Gnathophiuridea

Savigny’s brittle star Ophiactis savignyi, copyright Moorea Biocode.

Belongs within: Ophiurida.
Contains: Ophiotrichidae, Ophiactis, Amphiura.

The Ophiactidae are a family of brittle stars in which the disc bears a covering of granules or spinules.

Brittle stars, brittle taxa
Published 9 April 2017
Amphiura arcystata brittle stars extending their arms above the sediment, copyright James Watanabe.

The brittle stars are something of the poor cousin among echinoderm classes. Their tendency to relatively small size and cryptic habitats means that they do not attract the level of attention given to starfish, sea urchins or sea cucumbers. Despite this, they are perhaps the most diverse of the living echinoderm classes, with more recognised species around today than any other.

It should therefore come as no surprise that the internal classification of brittle stars remains decidedly up in the air. The basic framework of the surrent system was established over a hundred years ago by Matsumoto (1915) and changes to this arrangement since have been fairly cosmetic. However, a significant challenge to Matsumoto’s system has been arisen following the input of molecular data to the mix: many of Matsumoto’s higher groupings have not been supported by moleculat analyses. Perhaps the nail in the Matsumoto system’s coffin has come from a recent publication by Thuy & Stöhr (2016) who found that a formal analysis of morphological data also failed to support the pre-existing classification. At this point in time, we know that a new classification of brittle stars is needed but we don’t yet know what form it will take.

Excavated specimen of Amphiuridae, copyright Arthur Anker. The radial plates are visible as a pair of bars alongside the base of each arm; I don’t think that the genital plates are visible externally.

Perhaps one of Matsumoto’s groupings that will survive the transition is the Gnathophiurina. Notable features of this group include a ball-and-socket articulation between the radial shields (large plates that sit on the aboral side of the central body on either side of the insertion of each arm) and the genital plates (sitting below and alongside the radial shields), with the socket in the radial shield and the ball on the genital plate. The genital plates are also firmly fixed to the basal vertebra of each arm. I haven’t been able to find what the functional significance of this arrangement is, such as whether it renders the body more flexible that in other groups where the radial-genital plate articulation is more fixed. At least one of the families of Gnathophiurina, the Amphiuridae, includes species that commonly live in burrows with the tips of their arms extended into the water column, using their tube feet to capture food particles (Stöhr et al. 2012). In contrast, some Ophiotrichidae are epizoic, living entwined around black corals and the like. The Gnathophiurina as a whole seem to be most diverse in relatively shallow waters.

Matsumoto’s (1915) original concept of the Gnathophiurida included species that are now classified into four families, the Amphiuridae, Ophiotrichidae, Amphilepididae and Ophiactidae, and recent analyses have returned results not inconsistent with this association. In Thuy & Stöhr’s (2016) morphological analysis, Gnathophiurina species all belong to, and make up the bulk of, their clade IIIc. In the molecular analysis presented by Hunter et al. (2016), the families belong to two separate clades but the branch separating them is very weakly supported. Further research is needed, of course, but it may turn out that Matsumoto was on to something when he focused on that ball-and-socket joint.

