A MIDDLE DEVONIAN EPIZOAN CHONETOID BRACHIOPOD: EXAMPLE OF ATYPICAL LIFE HABIT

Chonetoid brachiopods (Brachiopoda, Chonetoidea) were typically living on the bottom of the sea with dorsal valve uppermost. According to data from literature it is likely that many juveniles and some paedomorhic forms had an epiplanctonic mode of life. This report describes a single small chonetoid brachiopod specimen with another mode of life: it was clearly an epizoan on a large coarsely ribbed spiriferid brachiopod. Specimens are from Penn Dixie Quarry, Hamburg, Erie County, New York. Quarry is of Middle Devonian Hamilton Group. Chonetoid brachiopod is tentatively assigned to Devonochonetes scitulus (Hall) and spiriferid to Spinocyrtia granulosa (Conrad). The same chonetoid species is locally abundant in the shale of this quarry and it is commonly present in presumable life position. Here described chonetoid brachiopod is attached with its dorsal valve, which is piritized, to the exterior of the ventral valve of Spinocyrtia. It is located on the posterior quarter of Spinocyrtia. Ventral valve of chonetoid brachiopod is not preserved. The anterior part of chonetoid is directed towards posterior part of spiriferid valve. The hinge of Devonochonetes is roughly perpendicular to the Spinocyrtia's ribs. The shape of dorsal valve of chonetoid brachiopod assumed the shape of the ribs of its host. The other epizoans which are on the anterior half of ventral valve of Spinocyrtia are two inarticulate brachiopods (order Craniida, generic assignement unclear), and a bryozoan. Dorsal exterior of Spinocyrtia is poorly exposed. The conclusions of this finding relate to several atypical features of a chonetoid brachiopod specimen: 1) it describes another, unconventional mode of life of chonetoid brachiopods; 2) marked plasticity (remodeling) of its valve; 3) dorsal valve (and not ventral valve) facing the substrate (spiriferid valve); 4) valves of the epizoan and host have different directions.