Ophiogaleus constrictus ( Hess, 1966 ) Thuy, 2013

Thuy, Ben, 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, pp. 1-242 : 115-118

Ophiogaleus constrictus ( Hess, 1966) comb. nov.

Figs 20 : 8-10; 21: 1

p.p. Ophiacantha? suprajurassica Hess, 1965: 1065 , 1077, figs 12, 14, 43.

Ophiacantha? constricta Hess, 1966: 1031, 1054 , figs 8, 11, 74-75, 78 [figs 76-77 show a different species which is here reinterpreted as Ophiocamax dorotheae sp. nov. (see below)].

non Ophiacantha ? oder Ophiothrix ? sp. – Hess 1960: 417, figs 39-40.

non Ophiacantha ? cf. constricta – Hess & Holenweg 1985: 164, fig. 17 [material re-described by Thuy & Meyer (2013) as Hanshessia trochitophila Thuy & Meyer, 2013 ].

non Ophiacantha ? constricta – Kutscher 1987a: 61, pl. 3 figs 1-2 [material here redescribed as Ophiomalleus beneficarum gen. et sp. nov. (see below)].

Diagnosis

Species of Ophiogaleus gen. nov. with relatively small LAPs displaying moderately coarsely meshed stereom on outer surface; up to ten spine articulations on strongly elevated distal edge proximally sharply bordered by undulose ridge; three poorly defined spurs on outer proximal edge paralleled by up to four well-defined spurs on inner distal edge in proximal LAPs; single large, well-defined spur on outer proximal and inner distal edges in median to distal LAPs; ridge on inner side of LAPs with strongly widened dorsal part with conspicuously pointed dorsal and ventro-proximal angles.

Material examined

GZG.INV.78624, GZG.INV.78625, GZG.INV.78626, GZG.INV.78627, GZG.INV.78628 (7 dissociated LAPs) from sample S1 of Gale (2011); GZG.INV.78629 (14 dissociated LAPs) from sample S2a of Gale (2011); GZG.INV.78630 (72 dissociated LAPs) from sample S2b of Gale (2011), and GZG.INV.78631 (4 articulated arm fragments) from sample S2b of Gale (2011), all from the upper Oxfordian Bifurcatus Zone of Savigna, France; 22 dissociated LAPs from the upper Oxfordian Bifurcatus Zone of Guldenthal, Switzerland, the original material of Hess (1966); 4 dissociated LAPs from the lower Oxfordian Renggeri Member of Chapois, France, the original material of Hess (1965a).

Description

Relatively small LAPs; at least twice higher than wide (proximal LAPs) to nearly as high as wide (distal LAPs); dorsal edge concave as a result of a well-developed constriction; distal edge convex; proximal edge concave in proximal LAPs, with three to four poorly defined, weakly prominent and very slightly protruding spurs, ventral one of which largest and best defined; proximal edge in median and distal LAPs irregularly undulose, with single large, moderately well-defined, prominent and strongly protruding spur probably corresponding to large, ventralmost spur in proximal LAPs; outer surface with moderately coarsely meshed stereom replaced by finely meshed stereom in very narrow band paralleling proximal edge of LAP; trabeculae of moderately coarsely meshed stereom proximally bordering spine articulations merged into very poorly developed vertical striation in a few LAPs; trabecular intersections slightly thickened into granules in ventral portion of distal LAPs. Ten (proximal LAPs) to six (distal ones) large, ear-shaped spine articulations freestanding on strongly elevated ridge; dorsal and ventral lobes of spine articulations merged into continuous volute; spine articulations proximally bordered by narrow, welldefined, undulose ridge; dorsalmost and ventralmost spine articulations slightly smaller than remaining, nearly equal-sized ones; gap separating spine articulations and distal edge very narrow in proximal LAPs, slightly wider and dorsally widening in median to distal LAPs; row of spine articulations strongly protruding ventralwards in proximal LAPs, slightly protruding in median ones and not protruding in distal ones. Ventral edge of LAPs nearly straight; tentacle opening generally invisible in external view. Inner side of LAP with very large, conspicuous, sharply defined, prominent ridge; relatively short, slender, oblique, straight central part of ridge, merged dorsally with very large, vertically elongate (in proximal to median LAPs), near-triangular dorsal part of ridge with concave edges and pointed dorsal and ventroproximal angles; central part of ridge merged ventrally with short, slender, ventro-proximally pointing part not merged with ventral portion of LAP; inner side of distal edge with three to four well-defined, weakly prominent, oval spurs generally with dorsalward increase in size and composed of more densely meshed stereom in proximal LAPs; single spur in median to distal LAPs similar to the ventralmost spur observed in proximal LAPs; inner side of tentacle notch relatively small, nearly vertical, moderately well defined laterally. Very shallow, narrow, moderately well-defined vertical furrow with small, irregularly spaced perforations dorsally bordering tentacle notch in proximal to median LAPs; no furrow in distal LAPs.

