Belongs within: Trepostomata.
Contains: Ptilodictyina, Fenestrata, Arthrostylidae.
Hidden mouths of the Palaeozoic
Published 11 February 2025
In the modern fauna, the bryozoans tend to be dismissed as a fairly minor component of marine diversity, far less prominent than other sessile filter-feeders such as sponges and corals. This was not always the case; the calcareous skeletons of most bryozoan species provide them with an excellent fossil record and hence a great deal of attention from palaeontologists. Among modern bryozoans, the most diverse class is the Gymnolaemata, characterised by recumbent zooids (individual polyps) that grow more or less parallel to the overall axis of colony growth. However, bryozoan diversity during the Palaeozoic was dominated by the Stenolaemata, whose zooids are more or less tubular and typically grow at a strong angle to the overall colony. Stenolaemates do persist to the modern day at lower levels than during their peak, but a number of their major lineages did not survive the Palaeozoic. One such lineage was the Cryptostomata.
The cryptostomes first enter the fossil record during the Ordovician, achieving their greatest diversity during the Devonian and early Carboniferous before disappearing at the end of the Permian (Bassler 1953). Most species grew as upright colonies, attached to the substrate by only a small holdfast. The entire colony could be unbranched, bush-like, or reticulate. Occasionally, colonies might be divided into articulated segments. I haven’t been able to find any indication of just how large these colonies could grow, but individual branches were typically slender, up to a few millimetres across. As with other stenolaemates, the colony is typically divisible between an inner endozone and outer exozone, with walls between zooids being thinner in the endozone. The name ‘cryptostome’ is derived from a characteristic feature of the order, a sharp bend in each zooid as it transitions from the endozone to the exozone. The inner cavity of the zooid is often further constricted at this bend by features such as partial septa. Earlier authors suggested that this bend might have represented the level of the actual terminal membrane of the live zooid (hence the name cryptostome, ‘hidden mouth’) but it seems just as likely that the zooid reached to the terminal opening as in living stenolaemates (Blake 1983).
The unity of the Cryptostomata has been questioned by some authors who have suggested that it may be an artificial assemblage of convergent forms. Three main colony forms have been identified within the cryptostomes; some authors have restricted to Cryptostomata to bifoliate forms, recognising the orders Rhabdomesonata for cylindrical forms and Fenestrata for unilaminate forms (with openings on one side only of the colony) that are often reticulately anastomosing. However, Blake (1975) argued that the distinctions between these forms becomes blurred in early cryptostomes, supporting their recognition as a single lineage. The phylogenetics of bryozoans as a whole remains poorly understood, so the prospect of further revision cannot be ruled out.
Cryptostomates seem to have typically been associated with shallow-water, relatively open habitats. Those species producing delicate colonies must have preferred fairly low-energy environments such as lagoons. In life, they must have looked every bit the ‘lace corals’ that bryozoans are oftentimes called.
Systematics of Cryptostomata
<==CryptostomataP98
| i. s.: Leioclema Ulrich 1882O69
| |--*L. punctata [=Callopora punctata]O69
| |--L. dozierenseN65
| `--L. porosa Crockford 1947F71
| SulcoreteporidaeB53
| CycloporidaeB53
| PalescharaMB12 [PalescharidaeB53]
| `--P. incrustansMB12
|--+--PtilodictyinaTE04
| |--FenestrataTE04
| `--Timanodictyina [Timanodictyoidea]P98
| |--TimanodictyidaeT93
| | |--Timanodictya dichotoma (Stuckenberg 1895)T93
| | `--Timanostrypa borealis Morozova 1970T93
| `--GirtyoporidaeT93
| |--Morozovapora akiyoshiensis Sakagami & Sugimura 1978T93
| |--Girtyoporina crassa Morozova 1970T93
| |--Girtypora Morozova 1966DX84
| | |--*G. ramosa Morozova 1966DX84
| | `--G. minorDX84
| `--Hayasakapora Sakagami 1960DX84
| |--*H. erectoradiata Sakagami 1960DX84
