Cyerce nigra

Image courtesy of Dave Mullins
4 metres, in the Lawadi muck, Milne Bay, PNG.
Sony DSC-RX100 in Nauticam Housing with wet macro diopter, Inon Z220 strobe.

Cyerce nigra Bergh, 1871

Cyerce nigra is a sacoglossan (sap-sucking) sea slug of the Caliphyllidae (Polybranchiidae) family. The members of this family are easily recognized externally by the possession of long bifurcated (forked) rhinophores and the distinctive shape of their cerata, being usually flattened and either leaf-like or wedge-shaped and sometimes cushion-like (inflated). The Cyerce are distinguished from other members of the family by having a transverse furrow dividing the sole of the foot at the anterior third mark but this is difficult to ascertain in the field or from the usual aspect at which photos are taken.

Cyerce nigra possesses leaf-like cerata densely crowded and overlapping on the dorsum that are readily autotomized. The dorsal or outside surface of the cerata is patterned with white transverse stripes on a black background whilst the ventral surface is black with orange/yellow spots. These contrasting patterns on opposite sides of the cerata are striking to say the least. The edging to both surfaces carries a fine black line with a sub-marginal faint white line and inside of that a broader orange/yellow band. The spots are actually raised pustules capable of secreting noxious substances for defensive purposes. The digestive diverticula only penetrate into the stem of the cerata and so are not to be seen in the cerata per se. The rhinophores are rolled (hollow) and bifurcated for approximately half their length (see photo of head at left). It lays a flat white spiral egg mass.

It is quite similar in appearance to the earlier described Cyerce nigricans (Pease, 1866) however that species exhibits the spots on both surfaces of the cerata without any stripes and having the edging to the cerata white followed successively by black then orange/yellow sub-marginal bands. Some authorities have suggested (though not too strongly) that they may be the same species. Most references report Cyerce nigricans feeding upon Chlorodesmis fastigiata algae, the distinctive Turtle Weed however the few feeding observations of Cyerce nigra only mention it dining upon Udotea geppii.

Bring on the DNA testing.


- Burn R. (1998) Order Sacoglossa Pp 961-974 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. & Valdes, A. 2008. Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books & California Academy of Sciences.
- Rudman 1998 - 2010. Cyerce nigra, Factsheet & Related Messages, Sea Slug Forum, Australian Museum, Sydney.

Dave Mullins
Queensland, Australia
May 2015
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Dave Mullins on location

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