Paracrinoidea
| Paracrinoid Temporal range: Early Ordovician - Early Silurian | |
|---|---|
 | |
| Comarocystites punctatus | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Subphylum: | Blastozoa |
| Class: | Paracrinoidea |
Paracrinoidea is an extinct class of blastozoan echinoderms. They lived in shallow seas during the Early Ordovician through the Early Silurian. While blastozoans are usually characterized by types of respiratory structures present, it is not clear what types of respiratory structures paracrinoids likely had. Despite its name, the paracrinoids are not closely related to crinoids.
Paracrinoids are characterized by a mouth with two to five feeding arms arranged asymmetrically, or somewhat bisymmetrically. They have a U-shaped gut, and their anus is located next to the mouth. They have irregularly shaped bodies (theca), and a stem, superficially similar to crinoids, and may have used the stem to attach themselves to a substrate, although some reconstructions show them partially buried in sediment.[1]
Only 13 to 15 genera are known. See List of echinodermata orders
References
- ↑ Fossil Invertebrates, 1987, Boardman, Richard S., Cheetham, Alan H., and Rowell, Albert J., editors, pp. 580-1. Blackwell Scientific Publications.