Stichomicropora oceani (d'Orbigny, 1852)
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publication ID |
https://doi.org/ 10.1111/j.1096-3642.2005.00179.x |
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persistent identifier |
https://treatment.plazi.org/id/6F0C243F-FF8A-2564-FCF9-615905CFFA85 |
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treatment provided by |
Diego |
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scientific name |
Stichomicropora oceani |
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STICHOMICROPORA OCEANI View in CoL (D’ ORBIGNY, 1852)
( FIGS 6A- D View Figure 6 , 22A View Figure 22 , 24B, E View Figure 24 )
Material: NHM D55549 View Materials , Cretaceous, Lower Cenomanian, saxbii-orbignyi Zones, Sables et Gres de Lamnay (lumachelle), Lamnay, Sarthe, France, P. D. Taylor Collection.
Description: All autozooids have two distal oral spines. Non-brooding zooids in addition often possess one proximal mural spine, situated medially on the proximal gymnocyst, indenting the mural rim, and having a diameter noticeably greater than the oral spines ( Fig. 6A- C View Figure 6 ).
Distal zooids constructing ovicells are characterized by a transverse row of 5–7 ovicell spine bases ( Figs 6C, D View Figure 6 , 24B, E View Figure 24 ). With the exception of the two outermost spines, these spines are positioned on the proximal slope of the mural rim and follow the outline of this rim which varies from gently concave distally to almost straight ( Figs 6C View Figure 6 , 24B, E View Figure 24 ). Ovicell spine bases partition the proximal, slightly concave part of the gymnocyst that forms the ovicell floor, from the more distal part of the gymnocyst and the cryptocyst. The outermost spine bases are often slightly offset from the others, being positioned more proximally and distant from the mural rim, and have a larger diameter ( Figs 6D View Figure 6 , 24B, E View Figure 24 ). The distance between adjacent ovicell spine bases is approximately equal to spine base diameter but can be larger or smaller. The gymnocyst forming the ovicell floor has a trapezoidal shape and is enlarged relative to that of zooids not bearing ovicells.
Remarks: Brooding zooids in type material of S. oceani from the d’Orbigny collection were figured by Voigt (1981: fig. 4g), while examples from non-type material was illustrated and briefly described by Taylor & McKinney (2002: fig. 1D).
STICHOMICROPORA MARGINULA ( BRYDONE, 1914)
( FIGS 7A, B View Figure 7 , 22A View Figure 22 , 24H View Figure 24 )
Material: NHM D44609, Cretaceous , Coniacian , Upper Chalk, Dover, Kent, England .
Description: All autozooids possess six oral spines of which the four distalmost are articulated; the two proximal spines are knob-like with closed ends and probably lacked basal articulations ( Fig. 7A, B View Figure 7 ). In distal brooding zooids there are 7–10 ovicell spine bases arranged in a distally convex arch on the proximal gymnocyst, indenting the broad, elevated mural rim ( Figs 7A, B View Figure 7 , 24H View Figure 24 ). The outermost spine bases are slightly offset from the others, being positioned more proximally. These two spines are set well apart from the mural rim, and are always distant from the distal edge of the maternal zooid. The gymnocyst forming the ovicell floor is concave and enlarged relative to that of zooids not bearing ovicells. The distance between neighbouring ovicell spine bases is equal to or less than spine base diameter.
Remarks: Brooding zooids in S. marginula were illustrated by Voigt (1967: pl. 20, figs 1, 3; 1989: pl. 17, fig. 8) and Taylor (1987: pl. 9, fig. 8; 2002: pl. 9, fig. 8). These authors described specimens, respectively, from the Upper Santonian of Chodsha Kasian Mountain (near Schaartus), Tadschikistan, and the Coniacian of Dover, England. The ovicells were neither described nor illustrated by Brydone (1914: 98, pl. 4, figs 8, 9) when he first erected this species as Homalostega marginula .
( FIGS 7C, D View Figure 7 , 22A View Figure 22 , 24A, D, G View Figure 24 )
Material: NHM D42263, Cretaceous, Campanian, mucronata Zone, Upper Chalk, Earlham Lime Works, Norwich, England. A.W. Rowe Collection.
Description: Autozooids possess two, rarely one, distal oral spines. Those constructing ovicells have a transverse row of 5–10 ovicell spine bases which are located on the proximal edge of the narrow elevated mural rim ( Figs 7C, D View Figure 7 , 22A View Figure 22 , 24A, D, G View Figure 24 ). This row of spines separates the proximal, slightly concave gymnocyst, forming the ovicell floor, from the distal cryptocyst forming the bulk of the frontal shield. The gymnocyst of the ovicell floor has a trapezoidal shape and may be wider than long or vice versa, depending on the shape of the proximal part of the autozooid. In contrast, nonbrooding zooids possess a very narrow strip of proximal gymnocyst.
