Lyracystis radiata

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A large stalked echinoderm with delicate lyre-shaped arms

Reconstruction of Lyracistis radiata.

Lyracystis radiata (USNM 165399) – Holotype. Specimen showing stem with rounded plates and partial theca with heavily ridged plates. Specimen height = 46 mm. Specimen dry – direct light (left), wet – direct light (right). Raymond Quarry.

Lyracystis radiata (ROM 57229) – Part and counterpart. Nearly complete specimen (missing stalk), showing large pyrite cluster around the theca. Specimen height = 138 mm. Specimen wet – polarized light (left), dry – polarized light (right). Walcott Quarry.

Taxonomy:

Kingdom: Animalia

Phylum: Echinodermata

Class: Eocrinoidea (Order: Gogiida, stem group echinoderms)

Species name: Lyracystis radiata

Remarks:

Lyracystis is an eocrinoid, related to the blastozoans, an early group of echinoderms (Sprinkle, 1973).

Described by: Sprinkle

Description date: 1973

Etymology:

Lyracystis – from the Greek lyra, “lyre, flute,” and kystis, “bladder, sac,” in reference to the globular theca bearing lyre-shaped arms.

radiata – from the Latin radiatus, “rayed,” in reference to the position of the arms.

Type Specimens: Holotype –USNM165399 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.

Other species:

Burgess Shale and vicinity: none.

Other deposits: L. reesei Sprinkle and Collins, 2006 from the Middle Cambrian Spence Shale in Utah.

Age & Localities:

Period:

Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).

Principal localities:

The Walcott, Raymond and Collins Quarries on Fossil Ridge and the Trilobite Beds on Mount Stephen.

History of Research:

Brief history of research:

This species was originally described as Gogia (?) radiata (Sprinkle, 1973), but new fossil material discovered by the Royal Ontario Museum led to a revision of the previously available specimens and the recognition of two different gogiid forms. Some specimens of G.(?) radiata were assigned to a new genus, Lyracystis radiata, and others were assigned to a new species of Gogia, G. stephenensis (Sprinkle and Collins, 2006).

Description:

Morphology:

Lyracystis is the largest eocrinoid from the Burgess Shale reaching up to an estimated 21 cm in height. The stem was longer than the length of the main body (theca) and arms combined. Three large lyre-shaped arms are attached to the edges of the top of the theca, each with numerous (up to 43) smaller and stiff biserial branches (brachioles), organized in heart-shaped array between the V-shaped arms. The theca is globular to ellipsoidal with primary and smaller secondary plates, both bearing ridged sutural pores (or epispires). The stem is very thin and cylindrical with multiple plates which tend to be rounded near the attachment with the theca. The morphology of the basal part of the stem, is not known.

Abundance:

This species is very rare, only a dozen complete to nearly complete specimens are known.

Maximum Size:

210 mm

Ecology:

Life habits: Epibenthic, Sessile

Feeding strategies: Suspension feeder

Ecological Interpretations:

Lyracystis was most likely attached to the sea floor by a stalk and fed by capturing small water-borne particles with its thin, tendril-like arms. Food particles were transported from the arms to food grooves (ambulacrum) into a central mouth at the top of the theca.

References:

SPRINKLE, J. 1973. Morphology and evolution of blastozoan echinoderms. Harvard University, Museum of Comparative Zoology Special Publication: 1-284 p.

SPRINKLE, J. AND D. COLLINS. 2006. New eocrinoids from the Burgess Shale, southern British Columbia, Canada, and the Spence Shale, northern Utah, USA. Canadian Journal of Earth Sciences, 43: 303-322.