Opisthobranch of the Week Data
Halgerda batangas is unknown from Okinawa's main island as of early-May, 2013, but the close proximity of Okinawa, as well as the similar opisthofauna to that of the Kerama Islands, suggests the possibility that it is also present here on the main island of Okinawa. The above featured animal, is one which was photographed and collected in the waters of Zamami Island (from Agonoura Bay), 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 December of 2011 in twenty-five meters of water from the base of a stony coral, Porites cylindrica. 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 single featured individual (pers. comm.).
The following description of external morphology of Halgerda batangas is taken from Carlson & Hoff (2000):
External morphology: The living animal is ovate with a smooth, firm gelatinous texture. Both ridges and tubercles are present, the major tubercles occurring at the juncture of the dorsal ridges. Other smaller tubercles may occur around the base of the major tubercles.
Both rhinophores and branchia arise out of low, smooth sheaths. A small postero-lateral tubercle is present on the rhinophore sheaths of all but one of the specimens we were able to view. The rhinophore club is thinner than the base and has a slight posterior angulation. The apex is somewhat pointed. The branchia has four main gills. In the three specimens examined there was secondary branching in the anterior gills. One of the 40-mm specimens had two major branches in the posterior gills.
The body is translucent white with a fine network of red-orange lines covering most of the dorsal surface. The tubercles are capped in red-orange surrounded by various intensities of white depending on the thickness of the dorsal surface. The foot is lined with orange, and oral tentacles are tipped in orange. Rhinophores and branchia are translucent with sparse dark brown spots. The genital opening is not marked.
There is also a good description of Halgerda batangas on the Sea Slug Forum by Bill Rudman (1999) and the following is taken from his presentation:
One of a group of white species of Halgerda with orange markings. This species is characterised by tubercles with an orange-red tip and a mantle colour pattern consisting of a network of solid red-orange lines. There is a white band around the mantle edge containing low rounded orange-capped tubercles. The mantle tubercles range in size from low rounded bumps to tall prominent structures. The small tubercles have an orange-red tip and a basal ring of white. The large tubercles are tipped with orange-red and have a broad subterminal white band. Beneath the white band the sides of the large tubercles have the reticulate pattern found on the mantle.
There are three species of Halgerda with a network of orange lines. In H. malesso the network of lines sometimes fuse to form orange patches in the depressions, there are multiple fine orange lines around the mantle edge, and the fairly high tubercles are capped with orange. In Halgerda batangas, which also has a network of orange lines, the ridges and tubercles are low and rounded. The tubercles are capped with orange-red and have a basal ring of white. The edge of the mantle is white with orange-red tubercles. The foot is edged with orange. The third species with an orange network is Halgerda terramtuentis. It has golden orange lines and the tubercles are capped with white.
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. batangas - The above featured animal H. albocristata H. brunneomaculata H. carlsoni H. dalanghita H. diaphana H. elegans H. malesso H. okinawa H. onna H. paliensis H. tessellata H. wasinensis H. willeyi