Protorophus hispanicus, Zamora & Smith, 2010
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publication ID |
https://doi.org/ 10.4202/app.2010.0012 |
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persistent identifier |
https://treatment.plazi.org/id/763387F1-FFE1-340D-1142-F881FD4273F2 |
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treatment provided by |
Felipe |
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scientific name |
Protorophus hispanicus |
| status |
sp. nov. |
Protorophus hispanicus sp. nov.
Fig. 2 View Fig .
Etymology: From the Spanish hispano, hispánico in reference to its occurrence.
doi:10.4202/app.2010.0012
Type material: Holotype and only known specimen, part and counterpart preserved as natural moulds in siltstones: MPZ2009 View Materials /1233a, b.
Type locality: Moncayo Natural Park , close to the village of Purujosa (north Iberian Chains, Zaragoza province, Spain) .
Type horizon: Purujosa 3 section (Pur3), level 10, Solenopleuropsis thorali Zone, Murero Formation , Lower Languedocian sensu Álvaro and Vizcaïno, 1998, Middle Cambrian (equivalent to Cambrian Series 3, Stage 5) .
Diagnosis.—As for genus.
Description.—Interambulacra AB, BC, CD, DE, EA following Bell (1976a). Orientation of specimen is based on the identification of a structure we interpret as the periproct. As this structure is in the interray CD in all known edrioasteroids, the other ambulacra are numbered according with this position.
Small (4.3 mm diameter) isorophid−like, circular in plan view, with a discoidal theca clearly separated into a peripheral rim and a central disc; thecal plating without ornament.
Central area of theca covered with large, prominent, oral cover plates that slope upwards towards the middle. Opposite the inferred position of the periproct there are a pair of oral plates to left and right of the U−shaped plate that we identify as left and right anterior orals ( Fig. 2A, C View Fig ). Two further plates sit in interambulacra AB and DE, which are left and right lateral bifurcation plates ( Fig. 2A, C View Fig ). Finally, in the CD interray there are three oral plates, two on the left−hand side and a single plate on the right−hand side, presumably equivalent to the posterior orals and hydropore plate of isorophids. The pattern thus conforms to the standard 2−1−2 symmetrical pattern of other edrioasteroids, although now slightly disrupted. Gonopore and hydropore unknown due to the state of preservation.
There is a single ambulacral flooring plate in each radius. This is a large ossicle with a U−shaped facet in oral view ( Fig. 2A, C View Fig ) and a flat aboral surface. The deep food groove defined by this U−shaped facet faces adorally. Cover plates are relatively large (ca. 250 µm), but lie scattered above the ambulacral plates and their poor preservation preludes detailed description. There are two or three coverplates to each flooring plate. Interambulacral plates few, with three or four preserved in each interray.
The CD interray is the widest and retains a few small lath−like plates that mark the remains of the periproct.
The peripheral rim is composed of 3 to 4 circles of plates that are tesselate on their aboral contact but which imbricate orally. These plates decrease in size towards the outer edge. Ten large peripheral plates, alternately radial and interradial in position, form the inner edge of the peripheral rim. Ten rhomb shaped and slightly smaller secondary peripheral plates are intercalated between each pair of primaries. They are rhomb shaped and slightly smaller. The other peripheral plates rapidly decrease in size distally.
Aboral surface unplated. The aboral surface of peripheral rim plates is flat and smooth and plate boundaries are clearly distinguished ( Fig. 2B, D View Fig ). It occupies ca. 30 % of the radius. Inside the peripheral rim there are two zones, an outer calcified zone that is in contact with the substrate at the same level as the peripheral rim, and an inner zone where plating is elevated away from the surface. Plate boundaries in the outer zone are difficult to discern but a small number of large, flat elements that are approximately oval in outline can be made out. The best defined of these coincide exactly in position with the U−shaped flooring plates. Although this might be a separate calcified surface, it seems more likely that what is observed is the aboral surface of the ambulacral flooring plates and interradial elements that have collapsed onto the substrate. Only the elevated oral plates remain separated from the base, creating the central cavity. The inner face of at least some of the oral cover plates appear to have a spike−like projection ( Fig. 2B, D View Fig ).
