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Cryptosula pallasiana

General description: 

Cryptosula pallasiana is an encrusting bryozoan, common to British shores and shallow subtidal waters. The colonies form white, pink or orange sheets, several centimetres in diameter. Deep brown opercula (flap-like folds of the body wall which close the orifice) are clearly visible across the colony surface.

 C. pallasiana colonises a range of algal and hard substrata. The species is distributed from Norway to the Mediterranean and Black Sea and on the Atlantic coast of Canada and the USA to Florida. C. pallasiana frequently fouls boat hulls and has been reported from docks and harbours in New Zealand.

 

Management: 

C. pallasiana is a common fouler of ships’ hulls and is thought to have been introduced into much of its present day range e.g. on the Pacific coast of America.

Growth: 

Like all bryozoans, C. pallasiana grows through asexual budding of new zooids at the periphery. Once formed, each zooid undergoes calcification.

Morphology: 

 Zooids are oval to hexagonal in shape and individual zooids are separated by deep grooves. The frontal surface is heavily calcified with regularly distributed pores, each bordered by calcification. The orifice is bell-shaped and framed by an erect, flared peristome. Small sub-oral avicularia are occasionally present. The zooids of C. pallasiana  have occasionally been observed to fuse together to form larger zooids which may develop two polypides (Jebram 1977). Polypides have 16-17 tentacles.

Size: 

Zooids are typically 0.6-1.0 by 0.35 – 0.5 mm

Evolution: 

C. pallasiana has a fossil record that extends back to the Miocene.

Associations: 

C. pallasiana will often colonise kelp hold fasts and button-like thalli of Himanthalia. Colonies are predated upon by nudibranchs such as Acanthodoris pilosa and Palio dubia.

Distribution: 

Cryptosula pallasiana is common on British shores and shallow subtidal waters. The species has been recorded from western Norway, south to the Mediterranean and Black Sea, and on the Atlantic coast of Canada and the USA, from Nova Scotia to Florida. C. pallasiana has been reported from docks and harbours in New Zealand and the Pacific coasts of North America.

Habitat: 

Cryptosula pallasiana is common on NW European shores from the mean tide level into the shallow sublittoral. Colonies are abundant on rocky overhangs and the underside of flat stones, but can also colonise shells and other hard substrata. Kelp hold fasts and the button-like thalli of Himanthalia are frequently colonised by C. pallasiana in British waters. This species has been recorded from brackish environments in boreal, warm-temperate and tropical locations (Winston, 1977).                        

Life cycle: 

The founding zooid (ancestrula) develops into a young colony, and later into an adult colony through asexual budding. Sexually produced embryos are brooded within the colony before the larvae are released. Larvae settle after liberation and metamorphose into an ancestrula.

Trophic strategy: 

Like all bryozoans, C .pallasiana is a suspension feeder. It feeds on small phytoplankton using ciliated tentacles of the lophophore.

Reproduction: 

Sexually-produced embryos, which are orange in colour, are brooded in internal brood sacs (as opposed to ovicells). In the British Isles, embryos are most abundant during the summer. The larvae of C. pallasiana are non-feeding coronate larvae, which lack a shell and have a densely ciliated belt (the corona) for locomotion. Larval settlement has been recorded from May to December in western Norway, peaking in July and September. In Britain settlement continues through October.