Gogiid Eocrinoids (Echinodermata) from the Lower and Basal Middle Cambrian, Yangtze Platform, Guizhou Province, China  

Thousands of new specimens of Sinoeocrinus and Globoeocrinus (basal Middle Cambrian: Kaili Formation) and Guizhoueocrinus (Lower Cambrian: Balang Formation), from the eastern margin of the outer shelf/upper slope of the Yangtze Platform (Guizhou Province, China) have greatly enhanced our knowledge of ontogenetic development, heterochrony and functional morphology in these groups.  Guizhou gogiids are similar to, but are more primitive than, those of western Laurentia and southern Gondwana.  Thecal height is used as a proxy for development.  Ontogeny and emplacement of brachioles is similar in all three genera. 

Guizhoueocrinus is the most primitive genus known.  In both the theca and the stalk, its plates are poorly organized, and independent of the ambulacra.  The number of thecal and stalk plates in Sinoeocrinus and Globoeocrinus is reduced by paedomorphosis.  Nearly half the stalk plates in Sinoeocrinus, and all those in Globoeocrinus, are juvenile in character.  Sutural pores are restricted to thecal plates, and are emplaced in three series: (1) just below the ambulacra; (2) just above the stalk/thecal juncture; and (3) over the rest of the theca.  Pores change from round to oval as the organisms mature; this transition is observed in juvenile Globoeocrinus, early mature Sinoeocrinus, and in the second row of plates in juvenile-to-mature specimens of Guizhoueocrinus. The pores peramorphically become triangular in mature Sinoeocrinus, and in late-juvenile to mature Globoeocrinus.

Apparent soft-part preservation associated with Guizhoueocrinus suggests that respiratory tissue resembled papillae, which bowed inwards like a pocket.  In Globoeocrinus and Sinoeocrinus, the (probable) respiratory surface area falls off relative to thecal volume.  Respiratory efficiency was maintained by pressurizing the theca, by covering both the mouth and anus, then circulating coelomic fluid by peristaltic gut pumping, to propel the fluids past the inwardly directed respiratory tissue.  The attachment disks of gogiids were ‘glued’ to the substrate, probably with collagen.