The row of ovicell spine bases essentially parallels the proximal edge of the mural rim. This may vary from distinctly or gently concave distally, to straight or almost straight with lateral parts slightly curved distally, to gently convex distally ( Figs 7C, D View Figure 7 , 24A, D, G View Figure 24 ). Depending on the curvature of the spine row, the two most lateral spine bases are either closest to or farthest from the distal edge of the maternal zooid. The distance between adjacent ovicell spine bases usually equals spine base diameter but can be larger or smaller. The diameter of ovicell spine bases increases towards the middle of the row, the outermost lateral spine bases having diameters similar to those of the oral spine bases.
Remarks: Material of this undescribed species in the NHM collections bears the manuscript name Homalostega cribraria Rowe. Brooding zooids were illustrated by Taylor & McKinney (2002: fig. 1A, B).
( FIGS 7E, F View Figure 7 , 22A View Figure 22 , 24G View Figure 24 )
Material: NHM D46004, Cretaceous, Campanian, mucronata Zone, Upper Chalk , Clarendon, Wiltshire, England, A.W. Rowe Collection .
Description: All autozooids have 4–6 oral spines of which the distal pair are the smallest. Ovicell-bearing zooids possess a transverse row of eight ovicell spine bases placed on the salient mural rim that separates the proximal, slightly concave gymnocyst, forming the ovicell floor, from the extensive distal cryptocyst ( Fig. 7E, F View Figure 7 ). The ovicell spine bases are arranged in a gently curved, distally convex arch ( Figs 7E, F View Figure 7 , 24G View Figure 24 ), with the outermost spine bases always distant from the distal edge of the maternal zooid. The spacing between adjacent ovicell spine bases is greater than their diameter, which is approximately the same as that of the oral spine bases.
( FIGS 8A- C View Figure 8 , 22A View Figure 22 , 24E, H View Figure 24 )
Material: NHM D4125, Cretaceous, Coniacian, cortestudinarium Zone, Upper Chalk, Chatham, Kent, England. W. Gamble Collection.
Description: The tiny autozooids in this species possess four oral spines of which the distal pair are the smallest ( Fig. 8A- C View Figure 8 ). The ovicell roof was apparently constructed of 5–6 spines surrounding the slightly concave ovicell floor formed by the proximal gymnocyst of the brooding zooid ( Figs 8A- C View Figure 8 , 22A View Figure 22 , 24E, H View Figure 24 ) which is enlarged relative to that of zooids not bearing ovicells. Ovicell spine bases are arranged either in a gently curved, distally convex arch ( Figs 8B View Figure 8 , 24H View Figure 24 ), or sometimes in an almost straight line ( Figs 8A, C View Figure 8 , 24E View Figure 24 ) with the two outermost spine bases well away from the mural rim of the zooid and from the distal edge of the maternal zooid. Medial ovicell spine bases often slightly indent the mural rim ( Fig. 8B View Figure 8 ). Ovicell spine bases have approximately the same diameter as distal oral spines or are larger. The distance between neighbouring ovicell spine bases is up to two times greater than their diameter.
Remarks: Many of the autozooids in this species are sealed by closure plates, convex laminae covering the cryptocyst and opesia ( Fig. 8A View Figure 8 ). Brydone (1936: 85, pl. 41, fig. 3) described what may be conspecific material as Homalostega sussexiensis .
( FIGS 8D View Figure 8 , 22A View Figure 22 , 24G View Figure 24 )
Material: NHM D8185, Cretaceous, Coniacian or Santonian (upper third of cortestudinarium Zone), Upper Chalk , Luton, near Chatham, Kent, England, W. Gamble Collection .
Description: Poor preservation makes it impossible to ascertain the exact number of oral as well as ovicell spine bases in this species. However, the ovicell roof was clearly constructed of several spines (possibly seven or eight), with bases arranged in a gently curved, distally convex arch on the proximal mural rim ( Figs 8D View Figure 8 , 24G View Figure 24 ). The slightly depressed gymnocyst forming the ovicell floor is enlarged relative to that of zooids not bearing ovicells.
( FIGS 8E, F View Figure 8 , 22A View Figure 22 , 24E View Figure 24 )
Material: NHM D55618, Cretaceous , Lower Cenomanian , Wilmington Sands, Wilmington, Devon, England .
Description: Ovicell spine bases number six or seven and are arranged in a straight line or a very gently curved arch on the proximal gymnocyst of the distal zooid. The outermost pair of spine bases are slightly offset from the others, being positioned more proximally ( Figs 8E, F View Figure 8 , 22A View Figure 22 , 24E View Figure 24 ). The distance between neighbouring ovicell spine bases is equal to or greater than spine diameter.
Remarks: The ovicell of this species was illustrated by Taylor & McKinney (2002: fig. 1C).
2. SPECIES WITH BASALLY FUSED OVICELL SPINES
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