Ordovician – Permian
Cryptostomata is an extinct order of stationary, epifaunal suspension feeders
Characteristics of the Order
- Zoaria erect, unbranching, bushlike; rare jointing
- Zooecia short, rarely elongate; bend at endozonal-exozonal boundary
- Apertures common; generally in regular or spiral rows; outlines vary
- Interzooecial pores lacking
- Vesicles rare
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Treatise on Invertebrate Paleontology, Part G (1983):
- Zoaria almost always erect; unbranched, bushlike, pinnately branched, or reticulated; jointing rare; stem cross section cylindrical or flattened; rarely developing overgrowths. Apertures commonly on alls tem surfaces, or some surfaces barren; apertures generally in regular longitudinal or spiral rows, apertural outlines elliptical, subcircular, or rectangular. Striae, ridges, peristomes, stylets, polymorphs, small nonpolymorphic depressions commonly well developed on surface. Budding loci linear or planar. Zooecia generally short, rarely elongate; usually with zooecial bend at endozonal-exozonal boundary; hemisepta, diaphragms, mural spines present in some taxa, interzooecial pores lacking. All erect walls compound, exozonal walls generally much thicker than endozonal walls; walls primarily laminated, nonlaminated material generally present (extensive in Fenestellina); in some taxa, extrazooecial skeletal material extensive and multizooecial skeletal material present. Vesicles rare.
Elias & Condra (1957)
- In the light of the present investigation the structure of the wall of fenestrate Cryptostomata is differentiated into three fundamental parts (Fig. 1):
- (1) Colonial or germinal plexus (new term) includes the “striated membrane” of Nicholson or striated “germinal plate” of Ulrich; it also includes the “primary carina” of Cumings and the “capillary canals” of Shulga-Nesterenko (but not her “capillary tubules”). The proposed term is not synonymous with the “coenoecium” or “polyzarium,” which Nicholson understood to be the external investment “of the colony … formed by the combined ectocists of the various polypides, and … varies greatly both in form and actual composition,” and “the only element of Polyzoa with which the paleontologist is concerned” (Nicholson, 1872, p. 192). Colonial plexus is the primary part of the coenoecium if the latter is understood in the broad sense.
- (2) Laminated sclerenchyma is a secondary calcareous deposit, whose laminae correspond to the rhythmic growth lines of the brachiopods, mollusks, and other invertebrates.
- (3) Transverse spicules or filaments are uprights which traverse the laminated sclerenchyma, usually producing distinct drag of the laminae around them in the direction of their growth. They were called minute tubuli by Nicholson and Ulrich, capillaries by Russian authors, and needlelike structures by Condra and Elias (1944).
- However, all fenestrate Cryptostomata possess a colonial skeleton (plexus), a continuous, foil-like structure, which is variously corrugated and expanded to produce a platy lattice, the honeycomb-like meshes of which determine the individual zooecia. While the shape of the zooecial chambers (excluding vestibulum) may influence the shape of these meshes, some properties of the plexus seem to have greater control over the meshes: (1) the foil-like nature, (2) tendency to produce more or less parallel, radiating ribs, and (3) tendency to produce regularly spaced, narrow, short, lateral outgrowths, the dissepiments.
- In his matured concept of the zoarium of Crisina, Cyclostomata, and of the part played by the common bud, Borg state, (1942, p. 38-40): “The zoids all originate within the common bud and are, consequently, all covered by its terminal membrane. … These zoids are thus never constricted off from the common bud but remain permanently covered by its terminal membrane just as do the kenozois. The whole zoarium in Crisina is thus to be considered as much widened and strongly complicated common bud. This easily explains the secretion of calcareous matter from the outside, e.g., the secondary thickening.” The discussed observations indicate that the structure, location, and zoarial extent of the colonial plexus in fenestrate Cryptostomata correspond so well with Borg’s description of the common bud in Cyclostomata that the two structures are considered homologous. If so, this is strong evidence of a close relationship between the living Cyclostomata and the late-Paleozoic fenestrate Cryptostomata. The following observations on other colonial structures known in some Bryozoa indicate lesser development of similar structure.
- The homology of the colonial plexus of fenestrate Cryptostomata to the common bud in extant Cyclostomata throws new light on their position among other orders of the phylum.
All Cryptostomata were originally classified in comprehensive suborder Cyclostomata (Ulrich, 1882, p. 149-151). In 1883 Vine removed from Cyclostomata the bifoliate and a few closely allied ramose forms were the last removed from Cyclostomata. The fact that they possess zoarial plexus, apparently homologous to the common bud of Cyclostomata, and the fact that comparable structures are absent in other Cryptostomata suggest a return to Vine’s concept of Cryptostomata and segregation of fenestrate forms into the new order Fenestrata to be added to Borg’s class Stenolaemata at a par with orders Trepostomata and Cyclostomata.
- This order of the Bryozoa was proposed by Vine in 1883 as a suborder to include mainly the bifoliate ptilodictyoid genera. Since that time the detailed studies of Ulrich have extended the limits of the order so that it now embraces such families as the Fenestellidae and Acanthocladiidae, in addition to the Ptilodictyonidae and related families. A concise definition of the order has been given by Ulrich in the English edition of Zittel’s Textbook of Paleontology. This is as follows:
- Primitive zooecium short, pyriform to oblong, quadrate, or hexagonal, sometimes tubular, the aperture anterior. In the mature colony, the aperture is concealed, occurring at the bottom of a tubular shaft (“vestibule”), which may be intersected by straight diaphragms or hemisepta, owing to the direct superimposition of layers of polypides. Vestibular shaft surrounded by vesicular tissue, or by a solid calcareous deposit; the external orifice rounded. Marsupia and avicularia wanting.
- Comparing the Cryptostomata with the other orders of Bryozoa, it is found to be most closely related to the Chilostomata; in fact, the cryptostomatous bryozoans are probably only the Paleozoic representatives of the Chilostomata so abundant in Mesozoic, Cenozoic, and recent times. As pointed out by Ulrich, the Cryptostomata differ, however, first, in having neither marsupia nor avicularia; second, in the much greater deposit of calcareous matter upon the front of the zooecia, thus producing the vestibule; third, in that successive layers of polypides are often developed, one directly over the other, in a continuous tube; and, fourth, in that whenever a zoarium attains an uninterrupted width of more than 8 mm., it exhibits clusters of cells differing more or less, either in size or elevation, from the average zooecia.
- The generic and even specific representation of the Cryptostomata in the Baltic Ordovician and early Silurian strata is exceptionally like that in the corresponding beds of America.