Author: Undescribed

Order: Nudibranchia  Family: Goniodorididae

Maximum Size: 7 mm

Sightings: Sunshine Coast

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Okenia cf. liklik Undescribed

The Okenia are a successful group, if success be measured by a speciose genus. There are nearly 60 described species of Okenia globally and more than a dozen putative, known, but still undescribed from the Indo-Pacific region alone. Over the years more than ten genera have been synonymized with Okenia. Compared to other major genera of the Goniodorididae, such as Trapania and Goniodoris, species of Okenia exhibit a greater diversity of body form. This species discussed here, Okenia cf.liklik, is undescribed but has some similarities to Okenia liklik such that we misidentified it as the latter for several years, until we photographed the real Okenia liklik in the Philippines and Ambon, and subsequently read its description more carefully.

The body of Okenia cf. liklik is elongate, flat, a little expanded anteriorly and tapering posteriorly. It possesses a distinct and continuous notal rim. The anterior portion of the notal rim carries a number of small and stubby papillae each side. The anterior-most pair (occasionally there are four) however, are directed forwards and are very elongate, even whip-like in appearance, although these may be damaged through some misadventure and therefore may present instead, as mere stubs of their former selves. At a small distance posterior to the rhinophores the stubby papillae continue evenly spaced but are located slightly inside to the notal rim proper. The mid-dorsum too carries a set of even smaller stubs and these are arranged in an elongate oval around the midline. The gills emerge from the posterior end of this oval being long and trailing posteriorly. Being a phanerobranch sea slug, the gills cannot retract into pockets. Behind the gills the notal brim converges towards the midline and terminates into two very long papillae on each side. The tail is devoid of papillae or other adornment. The rhinophores are large, carried erect and bear many fine “congested” lamellae posteriorly while its tip is smooth and bluntly pointed.

Okenia cf. liklik has a stunning and complex colouration. The background colour is pink, the lateral papillae are yellow tipped with brown dashes between each that eventually also run up onto the two posterior pairs of papillae that are basally pink and distally white. There is a long band of white pigment laterally on the notal brim, both sides, where the papillae run more medially. The two long anterior whip-like papillae have yellow bases with brown spotting and turn completely brown for the distal two thirds. In between and posterior to the rhinophores is a large white patch that bifurcates into two white lines within which lie the mid-dorsal papillae stubs that are yellow themselves with brown spots in-between some. The white pigment of these lines may be discontinuous or even peter out completely. The rhinophores are pink anteriorly sometimes with scattered white pigment while posteriorly their lamellae are translucent white for the basal half and brown for the distal half, as is the tip. The gills are translucent white basally, with some opaque white distally and yellow tipped.The foot and sides of the body are translucent. The tail is pink dorsally sometimes with white pigment posteriorly.

We have recorded its size up to 7 mm.

The spawn is laid flat onto the substrate as a full or partial circle in a wide ribbon of white egg capsules.

Distribution to date is only recorded from the Sunshine Coast of Eastern Australia on the offshore reefs and in the Mooloolah River.

Differences to Okenia liklik Gosliner, 2004: The two anterior-most papillae are very long and whip-like. None of the other papillae are long. The papillae of the notal brim run more medially, off the notal brim, once posterior to the rhinophores. There is no mid-dorsal serrated crest anterior to the gills. It also bears two medial rows of stubby papillae.The gills are not covered in solid white pigment. Colours and patterning are substantially different.

The specific epithet of liklik is the word for small in the Papuan pigeon language, reflecting upon the small size of the species. The holotype and paratypes were only 3-4 mm long.

David A. Mullins – May 2021

References:

– Gosliner, T. M. (2004). Phylogenetic systematics of Okenia, Sakismaia, Hopkinsiella and Hopkinsia (Nudibranchia: Goniodorididae) with descriptions of new species from the tropical Indo-Pacific. Proceedings of the California Academy of Sciences 55, 125–161.

– Rudman, W. B. (2004). Further species of the opisthobranch genus Okenia (Nudibranchia: Goniodorididae) from the Indo-West Pacific. Zootaxa, 695: 1-70.

– Gosliner, T. M., Valde ́s, A ́. & Behrens, D. W. (2018). Nudibranch & Sea Slug Identification – Indo-Pacific, 2nd Edition. New World Publications, Jacksonville, Florida, USA.

– MolluscaBase eds. (2021). MolluscaBase. Okenia Menke, 1830. Accessed through: World Register of Marine Species (WoRMS) at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=138042 on 2021-05-25