Ophiotoma Lyman, 1883

Martynov, Alexander, 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 2697, Zootaxa 2697, pp. 1-154 : 97-101

Genus Ophiotoma Lyman, 1883

Figures 66–70

Ophiotoma Lyman, 1883: 268

Ophiotrema Koehler, 1896b (type species Ophiotrema alberti Koehler, 1896 ): 251

Ophiopora Verrill, 1899 (type species Ophiacantha bartletti Lyman, 1883 ): 39, 43

Type species: Ophiotoma coriacea Lyman, 1883 , by monotypy

Diagnosis. The disk is covered with numerous small, uniform scales, obscured by a moderately developed skin layer. The dorsal disk surface is usually covered with spinelets of various lengths, rarely naked. The radial shields are well-defined, elongated, but concealed under a thin skin layer. The adradial and abradial genital plates are well-defined. The genital slits are long and conspicuous, the genital plates border about half of the slits. The articulation surface of the radial shield is a broad, low elevation. The jaw bears numerous short conical oral papillae similar in shape to the single (or double) apical papillae. The adoral shield papillae and adjacent oral papillae are slightly longer than other oral papillae and not separated by a gap. The half-jaws are relatively high. The adradial sides of the jaws bear a few convoluted folds distally. The dental plate is elongated, without folds, and with a few elongate narrow slit-shaped sockets, placed alternately. The sockets for apical papillae are small and rounded. The teeth are broad, conical to rectangular. There are 1–2 ventralmost teeth. Generally all teeth are similar in shape, but the dorsalmost teeth are usually longer. The oral shield is broadly arrow-shaped with a short distal lobe. The adoral shields have distal wings, proximally tapered. Dorsal and ventral arm plates are well developed. The arm spine articulations are placed at a small angle in relation to the lateral plate. The muscle opening is larger than the nerve opening. There is a voluteshaped perforate lobe, occupying the dorsal and distal part of the articulation. The sigmoidal fold is welldefined. The proximal edge of the spine articulation is entire and does not connect with the main part of the lateral arm plate. The spines are relatively long, rounded, contain small lumens inside, not hooked distally. Several small thin tentacle scales are placed both on the lateral and ventral plates, or absent. The tentacle pores are large. The vertebrae have a narrow keel, abruptly truncated distally; a dorsal medial furrow moderately expressed. The articulation is zygospondylous. The podial basins are of a moderate size.

Material studied. Ophiotoma coriacea Lyman, 1883 , holotype MCZ 2143 ( Figs 66F, G–H); Ophiotrema alberti Koehler, 1896 , 3 syntypes MNHN Ec Os 10380 and 20383 ( Figs 66A–E; 68); ZMMU D–809 and D– 810, one specimen ( Figs 6H–J; 13E, F; 18L–O; 28B; 67A–C); Ophiotrema gracilis Koehler, 1914 , holotype USNM 032301; Ophiotrema tertium Koehler, 1922 , holotype USNM 41150; Ophiotoma bartletti ( Lyman, 1883) , USNM 14675, one specimen, identified by R. Koehler ( Fig. 69); Ophiotoma paucispina ( Lütken & Mortensen, 1899) , USNM E 00699, one specimen, identified by H.L. Clark ( Fig. 70); Ophiotoma assimilis Koehler, 1904 , ZMMU D-807, 16 specimens ( Figs 6F–G; 13D; 28A; 67D–E); Ophiotoma megatreta (H.L. Clark, 1911) holotype USNM 25596; Ophiotrema sp. , 2 specimens MNHN EcOs 22484 and 22485.

Remarks. The composition of this genus has been contentious. H.L. Clark (1915) did not distinguish the genus Ophiotrema , already described by Koehler (1896b), and considered all species within the genus Ophiotoma , whereas Koehler (1914; 1922a), Paterson (1985) and O’Hara & Stöhr (2006) accepted both genera. In the present study, appropriate type material of the type species of both Ophiotoma ( O. coriacea Lyman, 1883 ) and Ophiotrema ( O. alberti Koehler, 1896 ) were studied, but no reliable differences were found. Both O. coriacea and O. alberti share a very similar external appearance. They are both large-sized ophiuroids, with their disks covered by a considerable amount of skin and with embedded oval to elongate radial shields ( Fig. 66). The disk of O. alberti is covered with numerous conspicuous spinelets, whereas O. coriacea possesses very small, hardly conspicuous spinelets, but these differences cannot be considered as generic. The oral frames of both species are also very similar, having the adoral shield and adjacent papillae slightly longer or similar in size to the rest of the oral papillae ( Figs 66D, H). The dental plates of both syntypes of O. alberti and O. coriacea are long, with several large massive teeth. One of the most pronounced differences between O. coriacea and O. alberti is the presence of several small spiniform tentacle scales in the former, placed both on lateral and ventral plates ( Fig. 66C). However, as has already been indicated, the number of tentacle scales of O. alberti varies from 5 to 0 ( Paterson, 1985). The ZMMU specimen of Ophiotrema alberti , otherwise very similar to the MNHN syntypes, completely lacks tentacles scales, except for an ambiguous single small tubercle on the proximalmost segments ( Fig. 67B).

Another species, considered within the genus Ophiotoma , O. assimilis Koehler, 1904 has a smooth disk without spinelets, but also a small single tentacle scale throughout the arms ( Figs 67D, E). The holotype of Ophiacantha megatreta H.L. Clark, 1911 is now considered within Ophiotoma , although it lacks the disk, but additional specimens mentioned by Matsumoto 1917, (see also O’Hara & Stöhr 2006) apparently possess numerous disk spinelets. The arm spine articulations of both Ophiotoma assimilis and O. alberti are similar ( Figs 28A–B). Thus, there are no reliable characters to distinguish these two genera and Ophiotrema is considered as a synonym of the genus Ophiotoma .

Ophiacantha bartletti Lyman, 1883 was considered to be a synonym of the type species of the genus Ophiotoma , O. coriacea by H.L. Clark (1915). But this decision was not supported by Koehler (1922a) and Mortensen (1933a). Verrill (1899) suggested the separate genus Ophiopora for O. bartletti . Type specimens of O. bartletti appear not to have been preserved, since the only “ Ophiacantha bartletti ” present in the MCZ, is the holotype of the true Ophiotoma coriacea Lyman, 1883 , subsequently, and incorrectly renamed by H.L. Clark as “ Ophiotoma bartletti ” ( Figs 66F–H). According to the type description ( Lyman, 1883), Ophiacantha bartletti has well-defined, relatively long spinelets both on dorsal and ventral sides, a sub-rhomboidal oral shield and apparently lacks the tentacle scales. The first two features differ considerably from Ophiotoma coriacea and thus a synonymy with O. bartletti is highly unlikely. Based on the presence of well-defined disk spinelets and some minor features of the oral frame, Ophiacantha bartletti is somewhat similar to the type species of Ophiotrema , O. alberti . Other characters, including arm segments and spine shape are also very different from both O. coriacea and O. alberti ( Fig. 66). In the present study a single available non-type, partially damaged specimen of O. bartletti (USNM 14675), identified by R. Koehler, was examined. The general appearance of the oral shields and arms is similar to the first description by Lyman (1883). The studied arm spine articulations show a typical ophiacanthid pattern, although they differ from O. alberti and O. assimillis ( Fig. 69). Thus, according to both external and microstructural characters O. bartletti is a wellestablished species.

Number of species: 8.