Neoasteroidea Gale, 1987.
Spinulosida Perrier, 1884.
Remarks. The Spinulosida, as defined by Gale (2011a, text-fig. 20) incorporates the families Asterinidae and Solasteridae, plus the Velatida. The close relationship of the Asterinidae and Solasteridae has also been demonstrated from molecular data (Matsubara et al. 2004; Janies et al. 2011; Mah and Foltz 2011b). The Spinulosida evidently split into two clades early in their history; one includes the extinct Plumasteridae (Gale 2011b) and the Jurassic to present-day Solasteridae. The other clade includes the Asterinidae and Jurassic Tropidasteridae. Evidently, this gave rise to the velatid clade (see above, and Fig. 18). This last relationship is in conflict with molecular phylogenies (e.g., Feuda and Smith 2015).
Chevronida nov.
Diagnosis. Spinulosida in which plate-roofed interradial channels extend from the distal surface of the primary interradial ossicles to the proximal surface of the odontophore. Stratigraphical range Hettangian to Recent.
Remarks. The Chevronida nov. comprise Tremasteridae, plus all the Velatida.
Tremasteridae Sladen, 1889.
Diagnosis. Abactinally domed Chevronida nov. in which the adambulacrals are broad and short and the large actinal interareas are constructed of numerous rows of small actinal ossicles, each running from the adradial margin of the adambulacral to the margin.
Remarks. The Tremasterinae is here elevated to family level, and includes Tremaster and Mesotremaster, which appear to be closely related. Protremaster is more derived and is placed in the basal Korethrasteridae (see below). The basic skeletal construction is closely similar between Tremaster and Mesotremaster (compare Fig. 6a–d with 6f; pl. 2 of Hess 1981), but it appears that in M. zbindeni the “chimney” of ossicles forming the actinal portion of the interradial duct in T. mirabilis (see Fig. 6c, left-hand side) has been lost, and that part of the duct is open actinally (Figs. 4k, 6f). Tremasterids are known from the Bajocian to the present day, but probably originated in the Triassic (Fig. 19).
Velatida Perrier, 1884.
Diagnosis. Chevronids nov. in which the actinal surface is constructed entirely from adambulacrals, which extend from the ambulacral grooves to the ambitus (Fig. 7); actinal ossicles are absent.
Korethrasteridae Danielsson and Koren 1884.
Diagnosis. Velatids in which the adambulacrals broaden distally from articulation with the oral to the 3rd or 4th ossicle (Fig. 5g–i), and possess an elongated adambulacral extension. The chevron-floored interradial grooves are open on the actinal surface.
Remarks. Korethrasterids are technically paraphyletic, as they do not include all the descendant taxa (Pterasteridae), but the term provides a useful handle for stem group pterasterids. The group has a long history, dating back to the Hettangian, but suffers from a rather poor fossil record. Undescribed forms of a genus that is close to Peribolaster are present in Cenomanian and Campanian chalks of the Anglo-Paris Basin (Fig. 19).
Protremaster Smith and Tranter, 1985.
Diagnosis. Korethrasterids with short arms and broad interradii, in which the interradial ducts are closed abactinally but open actinally (Figs. 4l, 6e). The abactinal surface is composed of small, robust imbricating ossicles set in diagonal rows.
Remarks. Protremaster is known from a single specimen from the Sinemurian (Lower Jurassic) of Alexander Island, Arctic Peninsula, BAS (British Antarctic Survey) KG 2986.17 (Fig. 6e). This is an external mould of a folded individual which provides excellent morphological detail of both actinal and abactinal surfaces.
Thuyaster gen. nov.
Diagnosis. Korethrasterid in which the arms are narrow, and the actinal surface is constructed from crescentic adambulacrals, which possess a short, arrowhead-shaped adambulacral extension bearing two spine attachment sites. The abactinal ossicles are oval to trapezoidal in outline and possess a central region constructed of coarsely perforate stereom and a margin of finer stereom.
Type species. Thuyaster fontenoillensis sp. nov.
Derivation of name. In honour of the work of Dr Ben Thuy (Luxembourg, Luxemburg) on fossil and living ophiuroids, who drew my attention to the site of Fontenoille which yielded the type material of the type species.
