Berthella & Pleurobranchus

Dear Magenta,
The most recent review would be Richard Willan's review (1987), but it is very difficult to find the characters unique to each genus as there is no simple summary for someone like me who, at this moment, wants to differentiate the genera, rather than understand the phylogeny of the pleurobranchs.

What I can say from a quick scan through the paper is that species of Pleurobranchus grow to a relatively large size (20cm) and have tubercles on the mantle and gill rachis (arrow in C). The anterior mantle is deeply cleft, there are flaps over the genital aperture in adults and the tips of the rhinophores pulsate. There is no penial gland and the reproductive system is diaulic.

In Berthella, species do not grow as large as Pleurobranchus, the mantle is relatively smooth, the anterior mantle margin is weakly cleft, and the gill rachis is smooth. The reproductive system is triaulic and there is a penial gland. I don't think the tips of the rhinophores pulsate, and I think a unique feature of Berthella is the anus opening 'in front of the middle of the gill's suspensory memebrane'.

I have added photos of the gills of Pleurobranchus and Berthella. I guess smooth and tuberculate gill rachis are quite distinctive differences but you then have to be able to differentiate Berthella from all the other genera with a smooth gill rachis.

Best wishes,
Bill Rudman.

Reference: Willan, R.C. (1987) Phylogenetic systematics of the Notaspidea (opisthobranchia) with reappraisal of families and genera. American Malacological Bulletin, 5(2): 215-241.