INFERED MORPHOLOGY AND FUNCTION OF SOFTPART SUTURAL PORE STRUCTURES BASED ON LOWER AND MIDDLE CAMBRIAN GOGIID EOCRINOIDS FROM GUIZHOU PROVINCE, CHINA

Mechanics of respiration is poorly understood in Echinoderms and is especially true in extinct groups like eocrinoids. Eocrinoids unlike other blastozoans have no tubular or fold structures preserved in stereom that give indication of respiratory surface area. Rather, there are simply sutural pores and presumed soft respiratory tissue covering them. Order of sutural pore emplacement is predictable – just under the ambulacrum in early juveniles; in the stalk attachment area in later juveniles and over the rest of the theca in late juveniles and in early mature specimens. The coverings could have been flat or outward blister-like bulges or, inward bulges or deeper inward facing pockets. Guizhoueocrinus yui Zhao et al., (L., Cam. Balang Fauna, Guizhou Province) has been found with what seems to be soft part, inward facing, sub circular to parabolic shaped pockets that are preserved as everted pockets. Eversion is secondary, apparently caused by putrefying gas. Surface area of the pockets was measured and compared to the volume of the theca and proximal stalk on a (visually informative) semi-log scale. Sinoeocrinus lui (Zhao et al.) (M. Cam., Kaili Biota, Guizhou Province) was studied and measured in a similar manner but respiratory area was calculated a more traditional manner, as if the pores were covered with out- or in- bowing soft tissue covers. In each case, respiratory pore area was rapidly added in juvenile and early mature stages and then, despite the great increase in pore size in mature specimens, was reduced in area relative to thecal volume. In both genera, brachioles are long thin with very tall covering plates. Their surface area is very high and respiration to support brachiolar functions is believed to be by local diffusion. Circulation of oxygenated coelomic fluids was probably generated by peristaltic waves in the gut; there is no evidence for a circulatory system. The theca was probably pressurized above ambient and this interpretation supported by presence of (probable) non-opening cover plates over the mouth, complex anal pyramids that acted as outward opening one way valves, and pyramids covering the gonopore opening.