Reconsidering Oxynoe jordani on seaslug.world

Jun 22, 2026 ·

When I rarely get both time and energy at the same time, I go back and re-audit entries on seaslug.world. This time I revisited Oxynoe jordani Krug, Berriman & Valdés, 2018, which has been bothering me for a while. Notes below.

Phylogenetic systematics of the shelled sea slug genus Oxynoe Rafinesque, 1814 (Heterobranchia : Sacoglossa), with integrative descriptions of seven new species
Phylogenetic systematics of the shelled sea slug genus Oxynoe Rafinesque, 1814 (Heterobranchia : Sacoglossa), with integrative descriptions of seven new species

Phylogenetic analyses indicate that, despite their close resemblance, O. jordani is not closely related to the superficially similar O. viridis. One diagnostic difference is that, although both O. jordani and O. viridis have blue eyespots ringed in yellow, in O. jordani there is a small black dot at the centre of each blue spot (except in some portions of the mantle), whereas the eyespots of O. viridis lack this central dot. In O. jordani, the thick white band that runs along the dorsal midline of the tail, tracing the parapodial margins, is densely packed with minute speckles (often visible only as a central black dot), whereas in O. viridis the white-bordered band carries faded blue spots that lack a central black dot. The ground colour of head, tail, and parapodia is green in both species, but in O. jordani the green tissue between the eyespots is dotted with pale yellow spots of varying sizes, whereas in O. viridis the tissue between eyespots is either green or has a mottled small-dark-spot pattern. In O. jacksoni, the centre of the eyespot is deep blue, but lacks the focal small black dot seen in O. jordani. Moreover, the ground colour of O. jacksoni specimens is closer to yellow, while O. jordani is green. Finally, O. jacksoni lacks the hair-like papillae, the yellow spots, and the white marginal band with microscopic hairs running along the parapodial and foot margins seen in O. jordani.

— Phylogenetic systematics of the shelled sea slug genus Oxynoe Rafinesque, 1814 (Heterobranchia : Sacoglossa), with integrative descriptions of seven new species

In short: small black dot in the centre of the blue spot = O. jordani. No central black dot = O. viridis.

Juvenile
Juvenile

I had previously identified this animal as O. jordani. Does it actually have the small central black dot? I had decided "yes" and went with O. jordani. Re-reading the description now, I think this is wrong, and I've moved it back to O. viridis. A definitive answer would require collecting this animal alongside the type-locality-style material from Osezaki and comparing them properly.

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