OKINAWAN
OPISTHOBRANCH OF THE WEEK

Halgerda paliensis Bertsch, H. & Johnson, S. (1982) (120mm)
Photo by Atsushi Ono

Opisthobranch of the Week Data

Taxonomy:

Frequency on Okinawa: Collection Data:

Species Account:

        Halgerda paliensis is considered to be very rare in Okinawan waters as I have never seen a specimen during numerous years of Okinawa diving and Atsushi reports seeing only two individuals, the above featured animal as well as one other. The featured animal was found on the underside of dead coral in ten meters off Gahi Island, one of a series of islands in the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.

        The following description of external morphology and coloration, as well as discussion concerning Halgerda paliensis is taken from Bertsch, H. & Johnson, S. (1982). [H. paliensis was originally described as Sclerodoris paliensis by Bertsch, H. & Johnson (1982) but was later placed into Halgerda by Fahey & Gosliner (2001)].

EXTERNAL MORPHOLOGY AND COLORATION: Maximum length of living animal is about 65mm; preserved lengths of 5 specimens were 28, 34, 37, 45 and 51mm. Dorsal surface is evenly convex and heavily crisscrossed with anastomosing ridges. The junctures of 3-5 major ridges are further raised as prominent papillae. One's immediate impression on viewing this animal is of the large size of the ridges compared with the gouged-out pits between them. Rhinophores of 42mm long animal were positioned 7mm from the anterior edge of body, 10mm apart (body width 22mm).

Body coloration is a dirty yellow to yellow-orange. Some of the ridges are a darker and denser yellow. A delicate, thin white line edges the notum; some have none, while others have a lightly frosted appearance. The gills are a dirty cream color; the rhinophores are yellow basally, dusty brown in the broader area of the perfoliations, tipped in white distally.

DISCUSSION: This species apparently has not been reported previously from Hawaii nor elsewhere in the Indo-Pacific, not even as a misidentified specimen, by other workers.

Rudman(1978) reviewed the genus Sclerodoris as comprised of 8 Indo-Pacific species. One of these, Sclerodoris sp. A., he separated from Halgerda rubra under which identification Kay & Young(1969) published a description of their specimens. We have shown that part of this material is actually our new species of Aldisa, and therefore need not be compared with Sclerodoris paliensis. Recently, Bertsch (l981) has recognized one other species in this genus: the Californian-west Mexican Sclerodoris tanya (Marcus, 1971), the first non-Indo-Pacific Sclerodoris known.

Sclerodoris tuberculaia Eliot, 1904, and Sclerodoris sp. B. (sensu Rudman,1978: 86) both have denticles on their outermost radular teeth; these teeth are smooth in Sclerodoris paliensis. The outermost teeth of Sclerodoris coriacea Eliot, 1904, have one large cusp and a number of irregular projections, a trait not shared by S. paliensis; moreover the body texture of S. coriacea is different-with many close tubercles, and without the prominent ridging of S. paliensis. The enigmatic Sclerodoris osseosa (Kelaart, 1859), reported from Ceylon and Africa, has an indistinct dorsal ridge, with "one pit larger and more conspicuous than the others" (Eliot, 1904: 380), traits not present in S. paliensis (see Rudman. 1978: 85-86, for a discussion of Hawaiian specimens identified as Trippa osseosa by Kay & Young, 1969). Both S. tuberculata and S. apiculata Alder & Hancock, 1864, have an accessory gland in their reproductive system, absent in S. paliensis. Notal texture is also useful for specific separation: Sclerodoris japonica (Eliot, 1913) has a back closely covered with villous papillae; S. tarka Burn, 1969, and S. apiculata have a delicate style or filament projecting from each tubercle; S. tarka has a complicated texture which includes pits or holes in the walls of the main concavities and depressions. These characters do not occur in S. paliensis.

The genus Peronodoris Bergh, 1904, has been variously synonymized with Scierodoris (Thiele, 193I ; Alan, 1947), considered a distinct genus (Marcus & Marcus, 1970) or thought in need of further material before a decision could be made (Rudman,1978). Without proffering an opinion regarding the status of Peronodoris, we feel that our new species should be compared with the 3 species placed within that genus because of their distinct notal ridging and possible close affinities with Sclerodoris. The differences can be summarized succinctly: Peronodoris cancellata Bergh, 1904, has no prostate; and P. denticulata Eliot, 1908, and P. rehderi Marcus & Marcus, 1970, have teeth with denticles.

        There's a photo of H. paliensis in the recent nudibranch book (Gosliner, et al. 2015, p. 185). In addition, there are currently images of H. paliensis posted on several sites, notably at several of the following locations: Mike Miller's Slug Site, Bill Rudman's Sea Slug Forum, Kwajalein Underwater, and Sea Slugs of Hawaii.

        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
  • H. okinawa
  • H. onna
  • H. paliensis - The featured animal above
  • H. tessellata
  • H. wasinensis
  • H. willeyi
  • Etymology:

    Literature Cited:


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


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