Remarks. Thuyaster gen. nov. differs from the other two basal korethrasterids, Protremaster and Korethraster, in the distinctive morphology of the adambulacral ossicles. It also differs from Korethraster in the absence of a tuft of spines (fascicle) on the abactinal plates.
Thuyaster fontenoillensis sp. nov.
Figure 14a–h, l, n–t.
Diagnosis. As for genus.
Material. Over 150 ossicles, including abactinals, ambulacrals, adambulacrals, a single chevron plate, and orals, from the middle Hettangian (Alsaites liasicus Zone), Fontenoille, southeast Belgium, bed C2 of Delsate et al. (2002).
Types. The adambulacral figured (Fig. 14c, d) is the holotype. NHMUK EE 16,954. The other illustrated ossicles (Fig. 14a, b, e–g, l, n, o–t) are paratypes (NHMUK EE 16,593, 16,595–16,606).
Description. Adambulacral ossicles (Fig. 14a–f, l) are morphologically highly distinctive, and it is possible to place proximal plates in their correct relative positions (Fig. 5g). The plate adjacent to the oral (adamb 1; see Fig. 14a, b) is proportionately narrow and is strongly imbricated by adamb 2. The actinal surface is gently curved and bears four spine pits. Adamb 3 is broad and short (Fig. 14c, d) and the short adambulacral extension is arrowhead shaped. The actinal surface bears four spine pits of which the lateral one is largest. Immediately distal adambulacrals are strongly crescentic and possess a distal spur at the base of the triangular adambulacral extension (Fig. 14f). The extension carries two elongated spine pits. The ambulacrals (Fig. 14g, h) have strongly waisted shafts, and enlarged proximal flanges on the ambulacral heads (compare Gale 2011a, text-fig. 9), but evidently lack distal flanges. The one poorly preserved chevron ossicle (Fig. 14n) has a well-developed proximal process. Several well-preserved oral ossicles are present in the material (Fig. 14q, r); the body of the oral is square and the apophyse is slightly oblique. Two rounded bosses for large suboral spines are present on each plate, and three oral spine bases are present on the proximal margin of the body. The abactinal ossicles (Fig. 14o, p, s, t) are flattened, with a thicker central portion and thinner margins, and have irregular oval to trapezoidal outlines. They imbricated strongly, and the abactinally positioned (originally external) portions of the plates are made up of coarser perforate stereo than the more actinal flanges which were covered by the adjacent plate.
Remarks. Although known only from disassociated ossicles, it is possible to provide a partial reconstruction of the overall morphology of T. fontenoillensis gen. nov., sp. nov. (Fig. 5g). The adambulacrals were relatively narrow in comparison to those of Protremaster or Korethraster, indicating that the arms were also narrow. The abactinal surface consisted of strongly imbricating small plates, similar to those of Korethraster hispidus (Fig. 14m), but these evidently lacked spines completely, rather like those in Mesotremaster zbindeni (Hess 1981, pl. 2).
Becuaster gen. nov.
Diagnosis. A korethrasterid in which the J- shaped adambulacrals bear three rounded adradial spine pits, and three elongated abradial pits.
Derivation of name. After Becu, the region of Andelot-Morval which yielded the type material.
Type species. B. fusiliformis sp. nov.
Remarks. The adambulacrals of Becuaster gen. nov. differ significantly from those of other korethrasterid genera in the distinctive distribution of the spine bases on the adambulacral extension (see below).
Becuaster fusiliformis sp. nov.
Figures 12c, d, 17h, i, m.
Diagnosis. As for genus.
Material. Ten adambulacral ossicles and five probable abactinal ossicles from the lower Oxfordian Marnes à C. renggeri, praecordatum to bukowskii subzones at Andelot-Morval, 6 km east of Saint-Amour, Départment du Jura, France. Samples And1–5, And 9, And 10; common only in And 9.
Types. The adambulacral figured here (Fig. 12c, d) is the holotype, NHMUK EE 16,587. The other figured adambulacrals (Fig. 17h, i, m) are paratypes. 17H, NHMUK EE 16,635; 17I, NHMUK EE 16,636; 17M, NHMUK EE 16,639.
Derivation of name. After the pistol-like appearance of the adambulacrals, hence fusil, pistol, and formis, in the shape of.
