FEATURED OKINAWAN MARINE INVERTEBRATE

Pearsonothuria graeffei (Semper, 1868) (size unrecorded)

Featured Invertebrate Data

Taxonomy:

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


Species Account:

        Pearsonothuria graeffei is considered to be common in Okinawan waters, frequently seen by divers on a regular basis during SCUBA excursions in the upper thirty feet of a coral reef environment.

        The following introduction to Pearsonothuria graeffei is taken, in part, from The Florida Museum of Natural History:

        Pearsonothuria graeffei is a member of the most diverse family of sea cucumbers on coral reefs, the Holothuriidae. Previously, it was considered a species of the genus Bohadschia, but was recently placed into its own genus, Pearsonothuria, because of its distinctly different chemical characteristics.

        Pearsonothuria graeffei is unusual in that it will choose to discharge its tubules only if it's highly distressed; in contrast species of Bohadschia discharge them under the slightest provocation. Many sea cucumbers, also known as beche-de-mer or trepang to consumers, are eaten in the Indo West Pacific; they are prepared for sale by drying or smoking the body wall. This animal is not valuable in this respect, however, because it has a thin body wall and a high composition of toxins. The most remarkable feature of Pearsonothuria graffei[sic] is its life history. As it grows, it goes through a transformation from a vividly colored juvenile of yellow and dark blue or black, to a full grown adult colored in beige and brown with black dots. The small and vulnerable juvenile evolved the adaptation to mimic an aposematic (brightly colored to denote toxicity) phyllidiid sea slug, Phyllidia varicosa. Once it grows to a size in which the mimicry becomes ineffective and its large size combined with more mild toxicity become more effective defenses, it begins to change its appearance.

        In addition to the images available on the above Florida Museum of Natural History page, there are several on-line sites with photos; one of these is from Wikipedia and the following information is taken from the Wikipedia site:

Description
Pearsonothuria graeffei is a roughly cylindrical, thin-walled sea cucumber that grows to about 30 centimetres (12 in) in length. Its mouth, at one end, is surrounded by a ring of up to 24 leaf-like, paddle-shaped tentacles with black stalks which are black on the upper side and white beneath. The anus is at the other end of the body and there are several rows of tube feet along the underside. The colour of the adults is pale brown and white, with black speckles and small thorn-like protuberances.
By contrast, the juveniles are brightly coloured, being white and blue or black, with a few large, yellow, thorn-like projections. This colouration makes them closely resemble the sea slug, Phyllidia varicosa, the bright colours of which warn predators of its toxicity. The appearance of the juvenile sea cucumbers begins to change when they grow larger than the slug and the mimicry is no longer effective.
Distribution
Pearsonothuria graeffei is found in tropical parts of the Indo-Pacific Ocean. The range extends from the east coast of Africa to the Philippines, Indonesia and the South Pacific. It is found on the seabed and on coral reefs at depths down to about 25 metres (82 ft).
Biology
Pearsonothuria graeffei is a scavenger and roams around on the seabed sifting through the sediment with its feeding tentacles. Any organic matter it finds is passed to its mouth by the tentacles. Its daily activities start within a few minutes of dawn and continue until half an hour after sunset after which time it adopts an inactive stance with its rear end raised and its tentacles retracted into its mouth. It then remains immobile during the night. They are known to spawn simultaneously with other Echinoderms, including the Crown of Thorns Starfish and the sea urchin Diaderma setosum.
When threatened or disturbed, many sea cucumbers eject cuvierian tubules, thin white sticky strands of viscera, from their cloacas. Pearsonothuria graeffei seems reluctant to do this except under conditions of extreme stress. The threads of this species contain glycosides that are toxic to the aggressor. The effect of these neuro-toxins is to prevent nerve impulses being transmitted, an effect similar to that produced by cocaine. The chemicals, echinoside A and ds-echinoside A, are being investigated for their possible use by humans as painkillers or anti-tumour drugs. Experiments in vitro show that they have marked anti-cancer activity in Hep G2 cells and that, when given to mice with H22 hepatocellular carcinoma tumors (liver cancer), the weight of the tumors was reduced by about 50%

        I've added a second page with several images of both adult as well as the dissimilar-appearing juveniles. There's a remarkable similarity between the juveniles of Pearsonothuria graeffei and a phyllidiid sea slug, Phyllidia varicosa. This similarity was earlier described on the Okinawan Slug Site where I featured an opisthobranch-like animal of the week (Bolland, 2004).

        In addition, there's a page with links to misc. phyla including this species phylum, as well as additional resources.

Literature Cited:


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