Articulated arm fragments: LAPs broadly in contact dorsally and ventrally in proximal to distal arm segments; dorsal arm plates relatively small, bell shaped, with slightly convex distal edge, pointed proximal angle with slightly concave edges; spine articulations meeting mid-radially forming continuous band at least in proximal segments, arm spines thus originally forming fan; ventral arm plates nearly T-shaped, weakly convex distal edge, deeply concave latero-proximal edges and obtuse proximal angle; proximal and latero-proximal edges of ventral arm plates slightly prominent; round, slightly swollen area of coarsely meshed stereom in centre of ventral arm plates; tentacle pores small, covered by single, spatulate, distally widening tentacle scale; arm spines slightly flattened, with coarsely reticulate stereom displaying small thorns, irregular longitudinal row of much larger thorns along both margins of the spines.

Remarks

The concept of Ophiogaleus constrictus comb. nov. has repeatedly caused confusion in the past. This form was originally described by Hess (1966) as Ophiacantha ? constricta when he noted that the type material from the Oxfordian of Switzerland and France previously described as Ophiacantha ? suprajurassica Hess, 1965 included more than one type of LAP. Hess (1966) based the distinction on the higher number of spine articulations and the lack of a vertical striation on the outer surface in O. constrictus comb. nov. These are, indeed, valid differences, yet the concept of O. constrictus comb. nov. was still not sufficiently specific because Hess (1966) also included LAPs which are here reinterpreted as Ophiocamax dorotheae sp. nov. (see Hess 1960, figs 39-40; Hess 1966, figs 76-77). Following this confusion, Kutscher (1987a) described dissociated LAPs from the Callovian of Germany as Ophiacantha ? constricta; these markedly differ from the holotype of the species but do have clear features in common with some of the LAPs erroneously included in that species by Hess (1966).

A re-examination of the type specimens, complemented by new, partially articulated, equivalent finds from the Oxfordian of France, has enabled a consistent reinterpretation of Ophiacantha ? constricta. Thanks to Hess’s (1966) careful choice of the holotype (a single well-preserved proximal LAP, rather than a less distinctive median LAP or a series of LAPs), the species in question is now unambiguously identifiable. It is chosen as the type species of Ophiogaleus gen. nov., an assumedly close relative of extant Ophiacantha (see above), since it is known from numerous well-preserved specimens, including articulated arm fragments, and most typically displays the distinctive features of the genus.

Occurrence

Early to Late Oxfordian of France and Switzerland.

Figures

Fig. 20. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views and articulated arm fragment. 1-2. Ophiogaleus dorecki (Hess, 1962) comb. nov. from the late Pliensbachian (Early Jurassic) of Seewen, Switzerland. 1. NHMB M11214, proximal LAP. 2. NHMB M11215, distal LAP. 3-5. Ophiogaleus stans sp. nov. from the early Bathonian (Middle Jurassic) of La Pouza, France. 3. GZG.INV.78615 (holotype), proximal LAP. 4. GZG.INV.78616 (paratype), median LAP. 5. GZG.INV.78617 (paratype), distal LAP. 6-7. Ophiogaleus sp. nov. innom 2 from the Callovian (Middle Jurassic) of Jumara, India. 6. GZG.INV.78619, proximal LAP. 7. GZG.INV.78620, distal LAP. 8-10. Ophiogaleus constrictus (Hess, 1966) comb. nov. from the late Oxfordian (Late Jurassic) of Savigna, France.8. GZG.INV.78624, proximal LAP. 9. GZG.INV.78625, distal LAP. 10. GZG.INV.78626, proximal arm fragment in ventral (a) and dorsal (b) views. One common scale bar per species except for 10.