Phallusia ingeria Trausdedt, 1883: morphology and development (Ascidiacea, Tunicata)

Abundant populations of the phlebobranch ascidian Phallusia ingeria Traustedt, 1883 previously only sporadically reported in the Mediterranean Sea, have been found in the Lagoon of Venice, allowing a description of its macroscopic and microscopic morphology and in vivo observation of its development from hatching to maturation. The body may be up to 4 cm high. The test shows pointed papillae in which the terminal ampullae of the test vascular system formed of characteristic paired vessels end. The prebranchial and epibranchial areas are densely papillated. The dorsal tubercle is small, and several openings of the neural duct are found in the atrial cavity. The branchial sac of the larger animals shows intermediate papillae and parastigmatic vessels. The dorsal lamina is ribbed on both sides and toothed at the edge. In large animals, it has papillae on right side. The stomach is irregularly plicated. The anus is posterior to the pole of the gut loop. Microscopic morphology was studied on serial sections (7 m). Development was studied in animals obtained by artificial fertilisation, reared in the laboratory. At 18°C, maturity is reached in 180 days, when the animals are about 10 mm height.