Texacrinacea

Belongs within: Dendrocrinida.

The Texacrinacea are a group of long-armed crinoids with a tall, slender crown known from the Carboniferous and Permian periods (Moore et al. 1978).

The month’s edition of Gigantic Asses

Published 27 October 2025

Echinoderm anatomy is weird. And crinoids are arguably the weirdest of the bunch (among living classes, at least). Though the overall animal may grow quite sizable between column and arms, the central body or calyx in which the bulk of the organs are contained is relatively tiny. As a result, the openings of the mouth and anus (which are both on the oral side of the calyx) are naturally quite close together. And as crinoids are mostly more or less sessile (even those ones that lack stalks tend not to be energetic movers), this arrangements risks leaving them with something of a bad taste in their mouths.

One potential solution to the problem is the one adopted by the Texacrinoidea, a lineage of stalked crinoids known from the Carboniferous and Permian. In these antediluvian sea lilies, the anus is situated at the top of a long anal sac, armoured by longitudinal rows of small plates. As ludicrous as this structure might appear, resulting as it does in an animal that is about one-third arse, in life it would have functioned to carry wastes away from the calyx and eject them safely into the water column. No mess, no fuss.

Other than their enormous poop-chute, texacrinoids are characterised by a tall crown with long, slender arms (Moore et al. 1978). The arms bore regular pinnules and could be present in large numbers—up to eighty arms each are recorded for members of the family Staphylocrinidae. Only one texacrinoid genus, the Late Carboniferous Allosocrinus, is known to have had the basic complement of five arms.

I have not found any direct discussion of the preferred habitat of texacrinoids but I imagine they would have occupied locations subject to consistent but not chaotic water movement. Their flexible stalk and extensive crown seem well suited for the production of a broad filtration fan held at an angle to the current, allowing the crinoid to capture particles as they floated past. The opening of the anal sac would have then been positioned even further downstream. It sounds an idyllic, carefree existence but it was doomed to come to an end, as the texacrinoids were just one of the numerous lineages to meet their end in the mass extinction that closed off the Permian.

Systematics of Texacrinacea

Characters (Moore et al. 1978): Crown tall and slender, cup bowl-shaped with basal concavity and steep sides near rim, arm facets plenary, one to three anals in cup, anal sac tall, composed of longitudinal rows of plates, arms long, commonly many (to 40) but five or 10 in some.

Texacrinacea
    |--Sellardsicrinus Moore & Plummer 1940 [Sellardsicrinidae]ML78
    |    `--*S. marrsae Moore & Plummer 1940ML78
    |--Galateacrinus Moore 1940 [Galateacrinidae, Galateacrininae]ML78
    |    |--*G. stevensi Moore 1940ML78
    |    `--G. ornatusML78
    |--Texacrinidae [Texacrininae]ML78
    |    |--Marathonocrinus Moore & Plummer 1940ML78
    |    |    `--*M. bakeri Moore & Plummer 1940ML78
    |    `--Texacrinus Moore & Plummer 1940ML78
    |         |--*T. gracilis Moore & Plummer 1940ML78
    |         `--T. associatusML78
    `--StaphylocrinidaeML78
         |--Staphylocrinus Burdick & Strimple 1969ML78
         |    `--*S. bulgeri Burdick & Strimple 1969ML78
         |--Abrotocrinus Miller & Gurley 1890ML78
         |    `--A. unicus (Hall 1861) [=Scaphiocrinus unicus; incl. *A. cymosus Miller & Gurley 1890]ML78
         |--Agnostocrinus Webster & Lane 1967ML78
         |    `--*A. typus Webster & Lane 1967Ml78
         |--Dinotocrinus Kirk 1941ML78
         |    `--*D. compactus Kirk 1941ML78
         |--Exochocrinus Burdick & Strimple 1969ML78
         |    `--*E. tumulosus (Miller 1892) [=Eupachycrinus tumulosus]ML78
         |--Hylodecrinus Kirk 1941ML78
         |    `--*H. sculptus Kirk 1941ML78
         `--Microcaracrinus Strimple & Watkins 1969ML78
              |--*M. delicatus Strimple & Watkins 1969ML78
              |--M. bellirugosusML78
              |--M. colubrosusML78
              `--M. conjugulusML78

*Type species of generic name indicated

References

[ML78] Moore, R. C., N. G. Lane, H. L. Strimple, J. Sprinkle & R. O. Fay. 1978. Inadunata. In: Moore, R. C., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt T. Echinodermata 2. Crinoidea vol. 2 pp. T520–T759. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).