Fenestellidae

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Elias & Condra (1957):

• In all these examples, the size of the openings ranges from about 6 to 15 µ, which is also the approximate range of the diameter in the so-called “capillaries” of Fenestellidae. However, none of the abundant and well-preserved limonitic molds of many species of Fenestella, Polypora, and Archimedes in Elias’ collection have any trace of limonitic filling of the “capillaries”.
• In view of all evidence and because of the erroneous implications connected with the terms, it seems advisable to discontinue to call the minute, (transverse to the laminated sclerenchyma) uprights in the wall of Fenestellidae “pores” or “capillaries”. Instead, a term such as spicule or filament should be used (Fig. 1) which will denote that they are structural entities and not merely openings.
• From these considerations follows that in Fenestrata the neighboring zooecia share a common primary wall. This conclusion is at variance with the expressed belief by Ulrich that “Theoretically it may be said that the zooecia of all the Paleozoic Bryozoa had perfectly independent and complete wall.” Thus, the composite wall between two zooecia would be doubled, and the “primitive duplex character of the zooecial walls of the Fenestellidae and Acanthocladiidae is generally shown in deep tangential sections of the early stages of zoaria” (Ulrich, 1890, p. 308, 312). No illustrations were published to support this observation , however, and it seems that it is the secondary sclerenchymatous crusts on both sides of the thin primary wall that correspond to what Ulrich called the “primitive duplex” wall.
• In most species apertures are circular and are separated by about the distance of their diameter. Their size is commonly proportional to the size of the zooecial chamber, but in a few species they are unusually small in comparison with the chamber and are spaced more than their diameter apart. Outline and ornamentation of apertures, where preserved, are diagnostic. Bifurcation of branches is typically symmetrical; however, in a few exceptions there is a marked unilateral branching, rare in Fenestellidae and generally characteristic of Septopora and other genera of Acanthocladiidae.

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