Mesenteripora meandrina (Wood, 1844)
Colonies are up to about 6 cm in diameter, spheroidal in overall shape and composed of broad bifoliate fronds, although usually recovered as broken, flake-like pieces. Fronds are typically corrugated and anastomose with adjacent fronds along their edges. They are relatively robust, about 0.7-1 mm thick, with a well-defined median budding lamina overlain by up to four generations of zooids on each side. Long, narrow bands devoid of autozooidal apertures (maculae) are occasionally developed. Early astogeny is unknown.
Autozooids are elongate with gently convex frontal walls containing circular pseudopores slightly less than 10 µm in diameter and sometimes having raised edges. Apertures tend to be slightly longitudinally elliptical, about 0.12-0.16 mm long by 0.10-0.14 mm wide, and are often closed by a terminal diaphragm containing scattered pseudopores. Rarely, a small aperture is present at the centre of the terminal diaphragm, probably indicating a secondary nanozooid. Preserved peristomes are short.
Kenozooids are developed sporadically. Most have polygonal, pseudoporous frontal walls and lack an aperture; however, patches of kenozooids with polygonal apertures and no frontal walls may be present.
Gonozooids are rare. The brood chamber is transversely ovoidal, about 1 mm long by 2 mm wide, and pierced by a few autozooids. The terminal ooeciopore is transversely elliptical and smaller than an autozooidal aperture.
At first glance this species is most likely to be confused with one of the commoner bifoliate genera of cheilostomes found in the Coralline Crag, such as Metrarabdotos, Pentapora or Acanthodesia. However, closer inspection reveals the simple, typically tubuliporine cyclostome skeletal structure of the zooids with their minutely pseudoporous frontal walls terminating in subcircular apertures that may be sealed by a terminal diaphragm.
Pliocene, Late Zanclean–Early Piacenzian, Coralline Crag Formation, Suffolk, including Rockhall Wood (Ramsholt Member).
Mesenteripora meandrina has been reported living in the Arctic and western North Atlantic at the present day and also off southern California (see Kluge 1975, p. 148). However, these records are in need of confirmation and must be treated with some scepticism until verified.