Class Ophiuroidea Gray, 1840
Order Ophiuridea Müller & Troschel, 1840
Family Ophiomycetidae Verrill, 1899
Diagnosis: Ophiuroids with highly flexible disc, covered by thin scales and often dorsoventrally elongated or sack-like; radial shields strongly reduced or absent; arms capable of being raised vertically above disc; oral plates commonly beset with multiple rows of papillae; some forms with highly distinctive parasol-shaped arm spines.
Genus Ophiotholia Lyman, 1880
Ophiotholia aurora sp. nov, Fig. 3
Etymology: from “Aurora”, the Roman goddess of the dawn, in reference to the early occurrence of the new species in the fossil record.
Diagnosis: Species of Ophiotholia with at least seven arm spines, and with ventral arm plates in contact in proximal arm segments.
Locus typicus: Schinznach, Canton Aargau, Switzerland.
Stratum typicum: Upper Hauptrogenstein Formation, Parkinsoni Zone, upper Bajocian.
Description: M11202 is an articulated specimen exposing the jaws and three nearly complete arms. Dorsal disc covered by arms. Thin, small, round scales discernible between proximal arm segments, suggesting a tall, cone-shaped dorsal disc. Very few, small spines, four to five times longer than wide, scattered on dorsal disc scales. Jaws forming a conspicuous, widely gaping ring. Oral plates large and thick, height nearly equal to width, tallest proximally. Lateral and ventral edges of oral plates beset with numerous large papillae, at least ten per pair of oral plates; the proximalmost and lateralmost papillae blunt, spine like, four to five times longer than wide, slightly flattened; papillae becoming increasingly spatulate distalwards; distalmost pair of papillae very large and conspicuously paddle shaped, widest at the tip, with fine longitudinal striation. No teeth or apical papillae preserved. Dental plate entire, slender, wedge shaped, with single series of small tooth sockets. Ventral interradial areas narrow and mostly hidden by oral papillae; outlines of oral and adoral shields not seen.
Three arms exposed, nearly complete, raised vertically above disc. Arms 1.5 mm wide near base. Longest arm length preserved 14.6 mm. Ventral arm plates large, with strongly concave lateral edges and gently convex distal edge; proximal ventral arm plates nearly as long as wide and with conspicuous longitudinal groove; distal ones slightly elongate and without groove. Ventral arm plate of proximalmost arm segment with deep proximal notch. Ventral arm plates in contact in proximal arm segments, and separated by lateral arm plates in median and distal segments. Tentacle pores very large, developed as interplate openings throughout the arm, covered by two blunt, spatulate scales in proximal and median arm segments, and probably by a single scale in distal segments. Lateral arm plates rather massive, slightly bulging distally, with conspicuous tentacle notch and protruding ventro-proximal tip. Ornament of outer surface consisting of coarse granulation or coarsely reticulate stereom. Proximal lateral arm plates taller than wide, distal ones slightly elongate. Row of spine articulations vertical, on slightly elevated distal portion of lateral arm plate. At least seven arm spines in proximal arm segments, slightly longer than one arm segment, flat; most arm spines of lanceolate outline: slender near the base, widest in the middle of the distal half, and with pointed tip. At least five arm spines in median segments and three in distal ones. Single, poorly preserved parasol-shaped spine discernible on one of the distalmost segments, nearly equalling half the length of an arm segment, attached to the middle part of the lateral arm plate. Dorsal side of arms not exposed.
The most striking character of M11202 is that the arms are raised vertically above the disc. Only four extant ophiuroid genera are known to display this extraordinary feature: Ophiomyces Lyman, 1869, Ophiotholia Lyman, 1880, Ophiohelus Lyman, 1880 and Ophiothauma H.L. Clark, 1938. Of these, only Ophiotholia presents the combination of parasol-shaped spines in distal arm segments and oral papillae on both lateral and ventral edges of the oral plates seen in M11202. A total of six species are currently considered valid in the genus Ophiotholia (Stöhr & O’Hara 2007), and similarities to the Middle Jurassic specimen are so strong that separation on the genus level would seem arbitrary rather than based on sound morphological differences. Particularly striking are the similarities in shape and arrangement of oral papillae to Ophiotholia spathifer (Lyman, 1879) and O. mitrephora H.L. Clark, 1910) and the presence of lanceolate arm spines to O. gibbosa Litvinova, 1992. Although assignment of the Hauptrogenstein specimen to an extant genus creates an excessively long stratigraphic generic range of some 160 myr, it effectively expresses the astonishing morphological similarity between the Jurassic and the extant forms. At the species level, M11202 differs from the modern species in the higher number of arm spines and i having ventral arm plates in contact in proximal arm segments. Since no comparable fossil form is known to date, we erect a new species for the Hauptrogenstein specimen.
