Type species of the genus: Ptilocrinus pinnatus A.H. Clark, 1907.
Synonymy: Ptilocrinus A.H. Clark, 1907: 551; Bather, 1908: 297; Ptilocrinus (Ptilocrinus) Mironov & Sorokina, 1998 b: 41; Ptilocrinus (Chambersaecrinus) Mironov & Sorokina, 1998 b: 52; Ptilocrinus Roux et al., 2002: 817, 822.
Emended diagnosis. Five unbranched arms; proximal arm pattern usually 1 + 2 3 4 5 + 6 7 + 8 or 7 8 + 9 with first pinnule on Br 4, or on Br 5 with 1 + 2 3 4 + 5. Four proximal brachials nearly equal in height and width. Pinnules relatively rigid without both conspicuous genital expansion and H-shaped plates; lateral plates of the same size or smaller than cover plates, and number and extension in proximal pinnule variable. Tegmen moderately to highly inflated with moderately sized orals and variable anal cone close to oral cone. Aboral cup usually smooth, rarely with small transverse ridges; primibrachials about 2 / 3 radial width; basals three or usually fused. Stalk symplexies with 6–9 crenular units; distal syzygies frequently with well-developed crenularium.
Remarks. Wanner (1916 a) erroneously used the generic name Ptilocrinus for a Devonian fossil species from Germany, which was finally assigned to the genus Eifelocrinus Wanner, 1916 b.
As he described P. a n t a rc t i c u s, Bather (1908: 297–298) gave the first diagnosis of the genus Ptilocrinus. He recognized the following main characters as significant at the generic level: first pinnule on Br 4; arm articulation restricted to 2 / 3 radial width; brachial pair at Br 5 + 6; other brachial pairs infrequent and irregular distally. According to Mironov & Sorokina (1998 b), the presence of H-shaped plates in pinnules justifies the distinction of the genus Dumetocrinus, and they include two subgenera in the genus Ptilocrinus sensu stricto, i.e. Chambersaecrinus and Ptilocrinus. The subgenus Ptilocrinus is based on derived characters in tegmen and distal stalk syzygies. The subgenus Chambersaecrinus is pragmatically maintained for the other species. Complementary studies might be conducted to determine if Chambersaecrinus could be raised to the genus level or if the distinction of two subgenera is not justified.