20
2
May
295
335
COPPER, P. 1977. Zygospira and some related Ordovician and Silurian atrypoid brachiopods. Palaeontology, 20, 2, 295–335.
Paul Copper The Zygospiridae are redefined to include 'primitive' atrypoid brachiopods with dorsally to dorsomedially directed spiralia, normally with fine ribs and a one-piece jugum dorsal to the spiralia. The Ordovician-Silurian family is divided into three: Zygospirinae, Catazyginae (new sub-fam.), and Tuvaellinae. Internal structures of Zygospira, Anazyga, Catazyga, Pentlandella, and Tuvaella are evaluated in terms of their evolutionary significance. A new genus Zygatrypa is erected. Eospirigerina, which was probably derived from zygospirid stock in the late Ordovician, differs in having ventrally located, separated jugal processes and trends towards 'frilly' shells: this represented a major jump towards a postulated Zygospiraella-Protatrypa-Gotatrypa lineage. In late Caradoc-Ashgill times Catazyga inhabited deeper water, whereas Zygospira lived in shallow-water communities. The Clintonellinae, including Alispira, are tentatively assigned to the Atrypidae, with Silurian taxa such as Nalivkinia and Anabaria. The Palaeontological Association (Free Access)