Description. The adambulacrals (Figs. 12c, d, 17h, i, m) are asymmetrically crescentic, J-shaped and three to five times taller than wide. The adradial part of the ossicle is angled to the axis, slightly curved, and carries four large, prominent, horseshoe-shaped spine bases. The adambulacral extension is of variable width, and bears two further spine bases, which are bifid and elongated. The most abradial spine base bore the large actinolateral spine. A rounded adambulacral extension articulation (adma, see Fig. 1g) is present on the more proximal ossicles (e.g., Fig. 17h, m). In the most proximal adambulacrals (Figs. 12c, d, 17h, m) the adambulacral extension is shorter; in more distal ones it is longer (Fig. 17i). The inner (abactinal) surface of the adambulacrals is flat (Fig. 12d), and the facet for insertion of the adadm muscle is well developed (compare with Gale 2011a, pl. 9, fig. 10, for Remaster gourdoni; compare also Fig. 12f for Peribolaster lictor). A possible radial abactinal is also illustrated here (Fig. 8f); this is four lobed, with a low central prominence constructed of ribs of stereom. The proximal two processes are shorter and blunter.
Remarks. Becuaster fusiliformis gen. nov., sp. nov. is probably closest to Peribolaster in overall adambulacral morphology, in the crescentic form of the ossicle (compare Fig. 12c–f). However, it differs in the raised spine bases, and the presence of a spine base halfway along the adambulacral extension. The possible abactinals (Fig. 8f) are also similar to those of Peribolaster (Fig. 15g).
Pterasteridae Perrier, 1875.
Diagnosis. Velatida in which the primary radial ossicles carry a vase-shaped pedicel. Muscles are present between abactinals and abactinal-chevron ossicle contacts.
Included genera. Gale 2011a, Longwyaster gen. nov., Propteraster gen. nov., Hansaster gen. nov., Pteraster, Benthaster, Calyptreaster, Diplopteraster, Hymenaster, Hymenasteroides and Euretaster.
Remarks. Definition of the family is based upon arbitrary criteria, because the transition between korethrasterids and pterasterids is gradual and represented by the progressive acquisition of characters (Figs. 18, 19). However, the presence of muscularised abactinal ossicles and enlarged primary radials, presumably supporting an osculum, is an indication that the respiratory mechanism characteristic of extant pterasterids (Nance and Braithwaite 1981) was at least in part functioning in fossil forms.
Longwyaster gen. nov.
Diagnosis. A basal pterasterid, which displays weak muscularisation of the abactinal ossicles, and in which the primary radial ossicle bears a low, broad pedicel.
Type species. Longwyaster delsatei sp. nov.
Remarks. Longwyaster gen. nov., from the lower Bajocian, is the oldest known pterasterid. Only the primary radial and a few other abactinal ossicles bear pedicels; the radial ossicles and most abactinals possess a raised area carrying a ring of spine bases and are similar to abactinals in Peribolaster.
Longwyaster delsatei sp. nov.
Figure 16a–s.
Diagnosis. As for genus.
Origin of name. For Dominique Delsate, who discovered and described the type locality.
Material. Over 75 ossicles, including adambulacrals, ambulacrals, orals, abactinals, chevron ossicles and actinolateral spines from a road cutting on the N52 near Longway (Ardennes, France); lower Bajocian (Laeviuscula Zone; Delsate 1993; Thuy 2015). Samples were recovered from the lower of two marl beds described by Delsate (1993) and referred to the Longwy Formation.
Types. The figured adambulacral ossicle (Fig. 16o) is holotype, NHMUK EE16628. The other figured ossicles (Fig. 16a–n, p–s) are paratypes, NHMUK EE 16,617–16,627, 16,629–32.
Description. The adambulacrals (Fig. 16o–q) are flat, and the adambulacral extension is set at an angle of about 120° to the body of the ossicle. The body of the ossicle bears two to three spine bases, and a further elongated spine attachment is present on the abradial end of the extension. The ambulacrals (Fig. 16r, s) have an enlarged, triangular proximal head, and a small, broken distal flange. The area of articulation with the adambulacrals is divided into a flat actinal region separated from the abactinal part by a concave surface. The oral ossicles (Fig. 16k, l) are poorly preserved, but show a square oral body, bearing one or two suboral spine attachment surfaces, and a tall, vertical apophyse. The abactinal ossicles show diverse morphologies. The primary radial ossicles (Fig. 16g, h) have well-developed lateral processes, and a single, broad distal process. The pedicel is low, robust, and expands slightly abactinally; the abactinal surface is concave.
