Hincksina flustroides (Hincks, 1877)

General description: 

Unlike the majority of species in the Flustridae family, Hincksina flustroides forms encrusting colonies. The colonies are typically light brown in colour and comprise circular or lobed patches. Hincksina flustroides occurs in the subtidal, most frequently on shells, but may also colonise stones.

Hincksina flustroides is essentially a warm water species, distributed throughout the Mediterranean and extending to the south and west of Britain and Ireland

Growth: 

Colonies grow through asexual budding of new zooids at the periphery.

Morphology: 

Colonies form circular or lobed encrusting patches which are light brown in colour. Zooids are oval with thick granular walls along the edge. The size of zooids varies from 0.38-0.5 by 0.2-0.28 mm. Short thick spines, frequently eight-nine, are regularly spaced around the non-calcified section of the frontal surface (frontal membrane) and the underlying space (opesia). Most of spines bend inwards across the opesia, except the two most distal spines which stand erect. A horizontal calcareous lamina (the cryptocyst) is present beneath the frontal membrane as a narrow, downward sloping rim around the proximal half (closest to the colony origin) of the opesia. The calcified section of the frontal surface (the gymnocyst) is small, smooth and frequently obscured by an avicularium. Small rectangular avicularia are interposed between the series of zooids. The avicularia are slightly raised at the distal end, furthest from the colony origin and bear a semicircular mandible.

This species is more heavily calcified than the species of the Flustridae family that form erect colonies.

Two forms of this species were described by Gautier (1962). The most common form has flattened spines, but in the western Mediterranean another form, named crassipinata, with 12-14 cylindrical slender spines is more frequent.

Size: 


Zooids are 0.38-0.5 by 0.2-0.28 mm

Distribution: 

Hincksina flustroides occurs throughout the Mediterranean, and the southern and western waters of Britain and Ireland. The species has been recorded from Belgian, Portuguese and Spanish waters.

Habitat: 

Hincksina flustroides is a subtidal warm water species. It is most frequently found on shells and stones.

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 larvae are released. Larvae settle after liberation and metamorphose into an ancestrula.

Trophic strategy: 

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

Reproduction: 

Hemispherical brood chambers (ovicells) are immersed within the zooid (endozooidal), with only the margin protruding above the surface of the colony. Ovicells are located at the distal end of the zooid, furthest from the colony origin. They are visible from the colony surface and embryos are yellow-orange in colour. The larvae of H. flustroides are non-feeding coronate larvae, which lack a shell and have a densely ciliated belt (the corona) for locomotion.