Middle silurian ludlovian and wenlockian sponges from Baillie-Hamilton and Cornwallis islands, Arctic Canada

Abstract

The Silurian sponge fauna described here from Baillie-Hamilton and Cornwalls islands is one of the most diverse known from North America. The fossils are from Wenlockian-Ludlovian age deposits of the Cape Phillips Formation, which accumulated on the slope and in the basin of the Franklinian Geosyncline. The Cape Phillips Formation consists of interbedded shale, calcareous shale, and limestone, and most of the fossils are found in allochthonous limestone beds, mass movements having transported much of the fossil material downslope. Silurian sponges described here are representative of a distinct sponge biogeographic province that occurs north and northwest of a line along the Transcontinental Arch and contrasts with one to the southeast where sphaerocladine lithistid and heteractinid calcareous sponges are dominant. New genera within the demosponges include the rhizomorine Parodospongia and the orchocladines Antrospongia and Cauliculospongia. New hexactinellid genera include Corticulospongia and Lumectospongia. New species described here include the rhizomorines Haplistion frustrum and Parodospongia euhydra and the extensive orchocladines Antrospongia aberans, Aulocopium nana, Calycocoelia micropora, Cauliculospongia solida, Dunhillia fistulosa, D. megaporata, D. pluraliporosa, Patellispongia alternata, Perissocoelia (?) gelasinina, Perissocoelia (?) spinosa, Psarodictyum attenuatum, and Somersetella amplia. Astylospongiella (?) lutera and Astylospongiella striola are the only new representatives of the Sphaerocladina. The hexactinellid Amphidiscosa are represented by Lumectospongia uncinata n. gen. et sp. and the Lyssacinosa by the new Corticulospongia floccosa n. gen. et sp. and Dictyospongia apache n. sp. Carpospongia globosa (Eichwald, 1830) is reported here from North America for the first time. The broadly distributed Archaeoscyphia minganensis (Billings, 1859), Hindia sphaeroidalis (Duncan, 1879), and species of Patellispongia and Psarodictyum add "universal" elements to the assemblage.

Silurian Archaeoscyphia from the Canadian Arctic: a case for simplified generic taxonomy in the anthaspidellid lithistids (Porifera)

“…The spicules are perhaps simply an artifact of preservation; nevertheless, the presence of specialized dermalia has been employed in differentiating Calycocoelia from Archaeosqphia (Rigby 1973, p. 108). Consistent with the findings of and Rigby and Chatterton (1989), a thin dermalium is present in a supposed representative of A. minganensis (Billings) of the studied collection. The dermalia described herein are strongly reminiscent of those of C. typicalis (according to van Kempen 1981) and of Somersetella.…”

“…. " (Rigby and Nitecki 1973, p. 3), and minganensids of Rigby and Chatterton (1989) and of the author's collection have rounded annulae separated by somewhat less rounded indentations; hence, annulation, by itself, apparently does not clearly distinguish Archaeoscyphia from closely allied sponges, such as Calycocoelia. Moreover, Archaeoscyphia spiculature is similar to that of Calycocoelia, yet this similarity has not been clearly addressed in the literature (van Kempen 1978, pp.…”

“…In fact, distinction of Somersetella within the current collection is not possible based on the diagnoses given in the literature. The fineness of Somersetella's skeleton was suggested as a means of differentiation (de Freitas 1987a), but Somersetella of Rigby and Dixon (1979), of Rigby and Chatterton (1989), and of the anthaspidellids of this study form a continuum of skeletal dimensions (Figs. 3, 4) above, and generic assignment based on this trait is subjective.…”

“…614 -615) was originally erected to include weakly annulate, obconical sponges with thin dermalia and trabs cored by monaxons. Differentiation of the Somerset Island genus based on gross morphology, as suggested by Rigby and Chatterton (1989), is extremely difficult. In fact, distinction of Somersetella within the current collection is not possible based on the diagnoses given in the literature.…”

“…Dendroclones, the basic structure of the skeletal net, tend to be extremely variable and intergradational, and complex terminology might be a potential result. For simplicity, currently used terminology (sensu Rigby and Chatterton 1989;Rigby 19866;Rigby and Webby 1988;van Kempen 1978) will be applied to the various dendroclone morphotypes, that is, I shaped (or amphiarborescent), X shaped (or quadraclonid), Y shaped (or triclonid).…”