Compsocrinina Ubaghs, 1978b

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

Suborder Compsocrinina Ubaghs, 1978b Superfamily Periechocrinoidea Bronn, 1849

Discussion.—In order to understand the oldest periechocrinids from the Brassfield Limestone (Aeronian) of southwestern Ohio, USA, Ausich (1987) emended the diagnosis of the family. This emended diagnosis was needed to accommodate morphological variability in the primitive Brassfield periechocrinids. Stratigraphically younger forms, as defined by Ubaghs (1978b), had more stable, basic morphology. Following Ausich (1987), six Silurian periechocrinid genera are now recognized, including Acacocrinus Wachsmuth and Springer, 1897 ; Ibanocrinus Ausich, 1987 ; Periechocrinus Morris, 1843 ; Stiptocrinus Kirk, 1946 ; Tirocrinus Ausich, 1987 ; and a new genus from Estonia, Saaremaacrinus .

Among these genera, only Periechocrinus and Saaremaacrinus gen. nov. have a biseries of alternating plates in the regular interrays. In contrast, Acacocrinus , Ibanocrinus , Stiptocrinus , and Tirocrinus have interradial plates above the first interradial plate arranged into more distinct ranges symmetrical about the interray midline. Furthermore, both Periechocrinus and Saaremaacrinus have more fixed brachials, interradials, and intraradials than other Silurian periechocrinids. Saaremaacrinus is also similar to Stamnocrinus and Pyrixocrinus from the Devonian. However, these two Devonian forms have 20 free arms and Saaremaacrinus has only 10.

This new periechocrinid is consistent with Ausich and Kammer (2008) in that the periechocrinids were only present on Baltica during the Silurian. Saaremaacrinus extends this range into the Pridoli. This new genus should be nested within the clade containing Periechocrinus , as discussed in Ausich and Kammer (2008).