Stomatopora Bronn 1825

“ Stomatopora ” sp.

(Fig. 19C, D)

Material examined. VNMN-0272 (CT-9), on SEM stub.

Measurements. AzL (excluding peristome), 0.33–0.67 (0.542 ± 0.110); AzW, 0.16–0.32 (0.215 ± 0.042) (n = 12). Or inside diameter, 0.057 –0.096 (0.079 ± 0.013) (n = 6).

Description. Colony encrusting; zooids in dichotomously branching uniserial series, each autozooid producing pair of distal buds giving rise to bifurcation; angle of branching variable, from acute to obtuse; in some cases, one of paired daughter zooids at branch point aborted. Some paired daughter zooids at branch points appressed to one another for one-third to one-half their length before diverging; others diverging immediately at branch point.

Zooids uniform in width, or up to twice as wide distally; wall with weak transverse striation, evenly perforated by minute pseudopores. Unbroken peristomes in our specimen not tall, length at most three times peristome diameter; acute projection on distal side at top of some peristomes. Some orifices partially closed, with restricted, circular opening in center.

Brood chamber and ancestrula not observed.

Remarks. The nominal genus Stomatopora has a stratigraphic range from the Triassic to Recent, with one Ordovician species of dubious status (Bock 2018). Harmelin (1979) discussed taxonomic problems associated with the genus, noting that the type species, Alecto dichotoma Lamouroux, 1821, described from a Jurassic fossil, initially forms a uniserial and biserial adnate colony but later forms erect branches, with the brood chamber arising as a simple swelling of the peristome. The generic placement of cyclostome species having a stable uniserial colony is thus problematic and will eventually require the erection of new genera based on information on budding patterns and the mode of formation the gonozooid (Harmelin 1979). While our specimen resembles several Jurassic species having a type-II budding pattern (Illies 1973), we cannot rule out that it is the adnate portion of a colony that will later form erect reproductive branches. Here we list this specimen as “ Stomatopora ” in the sense of a form-genus, making it accessible to literature searches in future studies of uniserial cyclostomes.