Actinocyclus verrucosus Ehrenberg, 1831 (61mm)

Opisthobranch of the Week Data


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

        *CASIZ: California Academy of Sciences, Invertebrate Zoology

Species Account:

        Actinocyclus verrucosus is considered to be very rare on Okinawa. The above featured animal is only one of three individuals collected from Okinawa and this specimen was collected from twelve meters, amid mixed silty-sand and oyster shell rubble, beneath a concrete pier and associated pilings.

        The above animal was previously listed here on the Okinawa Slug Site as Actinocyclus japonicus. With a recent review of the genus by Valdés (2002) I've decided to discarded the earlier page of A. japonicus to reflect the current view of Valdés and I'm therefore using the name A. verrucosus. The following comments in re A. japonicus are from Valdés (2002):

        Up to now, several names have been proposed for species of this genus, but no one knows for sure how many valid species it comprises. Most authors appear to agree that A. japonicus is the valid name for a widespread Indo-Pacific species (Kay & Young, 1969; Bertsch & Johnson, 1981; Willan & Coleman, 1984; Wells & Bryce, 1993; Gosliner & Johnson, 1994), but its relationships with the type species, A. verrucosus Ehrenberg, 1831, from the Red Sea, are unknown.

        The following description of external morphology of A. verrucosus is also taken from Valdés (2002):

External Morphology: The body is elevated, short, oval, almost as long as wide. The dorsum is covered with several simple conical tubercles scattered irregularly. Some of them are much larger and have a depression on the apex. The central part of the body is clearly elevated over the mantle margin, which is relatively narrow. The perfoliate rhinophores are composed of 20 lamellae in a 33 mm-long specimen (CASIZ 104697). There are 16 unipinnate branchial leaves in the 33 mm-long specimen. In the living animal they are pointing inward, with the apices very close to each other.

        The background color varies from cream brownish to dark brown or gray. Some specimens are almost black. There are paler areas, generally white or yellowish, irregularly distributed on the dorsum. The entire dorsum is covered with small, evenly distributed black spots. The depressions on the tips of the larger tubercles are dark brown or black. The gill is dark gray or black, with numerous small white spots, more densely distributed near the base. The rhinophores are the same color as the body.

        The anterior border of the foot is not grooved or notched, with anteriorly directed foot margins partially surrounding the mouth area. There are no oral tentacles.

Literature Cited:

Page Date: 05 Aug '02
Page Modification Date: 05 Aug '02
Digitally manipulated photo
Copyright © 2002 Robert F. Bolland