POSSIBLE PRE-ECHINODERM AND BASAL-MOST ECHINODERMS (SOLUTA): THEIR FUNCTIONAL MORPHOLOGY AND BIO-ORIENTATION

The pre-echinoderm is probably (but quite contentiously) something akin to the worm-like genus Yanjiahella ( Yanjiahe Formation, Hubei Provine China). This Fortunian age organism has an elongated non-stereom calcareous platted theca, an elongated homoiostele that is divisible into a proxistele and dististele and extending from the anterior margin, a pair of exothecal feeding appendages. Anterior and posterior appendages may be calcareous to some degree but lack stereom structure. The most closely related organisms and considered basal-most echinoderms by dint of stratigraphic position, derived morphology and having stereom calcareous plating over the entire organism are (Cambrian, Stage 3) solutans Coleicarpus (Wheeler Fm.) and Castericytis (Marjum Fm.) from Utah. These genera have polyplated thecae, an anal pyramid at the posterior left margin and a hydropore close to the brachiole at the anterior margin. A single brachiole is present, as in all solutes, (with the possible exception of Coleicarpus) has paired flooring plates with matching cover plates overarching the food groove. This biserial structure is shared with almost all blastozoans. The homoiostele is divisible into a nearly equal length flexible circular proxistele and a flattened stiffer dististele. Coleicarpus differs from all other solutes in that throughout ontogeny it is capable of both sessile and vagile modes of life. Many specimens have an enlarged, distalmost, deeply indented stele ossicle capable of “biogluing” the animal to the bottom or to biodetritus probably by excreting extensible collagen. Based on interpretative functional morphology, much has been published on which face solutes rested on the substrate and whether they were deposit feeders (cover plates facing down) or suspension feeders (cover plates facing up). In both Coleicarpus and Castercystis juvenile specimens attached to adult specimens. Juveniles that attached to the theca almost invariably did so on the face with the brachiole cover plates facing away from the substrate . The probability that juveniles attached to the other (under) thecal face and extended into the substrate is highly unlikely, this facing probably holds true for all solutues. Except for some Ordovician (pre- Hirnantian) genera that are found current oriented in oxic sands; all solutes occur in what appears to be dysoxic, siliciclastic silts and shales.