Author: Undescribed

Order: Nudibranchia  Family: Hancockiidae

Maximum Size: 25 mm

Sightings: Sunshine Coast; Gold Coast

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Hancockia sp. 01 Undescribed

Hancockia is the only genus within the Hancockiidae family. It is unusual in being the only genus outside of the Aeolidina group to possess cnidosacs in their cerata, with the possible exception of Embletonia. Hancockia also bear cnidosac nodules on their notum, body sides and rhinophore sheaths. Cnidosacs contain nematocysts (stinging cells) obtained from a hydroid food source and maintained and stored therein for defensive purposes.

The oral veil of Hancockia sp. 01 is bilobed with each lobe having at least seven digitate processes around the anterior edge, some processes being longer than others. Cerata are arranged down each side of the dorsum most usually numbering five pairs. The cerata are hand-shaped, “palm” facing outwards, each with a number of finger-like digits. The number of digits on each ceras seems variable, from five to eight; whether this difference is a natural variation or a result of damage is yet to be determined. When at rest the digits are usually extended and resting upon the substrate, but are contracted, fist-like when the animal is on the move. Located along the midline of the dorsum are a number of distinctive branched white papillae (at least seven) and referred to as secondary gills. The rhinophore sheaths are tall and flare open, with finely branched papillae around the rim. The rhinophores themselves project from the flared sheath opening as a substantial base, with vertical lamellae, that narrows to a fine white smooth stalk, tipped with a white bulb.  

The colour of the notum, body, oral veil, cerata and rhinophore sheaths is a translucent brown with a reticulation of fine opaque white lines. The white lines extend out upon the digits of the oral veil and cerata rendering a claw-like appearance.

Most often found on algae feeding upon epibiont hydroids. Their shape and colouration make them most cryptic on the algae.

Size recorded to 25 mm.

Distribution is known from Japan to PNG to the east coast of Australia.

This is the Hancockia sp. 2 of Gosliner et al., 2018, that specimen exhibiting a more greenish basal colour.

Previously known on this site as Hancockia burni Thompson, 1972. Hancockia burni was described from specimens collected intertidally at Point Lookout, North Stradbroke Island, Queensland, Australia. In that description no mention was made of the distinctive midline row of papillae (secondary gills) so distinct in our Hancockia sp. 01. Also, the colour pattern is reversed with Hancockia burni described as: “The body-colour was translucent white with a fine irregular pattern of reticulate brown markings and opaque white specks, giving a marbled appearance.”

Name changed on website 06/10/2024.

David A. Mullins – October 2024

References:
– Thompson, T. E. (1972). Eastern Australian Dendronotoidea (Gastropoda: Opisthobranchia). Zoological Journal of the Linnean Society, 51: 63-77

– Rudman, W. B., (2001 January 23). Hancockia sp. 1 [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/hancsp1

– Rudman, W. B., (2008 Nov. 13). Comment on Hancockia burni ? at Woody Point Queensland [1] by David Mullins. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22025

– Rudman, W. B., (2008 Nov. 13). Comment on Hancockia burni ? at Woody Point Queensland [2] by David Mullins. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22027

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