Author: (Ev. & Er. Marcus, 1970)

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 25 mm

Sightings: Sunshine Coast, Capricorn/Bunker Group GBR, Whitsundays

___________________________________________________

Verconia norba (Er. Marcus & Ev. Marcus, 1970)

Verconia norba is similar in appearance to several other species of Verconia.

The oval-shaped mantle is broad and flattened (Chromodoris-like), rounded anteriorly and posteriorly but does not cover the tip of the tail. The mantle edge can have small convolutions. There is a range of colour to the primary background from pinkish purple to reddish orange. The mantle margin carries a broad white to cream border that is scalloped on the inside edge with those scallops being partially filled by purple to reddish pigment. A broad white line or streak extends down the midline from anterior to and then between the rhinophores, posteriorly to surround the slightly raised gill pocket. The white streak may be continuous or thin out or even be in two parts, that thinning out or break most usually being at about the two thirds mark. The lamellate rhinophores are reddish, the simple gills paler so. The gills form a circle around the anus. The foot is translucent purple becoming darker on the tip of the tail dorsally. Size has been recorded to 25 mm.

Above: Verconia norba testing the substrate for its sponge prey. The buccal mass is partially extruded and the small oral tentacles can also be seen, especially towards the end of the video clip.

The creamy yellow spawn is laid upon the substrate, on edge, as a coil of four to five whorls.

Distribution is considered to be very widespread in the Indo-Pacific region.

Originally described as Noumea norba from a single specimen collected in Fiji.

Species of Noumea were transferred to Verconia in 2015 when it was realized that the genus Noumea was previously occupied.

Rudman, 1986 argued that Noumea norba was just a colour form of the earlier described Noumea purpurea Baba,1949 and designated it a junior synonym. Rudman,1999 had second thoughts about this and stated: “…. I considered this species to be a synonym of Noumea purpurea but now that we no (sic) more about the anatomy and colour variation in that species, they are clearly distinct.” and “In an earlier revision of chromodorids with this colour pattern (Rudman, 1986) the only information available on this species was the original description, and from that I decided that Noumea norba was a colour form of this species. From correspondence with Dr Baba, and exchange of anatomical information, I realise that the two species are quite distinct.”.

The Noumea purpurea of Gosliner, 1987 and Marshall & Willan, 1999 are most likely misidentifications.

Differentiation of similar looking species:

Verconia purpurea (Baba, 1949): Currently known only from Japan. White midline streak is continuous from just posterior to rhinophores back to gill pocket, but does not encircle gill pocket. White mantle margin is thin. Thin submarginal band of purplish red is streaky.

Verconia varians (Pease, 1871): Width of white mantle border consistent. No scallops with purple infills. May possess a thin reddish purple submarginal band that widens anteriorly and posteriorly. White midline streak may be in three segments or at least pinched in two places. Does not encircle gill pocket. There is a known “variation” where the midline white streak is absent.

Verconia alboannulata (Rudman, 1986): White midline streak splits into two lines just posterior to the rhinophores and travel posteriorly forming an oval to meet by encircling the gill pocket.

Mexichromis pusilla (Bergh,1874): Two large purple filled scallops in the white mantle margin down each side plus similar on the anterior and posterior.

David A. Mullins – March 2021

References:

– Baba, K. (1949). Opisthobranchia of Sagami Bay. Tokyo: Iwanami Shoten.

– Marcus, Er. & Marcus, Ev. (1970). Opisthobranch Mollusks from the Southern Tropical Pacific. Pacific Science, Vol. 24(2): 155-179

– Rudman, W. B. (1986) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Noumea purpurea and Chromodoris decora colour groups. Zoological Journal of the Linnean Society 86(4): 309-353.

– Gosliner, T. (1987). Nudibranchs of Southern Africa. Sea Challengers, Jeff Hamann & E. J. Brill.

– 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.

– Rudman, W. B., (1999 December 3) Noumea purpurea Baba, 1949. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/noumpurp

– Rudman, W. B., (1999, December 5) Noumea norba Marcus & Marcus, 1970. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/noumnorb and associated messages.

– Yonow, N. (2008). Sea Slugs of the Red Sea. Pensoft Publishers.