Author: Baba, 1949

Order: Nudibranchia  Family: Polyceridae

Maximum Size: 28 mm

Sightings: Sunshine Coast, Whitsundays

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Kaloplocamus acutus Baba, 1949

An uncommon and unpredictably encountered species of Polyceridae nudibranch, Kaloplocamus acutus is usually found under rocks or coral slabs sub-tidally. The bright red/orange, sometimes yellow, body has white specks scattered over the entire dorsum. Sometimes these white specks are closely sited in random groupings giving the impression of white patches especially along the lateral mantle edge and tail. Body shape is elongate and widest anteriorly. There is a remnant of the mantle edge present as a slight ridge running between the three or four pairs of processes situated laterally along each side of the notum. Usually there are three pair between the rhinophores and gills and a fourth pair posterior to the gills. The stalks of these processes are translucent white with the ends sprouting a number of slender, acutely pointed red papillae. Unlike the members of its sister genus Plocamopherus, these processes do not carry a terminal sphere. The oral veil bears a further six of these processes, termed velar appendages, situated around the anterior edge, in an arc, from rhinophore to rhinophore jutting directly outwards. All of the processes can be extended or contracted.

The lamellate rhinophores are comparatively large on tall stalks. The clavi are red/orange or yellow (or a combination thereof) with the distinctive finger-like apical tip red/orange. Some white pigment may be present. The stalks are similarly coloured to the clavi proximal portion but translucent. The non-retractable gill is small, consisting of five leaflets and forms an anterior arc around the anal papilla. The acutely pointed tips are red/orange, and white pigment, in varying amounts, is often present on the anterior face of the leaflets creating a similar appearance to the lateral processes. The foot is broad and the tail is acutely pointed. It is typically observed at 20 mm to 30 mm in length although there are records of up to 70 mm according to Marshall & Willan, 1999 & Coleman, 2008.

Diet is presumed to be bryozoans.

“Kaloplocamus acutus lays a pale orange-red spawn coil.” (Marshall & Willan, 1999)

First described from Japan the recorded distribution of Kaloplocamus acutus has expanded its range over the past few years and now encompasses from Japan, south to New South Wales, Australia and sites in between, and westward from New Caledonia through Indonesia to the Andaman Islands.

Kaloplocamus acutus has, at times, been considered a synonym of Kaloplocamus yatesi (Angus, 1864) but both are now considered to be good species. (WoRMS, 2020)

David A. Mullins – January 2021

References:

– Willan, R. C. & Coleman, N. (1984). Nudibranchs of Australia, Neville Coleman, AMPI: 10-11

– Marshall, J. G. & Willan, R. C. (1999). Nudibranchs of Heron Island, Great Barrier Reef: A survey of the Opisthobranchia (sea slugs) of Heron and Wistari Reefs; Backhuys: Leiden, The Netherlands.

– Bolland, R. F. (2004). Kaloplocamus acutus at http://rfbolland.com/okislugs/kaloacut.html. Okinawa Slug Site.

– Valles, Y. & Gosliner, T. M. (2006) Shedding light onto the genera (Mollusca: Nudibranchia) Kaloplocamus and Plocamopherus with description of new species belonging to these unique bioluminescent dorids. The Veliger 48(3): 178-205.

– Coleman, N. (2008) Nudibranchs Encyclopedia. Neville Coleman’s Underwater Geographic Pty Ltd, Springwood, Qld.

– MolluscaBase eds. (2020). MolluscaBase. Kaloplocamus Bergh, 1880. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=138567.

– This Species Profile has been modified from a previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #344 (March 2017): 12 by David A. Mullins.