Gogia parsleyi Zamora, 2009

Gogia parsleyi Zamora sp. nov.

Figs. 4A–F View Fig , 5–9 View Fig View Fig View Fig View Fig View Fig .

Etymology: In honour of Prof. Ronald L. Parsley (Tulane University, New Orleans), for his contributions to the understanding of gogiid eocrinoids and Palaeozoic echinoderms in general.

Type material: Holotype: MPZ2004 View Materials /162a, b, almost complete specimen without holdfast ( Fig. 5 View Fig ) . Paratypes: MPZ2004 View Materials /161, 163, 214, 215, 238; MPZ2006 View Materials /556–558, 560; MPZ2008 View Materials /160–164, complete or partial specimens.

Type locality: La Borraca Creek , four kilometers to the southwest of Purujosa village (Zaragoza, NE Spain) in the Moncayo Natural Park .

Type horizon: Murero Formation, uppermost Caesaraugustian or lowermost Languedocian, Middle Cambrian.

Diagnosis.—Eocrinid with globular−shaped theca and large, slightly convex thecal plates (slightly ornamented). Epispires are simple and numerous, with a well developed raised rim sometimes covered by a stereomic dome or by small plates. Thecal plates are arranged into six or seven subregular circlets. At least seven long, narrow biserial and spiralled brachioles. Almost no stalk, except for an expanded holdfast composed of tiny globular plates.

Material.—14 articulated and nearly complete specimens (ten with both part and counterpart), MPZ2004/161–163, 214, 215, 238; MPZ2006/556–558, 560; MPZ2008/160–162, 164. Two disarticulated specimens, MPZ2006/559 and MPZ2008/ 163, and 23 isolated plates (MPZ2004/216–237, 239). All fossils are preserved as natural moulds in a grey−green shale. Articulated specimens with delicate, intact structures suggest rapid burial while alive by a storm−induced obrution deposit.

Description.—The shape of the theca is ellipsoidal to rounded; the size of the holotype theca is 12 × 11 mm ( Fig. 5 View Fig ). All the recovered specimens have been flattened by collapse and/or compaction. There are 35 thecal plates per exposed side, which exhibit polygonal outlines and subregular arrangements in 6 or 7 circlets; a number of the plates are large (up to 3 mm) (see reconstruction, Fig. 6 View Fig ). There is no clear gradient in the size of the plates, but the larger ones are concentrated in the lower–middle portions of the theca; plates decrease in size aborally and especially adorally. Additional plates are intercalated along sutures, as shown by the juvenile specimen MPZ2006/556 ( Fig. 4A View Fig ). Plates are slightly domed on their external surface and are typically ornamented with tiny granules ( Fig. 4D View Fig ). On the internal surface, they are unornamented and slightly concave ( Fig. 4B View Fig ). Some stereomic structures are well preserved ( Fig. 7 View Fig ).

Sutural pores (epispires) occur over the entire theca, with a regular distribution and size ( Figs. 5 View Fig , 7B, C View Fig , 8A, B View Fig , 9C View Fig ). Epispires are surrounded by a prominent raised rim ( Figs. 6 View Fig , 7C View Fig , 8E, F View Fig , 9C View Fig ), which usually crosses the associated plate suture(s). Epispires are present on the sutures between two plates or at the corners between three plates ( Fig. 8F View Fig ); and they are sometimes more developed in one of the two adjacent plates. The pores show an almost uniform diameter. The number of epispires per plate ranges from 4 ( MPZ2004 View Materials /162a) to 17 ( MPZ2004 View Materials /217) and there are up to four epispires per plate side. Some epispires show an external dome−like stereomic cover ( Figs. 6 View Fig , 8E View Fig ), others are covered by numerous tiny plates ( Figs. 4E View Fig , 8F View Fig ). The covered epispires are only present in the lower–middle theca and sometimes these structures do not cover the whole pore. These epispires are rounded to elliptical and have an epispire H/W ratio varying from 1 to 3 .

Brachioles are attached in groups of two to a modified single thecal plate, which is projected at the periphery of the oral region ( Fig. 8C View Fig ). They are spiralled with a quite loose twist (approximately 0.5 mm) ( Fig. 8G View Fig ) and are sometimes coiled at their tips ( Figs. 5 View Fig , 8D View Fig ). The length of the brachioles is at least 25 mm, twice the length of the theca. Seven brachioles are preserved in the most complete specimens ( MPZ2004 View Materials /162a), there were probably more in living animals. Brachioles are biserial, with the alternating brachiolar plates numbering about three or four per millimetre ( Figs. 8A, G View Fig , 9A View Fig ). Cover plates are not well preserved; there are two on a brachiolar plate, with a spinous projection in lateral view. The preservation of the brachioles in the holotype suggests that they were flexible .

