Class Archaeocyatha Bornemann, 1884

Abstract

Archaeocyatha (Porifera) were an important group of marine sessile organisms during the Cambrian, being almost entirely Early Cambrian but with some relics persisting into the Middle and Late Cambrian. They were filter-feeders limited to the tropical zone. The vast majority were reef dwellers, contributing necessary substrate for the calcified cyanobacteria and cement although seldom themselves producing a true framework to Cambrian reefs. They were stenothermal, stenohaline, stenobathic organisms, favouring well-agitated waters. Archaeocyatha have been assigned to various phyla since their discovery but are now recognised as a class within Porifera based on similarities with calcified sponges in growth pattern, skeletal structure (primary or secondary), functional morphology and evolution- ary trends. The class consists of six orders (based on the number of walls and types of development), 12 suborders (based on the interval- lar elements of the first order), 48 superfamilies (based on the outer wall primary elements), 123 families (4 new) (based on the inner wall primary elements), and 304 genera considered valid here (differentiated on the basis of variations in the primary skeletal elements, distri- bution and size of pores and of intervallar structures). The present work revises, defines, comprehensively illustrates, provides syn- onymies and literature, and updates ages and distributions of all valid supraspecific taxa in the class. Archaeocyath systematics is based on: (1) study of the skeletal ontogeny; (2) morphological functional analysis; (3) establishment of the limits of homologous variability. The taxonomic hierarchy is established according to ontogenetic studies. Intraspecific variation is postulated on the basis of functional analysis coupled with palaeoecological observations.