Escharina milneana (Busk, 1859)
Colonies are encrusting, multiserial and sheet-like; Lagaaij (1952; see also Bishop & Hayward 1989, fig. 79) found vincularian colonies of this species in The Netherlands but this colony form has not yet been recorded in British material. The ancestrula and early astogeny are undescribed.
Autozooids are rhomboidal in outline shape, about 0.60 mm long by 0.35-0.45 mm wide (fide Lagaiij 1952, p. 70). The convex frontal shield is porous over its entire surface and has a granular texture. The primary orifice is hemielliptical, slit-like, much wider than long, about 0.07 mm long by 0.13 mm wide, with a small V-shaped sinus in the proximal edge. A thick peristome is present, outwardly flared especially on its proximal edge, which defines a secondary orifice less transversely elongated than the primary orifice. Oral spines are lacking. The ovicell is moderately small and prominent, with an ectooecium continuous with the frontal shield of the distal zooid and similarly covered by granules but lacking pores except at the very edges.
Adventitious avicularia are large, located proximolaterally of the orifice, one per zooid or sometimes absent, and have an inflated, imperforate cystid. The distolaterally or laterally directed rostrum is rounded arch-shaped and slightly narrower than the semicircular opesia from which it is separated by a calcified pivotal bar.
This species differs from E. woodiana in having a single, large avicularium proximolaterally of the orifice (cf. small paired avicularia laterally of the orifice in E. woodiana), pores all over the frontal shield (cf. marginal areolar pores only in E. woodiana) and a thick peristome.
Bishop & Hayward (1989, p. 20) questioned the generic assignment of E. milneana, noting that the evenly porous frontal shield was unlike that of the type species of Escharina, E. vulgaris (Moll, 1803), in which only marginal areolar pores are present. They considered transferring the species to Therenia David & Pouyet, 1978 (revised by Berning et al. 2008) but did not do so on account of differences in the structure of the ovicell.
Pliocene, Late Zanclean–Early Piacenzian, Coralline Crag Formation, Suffolk, UK.
Also recorded by Lagaaij (1952) from the Scaldisian of the Low Countries.