Crinoidea? (stem group echinoderms)
The taxonomic position of Echmatocrinus is uncertain. This animal is either considered as a primitive crinoid (Sprinkle, 1976, Sprinkle and Collins, 1998), a cnidarian (Conway Morris, 1993) or an octocoral (Ausich and Babcock, 1998, 2000).
Echmatocrinus – from the Greek echmatos, “holdfast, or stalk,” and krinos, “lily.” The name refers to the shape and the attachment part.
brachiatus – from the Greek brachiatus, “having arms,” in reference to the presence of arms.
Holotype – GSC25962 in the Geological Survey of Canada, Ottawa, Canada.
Burgess Shale and vicinity: none.
Other deposits: none.
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
The Walcott and Raymond Quarries on Fossil Ridge. A couple of specimens were also collected from the east side of Mount Field.
Brief history of research:
Echmatocrinus was first described by Sprinkle in 1973 as a primitive crinoid based on five specimens, four of which were originally collected by Walcott but never published. The fifth and best preserved specimen, now the holotype, was collected by the Geological Survey of Canada in 1967. Conway Morris reinterpreted Echmatocrinus as a possible cnidarian in 1993 and Ausich and Babcock (1998) suggested an octocoral affinity. Both of these newer interpretations were rejected by Sprinkle and Collins in a larger revision of all material available including new specimens collected by the Royal Ontario Museum (1998, but see Ausich and Babcock 1998).
The body consists of a small attachment disk (holdfast), a conical stalk ending into a wide cup (theca) with 7 to 10 short arms attached to the edge of it. Soft appendages are present on alternate sides of each arm. The stalk is at least the length of the cup and arms combined. A number of plates, presumably originally weakly mineralized cover the entire body. The plates are irregular in shape and might have sutures along them. Plates are more regular and pronounced in the arms. The arms are uniserial (i.e., they do not branch) and could fold on themselves. A surface texture or ornament is also present on the external parts of the plates. This ornament is interpreted by some authors as evidence of a stereom, the characteristic mineralized skeleton of all echinoderms. The locations of the mouth and anus are uncertain.
Echmatocrinus is very rare in the Walcott Quarry, where it makes up a negligible percentage (0.01%) of the community (Caron and Jackson, 2008). About two dozen specimens are known in total from three different localities.
Echmatocrinus was attached to skeletal debris on the seafloor and evidently it needed hard substrates for growth. It is often found in clusters of several individuals thus showing a gregarious habit. Food particles were likely transported along the arms to a central mouth near the summit of the cup.