Pseudoceros bimarginatus Meixner, 1907 (rfb #2562-B / 18mm / from 10ft))

Featured Invertebrate Data


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

Species Account:

        Pseudoceros bimarginatus is considered to be rare on Okinawa as I have collected four individuals animal over a period of more than twenty years of Okinawa diving. A fifth animal was collected and photographed, but apparently the collection and photo data have been lost(!@#$%^) over the years.

        A quick note on preservation of Platyhelminthes:                

Polyclad flatworms are notorious for being difficult to preserve. I used 10% formaldehyde stored frozen in a freezer on a piece of filter paper. The frozen paper is removed from the freezer and the animal placed onto the formaldehyde-soaked filter paper. The F/W and solution were allowed to thaw for 24-hrs and then x-ferred to 70% ETOH. This procedure was suggested to me by Leslie Newman and worked well. There is a good presentation of this technique in Neuman & Cannon, p.48 (2003).

        The following description of Pseudoceros bimarginatus is from EOL.

External morphology: white or cream dorsal surface with three marginal bands in the following order from the inner to outer: yellow-green, black and an orange rim. In some worms there is also a fine median white line that ends before the posterior margin. On the ventral side is pink-orange with the three marginal bands. The pseudotentacles are formed by simple folds of the anterior margin. Presence of a cerebral cluster formed by about 30 to 40 eyespots and the marginal eyes can't be detected because the presence of the intense black band. Ruffled pharynx with folded lateral branches.
Internal anatomy: The male apparatus is formed by the spermiducal bulbs dorsally directed and a rounded seminal vesicle connected to a coiled ejaculatory duct. The prostatic vesicle is small and oval. The penis stylet is short. The female system is characterized by a wide antrum with a short and muscular vagina surrounded by the cement glands.

Taxonomic Remarks
This species was described by Meixner (1907) from the original descriptions made by Gravier, possibly based on preserved animals. Stummer-Traunfels (1993) figured the same species but it was not named. Subsequently, Hyman (1954) described this species as P. corallophilus based on one preserve and immature specimen. Finally, Newman & Cannon (1994) re-described this species based on living worms and fresh material. Their description differs slightly from the original description, probably as a result of the examination of preserved animals made by Meixner (1907). They included this species in the group 2 characterized by the presence of marginal bands, according to the categories based on the color patterns (Newman & Cannon 1994). P. gamblei and P. heronensis resemble this species but the color of the marginal bands is a distinctive character for P. bimarginatus, and P. confuses has an extra black marginal band. The vivid orange, black and yellow color suggests an aposematic coloration.

        The diagnostic characters for P. bimarginatus are the color and color pattern which is white with three marginal bands: yellow, black and orange. There are several very similar-appearing animals, one of these (Pseudoceros cruentus) is shown on the second page of this series.

There are several excellent photographs of P. bimarginatus found on-line, several of these are:

  • Kwajalein Underwater
  • Nudi Pixel
  • Philippine Sea-Slugs, Look-alike
  •         Pseudoceros bimarginatus is the second polyclad flatworm added to the site as of the current date. The Previous featured animal was:

                    Pseudobiceros ferrugineus


    Literature Cited:

            I've added a second page w/ a series of images of the species as well as to a similar-appearing species.

            In addition, I've added a link to the current and past featured invertebrates via a list and thumbnails.

    Page Date: 15 Oct '17
    Page Modification Date: 15 Oct '17
    Digitally manipulated photo
    Copyright © 2017 Robert F. Bolland