Cyathocrinidida Bather, 1899 Family

Ausich, William I., Wilson, Mark A. & Vinn, Olev, 2012, Crinoids from the Silurian of Western Estonia, Acta Palaeontologica Polonica 57 (3), pp. 613-631 : 624-625

Order Cyathocrinidida Bather, 1899 Family Crotalocrinitidae Bassler, 1938 Genus Crotalocrinites Austin and Austin, 1843

Type species: Encrinites verucosus Schlotheim, 1820 ; Gotland, Sweden; Wenlock , Silurian .

Discussion.— Crotalocrinites rugosus was reported from Estonia by Hints and Stukalina (1997); however, to our knowledge, no specimens can be unequivocally assigned to Crotalocrinites . Similar to Anticosti Island, Quebec, Canada ( Ausich and Copper 2010), we suspect that isolated columnals and pluricolumnals with a wide outside diameter and a wide lumen have been assumed to belong to Crotalocrinites . However, this cannot be verified. Instead, Franzén−Bengtson (1983: 292, 296) noted that Abacocrinus , Clonocrinus , Crotalocrinites , and Enallocrinus from Gotland had either very wide columnals, wide lumens, or both. However, Franzén−Bengtson (1983: 298) was unable to identify any of these four crinoids based solely on columns or pluricolumnals.

This is a striking dendritic radice holdfast (sensu Brett 1981) that can grow to a quite large size. Although incomplete, the largest Enallocrinus holdfast has a total diameter in excess of 200 mm, and the largest columnal diameter in the holdfast region exceeds 40 mm.

As discussed in Donovan et al. (2007) for Gotland material (Wenlock), numerous holdfasts may occur along a single horizon with variable sizes (most probably representing multiple generations of settlement). On Saaremaa, horizons with numerous holdfasts occur in the Kaugatuma Formation (Pridoli). Franzén (1977: fig. 2D) regarded this holdfast as a cirriferous holdfast, and in side view it was recognized as a “holdfast with stout cirri” in Franzén−Bengtson (1983: fig. 5). However, note that these are now recognized as radices rather than cirri ( Donovan 1993; Donovan and Ewin 2010).

Geographic and stratigraphic range.—On Gotland, Sweden, this holdfast is reported from the Hemse Beds (Gorstian, lower Ludlow) ( Franzén 1977) and the lower Klinteberg Formation (Homerian, Wenlock) ( Donovan et al. 2007). In Estonia, this Enallocrinus holdfast is only known from the middle Äigu Beds, Kaugatuma Formation (Pridoli) at Kaugatuma Cliff, Saaremaa, where innumerable holdfasts occur.

Cladida indet.

Fig. 6A .

Material.—TUG 1395−9 from the middle Äigu Beds, Kaugatuma Formation (Pridoli) from Kaugatuma Cliff, Saaremaa Island, Estonia.

Discussion.—An unknown cladid is represented by specimen TUG 1395−9 with column, badly crushed calyx, and partially disarticulated arms. The calyx is much too disarticulated to allow any consideration of its identity ( Fig. 6A ). The arms are very convex, composed of uniserial brachials, and no pinnules, similar to Silurian cladids and perhaps some flexibles. In contrast, the column is circular, holomeric, heteromorphic with very convex latera on nodals and on the single priminternodals in the mesistele. This column morphology is more typical of camerate crinoids. However, based on the morphology of the arms, this specimens is assigned herein to Cladida indet.

Figures

Fig. 6. Crinoids from the Silurian of Estonia, middle Äigu Beds, Kaugatuma Formation (Pridoli, Silurian), Kaugatuma Cliff. A. Cladida indet., TUG 1395−9, lateral view of badly disarticulated calyx. B. Enallocrinus sp. holdfast, TUG 1395−39, column of Enallocrinus holdfasts lacking the rhizoids. C. Field photograph of an uncollected in situ Enallocrinus holdfast. Note wide, pentalobate lumen and long radices of holdfast. Scale bars 10 mm.