OKINAWAN
OPISTHOBRANCH OF THE WEEK

Paradoris sp. 1 (12mm)

Opisthobranch of the Week Data

Taxonomy:

Frequency on Okinawa: Collection Data:
[brackets indicate range for all Okinawa-collected specimens of the species]


Species Account:

        Paradoris sp. 1 is considered to be rare in the waters of Okinawa's main island as I have seen and collected a total of four individuals. Three of the animals were found at Horseshoe Cliffs (10ft, 60ft, 180ft) and another was found at Seragaki in 10ft from a relatively extensive area of strewn coral rubble and silty sand. The above featured animal was earlier (March 2005) identified as Discodoris sp. 1 on these pages, but Dayrat (2006) has recently shown it to be a Paradoris (listed by Dayrat as Paradoris sp. B). I've added a second page with images of the other three individuals collected from Okinawa.

        Bill Rudman has photos of this little discodoridid on the Sea Slug Forum (as Paradoris sp. 2). In addition, Atsushi Ono (1999) has a photo of the animal in his 1999 book (p. 105, fig. 168) from the Keramas.*

        The following description of external morphology and discussion is taken from Dayrat (2006):

        The ground colour of the dorsal notum is white; it bears many black stripes of different sizes, irregularly arranged. The rhinophores and the tips of the gills are black. The ventral surface is white in preserved specimens: its natural colour is unknown. This distinct, dorsal colour pattern is still distinguishable in all specimens after 10 years in alcohol. In addition to those black stripes, the notum bears minute black dots in the median part of the notum. However, those minute dots are not conspicuous in live animals.

        The body is significantly elongated. The longest specimens were 12 mm long alive. The foot is rounded posteriorly and anteriorly. The width of the foot equals approximately one-third or one-half of the width of the dorsal notum (in preserved specimens). The anterior margin of the foot is bilabiate and the upper lip is notched. The grooved oral tentacles are digitiform or conical. The preserved, dorsal notum is globally smooth, although it can bear minute tubercles that are not indecora-like. Numerous wide holes are present on the surface of the dorsal notum. Small holes (diameter <10 µm) and tufts of cilia can also be observed on the dorsal notum, including on gills and rhinophores. In preserved specimens, the margins of the rhinophoral and branchial sheaths are smooth. There are six, seven, nine tripinnate branchial plumes; the number of plumes could not be determined with certainty in the fourth specimen. The rhinophores have between eight and 12 lamellae.

        Discussion: There is little doubt that these four individuals belong to a single entity: their dorsal colour and their internal anatomy are not distinguishable. All minor differences are easily explained with individual variation. Whether or not this entity is new is more problematic. On the one hand, the dorsal pattern, distinct from all other Paradoris (with the possible exception of tsurugensis), suggests that this entity is new. On the other hand, the present description is biased because these four specimens were not fully mature, as suggested by the small size of the female gland mass (and the absence of a reproductive system in one specimen). One cannot exclude that adult, sexually mature specimens of sp. B could have different characters. For example, the colour and the radular formula may differ from what we know based on those four immature individuals. Therefore, I think that it is crucial that we know the anatomy of adult, sexually mature specimens before we address in greater depth the taxonomic status of sp. B, and give it a name.

Literature Cited:


        * Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.


Page Date: 16 Apr '07
Page Modification Date: 16 Apr '07
Digitally manipulated photo
Copyright © 2007 Robert F. Bolland