Author: Wilson & Willan, 2007

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 65 mm

Sightings: Sunshine Coast

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Hypselodoris jacksoni Wilson & Willan, 2007

Hypselodoris jacksoni is a nudibranch with a limited distribution in the south-western Pacific Ocean being reported from New Caledonia, Norfolk Island, Lord Howe Island and the subtropical and temperate waters of the Australian east coast. On the offshore reefs of the Sunshine Coast of Southern Queensland, Australia its occurrence is common, being observed upon almost every dive. Even though it was and is commonly sighted it was not described until 2007, perhaps due to this limited distribution combined with its occasional variable colouration.

Hypselodoris jacksoni is a medium sized nudibranch usually presenting between 20 to 35 mm although I have recorded specimens up to 65 mm in length. When crawling the tail is quite long. It has the “typical” high-sided Hypselodoris appearance. The mantle has a narrow overlap along the sides of the high-walled body although this widens anteriorly. The gill pocket sheath rises quite distinctly above the surrounding mantle and the simple, white gills, triangular in cross section with red-orange lines on the outer axes, form a complete circle around the anus. Each of the gill pinnae often carry one or two white spots on the outer face. The lamellate rhinophores are tall, red-orange in colour with a white tip. The colouration of Hypselodoris jacksoni is distinctive though variable. The most common presentation is of a distinct reticulum of dark brown or black infilled with yellow spots that are surrounded by white on the mantle, foot and tail. This reticulum has three recognizable longitudinal lines on the mantle of which the lateral-most form hemispherical loops towards the mantle margin. There is a consistently thin, red-orange band to the mantle margin and tail together with a submarginal opaque white band that extends inwards to fill the previously mentioned loops of the reticulum. Whilst most specimens have a striking intensity of colour and pattern others have a less distinct or much closer reticulation pattern together with a faded appearance to the colours. A number of different presentations are included in the image gallery above. Defensive glands are present around the entire mantle margin being largest and most densely arranged posterior to the gills where the mantle narrows and is rounded off.

Sightings are most usually of individual specimens or pairs but occasionally groupings are found, all competing for a share of a single, doomed sponge colony.

Spawn is laid as a upright coil and the free edge being longer than the attached edge causes it to have wavy appearance. It is orange in colour without extra-capsular yolk and consists of from one to three whorls. The hatched veligers exhibit lecithotrophic development whereby they only spend a short time swimming in the plankton, without feeding, before settling.

Hypselodoris jacksoni has been recorded feeding on sponges of the Euryspongia genus belonging to the Dysideidae family.

Below: Hypselodoris jacksoni glides slowly over the substrate with its gills held high.

Below: Hypselodoris jacksoni slowly raises its head into the water column and receives the full force of the surge that compresses its body. It grimly hangs on.

David A. Mullins – January 2020

References:
– Wilson, N.G. (2002) Egg Masses of Chromodorid Nudibranchs (Mollusca: Gastropoda: Opisthobranchia). Malacologia, 2002, 44(2): 289-305.

– Wilson, N.G. & Willan, R.C. (2007) Hypselodoris jacksoni, a new species from the south-western Pacific Ocean (Nudibranchia: Chromodorididae), with a discussion on intraspecific variation in mantle glands in Chromodoris willani Rudman, 1982. Zootaxa, 1549: 29-42

– Rudman, W.B., 2007 (Aug 29). Comment on Hypselodoris jacksoni from sthn Queensland by David Mullins. [Message in] Sea Slug Forum. Australian Museum, Sydney.

– Rudman, W.B., 2007 (Sep 1). Comment on Hypselodoris jacksoni feeding [1] by Bruce Wilkie. [Message in] Sea Slug Forum. Australian Museum, Sydney.

– Johnson, R.F., Gosliner, T.M. (2012). Traditional taxonomic groupings mask evolutionary history: A molecular phylogeny and new classification of the chromodorid nudibranchs. PLoS One 7 (4): e33479.

– Epstein,H.E., Hallas,J.M., Johnson, R.F., Lopez, A., Gosliner, T.M. (2018) Reading between the lines: revealing cryptic species diversity and colour patterns in Hypselodoris nudibranchs (Mollusca: Heterobranchia: Chromodorididae). Zoological Journal of the Linnean Society, 2018, XX, 1–74.

– This Species Profile has been modified from:
– Opisthobranch of the Week, Week #756, Hypselodoris jacksoni (12/09/2011), Mike Miller’s slugsite.tierranet.com by David A. Mullins
– A previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #350 (September 2017): 12 by David A. Mullins