Phyllaplysia smaragda or P. engeli from Florida

Dear Geoff,

I would agree that this is a species of Phyllaplysia but I have a problem with identifying it to species. Two species, P. engeli and P. smaragda have been reported from the Caribbean and they are reported to have some anatomical differences, but I doubt if enough specimens have been studied to determine whether these differences are inter or intra-specific in importance, or even based on distorsions during preservation. For example P. engeli has a crop between the buccal bulb and gizzard while P. smaragda doesn't and P. smaragda is said to have fewer spines on the penis. In external shape P. smaragda is said to be more elongate and have the oral tentacles joined at the base while in P. engeli the oral tentacles are said to be more separate and the body shorter and rounder, which are both variable characters dependent on whether the animal is extended crawling or sitting at rest.

Colour is very difficult to use as a character in these animals because it is variable and can be affected by the colour of the plant material being eaten. Kerry Clark observed green P. smaragda going reddish-brown after a few weeks in an aquarium feeding on reddish algal growths on the aquarium wall (Clark, 1977).

The uniform green colouration of your animals, and their blackish papillae don't fit the colour information we have on either of the Caribbean species, but I suspect it is just the normal colour variation of one species. Since the earliest name is P. engeli, that is the one I will use until a more comprehensive study on anatomical and colour variability is undertaken. Kerry Clark reported P. smaragda living on Syringodium and concluded its diet consisted of Erythrocladia subintegra, which lives on Syringodium, and scrapings of Syringodium, but as I mention above, it also in aquarium conditions can feed on other algae.

• Clark, K.B. (1977) Phyllaplysia smaragda (Opisthobranchia: Notarchidae), a new anaspidean from Florida. Bulletin of Marine Science, 27(4): 651-657.