OKINAWAN
OPISTHOBRANCH OF THE WEEK

Halgerda elegans Bergh, 1905 (7mm)
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 elegans is considered to be very rare on Okinawa's main island as I have seen and collected only two individuals. I've added a second page with photos of these two collected animals (unfortunately only very poor photos of the collected specimens). The above featured animal was photographed, but not collected, from the West Cave dive site, Kuba 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 July of 1998 in 10m of water on the wall of a cavern. Atsushi's photograph is used here with his kind permission. It should be noted that Atsushi considers the species to be common in the Kerama Islands as he has seen over fifty individuals (pers. comm.).

        The following description of Halgerda elegans is taken from Gosliner & Fahey's (1998) redescription of the species:

EXTERNAL MORPHOLOGY. - The living animals studied are 5-10 mm in length. The preserved specimens measure 5-6 x 3 mm. The body is firm and smooth, like gelatin, but rigid. The body profile is high and the dorsum has a series of angled ridges arranged in a reticulate pattern. There are no conical tubercles at the junctions of the ridges, as are present in some other Halgerda species. The ground color of the dorsum and foot are translucent white. The ridges are lined in orange-yellow, with additional short lines of the same color on the dorsum near the gill and rhinophores. There are four junctures where the color and ridges meet along the midline of the body; one in front of the rhinophores and three between the rhinophores and the gills. There are short, evenly-spaced black lines which run perpendicular to the margin and are present around the entire margin. The white viscera can be seen through the dorsum in the living animal.
        The upright rhinophores are tapered towards the tip with black subapical coloration and a translucent white background color. There are 11-15 rhinophoral lamellae.
        The four branchial leaves are sparsely and irregularly pinnate. The gills have black coloration approximately halfway up the stalk. The pigment completely encircles each branch. Within the gill rachis, running from the base to the apices, are numerous flattened, translucent structures which appear glandular. The anal papilla is translucent white.

        As of early May, 2013, thirteen described species of Halgerda have been featured on these pages, from Okinawa's main island and the Keramas. These thirteen species are:

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


    Page Date: 16 Sep '02
    Page Modification Date: 01 May '13
    Digitally manipulated photo
    Copyright © 2013 Robert F. Bolland