| |--H. capillaceaDX84
| |--H. matsudae Sakagami 1961DX84
| `--H. rugosa Liu in Ding, Xia et al. 1984DX84
`--Rhabdomesina [Rhabdomesoidea, Rhabdomesonata]TE04
|--Nudymiella [Nudymiellidae]T93
| `--N. singula Morozova 1981T93
|--Pseudascopora [Pseudoascoporidae]T93
| `--P. valentinae Goryunova 1985T93
|--Bactropora [Bactroporidae]T93
| |--B. granistriata (Hall 1881)T93
| `--B. simplex (Ulrich 1886)T93
|--Maychellina [Maychellinidae]T93
| |--M. aliena Goryunova & Morozova 1979T93
| |--M. edita (Morozova 1970)T93
| `--M. nervosa (Morozova 1970)T93
|--Maychella Morozova 1970DX84 [MaychellidaeT93]
| |--M. qubuensis Yang & Hsia 1975DX84
| |--M. rhomboidea Yang & Lu 1983T93
| `--M. tuberculata Morozova 1970T93
|--RhabdomesidaeT93
| |--OrthoporaT93
| | |--O. casualis Goryunova 1985T93
| | `--O. rhombiferaB75
| `--Rhabdomeson Vine 1883DX84
| `--R. libitumDX84
|--GoldfussitrypidaeT93
| |--Nicklesopora lepida Nikiforova 1939T93
| `--GoldfussitrypaT93
| |--G. abnormalis Goryunova 1985T93
| `--G. electa Goryunova 1985T93
|--ArthrostylidaeT93
|--NikiforovellidaeT93
| |--Tebitopora orientalis Zhao-xun 1984T93
| |--Pinegopora delicatula Shisova 1965T93
| `--NikiforovellaT93
| |--N. amazarica Nekhoroshev 1948T93
| `--N. nitida Troitskaya 1979T93
|--HyphasmoporidaeT93
| |--Ipmorella tobolensis Goryunova 1985T93
| |--StreblotrypaT93
| | |--S. etheridgei Bretnall 1926F71
| | |--S. parallela Crockford 1947F71
| | `--S. parva Morozova 1965T93
| `--Acanthoclema scutulataB75
`--RhomboporidaeT93
|--SaffordotaxisT93
| |--S. multigranulata (Bretnall 1926) [=Rhombopora multigranulata]F71
| `--S. yukonensis (Astrova 1972) [=Rhombopora yukonensis]T93
`--Rhombopora Meek 1872DX84
|--R. lepidodendroidesG31
|--R. lineinodisC01
|--R. mawiO69
|--R. ornata Shishova 1964T93
`--R. pulchra Bassler 1929DX84
*Type species of generic name indicated
References
[B53] Bassler, R. S. 1953. Treatise on Invertebrate Paleontology pt G. Bryozoa. Geological Society of America, and University of Kansas Press.
[B75] Blake, D. B. 1975. The order Cryptostomata resurrected. In: S. Pouyet (ed.) Bryozoa 1974 pp. 211–223. Université Claude Bernard: Lyon.
Blake, D. B. 1983. The order Cryptostomata. In: Robison, R. A., V. Ashlock, J. Keim & R. B. Williams (eds) Treatise on Invertebrate Paleontology pt G. Bryozoa. Revised vol. 1. Introduction, Order Cystoporata, Order Cryptostomata pp. 440–452. The Geological Society of America, Inc. and The University of Kansas.
[C01] Chapman, F. 1901. On some fossils of Wenlock age from Mulde, near Klinteberg, Gotland; with notes by Prof. T. Rupert Jones and Dr. F. A. Bather. Annals and Magazine of Natural History, series 7, 7: 141–160, pl. 3.
[DX84] Ding Y., Xia G., Duan C., Li W., Liu X. & Liang Z. 1984. Study on the early Permian stratigraphy and fauna in Zhesi district, Nei Mongol Zizhiqu (Inner Mongolia). Bulletin Tianjin Institure Geol. Min. Res. 10.
[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.
[G31] Grabau, A. W. 1931. The Permian of Mongolia: A report on the Permian fauna of the Jisu Honguer limestone of Mongolia and its relations to the Permian of other parts of the world. American Museum of Natural History: New York.
[MB12] Mistiaen, B., D. Brice, M. K. Zapalski & C. Loones. 2012. Brachiopods and their auloporid epibionts in the Devonian of Boulonnais (France): comparison with other associations globally. In: Talent, J. A. (ed.) Earth and Life: Global biodiversity, extinction intervals and biogeographic perturbations through time pp. 159–188. Springer.
[N65] Nicol, D. 1965. An ecological analysis of four Permain molluscan faunas. Nautilus 78 (3): 86–95.
[O69] Owen, D. E. 1969. Wenlockian Bryozoa from Dudley, Niagara and Gotland and their palaeogeographic implications. Palaeontology 12 (4): 621–636.
[P98] Prothero, D. R. 1998. Bringing Fossils to Life: An introduction to paleobiology. WCB McGraw-Hill: Boston.
[T93] Taylor, P. D. 1993. Bryozoa. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 465–489. Chapman & Hall: London.
[TE04] Taylor, P. D., & A. Ernst. 2004. Bryozoans. In: Webby, B. D., F. Paris, M. L. Droser & I. G. Percival (eds) The Great Ordovician Biodiversification Event pp. 147–156. Columbia University Press.