Japetella diaphana

Hoyle, 1885

Eyes large, elliptic, their relative length (% ML) gradually decreasing during growth. Larger eye diameter is 19-27% ML at ML <20 mm, 15-25% ML at ML 20-60 mm, and 12-20% ML at ML >60 mm. Lateral and ventral surfaces of eye covered by silvery reflecting layer. Optic nerves short, optic ganglia near the brain (easily visible because of transparency of tissues). Mantle opening reaching level of pupil. Suckers located near one another, distance between them not more than one sucker diameter, large, diameter averaging 6% ML. Suckers in middle part of 3rd right arm in adult males enlarged, urn-shaped. Hectocotylus absent. Maximum web depth 25-33% of length of longest arm. Funnel sunken into head tissues almost to its opening, located under anterior eye margin. Digestive gland large, elongate-ovoid, covered by silvery reflecting tissue. Gills with 8-11 lamellae per demibranch (half of gill). Egg length approx. 3 mm. Color mostly light-brownish in juveniles, dark-brown, not transparent in adults. ML up to 10 cm.
Larvae with narrow head, elliptical eyes, short arms (3-4 times shorter than ML) with 5-6 suckers (in early larvae), wide mantle and large ovoid digestive gland. Larvae almost totally covered by thick sticky jelly. Optic nerves not detectable in early larvae (ML <6 mm).

One species in the World Ocean.

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