Kaloplocamus acutus Baba, 1955 (10mm)

Opisthobranch of the Week Data


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

Species Account:

        Kaloplocamus acutus is considered to be rare in Okinawan waters; I've personally collected five specimens from Okinawa's main island and Atsushi Ono mentions (pers. comm.) seeing and collecting two individuals (at the same time and place) in the Keramas.* The above featured animal was found in 175 feet of water from a "hand-full" of miscellaneous green algae amid an area of mixed sand and coral rubble.

        In an earlier page (December, 1997) here on the site I originally had Kaloplocamus acutus listed as K. yatesi, but I've now decided this was in error and appropriate changes have been made. Also, I've previously featured two additional members of the genus, Kaloplocamus ramosus and Kaloplocamus peludo. I've now added a second page with an image of a drawing, taken from Baba's original description of the species from Sagami Bay, as well as a photo of an animal collected by Atsushi in the Keramas. Additionally, Tomohiko Kurihara (1999) has several photos posted on his Umiushi Site** of the yellow phase of this animal.

        Baba (1955) described the species from a single specimen collected off Sajima Island, Sagami Bay, Japan, in August of 1940. The following original description of K. acutus is taken from Baba (1955):

This species appears very close to K. ramosus (CANTRAINE) in the general body colour of orange-yellow, but it differs from the latter as follows:

        K. acutus---(1) Velar proceses 6. (2) The velar and the dorso-lateral processes have each a small number of acutely pointed branches, the tips of which are always marked with carmine-red. (3) Radula with 2 inner laterals (the formula 21 x 8-

        K. ramosus---(1) Velar proceses (7-) 8. (2) The velar and the dorso-lateral processes are thickly divided and dendritic, and have no carmine-red colouring as seen in the preceding species. (3) Radula with 3 inner laterals.

        In a subsequent paper by Baba (1989) he mentions the external and internal are almost as he described in the earlier publication (1955). From Baba's more recent publication (1989) I've added the following information concerning color of the species:

        The general color of the back and sides is orange-yellow (or better, saffron-yellow). It is sparsely spotted with opaque white. The rhinophore is red at the tip and orange-yellow on the club. The velar and dorso-lateral processes are whitish below, but their upper branches are tipped with red respectively. The gill plumes are orange-yellow, turning to red at their extremities. The sole is paler orange-yellow than above.

        In addition to Baba's description above, I've also added the following description of Kaloplocamus acutus, taken from Marshall and Willan (1999, p. 50):

This is a moderately large dorid nudibranch that cannot retract the gills into a pocket beneath the mantle. Kaloplocamus acutus has a broad foot and acutely pointed tail. There is no notal brim separating the mantle from the sides of the foot. The body carries tall, slender, compound processes arising from cylindrical stalks. There are six such processes on the oral veil and three (or more usually four) pairs along the sides. These processes do not bear swellings capable of emitting light flashes ("globes") as in Plocamopherus. The rhinophores are large, tall and lamellate, and the five gills are relatively small.

The body is rich, deep orange or apricot in colour and it is conspicuously speckled all over with white. All the processes have whitish bases and red tips. The rhinophores are reddish orange, consistently darker than the body, and they have an opaque white streak up the posterior edge towards the apex. The gills are translucent red with opaque white on the front face and red tips.

Kaloplocamus acutus is apparently unable to swim. Kaloplocamus acutus is distinctive and separable from both the Plocamopherus species in being slender, and in lacking papillae on the body and "globes" on the notal processes. Willan & Coleman (1984) used the name Kaloplocamus yatesi for this species, but according to Baba's (1989) subsequent study K. yatesi is a different species with more (eight) processes on the oral veil and (only ever) four notal processes. Therefore, K. yatesi actually resembles the widespread temperate water K. ramosus.

The diet is unknown. Kaloplocamus acutus lays a pale orange red spawn coil.


  • Baba (1955) probably(?) chose the specific name of this attractive little polycerid in reference to the acutely pointed branches of the velar and dorso-lateral processes of the animal.

Literature Cited:

  • Baba, K. 1955. Opisthobranchia of Sagami Bay: Supplement. Iwanami Shoten, Tokyo.
  • Baba, K. 1989. Review of the genus Kaloplocamus from Japan (Nudibranchia: Polyceridae s.l.). Venus, Japanese Journal of Malacology 48(4):231-243.
  • Kurihara, Tomohiko. 1999. Nudibranch Site (Umiushi).
  • 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 Publishers Leiden.
  • Rudman, W.B. & Darvell, B.W. 1990. Opisthobranch molluscs of Hong Kong. Part 1. Goniodorididae, Onchidorididae, Triophidae, Gymnodorididae, Chromodorididae, (Nudibranchia). Asian Marine Biology, 7: 31-79.

        * Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.
        ** Umiushi is a Japanese word for nudibranch.

Page Date: 18 Oct '04
Page Modification Date: 04 Dec '06
Digitally manipulated photo
Copyright © 2006 Robert F. Bolland