Stenuroidea

Stenuroidea; Temporal range: Ordovician–Permian PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Echinodermata
Subphylum:	Asterozoa
Order:	†Stenuroidea; Blake, 2013

Stenuroidea is an extinct order of asterozoan echinoderms first defined at ordinal level in 1951 by W. K. Spencer, and later raised to class level in 2013.

The order is restricted from the Ordovician to the Permian with their first appearance in the fossil record being in the Early Ordovician (Tremadocian - Floian).

Characteristics

Stenuroids have two to four rod-like "virgal ossicles", while somasteroids have a series of them. In the derived orders Asteroidea and Ophiuroidea the virgal series is reduced to a single ossicle.

Villebrunaster thorali (Somasteroidea)

Chiniaster (Somasteroidea)

Stuertzaster (Stenuroidea)

Differences in virgals between somasteroids and stenuroids; note that in somasteroids the number of virgals per ambulacral varies based on the width of the arm, while the number of virgals (labeled as inner and outer laterals) in stenuroids is the same along the entire length of the arm.

References

↑ W. K. Spencer. (1951). Early Palaeozoic starfish. Philosophical Transactions of the Royal Society of London, series B 235(B623):87-129
↑ Blake, Daniel B. (2013). "Early Asterozoan (Echinodermata) Diversification: A Paleontologic Quandary". Journal of Paleontology. 87 (3): 353–372. doi:10.1666/12-042.1. ISSN 0022-3360. Retrieved 2026-11-10.
1 2 3 Glass, Alexander; Blake, Daniel B.; Lefebvre, Bertrand (2024-10-31). "An unusual new ophiuroid (Echinodermata) from the Late Ordovician (early Katian) of Morocco". Comptes Rendus Palevol. 23 (25). doi:10.5852/cr-palevol2024v23a25. ISSN 1777-571X.

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[Spencer1951-1] W. K. Spencer. (1951). Early Palaeozoic starfish. Philosophical Transactions of the Royal Society of London, series B 235(B623):87-129

[2] Blake, Daniel B. (2013). "Early Asterozoan (Echinodermata) Diversification: A Paleontologic Quandary". Journal of Paleontology. 87 (3): 353–372. doi:10.1666/12-042.1. ISSN 0022-3360. Retrieved 2026-11-10.

[glass-3] 1 2 3 Glass, Alexander; Blake, Daniel B.; Lefebvre, Bertrand (2024-10-31). "An unusual new ophiuroid (Echinodermata) from the Late Ordovician (early Katian) of Morocco". Comptes Rendus Palevol. 23 (25). doi:10.5852/cr-palevol2024v23a25. ISSN 1777-571X.