Desmidocrinus laevigatus, Ausich & Wilson & Vinn, 2012
|
publication ID |
https://doi.org/ 10.4202/app.2010.0094 |
|
persistent identifier |
https://treatment.plazi.org/id/BF03720D-FFC0-FFFE-BF24-FC1F2170FC32 |
|
treatment provided by |
Felipe |
|
scientific name |
Desmidocrinus laevigatus |
| status |
sp. nov. |
Desmidocrinus laevigatus sp. nov.
Fig. 5G, H View Fig .
Etymology: From Latin laevigatus , smooth; in reference to the smooth plate sculpturing.
Type material: Holotype, TUG 1395−1; paratype, TUG 1395−2.
Type locality: Kaugatuma Cliff , Saaremaa Island, Estonia .
Type horizon: Middle Äigu Beds, Kaugatuma Formation, Pridoli, Late Silurian.
Material.— ATUG 1395−1 (holotype), TUG 1395−2 (paratype) from middle Äigu Beds, Kaugatuma Formation (Pridoli) at Kaugatuma Cliff , Saaremaa Island .
Diagnosis.— Desmidocrinus with bowl− to globe−shaped calyx. Smooth plate sculpturing. One fixed intrabrachial between primibrachials. Normal interrays plating 1−2. Ten free arms, free arms branch, and biserial brachials.
Description.—The calyx is medium in size for the genus and has a low bowl to globe shape ( Fig. 5G View Fig 3 View Fig ). Arms are not grouped. The calyx plates are convex with smooth sculpturing, and plate sutures are slightly impressed ( Fig. 5H View Fig ). The basal circlet is visible in side view ( Fig. 5G View Fig 3 View Fig ) and approximately 18% of calyx height. Three basal plates occur and are equal in size. The radial circlet averages 32% of calyx height and is interrupted in the posterior. The five radial plates are hexagonal ( Fig. 5G View Fig 1 View Fig ) and approximately 1.4 times wider than high. The normal interrays are in contact with the tegmen. The first interradial plate is octagonal, approximately 1.1 times wider than high, smaller than radial plates, and much larger than first primibrachials. The first interradial plate extends from shoulders of radial plates to the lower part of the first secundibrachial. Only one other interradial plate fixed in calyx resulting in 1−1 plating. The primanal is hexagonal, approximately equal in height and width, same size as radial plates, and interrupts the radial circlet. Plating in the CD interray is P−3−3 ( Fig. 5G View Fig 2), and an anitaxis of plates without anitaxial ridge. The CD interray is in contact with the tegmen. The first primibrachial is tetragonal, approximately 1.5 times wider than high, much smaller than radial plates, and somewhat smaller than primaxil. The second primibrachial is axillary and pentagonal to heptagonal in shape. The first secundibrachial is fixed and is the distal−most fixed brachial. Adjacent first secundibrachials within a ray are in contact medially. A single intrabrachial plate is in the center of each ray and sutured on upper shoulder of first secundibrachials. Tegmen unknown.
The 10 free arms branch ( Fig. 5G View Fig 3 View Fig ). The first few free brachials are uniserial and the remainder are biserial. Brachials are aborally very convex. Arms branch on approximately ninth free brachial. Pinnules and other aspects of free arms are unknown.
The most proximal columnal is circular and holomeric with a lumen pentalobate. Other aspects of the column are unknown.
Discussion.—Previously, only five species were recognized in Desmidocrinus , including D. heterodactylus Angelin ,
http://dx.doi.org/10.4202/app.2010.0094
1878; D. macrodactylus Angelin, 1878 ; D. pentadactylus Angelin, 1878 ; and D. tridactylus Angelin, 1878 from the Wenlock Slite Group of Gotland, Sweden. Desmidocrinus pentadactylus also occurs in the Ludlow Eke Formation ( Franzén 1983). A single North American species, D. dubius Springer, 1926 is recognized from the Laurel Limestone of Indiana, USA (Wenlock).
Therefore, Desmidocrinus laevigatus sp. nov., from the Pridoli of Saaremaa Island, is the youngest species recognized in this genus. It is the only Desmidocrinus with biserial arms and D. laevigatus and D. dubius are the only Desmidocrinus with 10 free arms. Desmidocrinus laevigatus is distinguished from its congeners as listed in Table 2.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.