Cambraster cannati ( Miquel, 1894 )

Zamora, Samuel, Sumrall, Colin D. & Vizcaïno, Daniel, 2013, Morphology and ontogeny of the Cambrian edrioasteroid echinoderm Cambraster cannati from western Gondwana, Acta Palaeontologica Polonica 58 (3), pp. 545-559 : 548-554

publication ID	https://doi.org/ 10.4202/app.2011.0152
persistent identifier	https://treatment.plazi.org/id/03E3FD7C-FFA1-477C-FC93-4F0DFEFC1719
treatment provided by	Felipe
scientific name	Cambraster cannati ( Miquel, 1894 )
status

Treatment

Cambraster cannati ( Miquel, 1894)

Figs. 2–5 View Fig View Fig View Fig View Fig .

1985 Cambraster cannati ( Miquel, 1894) ; Smith 1985 and references cited there: 750, text−figs. 2, 3, 18, 19.

2007 Cambraster cf. tastudorum ; Zamora et al. 2007: 255, fig. 4A, B.

Material.— This study is based on newly collected material from the middle Cambrian of the Iberian Chains ( Spain) and Montagne Noire ( France). Collection from Spain, include four specimens from Torrijo de la Cañada ( MPZ2011 View Materials /97–100), one specimen from Borobia ( MPZ2011 View Materials /96), and 33 from Villalengua ( MPZ2009 View Materials /1232, MPZ2011 View Materials /101–132). Material from Montagne Noire includes one specimen from Ferrières− Poussarou, two specimens from Favayroles, one specimen from Coulouma, five specimens from Sainte−Colombe, and 26 specimens from Ferrals−les−Montagnes. All specimens are preserved as natural moulds in shale that were studied from latex casts .

Diagnosis.—Large Cambraster bearing numerous epispires at maturity, smooth peripheral skirt, proportionately shorter ambulacra in submature stages, and poorly demarked and organized central ventral disk.

Description

General shape.— Cambraster has a circular outline, mainly in juveniles, becoming pentagonal with maturity, with ambulacra extending to the corners of the thecal outline ( Fig. 2 View Fig ). The aboral surface is flat and the oral surface is slightly convex ( Fig. 3 View Fig ). In cross section it is plano−convex but with a very low profile.

Oral and ambulacral area.—The oral area is composed of a series of 6 primary interradial oral frame plates; each interambulacrum bears one plate and two are present in the interambulacrum CD ( Figs. 2A View Fig , 3F 3 View Fig , G 2 View Fig , 5 View Fig ).

Interradial oral frame plates have a large, externally exposed area that forms the corners of the mouth frame and radially positioned limbs forming the proximal edges of the food grooves and peristomial opening. Around the ambulacral/peristomial margin are a series of large and small pits that mimic similar depressions of the ambulacral floor plates. The lateral margins of the plates extend into the food grooves where they contact adjacent plates forming the edge of the mouth frame. The distal adradial ends of the plates are notched by the proximal edge of the first podial pores of the ambulacral floor plates. The externally exposed portion of the interradial oral frame plates in the AB and AE position are large and broad, whereas they are smaller and more narrow in the BC and DE positions. In the CD position there are two plates with the plate on the left larger than the plate on the right; some specimens suggest a pore spanning the suture between the two plates ( Fig. 3F View Fig 1 View Fig ). The mouth frame is covered by a poorly documented series of cover plates. A single large cover plate is positioned diagonally above the smaller right CD interradial oral frame plate. A series of small cover plates encircle the proximal and adradial edges of the externally exposed portions of the CD interradial oral frame plate in an undocumented arrangement. These cover plates are smaller than the primary series of cover plates seen in the proximal ambulacral series, but larger than the adradial secondary series into which they appear to merge in most rays (see Fig. 2A View Fig : reconstruction).

