February 13, 2004
From: Bill Rudman
I have been uncomfortable with the identification of the Polycera in Linda Ianiello's recent message [#12126] as P. hummi. Although they both have blue and yellow bands on the the velar and extra-branchial processes, they are arranged in a different order. After a search through the literature I am pretty sure this animal is Polycera aurisula.
Although both P. hummi and P. aurisula have a brown speckled background colour and can have blue and yellow banding on the velar and extrabranchial processes they can be distinguished from one another on a number of characters. Firstly P. hummi can grow to at least 20mm in length while the largest specimens of P. aurisula have been no more than 10mm. In P. hummi the blue and yellow bands are close together and there is a central yellow band flanked on each side by a blue band. In P. aurisula there is usually a basal, or lower yellow (or orange) band, then a median dark blue band, and a light blue tip to the process. In P. aurisula the three bands can be close together, in smaller processes, or widely separated, in larger processes. P. hummi never has more than 2 velar processes on each side while P. aurisula can have up to 4. In P. hummi the 3-4 extrabranchial processes on each side of the gills are blunt and club shaped, and contracted into a thin 'stalk' at the base. In P. aurisula by comparison, the 2-3 extrabranchial processes on each side are 'carrot-shaped', pointed at the tip and broad at the base.
Although this is not a new record for Florida, I think it is the first time we have a colour photo of it publicly available
• Marcus, Er. (1957) On Opisthobranchia from Brazil (2). Journal of the Linnean Society of London, Zoology, 43(292): 390-486.
• Marcus, Er (1958) Notes on Opisthobranchia. Bol. Inst. Oceanogr. Univ. Sao Paulo, 7(1-2): 31-78,Pls.1-8.
• Marcus, Ev. & Marcus, Er (1960) Opisthobranchs from American Atlantic warm waters. Bull. Mar. Sci., 10: 129-203.