FEATURED OKINAWAN MARINE INVERTEBRATE

Baseodiscus mexicanus (Bürger, 1893) (size not recorded)

Featured Invertebrate Data

Taxonomy:

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


Species Account:

        Baseodiscus mexicanus is considered to be very rare on Okinawa. By way of explanation, I've never personally seen this spectacular nemertine in its natural environment. The featured animal was given to me by a diver who found it in 12m of water during a dive at Horseshoe Cliffs on 11 August. I photographed the animal later at home, followed by its relaxation in propylene phenoxetol and fixed 24-hrs in buffered formaldehyde, then transferred to 70% ETOH.

There is an excellent presentation on Nemertines, which are also commonly referred to as Ribbon Worms, on the Cronodon site

The following information on Baseodiscus mexicanus is paraphrased from Kajihara, Yoshida, & Uyeno. 2012 (references omitted from the following article):

        Baseodiscus mexicanus (Bürger, 1893) is a large heteronemertean in the family Valenciniidae (or Baseodiscidae). Its known distribution is largely restricted to the eastern Pacific: west coast of Mexico, Panama, Galapagos Islands, and Chile. Reports from the western Pacific are confined to a field guide by Colin and Arneson containing a photograph taken in a seagrass bed at Lighthouse Reef, Palau, and a museum catalogue by Chernyshev and Volvenko, listing a specimen collected in 1975 from Batu Moncho Bay, Komodo Island, Indonesia.

        Individuals of B. mexicanus are usually 20-80 cm, but occasionally up to 2-4 m, in length and are readily identifiable by a distinctive coloration pattern consisting of a brownish-green, maroon, deep red, mahogany, or brownish-violet background with numerous white rings encircling the body at irregular intervals. Living among shells and corals, it is apparently the largest and most abundant nemertean found in the tropical eastern Pacific.

        During fieldwork conducted by SCUBA diving off Cape Manza, On´na-son, west coast of Okinawa-jima, Japan, a specimen of B. mexicanus (Figure 2A) was collected from a crevice in coral growing on a rock mass (26o30´16" N, 127o50´39" E) at a depth of 3-4 m, on 31 March 2012. The specimen was fixed in 95% ethanol and deposited in the Ryukyu University Museum, Fujukan, in Okinawa, Japan.

Figure 2 from Kajihara, Yoshida, & Uyeno. 2012


        In life, the fully extended specimen was about 4 m long. The background body color was dark brownish purple, with numerous white bands (Figure 2A). In our specimen, the rounded head is demarcated from the body by a transverse cephalic furrow encircling the neck, from the entire part of which numerous secondary furrows extend anteriorly. Numerous, small, black ocelli are distributed along the lateral sides of the head. There are neither horizontal cephalic slits nor a caudal cirrus. The mouth opens mid-ventrally just posterior to the first white band on the trunk (Figure 2B).

        This is the first record of B. mexicanus from Japanese waters (new Japanese name: zebura-himomushi [= "zebra ribbon-worm"]), providing further evidence for an amphi-Pacific tropical distribution. Although there are no reports from the central Pacific, a similar, banded species, B. cingulatus, has been described and reported from Hawaii. Baseodiscus cingulatus, however, differs from B. mexicanus in having a light-colored body with many narrow, reddish-brown rings.

        Baseodiscus mexicanus exhibits a remarkable resemblance to the zebra moray eel, Gymnomuraena zebra, possibly indicating a relationship of mimicry. Near Cape Manza in Okinawa, B. mexicanus and G. zebra occur in exactly the same habitat, with the latter species much more abundant. The distributions of these two species broadly overlap; the moray eel is distributed from the Red Sea and eastern African coast to the Society Islands, north to the Ryukyu and Hawaiian Islands, and south to the Great Barrier Reef; it also occurs in the central eastern Pacific: along southern Baja California, Mexico; and from Guatemala to northern Colombia, including the Galapagos.



        I've added links to several videos of Baseodiscus mexicanus taken in Australian waters:

                Clip 1

                Clip 2

        Baseodiscus mexicanus is the forth nemertine added to the site as of the current date. Previous featured animals are:

                Baseodiscus hemprichii
                Baseodiscus quinquelineatus
                Lineus fuscoviridis

Etymology:

Literature Cited:


        I've added a second page w/ a series of images of the above featured species.

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


Page Date: 01 Apr '18
Page Modification Date: 01 Apr '18
Digitally manipulated photo
Copyright © 2018 Robert F. Bolland