Author: (Risbec, 1928)

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 40 mm

Sightings: Sunshine Coast, Capricorn/Bunker Group GBR

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Cadlinella ornatissima (Risbec, 1928)

Species of the genus Cadlinella are unusual in the family Chromodorididae for a number of reasons however, the most obvious is the large elongated tubercles on their dorsum. The only other chromodorids possessing something similar are some species of the Mexichromis genus. Cadlinella is considered to be among the most basal group of chromodorids. The genus currently holds three species united by a combination of radula morphology, spiculose mantle, mantle gland types and arrangements, large/long notal tubercles, reproductive system morphology and unique sperm morphology,

Cadlinella, unsurprisingly, has been called an enigmatic taxon as it has been shunted around over time by different authors variously as, its own separate family, a part of the subfamily Cadlininae and a member of both the subfamily Chromodoridinae and the family Chromodorididae. A recent paper by Korshunova et al (Feb. 2020) has resurrected Cadlinellidae, but at this stage I wait to see if this change is accepted by the broader taxonomic community.

Cadlinella ornatissima is a small to medium sized dorid nudibranch with a maximum recorded size of 40 mm but most often observed in the 20 to 30 mm range. The yellow to orange coloured mantle is oval and completely covers the foot with a large overlap apart from the white tail that protrudes slightly. The sole of the foot is white. The mantle carries a network of spicules causing it to be stiff and tough.

The most distinctive feature is the many tubercles that arise from the notum. These are tall, club-shaped with a rounded tip and are regularly spaced over the notum even anterior to the rhinophores. They are opaque white in colour with a red to magenta tip. In some specimens the coloured tip may be reduced to a minute apical speck. The tubercles also contain stiffening spicules. They are never autotomised.

The rhinophores are extremely long, narrow and tapering with opaque white clubs carrying large lamellae and having stalks that are translucent white. They can be retracted into protective pockets with slightly raised rims. When fully extended they may be between one quarter to one third of the mantle length, thus creating another distinctive feature of the species.

The five (sometimes up to seven) simple white gills form a complete circle around the anus posteriorly on the dorsum and can be retracted into a protective pocket below the mantle surface. The gills are large but not often fully extended. Rudman, 1984 states that the gills are: “… simple but with a tendency to branch.” . The gill pocket rim bears five tubercles.

The defensive glands of the mantle are most unusual in being arranged into three distinct bands, an arrangement unique to Cadlinella. The outermost band, at the very edge of the mantle, consists of minute but discrete white glands that discharge a whitish fluid when the animal is aggravated. They are either randomly sited or clustered in patches containing five or six. These are also located on the surface of the notal tubercle stalks. The middle band has slightly bigger glands arranged in larger clusters of up to 20 in each. The innermost band, according to Rudman, 1984, consists of: “… a row of large pits, each containing a large rounded white pustule and surrounded by a ring of smaller glands. There are about eight of these large glands on each side of the mantle and they open ventrally, beneath the mantle skirt …”. For further information about the action of these large glands we can look to Rudman, 1995 in his description of Cadlinella hirsuta. “Remarks: In all anatomical features this species matches the anatomy of Cadlinella ornatissima. The main difference is the development of the dorsal tubercles of C. ornatissima into long tapering papillae in C. hirsuta.” Therefore it would seem reasonable to take the following description in Rudman, 1995 of the large pustule-like innermost glands of C. hirsuta to be similar for C. ornatissima. “Embedded deeply in the mantle tissue, near the body, is a third gland type, a compound gland consisting of a translucent ring (of connective tissue or muscle) surrounding a ring of white spherical glands (Fig. 2). There is a pore in the centre of these compound glands, which opens ventrally on the mantle skirt. There are about eight of these compound glands on each side of the mantle. When irritated, all the white spheres are extruded out of the central pore.”. All of the gland types are believed to store antifeedant chemicals obtained from the digestion of some of their sponge prey. It is not known however if each gland type stores the same or different antifeedant chemicals, but all are considered to be of a defensive nature.

Cadlinella ornatissima feeds upon a number of sponges, the diversity of which is spread across three orders. Compared to other chromodorids its feeding preference is therefore less specialised, it being suggested this might be a reflection of their basal situation in the chromodorids. It has been recorded feeding upon certain sponges of the families Halisarcidae (Halisarca sp.), Darwinellidae (Darwinella sp.) and Callyspongiidae (Callyspongia sp.).