Discussion.— Protorophus is unique in having a single large flooring plate to each ambulacrum. This element is flat−based and has a prominent U−shaped notch on its oral surface. In specimens of the new edrioasteroid from China of similar size ( Fig. 4B, C View Fig ) there is an oral frame of interradial plates and paired ambulacral flooring plates (Zhao et al. in press: fig. 6). In early isorophid taxa the flooring plates are simple U−shaped elements underlying the ambulacra that decrease in size distally ( Bell 1976a, b; Sumrall 1996; Sumrall and Zamora in press). Chinese taxa, by contrast, has ambulacra that have a double biseries of flooring plates ( Fig. 4A View Fig ). Cambraster has a strongly developed marginal ring of ossicles and a fully plated aboral surface. The lack of a complete rim of stout marginal ossicles in Protorophus readily distinguishes it from similar sized juveniles of Cambraster .
Protorophus has greater similarity to the upper Cambrian Chatsworthia and Hadrodiscus from Australia in the plate arrangement of the marginal ring. Poor preservation in these Australian taxa prevents us making a detailed comparison, and their flooring plate arrangement remains unknown. Individuals in both taxa range from about 6 mm in diameter but by that stage both Chatsworthia and Hadrodiscus clearly show long straight series of ambulacral coverplates in contrast to Protorophus . None shows the large terminal U−shaped plates of Protorophus even in partially disarticulated material.
Geographic and stratigraphic range.—Iberian Chains (west Gondwana margin), lower Languedocian.
Isorophida gen. et sp. indet.
Fig. 3 View Fig .
Material.— One specimen, MPZ2010 View Materials /857, preserved as natural moulds in part and counterpart .
Description.—Theca in plan view subcircular in outline and preserving only the marginal ring and some collapsed plates of the central disc. The aboral face is uncalcified. The thecal diameter is 11 mm. The marginal rim is composed of tesselate plates, arranged into 5 to 6 circles of plates: plates are polygonal, diamond to rhombic in shape, and arranged in decreasing size towards the periphery.
Plating of the disc is largely lost, with just a few scattered plates remaining. Prominent amongst these are five spines, 2 mm in length and approximately cylindrical in cross−section ( Fig. 3B, C View Fig ). The specimen is attached to the glabella of a trilobite ( Fig. 3A View Fig ).
Discussion.—This specimen has a peripheral ring that is very similar to that seen in Protorophus , and in juveniles of the new edrioasteroid from China. Unlike both of those taxa, however, there are prominent spines, possibly associated with the innermost plates of the peripheral rim.
Edrioasteroids with spines are unusual and are confined to pyrgocystids and an aberrant?agelacrinitid. These include Pyrgocystis sp. from the middle Ordovician of North America, with spines around all the oral area ( Guensburg and Sprinkle 1994), Hystrichopsydrax sandersi from the late Ordovician of North America which has spines in the interambulacral area ( Guensburg 1988), Epipastron ixine and Isorophida gen. et. sp. indet, from the Silurian of Australia ( Holloway and Jell 1983) which have large spines in the interior part of the marginal frame, and Epipastron sp. from the Silurian of Tasmania which shows flexible spines in the marginal ring ( Holloway 1992).
This specimen comes from the same locality as Protorophus but from a slightly older horizon. It probably represents a new taxon, but as we know so little about its morphology we simply note its occurrence here and place it in open nomenclature.
doi:10.4202/app.2010.0012
Geographic and stratigraphic range.—From Moncayo Natural Park, close to the village of Purujosa (north Iberian Chains, Spain). Murero Formation, latest Caesaraugustan– earliest Languedocian of the Mediterranean stratigraphic chart of Liñán et al. 1993 and Ávaro and Vizcaïno 1998; Middle Cambrian (equivalent to Cambrian Series 3, Stage 5).
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