Function and attachment of the stem in Isocrinidae and Pentacrinitidae: review and interpretation

Abstract

A review is given of observations and interpretations of the attachment in Isocrinida. It is concluded that all adult Isocrinida discard distal parts of their column and live attached by distal cirri to the bottom or to objects lying on the bottom. From time to time the column may break below a nodal and the isocrinid drift along the bottom until it regains attachment with the cirri. In undisturbed environments a considerable length of the tapering distal part of the column may be maintained, and several specimens may be connected by the entangled distal parts of the columns lying on the bottom. Specimens of Seirocrinus subangularis attached to tree trunks in the Lower Jurassic Posidonia shale of Holzmaden, Germany, have been interpreted as pseudoplanktic. These are all adult specimens with distal parts of their column discarded before they attached themselves to the trunks. Furthermore, since adult specimens cannot swim to the surface, they must have attached themselves to sunken trunks lying on the bottom.

The Oldest Post-Palaeozoic Crinoid and Permian-Triassic Origins of the Articulata (Echinodermata)

“…Reorganisation of stalk ligaments and possession of cirri are intimately linked to the behavioural innovation of temporal relocation, which is achieved by autotomising the distal stalk and using the arms to crawl across the substrate (Rasmussen, 1977;Baumiller and Ausich, 1992). The ability to autotomise the distal stalk occurred in holocrinids by the Induan/Olenekian boundary and represents the only novel mode of life that appeared in benthic invertebrates during the Early Triassic (Foster and Twitchett, 2014).…”

Palaeoenvironmental Control on Distribution of Crinoids in the Bathonian (Middle Jurassic) of England and France

“…Those taxa with more cirri (and hence shorter inter− nodals) are present in the higher energy facies. This is not un− expected as cirri are the primary attachment structure of these crinoids (Rasmussen 1977), and higher energy settings are likely to have required more robust attachment. It is evi− dent that localised conditions within palaeoenvironments in− fluenced crinoid distributions.…”

Sedimentology of the Upper Triassic Charlie Lake, Baldonnel and Pardonet formations from outcrop exposures in the southern Trutch region, northeastern British Columbia

“…Although isocrinids likely used a holdfast for attachment to the substrate early in their ontogeny, they were likely able to autotomize the distal end of their stalks and relocate to other areas of the shoreface (Baumiller and Hagdorn, 1994;Baumiller et al, 1995). Most crinoids in the study area likely lived on shifting substrates in the offshore transition and lower shoreface, attached to the substrate via loosely rooted cirri (i.e., Rasmussen, 1977;Baumiller and Hagdorn, 1994). Although crinoid material occurred solely as completely disarticulated skeletal debris, much of this material was unabraded, Fig.…”