Systematics of Gnathophiuridea
Gnathophiuridea [Gnathophiurida, Gnathophiurina]SW66
    |--AmphilepididaeTS16
    |    |--Amphilepis Ljungman 1866SW66
    |    |    `--*A. norvegica (Ljungman 1865)TS16 [=Amphiura norvegicaSW66]
    |    `--Ophiochytra Lyman 1880SW66
    |         `--*O. epigrus Lyman 1880SW66
    |--Ophiactidae [Ophiactinae]S97
    |    |  i. s.: Ophiopus Ljungman 1866 [incl. Ophiaregma Sars 1872]SW66
    |    |           `--*O. arcticus Ljungman 1866SW66
    |    |         Hemipholis Lyman 1865SW66
    |    |           |--*H. elongata (Say 1825) [=Ophiura elongata]SW66
    |    |           `--H. cordiferaH04
    |    |--Histampica duplicata (Lyman 1875)TS16
    |    `--+--Ophienigma Stöhr & Ségonzac 2005TS16
    |       |    `--O. spinilimbatum Stöhr & Ségonzac 2005TS16
    |       `--+--+--OphiotrichidaeTS16
    |          |  `--Ophiopholis Müller & Troschel 1840TS16, SW66
    |          |       |--O. aculeata (Linnaeus 1767)TS16 (see below for synonymy)
    |          |       `--O. japonicaH04
    |          `--OphiactisTS16
    `--AmphiuridaeS97
         |  i. s.: Monamphiura Fell 1962SW66
         |           `--*M. alba (Mortensen 1924) [=Amphiura alba]SW66
         |         Pandelia Fell 1962SW66
         |           `--*P. hinemoae (Mortensen 1924) [=Amphiura hinemoae]SW66
         |         Acrocnida Gislén 1926SW66
         |           `--*A. brachiata (Montague 1804)SW66 [=Asterias brachiataSW66, Ophiocnida brachiataBK77]
         |         Ailsaria Fell 1962SW66
         |           `--*A. echinulata (Mortensen 1940) [=Amphioplus echinulatus]SW66
         |         Amphiacantha Matsumoto 1917SW66
         |           `--*A. acanthina (Clark 1911) [=Amphioplus acanthinus]SW66
         |         Amphichilus Matsumoto 1917SW66
         |           `--*A. trichoides Matsumoto 1917SW66
         |         Amphichondrius Nielsen 1933SW66
         |           `--*A. granulosus Nielsen 1933SW66
         |         Amphicontus Hill 1940SW66
         |           `--*A. minutus Hill 1940SW66
         |         Amphilycus Mortensen 1933SW66
         |           `--*A. androphorus Mortensen 1933SW66
         |         Amphinephthys Fell 1962SW66
         |           `--*A. crossota (Murakami 1943) [=Amphiura crossota]SW66
         |         Amphiocnida Verrill 1899SW66
         |           `--*A. putnami (Lyman 1871) [=Ophiocnida putnami]SW66
         |         Amphiomya Clark 1939SW66
         |           `--*A. notabilis Clark 1939SW66
         |         Amphioncus Clark 1939SW66
         |           `--*A. platydiscus Clark 1939SW66
         |         Anamphiura Clark 1939SW66
         |           `--*A. valida Clark 1939SW66
         |         Ctenamphiura Verrill 1899SW66
         |           `--*C. maxima (Lyman 1879) [=Amphiura maxima]SW66
         |         Diamphiodia Fell 1962SW66
         |           `--*D. violacea (Lütken 1856) [=Amphiura violacea]SW66
         |         ‘Gymnodia’ Fell 1962 non Robineau-Desvoidy 1863SW66
         |           `--*G. tabogae (Nielsen 1932) [=Amphiodia tabogae]SW66
         |         Monopholis Fell 1962SW66
         |           `--*M. vitax (Koehler 1904) [=Amphiura vitax]SW66
         |         Nannophiura Mortensen 1933SW66
         |           `--*N. lagani Mortensen 1933SW66
         |         Nullopholis Fell 1962SW66
         |           `--*N. nudipora (Koehler 1944) [=Amphipholis nudipora]SW66
         |         Ophiocnida Lyman 1865 [incl. Ophiocnidella Ljungman 1872]SW66
         |           `--*O. hispida (LeConte 1851) [=Ophiolepis hispida]SW66
         |         Ophiomonas Djakonov 1952SW66
         |           `--*O. bathybia Djakonov 1952SW66
         |         Ophionema Lütken 1869SW66
         |           `--*O. intricata Lütken 1869SW66
         |         Ophionephthys Lütken 1869SW66
         |           `--*O. limicola Lütken 1869SW66
         |         Ophiophragmus Lyman 1865 [incl. Amphispina Nielsen 1933]SW66
         |           `--*O. wurdemanii (Lyman 1860) [=Amphiura wurdemanii]SW66
         |         Ophiostigma Lütken 1856 [incl. Amphistigma Clark 1938]SW66
         |           `--*O. tenue Lütken 1856SW66
         |         Paracrocnida Mortensen 1940SW66
         |           `--*P. persica Mortensen 1940SW66
         |         Paramphiura Koehler 1895SW66
         |           `--*P. punctata (Forbes 1841) [=Ophiocoma punctata]SW66
         |         Silax Fell 1962SW66
         |           `--*S. verrilli (Lyman 1879) [=Aphiura verrilli]SW66
         |         Unioplus Fell 1962SW66
         |           `--*U. falcatus (Mortensen 1933) [=Amphioplus falcatus]SW66
         |         Icalia Fell 1962SW66
         |           |--*I. denticulata (Koehler 1896) [=Amphiura denticulata]SW66
         |           `--I. filiformisF67
         |         Amphiodia Verrill 1899SW66
         |           |--*A. pulchella (Lyman 1869) [=Amphiura pulchella]SW66
         |           `--A. urticaHD03
         |         Nullamphiura Fell 1962SW66
         |           |--*N. psilopra (Clark 1911) [=Amphiura psilopora]SW66
         |           `--N. felli Skwarko 1963SG93
         |         Ophiodaphne Koehler 1931MG-H11, SW66
         |           |--*O. materna Koehler 1931SW66
         |           `--O. formatus (Koehler 1905)MG-H11
         |         Ophiocentrus Ljungman 1867SW66
         |           |--*O. aculeatus Ljungman 1867SW66
         |           |--O. aspera (Koehler 1905)MG-H11
         |           |--O. dilatata (Koehler 1905)SM15
         |           |--O. inaequalis (Clark 1915)MG-H11
         |           `--O. verticillatus (Döderlein 1896)SM15
         |         Amphipholis Ljungman 1866SW66
         |           |--*A. gracillima (Stimpson 1852) [=Ophiolepis gracillima; incl. *A. januarii Ljungman 1866]SW66
         |           |--A. germinataE97
         |           |--A. kochiiGAS03
         |           |--A. squamata (Delle-Chiaje 1828)MG-H11 [=Amphiura squamataBK77; incl. Ophiocoma neglectaBK77]
         |           `--A. thorelliBK77
         |         DougaloplusSM15
         |--Amphilimna Verrill 1899TS16, SW66
         |    |--*A. olivacea (Lyman 1869) [=Ophiocnida olivacea]SW66
         |    |--A. granulosa Liao 1989MG-H11
         |    `--A. transacta (Koehler 1930)MG-H11
         `--+--Ophiopsila Forbes 1843TS16, SW66 [Ophiopsilinae]
            |    |--*O. aranea Forbes 1843SW66
            |    |--O. annulosaPP64
            |    `--O. guineensis Koehler 1914TS16
            `--+--AmphiuraTS16
               `--Amphioplus Verrill 1899TS16, SW66
                    |--*A. tumidus (Lyman 1899) [=Amphiura tumida]SW66
                    |--A. congensis (Studer 1882)TS16
                    |--A. depressa (Ljungman 1867)MG-H11
                    |--A. hastatus (Ljungman 1867)SM15
                    |--A. laevisPP64
                    |--A. lucidus Koehler 1922MG-H11
                    `--A. ochroleuca (Brock 1888)MG-H11

