Ctenocystoidea

Ctenocystoidea
Temporal range: WuliuanSandbian
A specimen of Ctenocystis
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Superphylum: Deuterostomia
Clade: Ambulacraria
Phylum: Echinodermata
Class: Ctenocystoidea
Robison & Sprinkle, 1969
Type genus
Ctenocystis
Robison & Sprinkle, 1969
Genera
  • Conollia
  • Courtessolea
  • Ctenocystis
  • Etoctenocystis
  • Gilcidia
  • Jugoszovia
  • Pembrocystis

Ctenocystoidea is an extinct clade of echinoderms, which lived during the Cambrian and Ordovician periods. Unlike other echinoderms, ctenocystoids had bilateral symmetry, or were only very slightly asymmetrical. They are believed to be one of the earliest-diverging branches of echinoderms, with their bilateral symmetry a trait shared with other deuterostomes. Ctenocystoids were once classified in the taxon Homalozoa, also known as Carpoidea, alongside cinctans, solutes, and stylophorans. Homalozoa is now recognized as a polyphyletic group of echinoderms without radial symmetry. Ctenocystoids were geographically widespread during the Middle Cambrian, with one species surviving into the Late Ordovician.

Description

A selection of early echinoderms, including the ctenocystoid Ctenocystis (middle).

Like other echinoderms, ctenocystoids had a skeleton made of stereom plates. Ctenocystoids had near bilateral symmetry, with some species exhibiting slightly asymmetric plate shapes. Like cinctans and Ctenoimbricata, most ctenocystoids had large marginal plates surrounding the sides of their body, but unlike cinctans and Ctenoimbricata, which had only one row of marginal plates, most ctenocystoids had two rows of marginal plates. Courtessolea had only one row of marginal plates, like cinctans and Ctenoimbricata, whereas Conollia lost the marginal plates entirely. The anus of ctenocystoids was surrounded by a pyramidal periproct as in other echinoderms. It was located at the posterior end, defining a clear anterior-posterior body axis unlike other echinoderms.

All ctenocystoids had a ctenoid apparatus, a comb-like arrangement of movable plates at the anterior end of the animal. Beneath the ctenoid apparatus was a mouth, bordered on each side by a food groove.

Classification

Relationships

Courtessolea

Jugoszovia

Conollia

Pembrocystis

Etoctenocystis

Gilcidia

Ctenocystis

Phylogenetic relationships within Ctenocystoidea

Ctenocystoids are likely among the most basal stem-group echinoderms. They have also been interpreted as aberrant blastozoans and as stem-group hemichordates. The presence of stereom plates indicates that they most likely belong to the echinoderm total group, rendering a hemichordate affinity unlikely.

Courtessolea was probably the most basal ctenocystoid, given its anatomical similarities to Ctenoimbricata and cinctans. Conollia and Jugoszovia may be closely related to each other, as both have a reduced marginal frame compared to other ctenocystoids.

Genera

The following genera of ctenocystoids have been named:

Genus Discoverers Named Age Location Notes
Conollia Domínguez Alonso 1999 Sandbian  United Kingdom The geologically youngest genus
Courtessolea Domínguez Alonso 1999 Wuliuan  France The most basal genus
Ctenocystis Robison & Sprinkle 1969 Middle Cambrian  United States The first genus discovered
Etoctenocystis Fatka & Kordule 1985 Middle Cambrian  Czech Republic
Gilcidia Domínguez Alonso 1999 Middle Cambrian  Australia,  Denmark,  France
Jugoszovia Džik & Orłowski 1995 Middle Cambrian  Poland
Pembrocystis Domínguez Alonso 1999 Middle Cambrian  United Kingdom

Distribution

Ctenocystoids were widespread during the Middle Cambrian, and have been found in the United States, the United Kingdom, Australia, France, the Czech Republic, Poland, Spain, and Morocco. The earliest ctenocystoids date to the beginning of Stage 5 of the Cambrian, now known as the Wuliuan age, or possibly slightly earlier, in late Cambrian Stage 4. Most species date to the Wuliuan and Drumian ages of the Cambrian. The geologically youngest ctenocystoid, the only one known from the Ordovician, is Conollia, from the Sandbian of the United Kingdom.

History

The class Ctenocystoidea was named in 1969 by Richard A. Robison and James Sprinkle. It originally contained one species, Ctenocystis utahensis. The name comes from the Greek words ktenos, meaning "comb", and kystis, meaning "sac". It was originally assigned to the echinoderm subphylum Homalozoa.


This page was last updated at 2024-01-19 15:57 UTC. Update now. View original page.

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