Chasmatopora

Classification
Phylum: Bryozoa
Class: Stenolaemata
Order: Fenestrida
Family: Phylloporinidae
Genus: Chasmatopora Eichwald, 1860

Taxonomic Details

Type Species: Retepora tenella (Eichwald, 1842)
Note (Bryozoa.net)

  • From 1935, the use of Fenestella was suspended because of the existence of a senior homonym as a genus name for a bivalve. For some years, species were referred to the genus Fenestrellina.
    In 1962 (Opinion 622 of the ICZN), Fenestella was validated for the bryozoan genus, and the name Fenestrella for a bryozoan was placed on the Official Index of rejected names.

Stratigraphic Occurrences

Chasmatopora_strat

Geologic Range
Middle Ordovician – Late Silurian

Geographic Occurrences

		
Map point data provided by iDigBio.

Stratigraphic Description

Sequences (Formations)

  • C2 Sequence (Fairview: Fairmount)
  • C1 Sequence (Clays Ferry/Kope: Southgate, McMicken)

Identification in Hand Sample:

  • Zoarium Morphology: Ramose (branching)
  • Zooecia: Four rows of autozooecia, two on either side of branch, with rounded, essentially circular autozooecial apertures, more closely spaced along central obverse rows than lateral rows.
  • Mesozooids: Mesozooecia and other heteromorphs apparently absent.
  • Monticules:
  • Maculae: Regularly spaced clusters of polymorphs, extrazooidal skeleton, or a combination of both.

Chasmatopora variolata from the Kope Formation of Maysville, Kentucky (OUIP 2414)

Published Description

McKinney & Jackson (2010):

  • In the synopses, overall colony habit (narrow unilaminate, irregularly anastomosed branches in erect colonies) was given as similar, but a medial wall separating an even number of rows (usually two) per branch was noted as characteristic of Chasmatopora, and Phylloporina was described as having no medial wall and either an odd or even number of rows of 442 PALAEONTOLOGY, VOLUME 53 zooecia.

Taylor & Lewis (2005):

  • Colonies of Chasmatopora are mesh-like, constructed of branches that bifurcate and anastomose in a single plane. The holes (fenestrules) are elongated parallel to the growth direction of the colony. Frontal sides of branches on one face of the meshwork bear 2-8 rows of circular zooidal apertures, their reverse sides lack apertures but are fairly striated. There are no polymorphic zooids.
  • The mesh-like colony of Chasmatopora typifies most bryozoan genera belonging the the order Fenestrata. It should be noted that colonies of very similar appearance subsequently evolved independently in two other bryozoan orders, Cheilostomata and Cyclostomata. In life a tentacle crown would have emerged from each aperture, pulling water towards the frontal side of the colony and expelling water filtered of plankton through the holes and away.

Fossils of Ohio (1996):

  • Forms meshwork colonies of anastomosing branches. There are two or more zooid rows per branch. Apertures are not strongly aligned.

Bassler (1911):

  • The generic type to which this name was first applied was best described under the name of Phylloporina by Ulrich, but it seems to me that the earlier designation of Chasmatopora has the best right to recognition. The facts in the case are as follows:
    • In 1860 Eichwald proposed the new genus Chasmatopora, giving a fair description for that date, and basing the genus upon a single species, C. tenella, which he compared with Hall’s Retepora angulata, from the Clinton group, of New York. His figure of C. tenella, although far from present standards, is sufficient to show that his type-specimen was an angular meshed form closely related to Hall’s species. Collections from the Borkholm limestone show numerous examples of such a species, and I have little doubt that this is the form Eichwald had in mind.
    • D’Orbigny’s Subretepora was based upon the well-known, widely distributed form Intricaria reticulata Hall, but the author of this generic name relied upon Hall’s faulty descriptions and figures for his definition. The result was that Supretepora was incorrectly defined, and for that reason Ulrich proposed the new name Phylloporina.
    • As pointed out by Ulrich, several distinct types of structure are included in Phylloporina. It is therefore probable that with more study both Phylloporina and Chasmatopora may be recognized.
    • In Chasmatopora the zoarium is of irregularly anastomosing branches with two to eight rows of apertures on one side and the other side noncelluliferous but striated.