Melibe mirifica & M. japonica - the same species

October 22, 2008
From: Bill Rudman

Following today's message of a huge Melibe in southern Queensland [#21984], which is almost certainly  M. japonica, I checked earlier records of large Melibe from the region and it became quickly apparent that Joyce Allan's description of Melibe mirifica from Cairns, in northern Queensland, fitted M. japonica very well. The size, and extremely large oral veil, and large pink and red pustules all over the cerata and body are identical.

PHOTO: Scan of part of Pl. 23 from Allan (1932) illustrating the preserved specimen of Melibe mirifica.

In the most recent review of the genus (Gosliner & Smith, 2003), Melibe mirifica is considered a possible synonym of M. viridis [based on what I would consider misidentified photos] and M. japonica is considered unidentifiable. However the large size of the animal, the proportionally large oral hood, reddish pigmentation, and gills all over the dorsum, have allowed Japanese workers to identify M. japonica with little difficulty, and Allan's M. mirifica is clearly the same species, so I have no hesitation in identifying them all as M. japonica.

Previously on the Forum I have identified some animals from Papua New Guinea and Indonesia as M. mirifica [see messages #3026, #12461, #19393], because of their size and conical pustules, but the smaller oral veil and lack of red pigmentation are rather different, so I have placed them separately as Melibe cf. mirifica. [Note added 24 October 2008: These three animals are most probably a colour form of M. viridis - see message [#21988]]

The only published record of Melibe mirifica is Allan's description of a specimen found swimming around the Cairns wharf in 1931. The following description is an edited version of Allan's original description:

"Animal very large, over a foot [30 cm] in length, gelatinous and fairly transparent, conspicuous. Foot very broad and solid, wider at the anterior end, rounded at the posterior end. At the front of the body the heda is replaced by an enormous circular membranous oral hood or veil, about 7-8 inches [20cm] in diameter, as long as the foot and about half the size of the animal. When expanded the veil looks like a large jelly-fish. Round its thickened edges are about four rows of numerous irregular-sized cilia, the largest ½ inch [1cm] long. The rows are interrupted for about two inches at the central posterior, and central anterior portion of the margins. Within the veil at the posterior end is a large rounded mouth with thick fleshy lips. The rhinophores are slender and can retract into large stalked sheaths, broad at their tops and slender at the base, situated about half-way along the dorsal surface of the oral veil. Along each side of the body are five to seven variously sized and bluntly shaped cerata with broad bases and their upper margins divided into about three lobes. The largest ceras was about four inches high [10cm] and stood well up beyond the back of the animal. It was constantly in movement and was one of the first to be cast off. When removed from the water after being cast off, it gave out a sickly sweet smell, showed signs of life for several days, and when touched would curl up its edges and exhibit general movement. The remaining cerata, ranging from half inch [1cm] to two inches [5cm] in size, grew rapidly. They were colourless, except for minute speckling, and by the time the animal died had all been cast off. The whole dorsal surface of the animal is covered with large and small blister-like pustules, which are capable of contracting and expanding. Along the central back is a dense mass of fluffy branched 'gills' which, with the pustules and cerata, are constantly in movement. The animal is transparent and gelatinous, with a beautiful pinky-blue tinge over it. The cilia round the veil are deep rose-pink, except the uppermost row, which is white. A minute speckling of rose-pink is over the animal, especially round the veil edge. Inside the veil edge is a deep border, about an inch wide, of this speckling, which shows through to the outer surface. The pustules over the surface are rich rose-pink or white. The branched filaments along the back are a smokey-grey with pinkish tinge. These are tipped with silvery-white. The small cerata had suggestions of pustules on them, but were practically colourless. The large one was a most vivid ornamentation to the animal. When on the animal it had a large thick rachis with the upper end expanded into a thick club-shaped structure. Gelatinous like the body, it had large fluffy white and ruby-red protuberances on it. On the upper portion of the side away from the body was a large brilliant magenta patch of colour with big white pustules on it. The branched filaments scattered over the animal were a pale brown with faint speckling on them. The foot was colourless."

• Allan, J.K. (1932) A new genus and species of sea-slug, and two new species of sea-hares from Australia. Records of the Australian Museum, 18(6): 314-320.
• Gosliner, T. M. and Smith, V. G. (2003) Systematic review and phylogenetic analysis of the nudibranch genus Melibe (Opisthobranchia: Dendronotacea) with descriptions of three new species.  Proceedings of the California Academy of Sciences, 54: 302-355.

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