The systematic position of the genera Ophiomyces, Ophiotholia, Ophiohelus and Ophiothauma has been a matter of debate ever since the discovery of the first representatives in the late nineteenth century. Lyman (1880) already pointed out that these forms stood quite apart from the other ophiuroids. Verrill (1899) proposed the new family Ophiomycetidae to include all forms with arms raised vertically over the disc known at that time, but Koehler (e.g. 1904, 1922) was the only one to adopt this view. In Clark’s (1915) standard compilation, Ophiomyces, Ophiotholia and Ophiohelus were considered to be members of the Ophiacanthidae. This assignment has been generally adopted since (e.g. Fell 1960). Even following Paterson’s (1985) revision and subdivision of the Ophiacanthidae, these genera were treated as ophiacanthids, albeit as members of a separate subfamily, the Ophiohelinae. For the first time, Martynov (2010) challenged the ophiacanthid affinities of the ophioheline genera, referring to fundamental differences in spine articulation morphology. He failed, however, to propose an alternative classification for the former Ophiohelinae.
The discovery of Ophiotholia in sediments as old as Middle Jurassic brings a new perspective to the debate. In fact, the astonishing similarity between the Jurassic and the modern forms suggests that former ophiohelines have been a morphologically highly distinctive and conservative lineage since at least 160 myr. Along with their unique morphology, unlike that of any other ophiuroid lineage, the long stratigraphic range of Ophiotholia strongly suggests that the former ophiohelines should be separated from the remaining ophiuroids on a higher level than subfamily. We, therefore, propose to resurrect Verrill’s (1899) Ophiomycetidae to accommodate Ophiomyces, Ophiotholia, Ophiohelus and Ophiothauma, pending a revision of ophiuroid phylogenies to substantiate further the position and the level of separation of the lineage with respect to other ophiuroid groups.
Family Ophiacanthidae Ljungman, 1867
Genus Hanshessia nov.
Etymology: named in honour of Hans Hess (Binningen, Switzerland) for his continuing contributions to echinoderm palaeontology, his pioneering work on the Hauptrogenstein echinoderms and for introducing both authors to the ins and outs of ophiuroid palaeontology.
Type, and only known, species: Hanshessia trochitophila sp. nov.
Diagnosis: Ophiacanthid ophiuroid with large, near-circular radial shields, numerous, granule- to stump-like oral papillae covering the oral plates and adoral shields in multiple rows, relatively small tentacle pores covered by a single, very large, leaf-like scale pointing to the arm midline and perpendicular to the axis of the arm, up to 11 arm spine articulations increasing in size dorsalwards.
Hanshessia trochitophila sp. nov.
1985 Ophiacantha? cf. constricta Hess (1966): Hess & Holenweg (1985), pp. 164-166, fig. 17.
Etymology: from “trochos”, Greek for wheel and sealily and the Latin suffix “philus”, meaning “loving”, in reference to the fact that the new taxon is found in close association with stalked crinoids.
Additional material: M11203.
Diagnosis: as for genus.
Locus typicus: Quarry Egg near Auenstein, Canton Aargau, Switzerland.
Stratum typicum: Upper Hauptrogenstein Formation, Parkinsoni Zone, upper Bajocian. Description of holotype: M9765 is a fragment of an articulated disc with two arms preserving proximal and, in one case, median segments. Originally on a large slab with articulated individuals of Pentacrinites dargniesi Terquem & Jourdy and exposing the dorsal side only, the ophiuroid specimen was detached from its matrix to enable examination of both dorsal and ventral sides.
Reconstructed disc diameter 15.4 mm. Disc originally circular in outline, dorsal side covered by small, round plates, very densely beset with large, conical spines, up to eight times longer than wide, bearing minute thorns. Spines longest in disc centre, becoming shorter towards disc edge. Radial shields stout, nearly circular, about one-third of disc radius, completely separated by round disc scales, surrounded and partially covered on their margins by short disc spines and stumps, two to four times longer than wide. Ventral interradial areas with small, round disc scales similar to those of the dorsal disc, beset with disc stumps and spines, two to five times longer than wide. Jaws nearly as wide as long, densely covered laterally and ventrally with multiple rows of small stump- to granule-like papillae, at most two times longer than wide, longest near apex of jaws. Single major apical papilla, triangular to tetrahedral, several times larger than oral papillae, followed dorsally by single row of slightly larger, pointed, tongue-like to tetrahedral teeth. Adoral shields relatively short, approximately two times longer than wide, abutting proximally, not separating oral shield from first lateral arm plate, covered by oral papillae. Oral shield arrow shaped, with slightly obtuse proximal angle and strongly concave latero-distal edges, slightly wider than long.