Ophiopholis aculeata (Linnaeus 1767)TS16 [=Asterias aculeatusSW66; incl. Ophiolepis scolopendrica Müller & Troschel 1840SW66, *Ophiopholis scolopendricaSW66]

*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.

[E97] Emig, C. C. 1997. Ecology of inarticulated brachiopods. In: Kaesler, R. L. (ed.) Treatise on Invertebrate Paleontology pt H. Brachiopoda, Revised vol. 1. Introduction pp. 473–495. The Geological Society of America: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[F67] Fell, H. B. 1967. Echinoderm ontogeny. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt S. Echinodermata 1. General characters. Homalozoa—Crinozoa (except Crinoidea) vol. 1 pp. S60–S85. The Geological Society of America, Inc., and The University of Kansas: Lawrence (Kansas).

[GAS03] Gulbin, V. V., I. S. Arzamastsev & V. M. Shulkin. 2003. Ecological monitoring of the water area of Port Vostochnyi (Wrangel Bay) in the Sea of Japan (1995–2002). Russian Journal of Marine Biology 29 (5): 284–295.

[H04] Haeckel, E. 1899–1904. Kunstformen der Natur. Bibliographisches Institut: Leipzig und Wien.

[HD03] Ho, J.-S., M. Dojiri, G. Hendler & G. B. Deets. 2003. A new species of Copepoda (Thaumatopsyllidae) symbiotic with a brittle star from California, U.S.A., and designation of a new order Thaumatopsylloida. Journal of Crustacean Biology 23 (3): 582–594.

Hunter, R. L., L. M. Brown, C. A. Hill, Z. A. Kroeger & S. E. Rose. 2016. Additional insights into phylogenetic relationships of the Class Ophiuroidea (Echinodermata) from rRNA gene sequences. Journal of Zoological Systematics and Evolutionary Research 54 (4): 269–275.

Matsumoto, H. 1915. A new classification of the Ophiuroidea: with descriptions of new genera and species. Proceedings of the Academy of Natural Sciences of Philadelphia 67 (1): 43–92.

[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.

[PP64] Peres, J. M., & J. Picard. 1964. Nouveau manuel de bionomie benthique de la mer Mediterranee. Recueil des Travaux de la Station Marine d’Endoume, Bulletin 31 (27): 5–137.

[SM15] Sampey, A., & L. M. Marsh. 2015. Kimberley marine biota. Historical data: echinoderms. Records of the Western Australian Museum Supplement 84: 207–246.

[SG93] Simms, M. J., A. S. Gale, P. Gilliland, E. P. F. Rose & G. D. Sevastopulo. 1993. Echinodermata. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 491–528. Chapman & Hall: London.

[S97] Smith, A. B. 1997. Echinoderm larvae and phylogeny. Annual Review of Ecology and Systematics 28: 219–241.

[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.

Stöhr, S. T. D. O’Hara & B. Thuy. 2012. Global diversity of brittle stars (Echinodermata: Ophiuroidea). PLoS One 7 (3): e31940.

[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.

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