The radial ossicles of the arm (Fig. 16b, j) are symmetrical and bear four processes, of which the proximal pair are shorter. The abactinal surfaces of the tips of the radials are concave and constructed of fine stereom, suggestive of some muscularisation. The radials possess a proximally situated low swelling which bears a crown of small bosses for spine articulation. Abradially positioned abactinal plates are asymmetrical (e.g., Fig. 16a, c, d, m) and also have a swollen central region with spine attachment bosses. The chevron plates (Fig. 16e, i) are Y-shaped, and the actinal surfaces close to the interradius are constructed of fine stereom, suggestive of muscle attachment. Unfortunately, the radially directed processes, which contact the abactinals, are insufficiently well preserved to permit the identification of muscle insertion sites. A single actinolateral spine was found (Fig. 16n), which expands distally, and bears longitudinal rows of perforations. This spine is very similar to those seen on the holotype of Savignaster wardi (see Gale 2011a, pl. 21, figs. 1, 2, 5).
Remarks. Longwyaster delsatei gen. nov., sp. nov. shares similarities with Savignaster wardi, notably the morphology of the primary radial ossicles, in which the pedicel is relatively low and broad (compare Fig. 13a, d with Fig. 16 g, h), but it has a short spur in S. wardi. The chevron plates are also similar in their overall construction (compare Fig. 13k, l with Fig. 16e, i), as are the adambulacrals, adambulacrals and the actinolateral spines. The genera differ most importantly in the morphology of the abactinals, which in S. wardi all bear a vase-shaped pedicel (Fig. 13g, i, j), similar to those present in some extant pterasterids. The abactinals of L. desatei gen. nov., sp. nov., bear a low, rounded protuberance, of variable height (compare Fig. 16a, d with Fig. 16c, f, m), which carries a ring of spine bases on the top; these are rather similar to abactinals in the korethrasterid Peribolaster (Fig. 15g).
Savignaster Gale, 2011a.
Diagnosis. Pterasteridae in which the radials abactinals are trapezoidal and bear a short, abactinally expanding pedicel; primary radial ossicle carries a short proximal spur.
Type species. S. wardi Gale, 2011a, by subsequent designation herein.
Savignaster wardi Gale, 2011a.
Figure 13a–r.
2011a Savignaster wardi Gale, p. 88, pl. 21, figs. 1, 2, 5; pl. 22, figs. 1–3; pl. 23, figs. 3–8, 11, 12; pl. 24, figs. 4–8, 10–11, 10–16.
2011b Savignaster wardi Gale; Gale, p.82 fig. 12a–i.
Diagnosis. As for genus.
Types. The articulated individual figured by Gale (2011a, pl. 21, figs. 1, 2, 5; pl. 22, figs. 1–3) is the holotype, NHMUK EE 13,610. Paratypes include isolated ossicles (NHMUK EE 13,611–13,632), all from the upper Oxfordian bifurcatus Zone of Savigna, Jura, France.
Remarks. There is little to add to the detailed description of Gale (2011a). More material of this species has since been obtained from Savigna, including, importantly, a primary radial ossicle (Fig. 13a–d; NHMUK EE 16,589). This has a short, abactinally expanding pedicel with a flat upper surface, surrounded by spine attachment scars, and a short proximal spur, into which muscles depressing the crown of spines must have inserted. The structure is, therefore, broadly similar to that of pterasterids which possessed a powerfully functioning osculum (compare with Fig. 9). However, the primary radial is only weakly muscularised, and an osculum, therefore, was weakly developed, if present at all. Gale (2011a) argued that the presence of large, broad actinolateral spines in S. wardi, similar to those in Remaster, precluded the possibility that a canopy was present.
Hansaster gen. nov.
