Lyracystis
| Lyracystis Temporal range:
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|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Class: | †Eocrinoidea |
| Order: | †Gogiida |
| Family: | †Lyracystidae |
| Genus: | †Lyracystis Sprinkle & Collins 2006 |
| Type species | |
| Gogia? radiata (pars) Sprinkle 1973
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| Species[1] | |
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Lyracystis is an extinct genus of Cambrian eocrinoid echinoderm and the type genus of the gogiid family Lyracystidae.[2] The type species, L. radiata, is known from several specimens from the Burgess Shale of British Columbia,[3] while L. reesei is known from a single specimen from the slightly younger Spence Shale of Utah.[4]
Description
Lyracystis radiata is among the largest echinoderms known from the Middle Cambrian. The multiplated stalk of Lyracystis could reach over 11 cm in length, making it one of the highest-level suspension-feeding echinoderms of its time.[5] Aside from the length, most stalk and theca featuers, such as epispires for respiration, are typical of of Early to Middle Cambrian eocrinoids.[6]
The feeding appendages of Lyracystis are its most dramatic feature, with three ambulacra (A, shared BC, and shared DE) extending to the edge of the oral surface of the theca before branching into two exothecal trunks forming a heart- or lyre-shaped structure with endotomously branching brachioles growing vertically from the trunks. Unlike in most echinoderms where the BC ambulacrum divides into B and C, and the DE into D and E, resulting in a total of five ambulacra, the A ambulacrum also divides, producing tri-radial ambulacral symmetry with three pairs of exothecal trunks.[7]
Notably, these appendages are not considered "arms" in the sense of crinoid arms, as they are not homologous to crinoid appendages.[8] A comparison of Lyracystis appendages to crinoid arms noted that the morphology of contemporary crinoid arms was quite different, with only much later (Ordovician) taxa having superficial similarities to Lyracystis.[6]
Classification
Lyracystis is a member of the Lyracystidae, a family defined by the long stalks and distinctive feeding appendage morphology shared by Lyracystis and the family's only other member, Balangiocystis.[8]
It is assigned to the order Gogiida based on the presence of epispires.[9] A 2017 phylogenetic analysis recovered Lyracystis as more basal within the Gogiida than the families Eocrinidae and Lichenoididae.[10]
Lyracystis radiata was originally identified as Gogia? radiata as the first fossils collected included only the theca and stalk, whith the feeding appendages collected separately and described as the "Burgess Shale 'Arms.'" The discovery of Lyracystis reesei confirmed that the "arms" matched the theca and stalk of the type specimen of Gogia? radiata, leading to its reassignment to Lyracystis. This connection was further confirmed by the discovery of additional L. radiata specimens.[11] Some other Gogia? radiata specimens were determined to be an actual Gogia species, now named G. stephenensis.[12]
References
- ^ Sprinkle et al. 2011, p. 254
- ^ Sprinkle & Collins 2006, p. 311
- ^ Sprinkle & Collins 2006, pp. 313–315
- ^ Sprinkle & Collins 2006, pp. 315–317
- ^ Sprinkle & Collins 2006, pp. 314–315
- ^ a b Sprinkle & Collins 2006, p. 306
- ^ Sprinkle et al. 2011, pp. 251–253
- ^ a b Sprinkle et al. 2011, p. 253
- ^ Sprinkle et al. 2011, p. 250
- ^ Nardin et al. 2017, p. 680
- ^ Sprinkle & Collins 2006, p. 304
- ^ Sprinkle & Collins 2006, p. 303
Works cited
- Nardin, Elise; Lefebvre, Bertrand; Fatka, Oldřich; Nohejlová, Martina; Kašička, Libor; Šinágl, Miroslav; Szabad, Michal (2017). "Evolutionary implications of a new transitional blastozoan echinoderm from the middle Cambrian of the Czech Republic". Journal of Paleontology. 91 (4): 672–684. Bibcode:2017JPal...91..672N. doi:10.1017/jpa.2016.157.
- Sprinkle, J.; Collins, D. (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. Bibcode:2006CaJES..43..303S. doi:10.1139/E05-107.
- Sprinkle, James; Parsley, Ronald L.; Zhao, Yuanlong; Peng, Jin (2011). "Revision of Lyracystid Eocrinoids from the Middle Cambrian of South China and western Laurentia". Journal of Paleontology. 85 (2): 250–255. doi:10.1666/10-072.1.
External links
- "Lyracystis radiata". Burgess Shale Fossil Gallery. Virtual Museum of Canada. 2025.