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

Abstract

Abundant anthaspidellid orchoclad lithistids occur in thin biostromes of Wenlockian age of the Canadian Arctic. The sponges are well preserved, and many have similar internal architecture. Synonymization of Calycocoelia Bassler, 1927, Rhopalocoelia Raymond and Okulitch, 1940, Somersetella Rigby and Dixon, 1979, and Steliella Hinde, 1889 under the genus Archaeoscyphia Hinde, 1889 is necessary in light of continuous morphological variation of the more than 100 specimens in the study collection. Synonymization takes into consideration various features formerly used to define the five taxa, including parietal width, canal diameter, annulation, presence of monaxons in trabs, dermalia, position of the trab-pinnation surface, spicule dimension, and canal disposition. Several features previously thought to be distinctive generically are shown to be species significant or to be a result of variation within a single species or specimen.De nombreuses tponges lithistides (anthaspidellides) sont prtsentes dans de petits biostromes d'gge wenlockien de I' Arctique canadien. Ces tponges sont bien pkservtes, et plusieurs posskdent une structure interne identique. Des variations graduelles de morphologie observtes sur plus de cent sptcimens suggkrent que les genres Calycocoelia Bassler, 1927, Rhopalocoelia Raymond et Okulitch, 1940, Somersetella Rigby et Dixon, 1979 et Steliella Hinde, 1889 tombent en synonymie sous le genre Archaeoscyphia Hinde, 1889. Ce regroupement tient compte des carattristiques morphologiques jusqu'k maintenant utiliskes pour distinguer les cinq genres dtjh mentionnts comme la << largeur parittale P, le diamktre des canaux, 1'<< anneau n , la pksence de monaxons dans les '< trabs P, les spicules derrnales, la position de la surface du << pimation *, la dimension des spicules et la disposition des canaux. La pksente ttude montre que plusieurs de ces caracteristiques considtkes comme repksentatatives au niveau du genre le sont plut6t au niveau de l'espkce ou encore sont le dsultat de variation chez une espkce ou un sptcimen.

Lower and Middle Ordovician Lithistid Demosponges from the Mingan Islands, Gulf of St. Lawrence, Quebec, Canada

“…These ostia on exterior and as canals in interior generally 0.4-0.5 mm in diameter, may be slightly longer than wide on exterior. Spacing of ostia range from side-by-side to separated by tracts 0.3-0.4 mm thick, in vertical sections may occur 6-8 per 5 mm within single rows, separated by parities, as that term was used by De Freitas (1989). In vertical sections, walls only 5-6 mm thick in troughs, but up to 7-9 mm thick on annulations, out from smooth gastral surface.…”

Ordovician sponges from the Lenoir Limestone, Tennessee: new evidence for a differential sponge distribution along the margins of Laurentia

“…regularis as having large canals, which were sketched as being somewhat bulbous toward the gastral margin. De Freitas (1989), in his revision of some of the anthaspidellid genera, recognized large straight, not bulbous radial canals with a 0.4–0.6 mm diameter in R . regularis .…”

A new Silurian (Llandovery, Telychian) sponge assemblage from Gotland, Sweden

“…-Bassler (1927) gave a very brief and loose definition of the species. De Freitas (1989), in his thorough study of Silurian anthaspidellids from Arctic Canada, referred Calycocoelia to Archaeoscyphia Hinde, 1889, on account of similarities in skeletal features and aquiferous systems. Although Johns (1994) followed de Freitas' opinions in many respects, he maintained Calycocoelia as a distinct genus with C. typicalis as the type species.…”

“…Rigby & Chatterton (1989) described somewhat older (Wenlock and Ludlow) sponge associations from Baillie-Hamilton and Cornwallis Islands (Arctic Canada). De Freitas (1989) described orchocladinid sponges of Wenlockian age, as well as a more varied sponge fauna consisting of lithistids and hexactinellids of Ludlovian age (de Freitas 1991), both from Cornwallis Island. Rigby & Chatterton (1994, 1999 described a hexactinellid sponge and an assemblage of Wenlockian demosponges from the Mackenzie Mountains (Northwest Territories, Canada).…”