Diagnosis. Pterasteridae in which the adambulacrals possess an elongated extension, and in which the base for the apertural spine is widely separated from those supporting the adambulacral spine membrane. The primary radials bear a proximally sloping face for spine articulation and a prominent proximal spur.
Type species. Hansaster trimbachensis (Gale, 2011a).
Derivation of name. In honour of the late Hans Hess of Basel.
Remarks. In many respects, H. trimbachensis is remarkably similar to extant species of Pteraster, in the overall development of the abactinal ossicles, ambulacrals, chevron ossicles and the mouth frame (see Figs. 8, 9, 10). However, the primary radial ossicles (Fig. 9a, b, f–j) display a number of important differences from those of extant Pteraster, most notably in the possession of a large, triangular, proximally sloping surface for attachment of spines supporting the osculum, and a prominent spur on the proximal margin, for insertion of the muscles depressing these spines. In all extant Pteraster examined (> 10 species) the spines attach to the narrow, crescentic, flattened summit of the primary radials, and the depressor muscles insert into a cavity on the proximal surface of the pedicel (Fig. 9m, n). Differences in the adambulacrals are also significant.
Hansaster trimbachensis (Gale, 2011a).
Figures 8a–c, e–l, o, 9a, b, f–h, 10c–e, i, j, m, o, p, q, s, t,12a, b, g, h, 17a–e.
2011a Savignaster trimbachensis Gale, p. 92, pl. 23, figs. 1, 2.
Types. The large adambulacral figured by Gale (2011a, pl. 23, figs. 1, 2) is the holotype, NMB M 11,143, from the upper Oxfordian at Rumperl, southwest of Trimbach, near Olten, Canton Solothurn, Switzerland.
Material. The species is abundant at Andelot-Morval in the basal Couches de Passage (bukowskii Zone), the level of sample And 5 (18–19 m; Fig. 20a). This material includes 15 orals, 3 circumorals, a single odontophore, 15 adambulacrals, 10 ambulacrals, 2 primary interradials, 4 primary radials, 22 abactinals and 3 interradial chevron ossicles. From Trimbach comes a single specimen each of an adambulacral and ambulacral, and from the Plettenberg near Dotternhausen, southern Germany, there is one adambulacral.
Description. Adambulacrals (Figs. 12a, b, g, h, 17a–e) are J-shaped and the long adambulacral extension is angled to the body of the ossicle. The ossicles are flattened and imbricated strongly. Two to three crater-shaped spine bases, arranged in an arc, are set on the adradial margin of the plates; these bore similar spines supporting an adambulacral membrane (Fig. 1h). An elongated spine base, set on the proximal margin of the ossicle, and separated from the adradial arc, probably carried the apertural spine (Fig. 1h). A short distal process on the base of the extension (e.g., Fig. 17a, b) carries the adamb extension muscle (adexm). The adjacent adamb extension articulation (adexa) is variable in size and shape (compare Fig. 12a, g). The elongated adamb extension carried a large actinolateral spine on the abradial margin, onto which a muscle inserted.
The ambulacrals (Fig. 8b, c, i) have waisted shafts and strongly asymmetrical heads. The proximal flange is enlarged and triangular, and a short distal flange is present. The ambulacral base expands abradially, and a concave region for articulation with the adambulacral us present. The dentition is concentrated on a central process. The chevron ossicles (Fig. 10m, o, q, t) are broken but compare well with those found in Pteraster (Fig. 10n, r). Plates with an abactinal position have elongated interradial processes (Fig. 10m, q) and thin lateral processes to contact abactinals. Chevrons with a lateral position have shorter lateral processes (Fig. 10t). Finally, plates positioned actinally, adjacent to the odontophore (Fig. 10o) have a single lateral process. Plates from the mouth frame include oral ossicles (Fig. 10i, j), which possess a trapezoidal body and an obliquely inclined apophyse. The oral body bears a rounded attachment site for a single, large, suboral spine, and the proximal margin carries a row of five closely spaced bases for oral spines. The circumoral ossicles (Fig. 8j, k) have an elongated, vertically orientated distal process, and a very short proximal process. The body of the ossicle is robust. A single odontophore was recovered (Fig. 10c–e), which is rectangular in actinal/abactinal view (Fig. 10c, d) with two wing-like lateral processes, which on the actinal surface (Fig. 10d) acted as attachment sites for the oral-odontophore muscles. The distal end (Fig. 10c) had an articulation structure which contacts the most proximal chevron ossicle.
