Periechocrinus longimanus ( Angelin, 1878 )

Ausich, William I., Wilson, Mark A. & Vinn, Olev, 2012, Crinoids from the Silurian of Western Estonia, Acta Palaeontologica Polonica 57 (3), pp. 613-631 : 616-618

Periechocrinus longimanus ( Angelin, 1878)

Fig. 3E .

1878 Actinocrinites longimanus sp. nov. Angelin, 1878: 6, pl. 15: 17; pl. 26: 16; pl. 28: 5, 5a, 6.

1881 Periechocrinus longimanus ( Angelin, 1878) ; Wachsmuth and Springer 1881: 132 (306).

1943 Periechocrinites longimanus ( Angelin, 1878) ; Bassler and Moodey 1943: 599.

1983a Periechocrinus longimanus ( Angelin, 1878) ; Franzén 1983: 6.

2003 Periechocrinus longimanus ( Angelin, 1878) ; Webster 2003.

Material.—Two Estonian specimens are assigned to P. longimanus : GIT 405−4−1 and GIT 405−4−2 from lower Wenlock, Jaani Formation.

Description.—Calyx small for the genus and is high bowl or globe shaped ( Fig. 3E ). Calyx plates are gently convex and smoothly sculpted with thin median ray ridges begining on the first primibrachials. Basal circlet is relatively low, truncate proximally, visible in side view. Three basal plates are subequal in size. Radial circlet is approximately 1.8 times higher than the basal circlet; interrupted in the posterior; radial plates five, hexagonal, and approximately 1.5 times higher than wide. In normal interrays, the first interradial is hexagonal, approximately as high as wide but tapers distally, and smaller than radials and first primibrachials. The second range of plates in normal interrays comprised of two plates, but more distal plating is not preserved. The first primibrachial is fixed, hexagonal, approximately 1.2 times wider than high, and smaller than radial plates. More distal ray plates, tegmen, free arms, and column are not preserved.

Discussion.— Periechocrinus is a cosmopolitan Silurian crinoid that characterizes many Silurian faunas. Franzén (1983) listed twelve species of Periechocrinus from Gotland, Sweden. Only two of these species are characterized by smooth calyx plating, P. grandiscutus and P. longimanus . From Angelin’s (1878) illustrations, P. grandiscutus has much more convexity to the radial plates than P. longimanus and the two Estonian specimens. Thus, Wenlockian specimens from Saaremaa are assigned to P. longimanus . The preserved portion of the calyx is approximately 15 mm wide and 17 mm high. Calyx plating is not evident on either specimen. Thus, the illustration ( Fig. 3E ) only illustrates the calyx outline.

http://dx.doi.org/10.4202/app.2010.0094

Geographic and stratigraphic range.— Franzén (1983) reported P. longimanus from the Wenlock (Sheinwoodian) Högklint Formation and Slite Group of Gotland, Sweden. Similarly, the Estonian specimens are from the lower Wenlock, Jaani Formation, Jaani Shore, Saaremaa Island, Estonia.

Figures

Fig. 3. Camerate crinoids from the Silurian of Estonia. A, B. Middle Äigu Beds, Kaugatuma Formation (Pridoli), Kaugatuma Cliff. A. Eucalyptocrinites tumidus sp. nov., GIT 405−243. A1, lateral view of crown, note modestly expanding partition plates; A2, basal view of calyx, note nodose calyx plates; A3, tegmen view of crown, note flat tegmen top. B. Calliocrinus sedgwickianus sp. nov., TUG 1395−8. Basal view of a portion of the basal and radial circlets, all circular pits are the trace fossil Oichnus. C. Eucalyptocrinites sp., GIT 405−238, Jaani Formation (Wenlock), Suuriku Cliff. Lateral view of calyx. D. Eucalyptocrinites sp. 2., TUG 1395−13, Ninase Member, Jaani Formation (Wenlock), Panga Cliff. D1, tegmen view of crown; D2, B−ray view of partial crown, note deep elongate groove on well−preserved partition plate. E. Periechocrinus longimanus (Angelin, 1878), GIT 405−4−1, Jaani Formation (Wenlock), Janni Cliff. Lateral view of partial calyx, calyx sutures very indistinct. F. Eucalyptocrinites sp. 1, TUG 1375−3, Jaani Formation (Wenlock), Undva Cliff. Lateral view of broken crown. G. Calliocrinus sp., TUG 1395−6, Ninase Member, Jaani Formation (Wenlock), Suuriku Cliff. Broadly bifurcating spine. H. Eucalyptocrinites sp. 1, TUG 1375−2, Jaani Formation (Wenlock), Undva Cliff. Lateral view of crown of juvenile. Scale bars 10 mm.