Regional faunal surveys have been carried out by Mortensen (in Indonesia, South Africa, New Zealand, Australia, Europe, Arctic and Antarctic); by H. L. Clark (in Australia, South Africa, Indonesia); Koehler (in Antarctica, Indonesia, Indian Ocean, India). H. L. Clark (1915) issued a Catalogue of genera and species, a work which remains a standard reference. During these fifty years a further 150 genera have been proposed. Over the last decade or so, although expeditions continue to be active, the number of genera recognized as valid has fallen, as various synonyms have been recognized.