A Silurian sphinctozoan sponge from east-central Cornwallis Island, Canadian Arctic

Abstract

The first Silurian sphinctozoan ever recorded is reported from the Canadian Arctic. The polysiphonate sphinctozoan, Rigbyspongia catenula n. gen., n. sp., is found associated with numerous anthaspidellid sponges. Diagnostic features of the new genus are its numerous axial siphons and vertical pillars within each chamber. Although it is structurally complex for a sphinctozoan of this age and is the only Silurian representative of the order, this new genus provides few clues to the still enigmatic problem of Paleozoic sphinctozoan phylogeny.

Wenlock (Silurian) graptolites, Cape Phillips Formation, Canadian Arctic Islands

“…Graptolites comprise by far the most abundant megafaunal element in any section. Other faunas found in either intimate association with graptolites, or in carbonate interbeds, include sponge spicules and radiolarians (Goodbody 1982(Goodbody , 1986, sponges (Rigby & Chatterton 1989;de Freitas 1987), brachiopods (Lenz 1986;Zhang 1989) and trilobites (Perry & Chatterton 1977). Other undescribed and less common groups include nautiloids and cardiolid bivalves.…”

Upper Permian Inozoid, Demospongid, and Hexactinellid Sponges from Djebel Tebaga, Tunisia

“…We now know that sphinctozoans extended far back into the Paleozoic, before the Carboniferous (Rigby and Blodgett, 1983;Rigby and Potter, 1986;de Freitas, 1987;Senowbari-Daryan, 1990), and that they were probably polyphyletic; therefore common origin of these two major groups in the late Paleozoic is improbable. The record is incomplete, but the nonspiculate inozoids could have evolved from the Carboniferous Des Moinesian-Missourian Maeandrostia and Fissispongia from a sphinctozoan lineage ( Fig.…”

“…Rigbyspongia de Freitas, 1987, a genus in the family Cryptocoeliidae Steinmann, 1882, from the Upper Silurian of Canada, has a trabecular filling structure, but it, too, is far removed from the apparently later Carboniferous, early roots for the inozoid sponges. Senowbari-Daryan (1990, p. 172) noted that all of the then known Carboniferous sphinctozoan genera lack filling structures, so an obvious connection of the early to middle Paleozoic sphinctozoans to the later inozoids and inozoans must remain uncertain.…”

A new Cambrian sphinctozoan sponge from North America, its relationship to archaeocyaths and the nature of early sphinctozoans

“…Other early Palaeozoic sphinctozoan faunas have been documented: Ordovician, from Australia, California, and the Yukon and Alaska (Webby & Rigby, 1985;Rigby & Potter, 1986;Rigby, Potter & Blodgett, 1988); Silurian, from the Canadian Arctic (de Freitas, 1987); and Devonian, from Australia and Alaska (Pickett & Rigby, 1983;Rigby & Blodgett, 1983). Attempts have been made to place all these forms in a general early Palaeozoic scheme of sphinctozoan evolution (Zhuravleva & Myagkova, 1974;Beljaeva & Nikitini, 1984;Rigby & Potter, 1986;Kruse, 1987).…”