Belongs within: Ophiurida.
Contains: Ophiacantha.
The Ophiacanthidae are a group of brittle stars with slender arms bearing numerous long, often glassy spines (Spencer & Wright 1966).
Rise to the surface, retreat to the depths
Published 7 December 2022
Despite being the most speciose of the recognized modern classes of echinoderms, the brittle stars (Ophiuroidea) are perhaps the least well known. There are several reasons for this, such as their often small size and low economic significance to humans. And for some significant subgroups, there is their tendency to keep to the deep ocean waters where humans rarely look. One such group is the family Ophiacanthidae.
Brittle stars of the Ophiacanthidae have slender arms that are often constricted at nodes. The arms bear numerous long spines, often glassy and serrate, that sit at an angle to the arm (Spencer & Wright 1966). The central disc is usually covered with several small scales and spinelets, and the arms bear small dorsal and ventral plates together with well-developed lateral plates. Skeletally, the family is distinguished by volute-shaped sockets for the arm spines, marked by a sigmoidal fold, that sit raised above the surrounding stereom (Martynov 2010). The base of each spine generally bears a compact condyle that articulates with the socket, presumably holding the spine firm.
In the modern fauna, ophiacanthids are almost entirely restricted to depths of 200 m and below (Thuy 2013). They may be very abundant in some locations with recorded densities of hundreds of individuals per square metre (Metaxas & Giffin 2004). They are slow-moving suspension feeders, using the spines and tube feet on the arms to capture prey. Often, they will raise themselves on sponges or deep-sea corals to better position themselves in the water column.
The earliest ophiacanthids appear in the fossil record in the Triassic but remain rare until the Jurassic. During the Jurassic and Cretaceous, they increase significantly in diversity, reaching their peak in the Late Jurassic (Thuy 2013). However, this apparent trajectory may be subject to bias. Though modern ophiacanthids are strictly deep-sea inhabitants, and the deep sea seems likely to have been their original home, the Jurassic and Cretaceous periods saw them diversify into more shallow-water environments. Shallow-water faunas are better represented in the known fossil record than deep-water faunas (particularly during the early Mesozoic). The reasons for the ophiacanthids’ advance onto the continental shelf and subsequent return remain open to question but Thuy (2013) advanced two major suggestions. One is that differing patterns of ocean circulation meant that Jurassic and Cretaceous oceans would have been less strongly stratified than modern waters. The other is that other long-spined brittle star families such as the Ophiothricidae that dominate modern shelf environments were less diverse during the Mesozoic. Maybe the Jurassic ophiacanthids were able to take advantage of a gap in the market, eventually beating a retreat as conditions became less amenable and competition more fierce.
Systematics of Ophiacanthidae
Characters (from Spencer & Wright 1966): Arms slender, commonly constricted at nodes. Dorsal and ventral arm plates very small. Arm spines long, numerous, at angle to arm, commonly glassy and serrate. Disc with granules and spinules. Distal vertebrae may be partly divided longitudinally by series of pores.
<==Ophiacanthidae |--Ophiotreta Verrill 1899TS16, SW66 | |--O. eximia (Koehler 1904)MG-H11 | |--O. stimulea (Lyman 1878)MG-H11 | `--O. valenciennesi (Lyman 1879)MG-H11 `--+--Ophiolimna Verrill 1899TS16, SW66 | |--*O. bairdi (Lyman 1883) [=Ophiacantha bairdi]SW66 | `--O. perfida (Koehler 1904)TS16 `--+--OphiacanthaTS16 |--Ophiochondrus Lyman 1869TS16, SW66 | |--*O. convolutus Lyman 1869SW66 | `--O. stelliger Lyman 1879TS16 `--+--Inexpectacantha Thuy 2011TS16 | `--I. acrobatica Thuy 2011TS16 `--Ophiocopa Lyman 1883TS16, SW66 `--*O. spatula Lyman 1883SW66 Ophiacanthidae incertae sedis: Sinophiura multispina (Koehler 1922)MG-H11 Ophiomedea Koehler 1906F61 `--*O. duplicata Koehler 1906SW66 Ophiocamax Lyman 1878SW66 `--*O. vitrea Lyman 1878SW66 Ophiocymbium Lyman 1880SW66 `--*O. cavernosum Lyman 1880SW66 Ophiotoma Lyman 1883 [incl. Ophiopora Verrill 1899]SW66 `--*O. coriacea Lyman 1883 [incl. O. bartletti Lyman 1883]SW66 Ophiotrema Koehler 1896SW66 `--*O. alberti Koehler 1896SW66 Glaciacantha Fell 1961F61 `--*G. jason Fell 1961F61 Amphipsila Verrill 1899SW66 `--*A. maculata Verrill 1899SW66 Microphiura