MORPHOLOGIC FEATURES OF PRIMITIVE ECHINODERMS NOT SEEN IN MODERN FROMS AS DEMONSTRATED BY MIDDLE CAMBRIAN SOLUTES AND STYLOPHORANS FROM UTAH

Cambrian and later (Lower Paleozoic) homalozoan and blastozoan echinoderms possess characters that differ greatly from and are not retained in more modern groups. The solutes Coleicarpus (Wheeler Shale) and Castericystis (Marjum Formation) both Middle Cambrian, Utah are arguably the most primitive members of the Echinodermata. They are (antero- posteriorly) nearly bilaterally symmetrical. Thecae are transversely oval in cross-section and irregularly and flexibly plated except for framing plates adjacent to arm, proxistele, and the anterior thecal margin. Thecal plates are thin and have stereom structured calcite plates of an undetermined growth-mode. A well-defined hydropore, (located adjacent to the single feeding arm), is indicative of an internal water vascular system, and a robust anal pyramid made up of concertina-folded lath-like platelets. The arm is biserial, somewhat thicker proximally than distally, deeply hollowed feeding furrow opening directly into the body cavity. Tall pointed alternating cover plates extend to end of arm. There is no evidence for an exothcal water vascular system associated with the food groove. Stele in both genera ends in an attachment nubbin where juveniles are bioglued to the bottom. Coleicarpus never loses its sessility in adult forms: in specimens of mature Castericystis the stele ends in a curved, multiplated spine-like anchor to attach the otherwise vagile adult organism. The proxistele in both genera is polymerous, turgor is muscular and hydrostatic, and in Coleicarpus helps to place theca and arm to into favorable food laden currents: in Castericystis it provides locomotive forces to wriggle animal along the seafloor. The mesi- and dististele in Coleicarpus is similar to the proxistele and serves as a stalk. In Castericystis the mesi- and flattened (tail-like) dististele have developed massive plates and spines which serve reinforce the structure and help to anchor the animal. Essentially bilateral flexible thecae (including genera with marginal frames in other solutans), robust anal pyramids, hollow arm cavities, (suggestive of a hydrostatic skeleton), and a water vascular system restricted to the theca are viewed as solutan characters which are widely shared with Stylophora. Many of these characters are also shared with all other homalozoans and blastozoans.