Hemitrypa Phillips, 1841

Ernst, Andrej, Fernández, Luis Pedro, Fernández-Martínez, Esperanza & Vera, Carmen, 2012, Description of a bryozoan fauna from mud mounds of the Lebanza Formation (Lower Devonian) in the Arauz area (Pisuerga-Carrión Province, Cantabrian Zone, NW Spain), Geodiversitas 34 (4), pp. 693-738 : 724-725

Genus Hemitrypa Phillips, 1841

TYPE SPECIES. — Hemitrypa oculata Phillips, 1841 , by original designation. Devonian ; Barton, South Devon, England .

OCCURRENCE. — Lower Devonian to Middle Permian; worldwide.

DIAGNOSIS. — Reticulate colonies, conical or fan-shaped, planar or longitudinally pleated, frontal surface exterior if conical. Branches intermediate in width, linear to moderately sinuous, closely or intermediately spaced, dichotomously divided. Two rows of autozooecia per branch, increasing to four rows proximal of branch bifurcations in some species; low straight to sinuous central keel on obverse side of branch with high nodes, composed of core of granular skeleton and sheath of laminar skeleton. Laminar wall extensions of keel nodes fused together forming a fine meshwork of polygonal openings, each opening centred over a zooecial aperture in the branch below. Axial wall between autozooecial rows zigzag in tangential sections; zooecia not strongly inflated laterally, commonly quadrangular or pentagonal in tangential section deep within endozone, less commonly elongate triangular or semicircular, pentagonal to bean-shaped in shallower endozone; maximum diameter of zooecia corresponds with either length or height; transverse walls at intermediate or high angle to reverse wall; superior hemisepta absent or weakly developed, other interior structures absent. Small- to large-diameter distal tube typically short, opening frontally or slightly inclined laterally and perhaps distally; apertural peristome present or absent; terminal diaphragms planar where present, with central boss in some species. Heterozooecia are isolated zooecia with enlarged endozonal chambers (?gynozooecia) present in proximal parts of colonies, or spherically inflated distal tubes with diameters greater than branch width (? brood chambers). Zooecial walls of granular material that may be absent on obverse side near apertures; laminar extrazooecial skeleton traversed by small to moderate microstyles (modified after F. K. McKinney, pers. comm. 2007).

COMPARISON

Hemitrypa Phillips, 1841 is similar to Pseudounitrypa Nekhoroshev, 1926 , but differs from it in the composition of the superstructure. The superstructure of Hemitrypa is produced by laminar wall extensions of keel nodes forming a meshwork of polygonal openings which are centred over zooecial apertures in the branch below, whereas openings in Pseudounitrypa are centred over the branches and terminate laterally over the centres of the fenestrules where the superstructural elements from adjacent branches meet and fuse.