(Oken, 1815)
For this subspecies two forms are recognised in the region:
¥ Pneumoderma atlanticum (Oken, 1815) atlanticum (Oken, 1815) forma eurycotylum Meisenheimer, 1905
P. atlanticum atl. f. eurycotyl
Body oval to conical, semi-transparent, visceral mass visible through body wall. Lateral and posterior footlobes well-developed, lateral ones long, posterior one rounded. Lateral gill with long lateral and median folds, but without fringes. Posterior gill with 4 relatively long branches, with clear fringes. Each acetabuliferous arm bears 16 to 20 suckers. In larger specimens 25 to 30 suckers on long stalks, arranged in two rows along arm. Basal suckers larger than lateral ones. Radula formula: 4-1-4. Median plate seems to persist in older specimens. Body length: 6 mm.
¥ Pneumoderma atlanticum (Oken, 1815) atlanticum (Oken, 1815) forma pygmaeum (Tesch, 1903)
P. atlanticum atl. f. pygmaeum
Body rounded, slightly transparent, skin usually pigmented. Wings small, posterior footlobe long. Two short lateral arms, each with up to 8 subequal suckers. Rays of posterior gill with two small fringes at their median side. Lateral gill small, with fringed, lateral somatic crests. Hook sacs well-developed, each with up to 100 hooks. Jaw with 6 spines. Median footlobe blunt. Radula formula: 4-0-4. Lateral teeth subequal with square basal plates, outermost ones with larger basal plates. Body length: 3 mm.