Two arm fragments visible, preserving proximal and median segments. Ventral arm plates slightly wider than long, widest distally, with strongly convex distal edge and notched lateral edges, separated by lateral arm plates on all visible arm segments. Tentacle pores medium sized, smaller than two times the width of the ventral arm plate, covered by a single very large, leaf-like scale pointing to the arm midline and perfectly perpendicular to the axis of the arm. Three proximalmost ventral arm plates approximately two times wider than long, grooved proximally. Dorsal arm plates fan- to bell-shaped, slightly wider than long, with pointed proximal angle, slightly concave lateral edges and convex distal edge; abutting on all observable arm segments except for the distalmost preserved (median arm segments). Lateral arm plates several times taller than wide, strongly arched, ventral tip protruding and with conspicuous tentacle notch; outer surface of proximal and median lateral arm plates without conspicuous spurs on the proximal edge or ornament; large, ear-shaped spine articulations with sigmoidal fold in continuous row on large, strongly elevated ridge on distal part of lateral arm plate; ridge only weakly protruding on ventral side of the arms; dorsalmost or second-dorsalmost spine articulation largest; progressive ventralward decrease in size of spine articulations and gaps separating them; at least 10 spine articulations in proximal and median arm segments. Arm spines very large, cylindrical, pointed, finely striated, as long as three to four arm segments; ventral arm spines much smaller than dorsal ones, slightly curved but not developed into hooks on observable arm segments.
Paratype supplements and variation
M11203 is a semi-articulated disc (dd: 10.1 mm) exposing the dorsal surface and preserving proximal portions of at least three arms. The morphology of the dorsal disc and arm skeleton agrees well with that of the holotype. Due to the partial disintegration of the skeleton, vertebrae are exposed and show large, vertical, wing-like muscular fossae and streptospondylous articulation pegs.
The presence of a single row of teeth in combination with large, ear-shaped spine articulations presenting a sigmoidal fold and positioned on a strongly elevated ridge unquestionably places these specimens in the family Ophiacanthidae. Within this family, the specimens fall into the group including the former ophioplinthacines and ophiochondrines, characterised by well-developed disc plates, large radial shields and relatively small tentacle pores, and grouping on top of the large clade of nestled ophiacanthid lineages recently found by Thuy et al. (2012). The combination of large, near-circular radial shields and numerous small, granule- to stump-like oral papillae densely covering the oral plates and adoral shields in multiple rows is unique among these lineages. The peculiar, large tentacle scales pointing to the arm midline are not found in any other ophiacanthid genus either, thus underscoring the unique status of this material. We therefore erect the new genus Hanshessia within the Ophiacanthidae to accommodate the Hauptrogenstein specimens.
A number of Jurassic ophiacanthid species have been described on the basis of dissociated lateral arm plates (Thuy et al. (2012)). Among these, the lateral arm plates of Ophiacantha? constricta Hess, 1966 from the Oxfordian of Switzerland and France share the greatest similarities with the Hauptrogenstein specimens. Hess and Holenweg (1985), who mentioned the above-mentioned specimens for the first time, already noted these similarities and tentatively assigned them to Ophiacantha? cf. constricta. In the lateral arm plates of the Hauptrogenstein specimens, however, the spine articulation ridge protrudes much less strongly ventralwards than in Ophiacantha? constricta, and the spine articulations show a slight but clear dorsalward increase in size. Based on these differences, we consider the Hauptrogenstein to be a distinct species. It cannot be decided on the basis of the material available whether the Hauptrogenstein species and Ophiacantha? constricta are congeneric. In spite of the similarities in lateral arm plate morphology, transfer of O.? constricta to the new genus Hanshessia appears to be premature.
Genus Alternacantha nov
Etymology: name composed of “alternans”, Latin for alternating, and “acantha”, the name of a Greek nymph, literally translating into “thorny”, in reference to the alternating position of the dorsalmost arm spine articulation.
Type, and only known, species: Alternacantha occulta sp. nov.
Diagnosis: Large ophiacanthid with arms displaying a conspicuous alternating pattern in the position of the dorsalmost arm spine articulation, varying between close to the remaining spine articulations and separated by the latter by a large gap; arm spines as long as three arm segments; radial shields thin, oval, as long as one-third of the disc radius or slightly longer; dorsal disc covered by minute spherical granules.
Alternacantha occulta sp. nov.
