Re: Placida dendritica (?) from French Polynesia

February 16, 2002
From: Kathe R. Jensen

Dear Bill,
Erwin Koehler sent me a message about this species, which you tentatively identified as Placida dendritica. I remember seeing it - and shoving it to the back of my memory (where things tend to get lost nowadays!). However, I think that this is more likely a species of Ercolania. There are a number of reasons for this: The cerata appear inflated, and the digestive gland tubules do not have conspicuous side-branches. Also, there is a large white area middorsally, corresponding to the reno-pericardial ridge, where Placida dendritica usually has a network of digestive gland tubules. Also, the rhinophores appear to be "simple" or slightly flattened at the bases, whereas P. dendritica has folded or deeply grooved rhinophores containing branches of the digestive gland. I do not not dare to put a species name on this one. It seems similar to Ercolania translucens, which I described from Rottnest Island (Western Australia) some years ago, but it also has a certain resemblance to a juvenile E. coerulea, which lives on Dictyosphaerea or Valonia, and the last time I visited Rottnest Island, I found a few specimens of what I think is an undescribed species of Ercolania, which I think occurred on Struvea and Cladophoropsis, and which had a purple "spot" (probably the genital receptacle visible through the epidermis) in the neck. The only way to find out whether this is Ercolania or Placida (or even Stiliger) is to look at its radular teeth, which are blade-shaped in Placida (and Stiliger - which does not have a penial stylet), and "sabot-shaped" in Ercolania. Ercolania and Placida both have short, curved penial stylets (very short and pointed in E. coerulea).

Cheers,
Kathe

jensen@ait.ac.th

Jensen, K.R., 2002 (Feb 16) Re: Placida dendritica (?) from French Polynesia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/4177

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