Securiflustra securifrons (Pallas, 1766)

General description: 

Securiflustra securifrons is a subtidal species, present off all British coasts and particularly abundant towards the north of the country. The species is the disturbed throughout the subarctic boreal zone, down to the south coast of Spain. Colonies often exceed 10 cm in height, forming erect branched tufts, with terminally-squared or wedge-shaped fronds that are laterally flattened. Securiflustra securifrons attaches to hard substrates including stones and shells by an encursting basal portionof the colony. The colonies are whitish to light brown, becoming lighter towards the end of each frond.

Growth: 

Colonies grow through asexual budding of new zooids.

Look alikes: 

Securiflustra securifrons bares a superficial resemblance to other species in the Flustridae family. In particular F. foliacea may be confused with Securiflustra securifrons, but the fronds of  S. securifrons are typically narrower, and divided into wedge-shaped segments, unlike F. foliacea.

Morphology: 

S. securifrons forms erect branching colonies, comprised of angular, wedge-shaped fronds, which fork towards the distal end. Colony colour varies form whitish to light brown. Zooids are typically narrow, elongated and rectangular shaped, but may be distorted by developing brood chambers (ovicells). The zooid structure is simple without spines and the thin body wall is only lightly calcified. The frontal surface is entirely membranous and the colony as a whole is flexible. Zooids are arranged with two layers “back to back” to form a bilaminar sheet. The colony is edged by rows of narrow kenozooids (specialised zooids, lacking a polypide) which branch frequently to give rise to a new row autozooids. Avicularia, which are about a quarter of the length of zooids, are inserted in the zooid rows. The rostrum is raised and thickened, bearing a semicircular brown chitinous mandible.

Size: 

Erect colonies often exceed 10 cm in height. Zooids are between 0.7 and 1.1 by 0.14 and 0.2 mm.

Associations: 

S. securifrons is predated upon by nudibranchs including Crimora papillata.

Distribution: 

S. securifrons is a cold temperate species, widely distributed throughout boreal zone of the northern hemisphere. The species extends to the south coast of Spain.

Habitat: 

S. securifrons colonises rocks, boulders and other hard substrata. It has been reported from nearshore environments (~10 m) down to 100 m. This species has been recorded from brackish environments in the Netherlands, as well as the Baltic Sea (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 and larvae released. Larvae settle soon after liberation and metamorphose into an ancestrula.

Trophic strategy: 

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

Reproduction: 

Colonies are hermaphroditic. Sexually-produced embryos, which are dull pinkish to orange in colour, are brooded within specialised brood chambers (ovicells) before larvae are released. The larvae of S. securifrons are large non-feeding coronate larvae, which lack a shell and have a densely ciliated belt (the corona) for locomotion. They have a short pelagic life span.