(No common name)

ORDER

Lithonida

FAMILY

Petrobionidae

TAXONOMY

Petrobiona masselina Vacelet & Levi, 1958, Mediterranean.

OTHER COMMON NAMES

None known.

PHYSICAL CHARACTERISTICS

Massive, subspherical or multi-lobate growth form, encrusting in high energy habitats or dead stalk in calm habitats. Maximum size of up to 2.4 in (6 cm) in diameter when encrusting, if not, living "head" of 0.39–0.47 in (1.0–1.2 cm) in diameter with a stalk 0.79 in (2 cm) long. Stony texture, white color, smooth surface. In subspherical specimens apical oscules, 600–800 µm in diameter. Living tissue only located at the surface and between crests of basal skeleton, with a choanosome 600 µm thick. Spicules are sagittal triactines (with actines 25–200 6–40 µm), tuning-fork (diapason) triactines (basal actines 30–70 5–8.5 µm, apical actines 20–50 4–7 µm), two size categories of tetractines (pugioles) (apical actines 40–130 22–28 µm and 16–40 5.5–8.5 µm, actines of basal triradiate system 8–100 10–28 µm and 30–70 5.5–8.5 µm), spined microdiactines 30–60 2–3 µm. Elongate, irregular skeletal elements, with a radial orientation of the crystals giving them a pseudo-spherulitic appearance, form solid calcareous basal skeleton of Mg-calcite, with crests and depressions on the surface. Some spicules entrapped in basal skeleton, randomly arranged. Leuconoid grade of aquiferous system.

DISTRIBUTION

Mediterranean: eastern basin (Adriatic, Ionian Sea, Crete, Malta, Tunisia), western part of the eastern basin (not recorded west of the Rhone delta and Algeria).

HABITAT

Common near the entrance of dark caves, more rarely on the under surface of stones, 1.6–82 ft (0.5–25 m) depth.

BEHAVIOR

Sessile.

FEEDING ECOLOGY AND DIET

Sessile filter feeder.

REPRODUCTIVE BIOLOGY

Viviparous. Amphiblastula larva.

CONSERVATION STATUS

Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

None known.