OKINAWAN
OPISTHOBRANCH OF THE WEEK

Halgerda malesso Carlson & Hoff, 1993 (40mm)
Photo by Atsushi Ono

Opisthobranch of the Week Data

Taxonomy:

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


Species Account:

        Halgerda malesso is unknown from Okinawa's main island as of late-November, 2005. The above featured animal is one which was collected from a cliff wall in the waters of Zamami Island, one of a series of islands in the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. This featured animal was photographed by Atsushi Ono during March of 2005 in 13m of water. Atsushi's photograph is used here with his kind permission. It should be noted that Atsushi considers the species to be very rare in the Kerama Islands as he has seen only the above featured individual (pers. comm.).

        The following information on external morphology is taken from Carlson & Hoff (1993):

        The living animals are ovate with a broad, thin, slightly undulating mantle edge. A 55 mm specimen was approximately 30 mm wide at the broadest point. As is true of other species of Halgerda, the body texture is gelatinous, smooth, and firm. The dorsum has three distinct, irregular, longitudinal ridges with elevated tubercles and numerous depressions. The median ridge, with the highest tubercles, extends from in front of the rhinophores almost to the branchia. There are four major tubercles on this ridge, one anterior to the rhinophores and three between the rhinophores and branchia. The lateral ridges extend from behind the rhinophores to either side of the branchia. A few tubercles are scattered outside the lateral ridges. The foot is about one third of the body width. The anterior end is grooved with the upper lamina split. The rounded tail is sometimes visible when an animal is crawling. Oral tentacles appear short and rounded when an animal is at rest; digitiform when crawling.
        The rhinophores are long and tapering, with the club angling posteriorly. The club and base are about equal in length. The branchia has four gills with numerous large pinnae. In one specimen the posterior two gills were split about two thirds of the way up from the base. The branchial and rhinophore sheaths are low and smooth. The anus is long and thin.
        The body is translucent white with numerous irregular networks of orange lines extending over most of the dorsal surface. These networks are most predominant in the depressions adjacent to the mid dorsal ridge, where they may fuse, creating pale patches of orange. They may or may not join between depressions. The mantle margin is translucent white with two fine submarginal orange lines. Often these lines attach to the lines on the higher part of the dorsum. The apex of the tubercles is orange. The orange lines on the body do not extend to the tips of the tubercles, thus leaving an unpigmented area surrounding the orange tips. The rhinophores are translucent white with brown spots, brown lamella, and white tips. The branchia is translucent white with brown spots and white tipped brown pinnules. The anus is light brown with darker brown spots and a white tip. The foot is white, rimmed in orange. The oral tentacles have an orange tip. The orange lines toward the edge of the dorsum can be seen from below.

        As of early June, 2016, fourteen described species of Halgerda have been featured on these pages from Okinawa's main island and the Keramas. These fourteen species are:

  • H. albocristata
  • H. batangas
  • H. brunneomaculata
  • H. carlsoni
  • H. dalanghita
  • H. diaphana
  • H. elegans
  • H. malesso - The above featured animal
  • H. okinawa
  • H. onna
  • H. paliensis
  • H. tessellata
  • H. wasinensis
  • H. willeyi
  • Etymology:

    Literature Cited:


    Page Date: 28 Nov '05
    Page Modification Date: 01 Jun '16
    Digitally manipulated photo
    Copyright © 2016 Robert F. Bolland