Mollusca		CONCHIFERA
Basal Mollusca		Coreospiridae

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Coreospiridae

Basal Mollusca |--Polyplacophora `--CONCHIFERA (Helcionelloida) |--SCENELLIDAE `--+--HELCIONELLIDAE |?-YOCHELCIONELLIDAE |?-STENOTHECIDAE |?-COREOSPIRIDAE |--Monoplacophora `--+--Diasoma | |--Rostroconchia | `--Bivalvia `--Cyrtosoma

Introduction   Diagnosis   Representative Genera

Introduction

Early Cambrian to Furongian

Coreospira rugosa Saito 1936 - side (top) and front views. Late Early Cambrian (= Botomian?), xxxx (Korea); length about 3 mm	Cycloholcus nummus Knight 1947 Furongian (Paiban), Laurentia (Tennessee); length about 1 cm	Sinuella minuta Knight 1947 Furongian, Laurentia (Texas); length about 1 mm.

These are a small group of mostly tiny, laterally compressed, untorted, endogastrically-curved molluscs, superficially resembling tiny bellerophontid gastropods. In fact they resepresent an early side-branch of the Helcionelloid line; one of a number of "gastropod-like" molluscs of the early Palaeozoic. Most workers place them in the Helcionelloida, while Wagner seems to imply a seperate clade as an unresolved dichotomy of "Tergoymya," Paragastropods, and assorted forms. Unlike gastropods, the head was probably very primitive, although the relatively high profile probably means it could crawl reasonably fast (relative to infaunal Helcionellids), so the eyes may have been reasonably developed, at least relative to its forbears . The animal crawled with the spire of the shell facing backwards, unlike pre-torted Bellerophontids. The Coreospirids did not survive the end Cambrian extinction event.

Diagnosis

The following diagnosis is modified from the Treatise:

Family Coreospiridae Knight 1947

"Shell with complete or incomplete bellerophontiform coiling [cyrtoconic to planispiral]; with septum or septa partitioning off the apex. No anal emargination; flattenod, with nearly rectangular cross section; with posterior trainlike extension of shell margin."

Representative Genera

Coreospira Late Early to Early Middle Cambrian (Toyonioan to Amgan). N.Am., NE.Asia. Cycloholcus, early Furongian (Paiban). N.Am. Sinuella Furongian. N.Am.

note: [Sinuella a sinuitid Bellerophontid in the Treatise, but according to Wagner is the sister taxon to Coreospira]