Pentapora foliacea

General description: 

Pentapora foliacea, commonly known as “Potato Crisp Bryozoan” or “Ross Coral” is the largest bryozoan inhabiting British waters. Colonies attach to the substrate via an extensive encrusting base and develop folded three-dimensional branching plates. Plates are composed of two layers of autozooids arranged back-to-back. Colonies are deep orange in colour when alive, fading to a pale buff after death. The species is found in the north-eastern Atlantic.

There is continuing disagreement about whether Pentapora foliacea and Pentapora fascialis are separate species, with the majority of the more recent work, up until Lombardi et al (2010), tending to regard P. foliacea as a junior synonym of P. fascialis. Lombardi et al (2010) again split the two species pending the results of molecular analysis, which is currently being undertaken

Diagnostic description: 

Colonies developing three-dimensional box-like growth comprising folded and anatomosing bilamellar plates from an extensive encrusting base. Early astogeny unknown.

Autozooids longer than wide, 0.67-0.93 mm long (mean 0.81 ± 0.09 mm; N= 20) by 0.28-0.44 mm wide (mean 0.36 ± 0.04 mm; N=20), roughly rectangular in shape, initially elongate, but becoming more equidimensional during ontogeny; arranged quincuncially; zooidal boundary walls salient. Frontal shield lepraliod, granular, with areolar pores and pseudopores, both becoming less distinct through wall thickening during ontogeny, which also obscures zooidal boundaries. Primary orifice 0.11-.020 mm long (mean 0.18 ± 0.2 mm; N=15) by 0.16-0.19 mm wide (mean 0.18 ± 0.01 mm; N=15), a pair of downturned condyles between anter and poster; secondary orifice slightly oval to trifoliate because of the development of lappets. Operculum brown, lustrous. No oral spines. Basal walls with short median septum extending distally from transverse wall. Multiporous septula in lateral and transverse vertical walls near their bases; circular to ovoidal, shallow muscle impressions may be visible close to septula. Ovicell elliptical, wider than long, 0.21-0.25 mm long (mean 0.23 ± 0.01 mm; N=20) by 0.27-0.35 mm wide (mean 0.31 ± 0.02; N=20), a few scattered pores arranged in a band proximally above orifice, becoming overgrown by secondary calcification.

Avicularia monomorphic, adventitious, suboral, usually placed on an umbo, inconspicuous, small, longer than wide, 0.09-0.11 mm long (mean 0.100 ± 0.005 mm; N=10) by 0.08-0.10 mm wide (0.090 ± 0.007 mm; N=10); rostrum semielliptical; orifice 0.050 ± 0.005 mm long by 0.030 ± 0.004 mm wide; crossbar averaging 0.060 ± 0.008 mm long. Giant avicularia not observed, presumed lacking.

(Lombardi et al., 2010)


Colonies are commonly 40 cm in diameter. Autozooids range in size from 0.67-0.93 by 0.28-0.44 mm.


Pentapora foliacea is distributed in the north-eastern Atlantic from St. Kilda south to the coast of Morocco. It is found in the English Channel as far east as Hastings. Mediterranean records require reassessment owing to the similarities of P. foliacea to Pentapora fascialis.


The species usually colonises boulders or bedrock, with small colonies occasionally found on kelp holdfasts. Pentapora foliacea is found in subtidal waters and is most common below 18 m and often abundant between 25-35 m.