The primary radials from Andelot-Morval are remarkably well preserved (Fig. 9a, b, f–h), and have a four lobed basal structure (bp), and a tall, abactinally expanding pedicel column (co), divided into a shaft and head. The distal surface of the pedicel bears weak ridges and grooves, and is weakly convex. The proximal surface is triangular, and slopes down towards a proximal spur; it bears irregular grooves and ridges (Fig. 9b, h) which must have supported an array of spines. The spur forms a blunt projection near the base of the proximal surface (Fig. 9g), onto which the muscle fibres depressing the spines inserted. The other abactinal ossicles (Fig. 8a, e, g, h, l, o) are delicately constructed and carried very tall, narrow pedicels (Fig. 8g, h). The radial ossicles (Fig. 8l) are four lobed and symmetrical, with elongated proximal processes and shorter distal ones. The abradial abactinals are less symmetrical (Fig. 8a, g, o). The articulating basal processes of abactinals bear facets for insertion of interabactinal muscles (e.g., Fig. 8l, bottom right).
Remarks. In many ways, Hansaster trimbachensis closely resembles a living species of Pteraster; the abactinals have a similarly delicate construction with large spaces between for papulae, and the tall pedicels must have supported a canopy (compare abactinals in Fig. 8). Similarly, the chevron ossicles and mouth frame ossicles are nearly identical. However, two significant differences exist. Firstly, and importantly, the primary radial ossicles appear similar between Pteraster and Hansaster gen. nov. in distal view (Fig. 9a, f, k), but the proximal surfaces and muscle insertion sites are very different. In Pteraster corynetes (Fig. 9l, m) and P. temnochiton (Fig. 9n) the spines surrounding the osculum are restricted to the crest of the ossicle, and the muscles depressing these spines run down and insert into a cavity on the spur. In Hansaster gen. nov. (and Propteraster gen. nov., see below) the oscular spines were attached across a large triangular surface which sloped proximally (Fig. 9b, g, h), and the muscles depressing these must have attached to the outside of the spur beneath. Secondly, there are minor differences in the morphology of the adambulacrals. The group of spine bases which probably supported the adambulacral spine membrane (see Fig. 1h) can be identified in H. trimbachensis (e.g., Fig. 12g). The spine base of the apertural spine can also be identified, but it is in a slightly different position to that in living pterasterids, in which it is closer to the adambulacral extension (Fig. 12m, n). A well-developed adamb extension articulation (adexa) is present in both Hansaster gen. nov. (Fig. 12g) and Pteraster (Fig. 12m, n), but the adamb extension muscle (adexm) appears to be smaller in the Jurassic forms. However, this may be a matter of preservation, as the muscle is set on a thin, fragile flange.
Propteraster gen. nov.
Diagnosis. Pterasterids characterised by very tall, slender vase-shaped primary radials, which possess an elongated waist. Adambulacrals with short adex, flattened form, and apertural spine positioned on proximal margin of ossicle.
Type species. P. amourensis sp. nov.
Remarks. Propteraster gen. nov. differs from existing pterasterids in the tall form of the primary radial ossicles and the position of the apertural spine on the adambulacrals. From Hansaster gen. nov. it differs in the short adambulacral extension and the well-developed row of spine bases on the proximal, adradial margin.
Propteraster amourensis sp. nov.
Figures 9c–e, i, j, r, 10a, b, 12i, j, 17f, g, j-l.
Material. Five adambulacral ossicles, three orals and five primary radial ossicles from samples And 7–10, Marnes à C. renggeri, C. praecordatum Zone, Andelot-Morval (Fig. 20a). The orals and primary radials are associated with the adambulacrals and all are thought to belong to the same taxon.
Types. The well-preserved adambulacral (Figs. 12 i, j, 17f, g) is the holotype, NHMUK 16,588, from sample And 7. The other figured adambulacral ossicles are paratypes; Fig. 17j, k NHMUK EE 16,637. Figure 17l, NHMUK EE 16,638.
Derivation of name. After Saint-Amour, the neighbouring town to Andelot-Morval (Fig. 20b).