The holdfast is preserved in some specimens, but no stalk is apparently present. In MPZ2004 View Materials /161a ( Fig. 5 View Fig ) the holdfast appears disarticulated, in specimens MPZ2004 View Materials /215 ( Fig. 4D View Fig ) and MPZ2008 View Materials /162 ( Fig. 9A View Fig ) it is apparently still connected to the base of the theca. It is composed of numerous tiny, globular plates, which are clearly visible in SEM images ( Fig. 7A View Fig ). The transition between the holdfast and theca is abrupt, consisting of a change in the type and size of plates .

Discussion.— Gogia parsleyi Zamora sp. nov. conforms to the diagnosis proposed by Walcott 1917 (see also, Sprinkle 1973; Sprinkle and Collins 2006) for the genus Gogia . It has a unique character combination of simple covered epispires; large thecal plates arranged in subregular circlets; spiralled brachioles; and the absence of a stalk connecting the expanded holdfast with the theca.

The general body structure of Gogia parsleyi Zamora sp. nov. ( Fig. 6 View Fig ) shows many features that are shared with other gogiids, such as erect biserial brachioles, thecal plates arranged in poorly developed circlets, epispires and an attachment appendage consisting of only a holdfast.

This species differs from other Cambrian gogiids in several characteristics; for example, thecal plates organised into subregular arranged circlets and the presence of covered epispires. One undescribed species of Gogia from North America also shows stereomic domes covering epispires (James Sprinkle, personal communication 2008). Gogia parsleyi Zamora sp. nov. is similar to Gogia hobbsi Sprinkle, 1973 , particularly in the ornamentation of the thecal plates and the spiralled brachioles; however, Gogia hobbsi has a conical thecal shape, is smaller in size with fewer plates and has a stalk.

Gogia parsleyi is likely to be closely related to Alanisicystis Ubaghs and Vizcaïno, 1991 , because both have stereomic cover domes on some epispires in the lower part of the theca, but it differs from this species by having simple epispires and plate ornamentation composed of a slightly rough surface texture. Moreover, in Gogia parsleyi some epispires are covered by tiny plates rather than domes, which are always observed in Alanisicystis ( Fig. 1 View Fig ). This feature is equally well shown in Rhopalocystis destombesi Ubaghs, 1963 , in which a group of small plates covers the sutural pores ( Ubaghs 1963: fig. 8.5–7) and in Globoeocrinus globulus Zhao, Parsley, and Peng, 2008 . A new gogiid from Morocco that is under description ( Nardin 2006) shares many features with Gogia parsleyi , such as the presence of covered epispires, but they differ mainly in the type of epispires, which are simple in the Spanish material and complex in the Moroccan specimen (Elise Nardin, personal communication 2006).

Sinoeocrinus Zhao, Huang, and Gong, 2004 differs by lacking the stereomic domes or tiny plates covering epispires. Gogia parsleyi differs from Akadocrinus Prokop, 1962 in the stalk, which is nearly absent in the former and composed of many fusular rings in the later. Furthermore, they differ in general thecal shape.

Marjumicystis Ubaghs and Robison, 1985 also appears to lack a stalk, but differs principally in lacking well developed epispires.

Parsley and Zhao (2006) provided a complete ontogenetic sequence for the Cambrian eocrinoid Sinoeocrinus lui Zhao, Huang, and Gong, 2004 , describing, for the first time, the ontogenetic changes occurring in a gogiid population. These ontogenetic stages were described in terms of thecal height (TH) and were thus divided into juvenile, advanced juvenile, mature and advanced mature, or gerontic, stages. The material of Gogia parsleyi described in this paper is not very abundant, but a few different ontogenetic stages can be recognised; these stages are important to understand feature changes in specimens of different sizes. The TH of specimens ranges from 5 mm to 12 mm. The smallest specimens ( Figs. 4A View Fig , 9A View Fig ), with a TH of 6 mm and 5 mm, respectively, probably represent juveniles or early advanced juveniles (sensu Parsley and Zhao 2006). They have a 2−2 ambulacral pattern ( Fig. 9A View Fig ), lack of ornamentation and very small epispires without a raised rim. The specimen which is intermediate in size, with a TH of ca. 7.5 mm ( Fig. 9B View Fig ), shows intermediate features, lacking ornamentation and possessing an incipient raised rim bordering epispires, which are very small. It probably represents an advanced juvenile. The largest specimens have a TH of ca. 12 mm and show some very distinctive features. They possess more than five brachioles, probably in a 2−1−2 pattern, ornamented thecal plates and well developed, sometimes covered epispires with prominent raised rims. All these features are probably indicative of early mature specimens.

Stratigraphic and geographic distribution.—Upper part of Murero Formation, uppermost Caesaraugustian or lowermost Languedocian (middle Cambrian).