A guide to identifying trepostomes from the type Cincinnatian
Overview
Although the external growth form of a trepostome is the most obvious feature, internal structures are the most critical for identification. Because these structures must be revealed by making thin sections or acetate peels, bryozoan identification is commonly thought to be difficult. Furthermore, thin sections and peels are sections through a three-dimensional structure of initially unfamiliar parts, adding to the complexity of identification. Even so, identification of bryozoans is not that difficult. This guide will show you how.
Start with the growth form
The first step in identification is to use the growth form to narrow the list of possible genera.
Ramose trepostomes
First, check to see if any of these distinctive features occur:
Are there cystiphragms?
- Homotrypa has cystiphragms that form overlapping series in the exozone, mesozooids that occur in clusters, and diaphragms.
- Gortanipora is similar to Homotrypa, but it has incomplete cystiphragms that do not form overlapping series and it lacks diaphragms.
- Monticulipora has cystiphragms that form overlapping series in both the endozone and exozone. Styles and mesozooids are variably abundant, but diaphragms are consistently abundant.
- Peronopora is similar to Monticulipora, but has mesozooids and styles.
- Atactoporella has thin walls, abundant diaphragms, and numerous styles that give zooecia a petaloid outline.
Are there blunt hemiphragms?
- Balticoporella is thick-walled, has common diaphragms, sparse mesozooids, and no styles.
Do the zooecia in the endozone have square cross-sections?
- Rhombotrypa is thick-walled, with common diaphragms in the exozone, and no mesozooids or styles. In slightly oblique longitudinal sections, the square endozonal zooecia appear diamond-shaped.
Are there star-shaped monticules?
- Constellaria was formerly classified as a trepostome, but is now regarded as a cystoporid.
Are there wide zooecia in the central endozone that markedly thin before the exozone?
- Batostomella has thick walls, mesozooids that generally do not reach the surface of the colony, and it has few or no diaphragms within zooecia.
- Eridotrypa has oval zooecial openings, common diaphragms near the zooecial bend, aggregates of mesozooids, and numerous styles.
If none of those are present, check for mesozooids:
Are there abundant mesozooids with many diaphragms?
- Parvohallopora is abundant and widespread, and it is characterized by small mesozooids, a lack of styles, and commonly lined zooecia.
- Heterotrypa is also abundant and widespread, and it is recognized by its beaded mesozooids, walls of varying thickness, abundant styles in both the endozone and exozone.
- Batostoma has round apertures, lined zooecia, styles, thin and irregularly spaced diaphragms, and some mesozooids with more than one row of curved diaphragms.
- Nicholsonella commonly has mesozooids filled with calcareous material, as well as thick, recrystallized zooecial walls.
Are mesozooids present but not abundant?
- Heterotrypa has abundant styles in both the endozone and exozone, beaded mesozooids, walls of varying thickness, and abundant diaphragms mostly in the exozone.
- Dekayia has abundant styles, few diaphragms, and thick walls that are crenulated, undulatory, and that vary in thickness.
- Amplexopora has abundant styles that may inflect zooecial walls. Cystoidal diaphragms and cystiphragms common in some species, as are lined zooecia.
- Stigmatella has abundant styles and relatively few diaphragms, like Stigmatella, but has much thinner zooecial walls, with regular thickenings.
Are mesozooids absent?
- Bythopora is slender, with scarce diaphragms, a thin exozone, and zooecia that are inclined to the surface of the colony.
Leaf-like (frondose or bifoliate) trepostomes
Are there cystiphragms in overlapping series?
- Peronopora has mesozooids and styles, and generally has zooecia that bud from opposite sides of a median line (that is, it is bifoliate). The other two genera do not have zooecia that bud from a median line and are called frondose.
- Monticulipora is frondose, has cystiphragms throughout, with variable numbers of mesozooids and styles.
- Homotrypa is frondose, and has cystiphragms limited to the exozone, with clusters of mesozooids.
Are cystiphragms absent?
- Heterotrypa is an abundant and widespread sheet-like trepostome. It has beaded mesozooids, styles in both the endozone and exozone, walls of varying thickness, and common diaphragms, mostly in the exozone.
- Amplexopora has abundant styles that commonly inflect the zooecial walls. It also lacks mesozooids.
- Stigmatella is thin-walled with regular thickenings, has few diaphragms, abundant styles, and sparse mesozooids.
- Nicholsonella commonly has mesozooids filled with calcareous material and has thick, recrystallized zooecial walls.
Encrusting trepostomes
Are there cystiphragms in overlapping series?
- Peronopora has abundant mesozooids and styles.
- Monticulipora has abundant diaphragms, with variable numbers of mesozooids and styles.
- Atactoporella is thin-walled, and has abundant diaphragms, inflecting styles, and petaloid apertures.
Are both styles and diaphragms abundant?
- Batostomahas round apertures, lined zooecia, styles, thin and irregularly spaced diaphragms, and some mesozooids with more than one row of curved diaphragms. Mesozooids often nearly surround zooids.
- Heterotrypa has beaded mesozooids and walls of varying thickness.
- Amplexopora has abundant styles that may inflect zooecial walls. Cystoidal diaphragms and cystiphragms are common in some species, as are lined zooecia.
- Mesotrypa has few curved, flat, or sloping diaphragms, with abundant mesozooids.
Are styles abundant, but diaphragms sparse or absent?
- Dekayia has variably thick and crenulated walls, and may have a few beaded mesozooids.
- Stigmatella has thin walls with regular thickenings.
- Petigopora is similar to Dekayia, lacks mesozooids, and forms small circular patches.
- Atactopora has strongly petaloid apertures, usually encrusts nautiloids, and has conspicuous monticules.
Are styles sparse to absent?
- Orbignyella is thin-walled, with abundant diaphragms and isolated cystiphragms, and no mesozooids.
- Discotrypa is thin-walled, with abundant diaphragms, and rhomboidal zooids.
- Spatiopora commonly encrusts nautiloids and may have elongated monticules.
- Leptotrypa has almost no diaphragms, sparse mesozooids, thin walls, and sharp monticules.
Hemispherical and disk trepostomes
Are there cystiphragms in overlapping series?
- Prasopora is domal to hemispherical, has abundant mesozooids, and diaphragms that link cystiphragms.
Does it lack cystiphragms in overlapping series?
- Aspidopora forms thin disks, with a spiral arrangement of zooids like a sunflower.
- Stigmatella has abundant styles, thin walls with regular thickenings, and sparse mesozooids and diaphragms.
- Mesotrypa has abundant styles, mesozooids, and few curved, flat, or sloping diaphragms.
- Discotrypa is thin-walled, has abundant diaphragms, and rhomboidal zooids.
Massive trepostomes
Are cystiphragms in overlapping series present?
- Peronopora has abundant styles and relatively thin diaphragms.
- Monticulipora has abundant diaphragms, but lacks inflecting styles.
- Atactoporella has both diaphragms and inflecting styles.
Does it lack cystiphragms but have well-developed styles?
- Heterotrypa has beaded mesozooids, walls of varying thickness and common diaphragms in the exozone.
- Amplexopora lacks mesozooids and has numerous inflecting styles, often making apertures irregular.
- Dekayia has few diaphragms, crenulated and wavy thick walls, and possibly a few beaded mesozooids.
- Stigmatella has few diaphragms, like Dekayia, but has thin walls with regular thickenings.
- Cyphotrypa also has thin walls, but has numerous diaphragms in the exozone, and lacks mesozooids.
Does it lack both cystiphragms and styles?
- Monotrypa lacks mesozooids, has few diaphragms, and has undulating walls.
