Colonies are multiserial, forming extensive encrusting sheets. Early astogeny is unknown.
Autozooids are about 0.50-0.55 mm long by 0.28-0.36 mm wide, typically elongate rhomboidal in outline shape. A pair of pores, sometimes with raised rims, may be visible in the transverse vertical walls of the autozooids. The frontal wall is an extensive, slightly depressed, granular cryptocyst with a pair of long, curved opesiules occasionally broken into two shorter pairs of opesiules separated by a calcified bridge. The opesia is hemielliptical, about two times broader than long, the length approximately 0.10 mm, with a gently arched proximal edge ornamented by tubercles. Ovicells have not been observed.
Vicarious avicularia are developed at zooid row bifurcations and form one of the two daughter zooids. They are the same length or slightly shorter than autozooids but significantly narrower, measuring about 0.2 mm in width, and have a similarly granular cryptocyst. A narrow, trifoliate opesia that includes rounded opesiules in the proximolateral corners occupies more than half of the frontal surface. The rostrum is rounded.
The only named species likely to be mistaken for Manzonella fissurata is Verminaria oblonga (Busk, 1859). However, the latter species lacks avicularia and has smaller autozooids with conspicuous tubercles at their corners. An un-named species of Manzonella differs from M. fissurata in having tubercles at the two distolateral corners of the autozooids and spatulate avicularia.
This rare species is represented by only two specimens in the NHM collections, the holotype (NHM D6835) from the Searles Wood Collection, which encrusts a red-stained specimen of Metrarabdotos moniliferum and is labelled ‘Red? Crag’, and a smaller, recently collected colony encrusting a bivalve shell fragment from the Ramsholt Member of Broom Pit. Despite the red staining, the holotype is almost certainly from the Coralline Crag; even though derived fragments of M. moniliferum are quite common in the Red Crag, the preservational quality of the calcitic encrusting colony of Manzonella fissurata is unlike that of Red Crag encrusting bryozoans, which are invariably preserved as ferruginous ‘mummies’.
Pliocene, Late Zanclean–Early Piacenzian, Coralline Crag Formation, including Ramsholt Member of Broom Pit, Suffolk, UK.
Although recorded from the Scaldisian of Wilmarsdonck, Belgium (see Lagaaij 1952, p. 42; Bishop 1987, p. 9), and also from Anvers in France (Lagaaij 1952, p. 43), it is uncertain whether these records are the same as the Coralline Crag species. The Belgian material as figured by Bishop (1987, figs 8, 9) has avicularia that possess an ovoidal opesia plus two separate, round opesiules (cf. the trifoliate opesia with confluent opesiules in the Coralline Crag specimens). An additional hole at the distal end of the rostrum may also occur in the avicularia from Belgium but has not been observed in the Coralline Crag material.