The oral surface bears five, straight, relatively wide ambulacra that show little taper and a somewhat pointed termination. They arise from the oral area in a distinct 2−1−2 pattern and extend from the mouth frame to the marginal ring. In larger specimens, an embayment is formed into the upper surface of the marginal frame where the ambulacra are inset ( Figs. 3A View Fig 1 View Fig , 4A View Fig 1 View Fig ). The ambulacra are formed from underlying biserial floor plates that structurally form the thecal wall and overlying cover plates arranged into multitiered series. The

http://dx.doi.org/10.4202/app.2011.0152

floor plates are weakly exposed along the lateral margins, approximately 1.5 times as wide as long, and relatively thick. The perradial zig−zag suture is weakly developed and the floor plates are biserially alternate. Adjacent sutures between floor plates of the same side are marked by two pores that pass into the thecal interior. These pores are flared into the ambulacral tunnel and bear a weakly developed rim. The upper surface of the floor plates in the ambulacral tunnel is marked by two well−developed depressions abradially near the articulating surface for the cover plates. These depressions lead to a narrow dendritic network of strongly demarked, extremely thin channels that extend in branching arcs towards the perradial suture ( Fig. 4A View Fig 3 View Fig ).

Cover plates are arranged into a multitiered series. Primary series are arranged with less than one set of primary plates per floor plate. A primary series consists of a large triangular plate with a smaller primary wedged between. A secondary series of smaller equant to elongate plates of unknown arrangement lie adradial to this series, and there is a hint of a tertiary series. Cover plate interiors poorly documented.

Interambulacra.—Interambulacral plates abut along vertical sutures forming a tessellate membrane ( Figs. 3F View Fig 1 View Fig , 4C View Fig 2 View Fig ). Plates in each interarea are differentiated into larger primary plates that are separated in plate corners by a series of smaller secondary plates. Primary plates are largest in proximal central interareas and smaller adradially and distally. Along the adradial edges of the interambulacra these plates are all small and radially elogate, forming one to two rows that articulate to the abradial notch on the floor plate series. Distally these plates are smaller and somewhat transversely elongate where they abut along the edge of the marginal ring articulating into a small notch along the proximal extremity of the ring. Interambulacral plates are also smaller along the margin of the periproct but do not form regular circlets.

Epispires are found only along the edges of interambulacral plates ( Fig. 4C View Fig 2 View Fig ). These pores are small, vertical, and evenly spaced around the edges of each plate except at the extreme edges of the interambulacra where plates are smallest. Epispires are ovoid with the long axis perpendicular to the plate sutures and are equally developed on primary and secondary interambulacral plates. Small isolated platelets suggest that the epispires were covered with a few loosely articulated platelets embedded in soft tissues ( Fig. 3A View Fig 2 View Fig ).

Marginal ring.—The marginal ring forms a stout frame of larger elements that are strongly differentiated from other plate series by their shape and position ( Figs. 3 View Fig , 4 View Fig ). The number of plates is slightly variable in different interambulacra of the same specimen and in the same interambulacra of different specimens, but does not seem to be diagnostic between different species ( Table 1).

There are two somewhat different types of marginal plates constructing the frame; interradially positioned, rectangular marginals that do not support the distal ambulacra and pairedperradial marginals that together support the distal ambulacra. The interradial marginals vary between one and three per interambulacrum and, except for the CD interray where marginals are usually more numerous, the number does not follow any pattern within or between specimens nor ontogenetically ( Table 1). They are triangular in radial cross section with an acute distal margin and slightly invaginated proximal margin. They have flat ventral surfaces and joint adjacent marginals by a weakly developed suture. In plan view they are transversely elongate but are more equant in juveniles. Perradial marginals are similar to interradial plates in gross features but differ along perradial margin. These plates are paired along the radii and meet along a long, radially positioned suture. They are trapezoidal in ventral aspect becoming widest along perradial margin, but triangular in dorsal aspect becoming narrowest perradial. The proximal edge of the dorsal surface is curved to create a radial invagination where the ambulacrum lies directly along this contact, becoming more exaggerated with age. The ambulacral embayment is cored by the ambulacral floor plates and radially elongate interambulacral plates extend along the ambulacrum in this area.