Figs. 5, 6
Etymology: from “occultus”, Latin meaning “well hidden” in reference to the new species that is almost invisible amongst the dense colonies of crinoids.
1972 Dermocoma wrighti Hess 1964: Hess, pp. 36-39, figs. 39-41; pl. 13, fig. 1.
1985 Dermocoma wrighti Hess 1964: Hess & Holenweg, p. 157, fig. 10.
Additional material: M9599, M9384/1-2 and M11200 (paratypes); M11205 and M9527.
Diagnosis: as for genus.
Locus typicus: Sichtern near Liestal, Canton Basel-Country, Switzerland.
Stratum typicum: Varians beds, middle Bathonian.
Occurence: Lower Hauptrogenstein Formation, Niortense Zone; upper Bajocian; Upper Hauptrogenstein Formation, Parkinsoni Zone, upper Bajocian; Klingnau Formation, Parkinsoni Zone, upper Bajocian; Varians beds, middle Bathonian.
Description of holotype: M9761 (Fig. 5) is an articulated specimen preserving four near-complete arms and exposing the ventral side. Dorsal side of disc embedded in matrix (dd = 6.6 mm). Disc nearly circular in outline. Ventral interradial areas covered by very small, thin scales. Jaws slightly wider than long, beset with a single continuous row of seven leaf-like oral papillae: three to four large, flat, blunt distal oral papillae followed by a single slightly smaller blunt papilla and two to three much smaller, pointed proximal papillae. Tip of jaws with two to three apical papillae similar in size and outline to the middle, medium-sized oral papilla. Teeth of similar size but cone-shaped and pointed. Oral shields very large, wider than long, nearly oval with slightly pointed proximal edge. Adoral shields long and relatively narrow, separating oral shield from lateral arm plates; proximal tips of adoral shields relatively broad, blunt, in contact. Few scattered granules on oral shields, adoral shields and jaws.
Four arms exposed, entangled with stalks and cirrals of the isocrinid crinoid Hispidocrinus leuthardti (de Loriol) and arms of Ophiomusium
ferrugineum. Longest arm preserved almost as long as three times the disc diameter. Ventral arm plates very large, nearly as long as wide (proximal and median arm segments) to slightly elongate (distal ones), widest distally, with pointed proximal edge, gently notched lateral edges and evenly convex distal edge. Ventral arm plates abutting on all observable arm segments. Tentacle openings smaller than half the width of the ventral arm plate, covered by two short, flat, leaf-like tentacle scales on all observable arm segments. Lateral arm plates taller than wide in proximal segments, elongate in distal ones; well-developed constriction, resulting in bulging distal portion of lateral arm plate; ventral portion strongly protruding, with large tentacle notch; outer surface with vertical striation, best developed near spine articulations, fading into finely reticulate stereom towards proximal edge of lateral arm plate; at least two moderately well-defined, prominent and protruding spurs on proximal edge of lateral arm plate; four spine articulations in all observable arm segments, freestanding on bulging distal portion of lateral arm plate, encompassed by gentle notches interrupting the vertical striation of the outer surface; lateral arm plates in contact ventrally underneath ventral arm plates on all observable arm segments; spine articulations large, ear shaped with sigmoidal fold, dorsalward increase in size of spine articulations; position of dorsalmost spine articulation variable, closer to remaining spine articulations or separated from the latter by a considerable gap, irregularly alternating between segments. Arm spines large, cylindrical and almost as long as three arm segments. Dorsal arm plates exposed on distal segments only, fan shaped, more than two times longer than wide, with acutely pointed proximal angle and strongly convex distal edge, separated by lateral arm plates, slightly arched and with fine transverse striation.
Paratype supplements and variation
M9599 [amply figured by Hess (1972)] is a fragment of an articulated disc (reconstructed dd = 18.6 mm) completely free of matrix and preserving the ring of jaws and two arm bases. The ventral disc plating agrees well with that of the holotype. Ventral interradial areas much better preserved, densely covered by minute granules. Jaws beset with a single continuous row of nine to ten oral papillae, including five large, flat, leaf-like distal ones, two medium-sized blunt middle ones and two to three small pointed proximal ones. First ventral arm plate about half the size of successive ones, wider than long, with rounded proximal and lateral edges and pointed distal edge. Following three ventral arm plates with proximal, protruding keel lined on both sides by grooves, best developed on second ventral arm plates, grooves gradually shallowing in third and fourth ventral plates and completely lacking in successive ones. Five arm segments observable, all incorporated into disc, best preserved arm broken at disc edge. Five spine articulations on fourth and fifth arm segments.
