June 17, 2002
From: Dong Bum, Koh
I suspected that this was Aglaja depicta (Renier, 1807) but when I look closely I realised that it was not one but two animals. I presume they are mating. Can you tell me if this is really two, and if this is the mating position.
Location: Seogwipo, Cheju Island, Korea.
Photo by: Dong Bum, Koh
With best Regards.
Dong Bum, Koh
firstname.lastname@example.orgKoh, D.M., 2002 (Jun 17) Philinopsis mating from Korea. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/7231
Dear Dr Koh,
Thanks for this interesting photo. Yes these are two aglajids mating. The penial sac is on the anterior right corner of the head, the penis only extending out of the sac during mating. The common male & female genital opening is at the back of the body on the right side, on the floor of the reduced mantle cavity. Sperm reaches the penis in a ciliated groove running along the right side of the body from the common genital opening. As in the Sea Hares, aglajids mate 'head to tail' the anterior one acting as female and the posterior one as male. As with Sea Hares, a number of animals can mate simultaneously by forming a mating chain, in which the animals in the middle of the chain act as both male and female. Although I have no photos, I have observed 10 or more animals of the little black aglajid from New Zealand, Melanochlamys cylndrica in such a chain.
Now to the identity of your animal. The colour of the two animals in your photo show just how variable some of these species can be. It does look quite like A. depicta but it is unlikely that that mediterranean species would be found in the tropical NW Pacific. I am pretty sure your animal is a colour form of the widespread Indo-West Pacific species Philinopsis cyanea. It ranges in colour from animals with a dark blue black background colour to those like yours woth a translucent body with a brownish reticulate pattern. What all these colour forms have in common is traces of two or three large whitish patches down the midline of the headshield and two pairs of orange-yellow longitudinal lines on each side of the headshield. Another species, P.gigliolii (Tapparone-Canefri, 1874) was described from Japan from preserved specimens. The colour was reported to be a buff-white reticulated with brown or ash-coloured lines, and the head shield was said to have a median longitudinal pale line. In Okutani, 2000 [Marine Mollusks in Japan: Pl.374 fig.2] there is a photo which fits that description. It appears to be distinct from P. cyanea.
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