Description. The adambulacrals (Figs. 12i, j, 17f, g, j–l) are obliquely flattened and have a long, gently curved proximal margin and a short adambulacral extension. The adradial proximal margin bears three to five, closely spaced, rounded spine pits, set on a slightly raised ridge; these presumably carried the adambulacral spine membrane (see Fig. 1h). The most abradial spine pit on the proximal margin is separated from the others and has a different orientation (Fig. 17j), as it is directed abradially. This carried the apertural spine (see Fig. 1h). The adambulacral extension is short and carried a single actinolateral spine at its abradial extremity. A well-developed adexa surface is present, and a very narrow strip of stereom on the distal border of the ossicle (Fig. 17j) provided an insertion site for the adexm.
The oral ossicles associated with the adambulacrals (Fig. 10a, b) have a highly distinctive morphology. The oral body is rhombic, the apophyse tall and vertically orientated. Two suboral spine attachment sites, of different sizes, are present. On the proximal margin, five small attachment sites for oral spines are present.
The primary radial ossicles associated with the adambulacrals (Fig. 9c–e, i, j, r) are tall (up to five times taller than the maximum width), slender, waisted and vase shaped. The basal portion is only preserved on one specimen (Fig. 9c–e) and the processes are broken away. The proximal surface of this specimen (Fig. 9e) carries a spur, which is asymmetrical and displaced to one side. The abactinal surface is triangular and slopes proximally; it has ridges and grooves for spine articulation. The other specimens (Fig. 9i, j, r) are broken abactinal fragments of very tall, strongly waisted primary radials.
Remarks. The adambulacral ossicles are remarkably similar to those of some living species of Pteraster (compare Fig. 12i and m) in their shape, possession of a row of spines to support the membrane on the proximal, adradial margin, the short adamb extension and the very flattened form of the ossicles. They differ in the position of the apertural spine, which in living Pteraster is set close to the base of the adamb extension (Figs. 11j, 12m, n), but in P. amourensis gen. nov., sp. nov. is positioned on the proximal margin (Fig. 17f, j, l). They differ also in the relative development of the flange which bears the adex muscle. In living Pteraster (Fig. 12m, n) this is prominent and relatively large, but it appears as a very narrow strip in P.amourensis (e.g., Fig. 17j). As in Hansaster gen. nov., this may simply be a preservational difference. The primary radials, however, differ considerably from those of any of the twenty or so living pterasterids which I have examined, in their very tall pedicels.
Pterasteridae? indet.
Figure 15a–f, h–l.
Material. 25 ossicles, including chevron plates, ambulacrals, abactinals, circumorals and orals from a construction site for a lorry park adjacent to dual carriageway N43, Sedan, Ardennes. Most materials were obtained from the 2–4 m level; Pliensbachian, Prodactylioceras davoei Zone (for details, see Thuy et al. 2011).
Description. The Sedan site yields abundant asteroids of the families Plumasteridae and Tropidasteridae (Thuy et al. 2011), both articulated fragments and loose ossicles. Less common are forcipulatid asteroid ossicles, and a range of ossicles which originate in velatid starfish. However, the absence of the important adambulacrals and primary radial ossicles makes these hard to place taxonomically. They include chevron ossicles (Fig. 15a–e), which are well differentiated into more symmetrical, abactinally positioned forms (Fig. 15a–c) and asymmetrical, more actinal ones (Fig. 15d, e). The terminal depressions on the lateral processes of some chevrons which contacted abactinal ossicles (Fig. 15a–c; compare with Fig. 4f) is suggestive of the presence of muscles linking these with the abactinal ossicles, as in Longwyaster gen. nov. (Fig. 16e, i) and Savignaster (Fig. 13k, l). The single four-lobed abactinal radial ossicle (Fig. 15f) which has a low, central boss, is similar to those of Longwyaster gen. nov. (compare with Fig. 16b, j). The delicately constructed single circumoral ossicle (Fig. 15k) is comparable with circumorals attributable to Hansaster gen. nov.(compare with Fig. 8k). However, suggestive these comparisons are, none of the ossicles are entirely diagnostic of the Pterasteridae, so their affinities will remain uncertain, at least for the time being.