Author: Rudman, 1982

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 60 mm

Sightings: Sunshine Coast, Capricorn/Bunker Group GBR

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Chromodoris lochi Rudman, 1982

The Chromodoris nudibranchs are now known and recognized for the longitudinal black striping on their mantle. Another feature in common is the spawn, that they lay as a flat spiral on the substrate.

Chromodoris lochi is elongate in shape with minimal mantle overhang, described by Rudman as: “…a spatulate shape.” The mantle colour is pale blue to white with a narrow white margin. What appears to be three black longitudinal lines is actually a continuous black line down each side that join together anterior to the rhinophores and posterior to the gills plus another along the midline that may be continuous, or broken, that runs from anterior to and between the rhinophores posteriorly to the gill pocket. There are reports of specimens lacking the midline. These lines may exhibit some diffuse dark blue pigment along their edges. Both rhinophores and gills are uniformly-coloured translucent straw to light pink (sometimes as dark as orange). The rest of the animal, sides of body and dorsum of foot and tail are coloured the same as the mantle also with white edging. The sides of the body may carry up to three black longitudinal lines, often broken, the lateral-most on each side reaching back to be visible on the tail. The rhinophores are lamellate and the five to six simple gills form a circle around the anus, open posteriorly.

Like all the Chromodorididae family members (indeed like all the cryptobranchs) Chromodoris lochi is a spongivore. Most reports have it feeding upon Thorectidae sponges including Petrosaspongia mycofijiensis and Semitaspongia sp.

The spawn is laid as a flat spiral of up to three whorls. It is translucent cream in colour without extra-capsular yolk. The larvae is reported to have planktotrophic development where the larvae spend significant time living and feeding in the plankton before settling and metamorphosing into the adult. The laying of a flat egg spiral is a feature of all the true Chromodoris species as defined by the molecular sequencing of the Chromodorididae family by Johnson & Gosliner, 2012.

Chromodoris lochi seems to prefer being on the underside of overhangs on rocky reefs. Perhaps this is where its preferred prey is to be most often found.

Distribution is widespread in the Indo-Pacific.

Regarding the name, Rudman the author states: “This species is named after Mr Ian Loch, Technical Officer in the Malacology Department of The Australian Museum, who collected and photographed large collections of opisthobranchs for the Museum, while living in Queensland.”

Chromodoris lochi is similar in appearance to:

– Chromodoris willani Rudman, 1982 – but that species possesses a wider mantle. Also the rhinophores and gills vary in colour from bluish white to brown but the significant feature is the dense white speckling to be found on both the rhinophores and gills.

– Chromodoris dianae Gosliner & Behrens, 1998 – but that species possesses a wider mantle that is covered in small white specks, plus rhinophores and gills that are translucent yellow-orange or alternatively, white to the basal half and yellow to the distal half and all variations in between.

– Chromodoris boucheti Rudman, 1982 – but that species possesses gills that are white to the basal half and yellow to the distal half and carrying a black line running up both inner and outer faces for a varying distance. Although Rudman is adamant, that C. lochi and C. boucheti have “quite distinctive” radular morphology, Gosliner, Valdes & Behrens, 2018 (NSSI II) under Chromodoris lochi state: “Indian Ocean specimens have been considered to be a separate species, Chromodoris boucheti, but molecular evidence suggests they are the same species.”

Prior to its description the specimens that now represent Chromodoris lochi were misidentified as Chromodoris elisabethina Bergh, 1877 and Chromodoris quadricolor (Ruppell & Leuckart, 1830).

Above: Chromodoris lochi moving across the substrate.

David A. Mullins – June 2021

References:
– Rudman, W. B. (1982). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris quadricolor, C. lineolata and Hypselodoris nigrolineata colour groups. Zoological Journal of the Linnean Society 76: 183-241.

– Willan, R. C. & Coleman, N. (1984). Nudibranchs of Australia, Neville Coleman, AMPI: 24-25

– Rudman, W. B., (1998, November 29). Chromodoris willani Rudman, 1982. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/chrowill

– Rudman, W. B., (1999, March 4). Chromodoris lochi Rudman, 1982. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/chroloch and associated messages.

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

– Rudman, W. B., Bergquist, P. R. (2007). A review of feeding specificity in the sponge-feeding Chromodorididae (Nudibranchia: Mollusca). Molluscan Research, 27(2): 60-88.

– 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.

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