Odontoglaja guamensis

Image courtesy of Dave Mullins
5 metres, Albatross Passage, Bismarck Sea, New Ireland, PNG
Canon G10 in Ikelite Housing with wet macro diopter, Inon Z220 strobe.

Dave Mullins on location

Odontoglaja guamensis Rudman, 1978

Odontoglaja guamensis is a cephalaspidean or head-shield slug belonging to the Aglajidae family. It takes a sharp or practiced eye to locate this small (to 15 mm, usually 8 - 11 mm) and cryptic species. It exhibits all of the usual Aglajidae external features - elongate narrow cylindrical body, broad tapering head-shield, well developed parapodia folding up the sides of the body and two caudal lobes (tails), one longer than the other. There are also special internal structures that have caused taxonomists to place it in this family.

Odontoglaja guamensis presents with a beautiful combination of colours and pattern most noticeable under magnification. The background colour is cream with a diffusion of green or light brown that is more intense at the anterior and posterior ends. Randomly scattered over the entire animal are round or oblong pink pustules each surrounded by a white ring. Some pustules appear less well developed. Finally there is a peppering of small light brown spots distributed over the body. At certain consistent locations there are dense irregular concentrations of these brown spots producing distinctive brown markings - one pair fore and one pair aft on the headshield, one pair almost at the parapodial peaks, one pair on the posterior shield and a single mark at the base of the tail. Across its distribution there are a number of variations on this presentation. The anterior end of the headshield is rounded and extends for more than half the length of the body. The parapodia (lateral foot extensions) fold up the sides of the body to almost meet at the gap between anterior and posterior shields. The left tail is elongated however the right is almost non-existent. The white shell is reduced, thickly calcified and wholly internal.

First discovered in Guam by Clay Carlson & Patty-Jo Hoff Odontoglaja guamensis, and the other later described Odontoglaja, are unusual in possessing radula teeth and gizzard (albeit rudimentary - ridges lined with chitin) not unlike the philinids because all of the other aglajids have evolved to lose these structures. To quote the species' author:

"... Although modern taxonomists shouldn't talk about 'missing links' this species has an interesting mixture of ancestral and 'modern' (derived) characters..."

It is a fast moving predatory sea slug epifaunally hunting polychaete worms, acoel flatworms, other sea slugs and perhaps small crustaceans such as isopods.

Bill Rudman's name for this species says it all - An aglajid with teeth, found in Guam.

References:

- Burn R. & Thompson T.E. (1998). Order Cephalaspidea Pp 943-959 in Beesley,
- P.L., Ross, G.J.B. & Wells, A. (eds) Mollusca: The Southern Synthesis. Fauna of Australia. Vol. 5. CSIRO Publishing: Melbourne, Part B.
- Gosliner, T.M., Behrens, D.W. & Vald├ęs, A. (2008). Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books & California Academy of Sciences.
- Gosliner, T. M. (2011). Six new species of aglajid opisthobranch mollusks from the tropical Indo-Pacific. Zootaxa 2751: 1-24
- Marshall J. G. & Willan R. C. (1999). Nudibranchs of Heron Island, Great Barrier Reef, Backhuys Publishers.
- Rudman, W. B.,(1978).A new species and genus of the Aglajidae and the evolution of the philinacean opisthobranch molluscs. Zoological Journal of the Linnean Society, 62: 89-107.
- Rudman W. B., 1998 - 2010. Odontoglaja guamensis, Factsheet & Related Messages, Sea Slug Forum, Australian Museum, Sydney.

Dave Mullins Queensland, Australia
marineimages@hotmail.com
July 2015
Send Dave email at marineimages@hotmail.com

WEBMASTER'S NOTES: Dave has been active in underwater photography since the early 70's and is presently the Webmaster/Publisher of Insights , a web site you definitely should put on your list of sites to visit!


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