Dorsal side poorly preserved. Dorsal disc plates very thin but outline not discernible. One radial shield preserved, oval, slightly longer than one-third of the disc radius. Dorsal disc including radial shield densely covered by small, spherical granules.
M9384/1-2 (Fig. 6b) is a slab containing two large arm fragments, one approximately 65 mm long and exposing the ventral and lateral sides, and one largely covered by matrix and exposing the dorsal side of several proximal to median segments. Ventral and lateral arm morphology agrees well with that of the holotype. Four arm spine articulations on all observable segments. Position of dorsalmost spine articulation alternating between close to the remaining spine articulations and separated from the latter by a large gap. Proximal and median dorsal arm plates in contact, slightly longer than wide, bell- to fan-shaped, with acute proximal angle; straight to slightly convex lateral edges and convex to pointed distal edge, with fine transverse striation; proximal dorsal arm plates clearly arched longitudinally, median ones only slightly arched.
M11200 (Fig. 6a) is an articulated specimen exposing the dorsal side and preserving a major portion of the disc (dd = 10.2 mm) and three arm fragments, the longest of which measures 30.4 mm in length. Overall morphology agrees well with other type specimens. Disc preserving several radial shields in place, oval, approximately 1.8 times longer than wide, equalling one-third of the disc radius, widely separated and apparently covered by fewer granules than remaining disc plates. Outline of jaws discernible underneath relatively thin disc plates impressed on jaws; oral plates relatively short and devoid of lateral wings.
The above-described specimens are unquestionably assignable to the Ophiacanthidae on account of the large, ear-shaped spine articulations positioned on an elevated ridge, the lack of tooth papillae and oral plates that are devoid of lateral wings. Although the exact phylogenetic position within the Ophiacanthidae requires further research, the specimens fall within the group composed of former ophioplinthacine and ophiochondrine genera characterised by well-developed disc plates, relatively large and radial shields which are not bar like, and small tentacle pores (Thuy et al. 2012). Within this group, only Ophiocamax displays a slight alternation in the position of the dorsalmost spine articulation. The main alternation pattern in this genus, however, concerns the position of the largest spine articulation, which is alternately the dorsalmost or the second or third dorsalmost. In addition, Ophiacamax displays spine-like oral papillae arranged in multiple rows and erect tentacle scales enclosing the two or three basalmost tentacle pores. The above-described specimens thus clearly differ from any known extant ophiacanthid.
Striking similarities in disc morphology are shared with the type specimens of Dermocoma wrighti Hess, 1964 from the Bathonian of England. The latter differ mainly in having adoral shields with conspicuously pointed proximal tips and slightly smaller oral shields. The arm skeleton, in contrast, is markedly different. The English specimens display much less strongly bulging distal portions of the lateral arm plates, five spine articulations even in segments not incorporated into the disc, ventral arm plates with a near-straight distal edge, small spine-like tentacle scales in median to distal segments, much shorter arm spines, and, most importantly, no alternation in the position of the dorsalmost spine facet. In spite of the admittedly strong similarities in disc plating, the utterly different arm morphologies, in particular the alternating spine articulation pattern, justify the creation of a new genus.
The close resemblance in disc morphology between Dermocoma wrighti and the present specimens prompted Hess (1972) and Hess and Holenweg (1985) to place their Hauptrogenstein material in that species. While this is most probably true for the specimen in Fig. 2 of Hess and Holenweg (1985), in view of the short arm spines and gently bulging distal portions of the lateral arm plates, all other specimens figured and described by Hess (1972) and Hess and Holenweg (1985) are assignable to the new genus. Examination of the type material of Dermocoma wrighti housed at the Natural History Museum in London (UK) confirmed the presence of ear-shaped spine articulations displaying a sigmoidal fold. This clearly places D. wrighti in the extant family Ophiacanthidae. As a consequence, the family Dermocomidae, as introduced by Hess (1972), should be suppressed.
As already noted by Hess (1972), the specimens described here share a remarkable similarity, especially in terms of alternating spine articulation pattern, with arm fragments described by d’Orbigny (1850) as Ophiurella bispinosa and later redescribed by de Loriol (1872) as Ophiurella royeri, probably on the basis of the same material (Hess 1972). An allegedly closely similar individual from the Oxfordian of France was described by Hess (1960) and assigned to the same species. Examination of Hess’s specimen deposited in the Naturhistorisches Museum Basel suggests that it most probably belongs to the new genus Alternacantha. Yet, transfer of Ophiurella bispinosa (and its probable synonym O. royeri) to Alternacantha awaits re-examination of d’Orbigny’s type material.