The marginal ring is surrounded by a peripheral skirt of tessellate to squamose and very tiny plates ( Figs. 2A View Fig , 3A 3 View Fig ). Taphonomically, these plates appear to be somewhat flexible. These plates are variable in shape but most are rectangular and highly transversely elongate especially distally. The peripheral skirt articulates to the external part of the marginal plates along the distal dorsal surface. Up to 8–10 rows of these plates constitute this structure. In better−preserved specimens, the largest and more irregularly shaped plates lie proximally and smallest and more regularly plates distally. The peripheral skirt has a sharp transition between the plates of the oral surface and the equant tessellate plates of the aboral surface.

Aboral surface.—The aboral area is fully plated ( Figs. 3C, E, D View Fig 2, F 2 View Fig , 4A View Fig 2 View Fig ). Plates from this surface are nearly smooth, flat, polygonal, and sub−regularly arranged. The outermost edge of the aboral surface is formed from an irregular circlet of

http://dx.doi.org/10.4202/app.2011.0152

small equant peripheral plates that articulate with the plates of the peripheral skirt with a sharp transition. Distal to this peripheral plate series is a series of 5–6 poorly organized circlets that are arranged into a regular mosaic of larger plates toward the periphery and smaller plates centrally. Plates in this zone are thick, with vertical sutures and equant in outline. This zone lies directly beneath the marginal ring and may be functionally related. This zone shows an irregular transition over several irregular circlets to the central disk defined by thinner plates and differentiated plating style. The cental disk is demarked by a large circular suture and is plated with large, radially elongate primary plates that typically are twice as large as the largest plates of the peripheral series. These plates are irregularly arranged and separated in most places by smaller plates that vary between radially elongate to more equant. The central−most plating becomes irregular with many more small plates.

Anal pyramid/hydropore–gonopore.—Periproct placed in the distal interambulacrum CD left of the midline almost abutting the marginal ring. The structure is formed into a low cone and is plated with several highly irregular circlets of very thin, lathe−shaped plates that are radially arranged. The periproct is relatively large and becomes more complex adding plates ontogenetically.

Placement and nature of the hydropore and gonopore is poorly constrained. A possible pore between the two CD positioned interradial oral frame plates is not consistently seen in different specimens, and the proximal right interambulacrum CD is poorly preserved in all specimens. Interior views of the oral frame are obscured by the plating of the ventral integument, but one specimen suggests a bean−shaped mouth and a hydropore structure in the proximal right interambulacrum CD ( Fig. 3F 3 View Fig ), similar to that reported for C. tastudorum by Jell et al. (1985).

Discussion.— Cambraster from the Western Mediterranean region includes only one species C. cannati . A recent specimen described from Spain as Cambraster cf. tastudorum ( Zamora et al. 2007) corresponds to an aboral surface assignable as a later juvenile of C. cannati . Cambraster cannati differs from C. tastudorum ( Fig. 6 View Fig ) primarily in the aboral plating, the relatively shorter ambulacra that do not extend as far over the perradial marginals, the lack of radial spines on the tiny peripheral skirt plates, and the relatively smaller number of marginals per interambulacrum.

well−preserved interambulacral plates, ambulacral flooring plates, and periproct.Also note the duplicated marginal ring in interambulacrum AB and close to the A ambulacra. General view (C 1) and detail of the interambulacra CD showing the periproct and interambulacral plating (C 2). D. MNHN.F.A45789, complete adult specimen with a well preserved marginal ring in which the tip of ambulacrum C extends within a single marginal plate rather than between two adjacent marginals. Abbreviations: cf, cover plates; fm, peristomial frame plate; fp, flooring plates; m, marginal plates; pe, periproct; ps, peripheral skirt. 1–5, peristomial frame plates. All specimens are photographs taken from latex casts whitened with NH 4 Cl sublimate.

http://dx.doi.org/10.4202/app.2011.0152

Stratigraphic and geographic range.— Solenopleuropsis (Solenopleuropsis) Assemblage Zone from the lower Languedocian Borobia and Coulouma Formations of Spain and France respectively. Jincella convexa Zone from the middle Languedocian Coulouma Formation only in France.

The specimen of Cambraster described by Zamora et al. (2007) was based on museum collections and was assigned to the upper Caesaraugustan Murero Formation, but this age is in doubt because none of the more recent specimens come from this age or formation.