The spawn of Cadlinella ornatissima is laid as a planar spiral, that is, flat upon the substrate and not on edge. This is similar to species of Chromodoris. Interestingly, extra-capsular yolk is present in the egg mass of Cadlinella ornatissima but not in the egg mass of Chromodoris species. This extra-capsular yolk has a granular appearance and is unevenly distributed as individual or clusters of granules throughout the spawn spiral. The egg spiral of Cadlinella ornatissima is translucent white and consists of approximately 16 whorls. It has the appearance of a disc due the overlapping nature of the free edges providing for a tight coil. Larvae were observed to hatch as free swimming veligers.

Distribution of Cadlinella ornatissima is broadly tropical/sub-tropical Indo-West Pacific. Recorded from the Red Sea to South Africa across the Indo-Pacific to the Marshall Islands, north to Japan and south to Jervis Bay, NSW and North Island, New Zealand.

This species cannot be confused with any other, having a yellow/orange mantle, a network of spicules in the body and mantle, numerous tall pink-tipped white tubercles on the notum and extremely long white rhinophores with large lamellae.

Originally described as Cadlina ornatissima by Risbec in 1928, it was placed in a newly erected genus – Cadlinella by Thiele in 1931 making it therefore the type species by monotypy. At the time his reason for doing so was a difference in the radula.

David A. Mullins – May 2020

References:
– Boucher, L. M., (1983). Extra-capsular yolk bodies in the egg masses of some tropical Opisthobranchia. Journal of Molluscan Studies, 49: 232-241.

– Rudman, W. B. (1984). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: a review of the genera. Zoological Journal of the Linnean Society, 81: 115-273.

– Rudman, W. B. (1995). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: further species from New Caledonia and the Noumea romeri colour group. Molluscan Research, 16: 1-43.

– Rudman, W. B., (1998, December 8). Cadlinella ornatissima (Risbec, 1928). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/cadlorna and associated messages.

– Gosliner, T. M. & Johnson, R. F., (1999). Phylogeny of Hypselodoris (Nudibranchia: Chromodorididae) with a review of the monophyletic clade of Indo-Pacific species, including descriptions of twelve new species. Zoological Journal of the Linnean Society. 125, 1–114.

– 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.

– Wilson, N. G., (2002). Egg masses of chromodorid nudibranchs (Mollusca: Gastropoda: Opisthobranchia). Malacologia 44, 289–305.

– Wilson, N. G. & Healy, J. M. (2002). Is Cadlinella ornatissima a chromodorid? Sperm ultrastructure in an enigmatic nudibranch (Opisthobranchia, Mollusca). Invertebrate Reproduction and Development, 42, 179–188.

– Wilson, N. G. & Lee, M. S. Y. (2005). Molecular Phylogeny of Chromodoris (Mollusca: Nudibranchia) and the identification of a planar spawning clade. Molecular Phylogenetics and Evolution, 36, 722–727.

– Wilson, N. G. & Healy, J. M. (2006). Basal chromodorid sperm ultrastructure (Mollusca, Gastropoda, Nudibranchia). Zoomorphology, 125, 99–107.

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

– Turner, L. M. & Wilson, N. G. (2008). Polyphyly across oceans: a molecular phylogeny of the Chromodorididae (Mollusca, Nudibranchia). Zoologica Scripta 37: 23–42.

– Johnson, R. F., (2010). Breaking family ties: taxon sampling and molecular phylogeny of chromodorid nudibranchs (Mollusca, Gastropoda). Zoologica Scripta 40(2): 137–157.

– 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.

– Yonow, N., (2012). Opisthobranchs from the western Indian Ocean, with descriptions of two new species and ten new records (Mollusca, Gastropoda). ZooKeys 197: 1-130.

– Korshunova, T., Fletcher, K., Picton, B., Lundin, K., Kashio, S., Sanamyan, N., Sanamyan, K., Padula, V., Schrödl, M. & Martynov, A. (2020). The Emperor’s Cadlina, hidden diversity and gill cavity evolution: new insights for the taxonomy and phylogeny of dorid nudibranchs (Mollusca: Gastropoda). Zoological Journal of the Linnean Society, XX, 1–66.