Mortensen 1911SW66 `--*M. decipiens Mortensen 1911SW66 Ophiacanthella Verrill 1899SW66 `--*O. troscheli (Lyman 1878) [=Ophiacantha troscheli]SW66 Ophialcaea Verrill 1899SW66 `--*O. tuberculosa (Lyman 1878) [=Ophiacantha tuberculosa]SW66 Ophiambix Lyman 1880SW66 `--*O. aculeatus Lyman 1880SW66 Ophientrema Verrill 1899SW66 `--*O. scolopendrica (Lyman 1883) [=Ophiacantha scolopendrica]SW66 Ophioblenna Lütken 1859SW66 `--*O. antillensis Lütken 1859SW66 Ophiochondrella Verrill 1899SW66 `--*O. squamosa (Lyman 1883) [=Ophiochondrus squamosus]SW66 Ophiodaces Koehler 1922SW66 `--*O. inanis Koehler 1922SW66 Ophiodelos Koehler 1931SW66 `--*O. insignis Koehler 1931SW66 Ophiodictys Koehler 1922SW66 `--*O. uncinatus Koehler 1922SW66 Ophiogema Koehler 1922SW66 `--*O. punctata Koehler 1922SW66 Ophioglyphoida Chapman 1934SW66 `--*O. fosteri (Chapman 1934) [=Ophiacantha (*Ophioglyphoida) fosteri]SW66 Ophiolebes Lyman 1878SW66 `--*O. scorteus Lyman 1878SW66 Ophiologimus Clark 1911SW66 `--*O. hexactis Clark 1911SW66 Ophiomelina Koehler 1922SW66 `--*O. placida (Koehler 1904) [=Ophiomitrella placida]SW66 Ophiomitra Lyman 1869SW66 `--*O. valida Lyman 1869SW66 Ophiomytis Koehler 1904SW66 `--*O. weberi Koehler 1904SW66 Ophiophrura Clark 1911SW66 `--*O. liodisca Clark 1911SW66 Ophiopinna Hess 1960SW66 `--*O. elegans (Heller 1858) [=Geocoma elegans]SW66 Ophioplinthaca Verrill 1899SW66 `--*O. dipsacos (Lyman 1878) [=Ophiomitra dipsacos]SW66 Ophioprium Clark 1915SW66 `--*O. curvicornis (Lyman 1883) [=Ophiacantha curvicornis]SW66 Ophioripa Koehler 1922SW66 `--*O. marginata Koehler 1922SW66 Ophiothauma Clark 1938SW66 `--*O. heptactis Clark 1938SW66 Ophiomitrella Verrill 1899SW66 |--*O. laevipellis (Lyman 1883) [=Ophiacantha laevipellis]SW66 `--O. clavigeraBK77 Ophiophthalmus Matsumoto 1917 [incl. Ophiosemnotes Matsumoto 1917]SW66 |--*O. cataleimmoidus (Clark 1911) [=Ophiacantha cataleimmoida]SW66 `--O. relictus (Koehler 1904)MG-H11 Ophiothamnus Lyman 1869 [incl. Ophioleda Koehler 1906]SW66 |--*O. vicarius Lyman 1869SW66 `--O. biocal O’Hara & Stöhr 2006MG-H11 Ophiurothamnus Matsumoto 1917SW66 |--*O. dicylus (Clark 1911) [=Ophiomitra dicyla]SW66 `--O. clausa (Lyman 1878)MG-H11 OphioplinthacaMG-H11 |--O. plicata (Lyman 1878)MG-H11 `--O. rudis (Koehler 1897)MG-H11 Clarkocoma canaliculata (Lütken 1869)TS16 Ophiomoeris Koehler 1904TS16, SW66 [incl. Ophiurases Clark 1911SW66] |--*O. spinosa Koehler 1904SW66 `--O. obstricta (Lyman 1878)MG-H11 OphiolanceaJB12
*Type species of generic name indicated
References
[BK77] Barel, C. D. N., & P. G. N. Kramers. 1977. A survey of the echinoderm associates of the north-east Atlantic area. Zoologische Verhandelingen 156: 1–159.
[F61] Fell, H. B. 1961. New genera and species of Ophiuroidea from Antarctica. Transactions of the Royal Society of New Zealand 88 (4): 839–841.
[JB12] Johnson, M. E., & B. G. Baarli. 2012. Development of intertidal biotas through Phanerozoic time. In: Talent, J. A. (ed.) Earth and Life: Global biodiversity, extinction intervals and biogeographic perturbations through time pp. 63–128. Springer.
Martynov, A. 2010. Reassessment of the classification of the Ophiuroidea (Echinodermata), based on morphological characters. I. General character evaluation and delineation of the families Ophiomyxidae and Ophiacanthidae. Zootaxa 2697: 1–154.
[MG-H11] McEnnulty, F. R., K. L. Gowlett-Holmes, A. Williams, F. Althaus, J. Fromont, G. C. B. Poore, T. D. O’Hara, L. Marsh, P. Kott, S. Slack-Smith, P. Alderslade & M. V. Kitahara. 2011. The deepwater megabenthic invertebrates on the western continental margin of Australia (100–1100 m depths): composition, distribution and novelty. Records of the Western Australian Museum Supplement 80: 1–191.
Metaxas, A., & B. Giffin. 2004. Dense beds of the ophiuroid Ophiacantha abyssicola on the continental slope off Nova Scotia, Canada. Deep-Sea Research I 51: 1307–1317.
[SW66] Spencer, W. K., & C. W. Wright. 1966. Asterozoans. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt U. Echinodermata 3 vol. 1 pp. U4–U107. The Geological Society of America, Inc., and The University of Kansas Press.
Thuy, B. 2013. Temporary expansion to shelf depths rather than an onshore-offshore trend: the shallow-water rise and demise of the modern deep-sea brittle star family Ophiacanthidae (Echinodermata: Ophiuroidea). European Journal of Taxonomy 48: 1–242.
[TS16] Thuy, B., & S. Stöhr. 2016. A new morphological phylogeny of the Ophiuroidea (Echinodermata) accords with molecular evidence and renders microfossils accessible for cladistics. PLoS One 11 (5): e0156140.