Atalodoris inconspicua

Atalodoris inconspicua (Alder & Hancock, 1851)

Atalodoris inconspicua Gulen dive resort, March 2012. Collected by Torjus Haukvik by Bernard Picton

Taxonomic note: The family Onchidorididae Gray, 1827 includes 5 genera: Acanthodoris Gray 1827; Adalaria Bergh, 1878; Atalodoris Iredale & Donoghue; 1923, Onchidoris Blainville, 1816; and Onchimira Martynov, Korshunova, N. Samayan & K. Samayan, 2009; and includes a total of 56 currently accepted species (WoRMS, 2022). Except for the genus Acanthodoris, which includes 15 accepted species and three dubious ones (one nomen dubium and two taxa inquirenda) (WoRMS, 2022; Hallas et al., 2016), and the recently described monospecific Onchimira genus, represented by Onchimira cavifera Martynov et al. (2009), the rest of the genera show a troubled systematic history. In fact, Adalaria, Atalodoris, and Onchidoris (including respectively, 7, 17, and 16 currently accepted species) have undergone numerous revisions over the last few years, producing dissimilar systematic assessments, according to the different opinions of various authors (Hallas & Gosliner, 2015; Martynov et al., 2009). The validity of the genus Adalaria is nowadays disputed; Hallas & Gosliner (2015) treated it as a synonym of Onchidoris whereas Martynov et al. (2009) considered it as a valid genus. Furthermore, Hallas & Gosliner (2015) established the genus Knoutsodonta to include all Onchidorididae without a rachidian tooth, but this diagnostic character was previously stated as the synapomorphy of the genus Atalodoris, originally described by Iredale and Donoghue (1923), and for this reason, was recently re-established by Ortea (2021) and is currently considered as valid.

Synonyms

• Doris inconspicua Alder & Hancock, 1851
• Onchidoris inconspicua (Alder & Hancock, 1851)
• Knoutsodonta inconspicua (Alder & Hancock, 1851)

Description
The body is white or light brown, sometimes with a purple tint, with a maximum reported length of about 12 mm. It has numerous superficial purple, brown and yellow spots that cover the mantle. The mantle is covered with rounded tubercles, the most central ones are larger and lack spicules or have very reduced ones, while those near the edge of the mantle are smaller, but more spiculose. The rhinophores have a rounded apex and about 14 lamellae arranged closer together than in other species of the genus, and they could be pigmented brown. On the edge of each rhinophoric opening there are two large tubercles, one in an anterior position and the other on the external side. On the back of the dorsum there are 7-10 unipinnate gill leaves of very similar size surrounding the anus. Each gill leaf has 7 lamellae, sometimes pigmented brown, with a transparent rachis. The outer edge of the gill circle and the anal area are also pigmented brown. The foot is the same colour as the body, with the dark-brown viscera visible through it due to transparency. The oral veil is light in colour with some small brown spots.

Biology
The two original specimens were collected by Alder & Hancock “from deep-sea fishing boats” on the bryozoan Cellepora pumicosa. Miller subsequently published that Atalodoris inconspicua fed on Cellaria sinuosa, but this is probably a misidentification of Atalodoris oblonga. Chris Todd found several specimens at Robin Hood’s Bay and these apparently fed on Cellepora pumicosa and Porella concinna, so Miller’s feeding report must be considered doubtful. The only specimen of A. inconspicua collected in Galicia was found on (unidentified) intertidal encrusting bryozoans on the underside of large stone blocks exposed at low tide. The spawn, which is deposited on the bryozoan itself, is a pinkish-yellow cord 0.5 mm wide and coiled into a spiral of about 8 whorls. The yellowish eggs measure on average about 90 microns (between 85 and 99 microns).

Similar Species
Atalodoris sparsa, also feeds on Cellepora pumicosa and has a similar colour. However, they can be distinguished because its rhinophores have only 8 or 9 slightly separated lamellae and a rather conspicuous pattern of large tubercles arranged around the bases of the rhinophores. These tubercles have a dark spot at the apex.

Etymology

• Atalodoris, from  “atalo”, youthful, and “Doris”, name of a marine nymph.
• Inconspicua. From latin prefix “in-“, negation + “conspicuus”, illustrious, notable, famous, striking, visible, clearly seen, in sight, in full view.

Distribution
A. inconspicua is a rather rare species known from the British, Norwegian and Breton coasts. It seems to have also been found in the Bassin d’Arcachon. Its capture in Galician waters (Ortea & Ballesteros, 1982) extends its distribution area towards the south. [map]

More pictures

Bibliography

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Bibliography based on the works by Steve Long, 2006. Bibliography of Opisthobranchia 1554-2000 and Gary McDonald, 2009. Bibliographia Nudibranchia, with later updates from other resources.

Further reading

• Biodiversity Heritage Library
• Encyclopedia of Marine Life of Britain and Ireland
• European Sea Slugs by Morddyn
• Flickr pictures
• Interim Register of Marine and Nonmarine Genera
• NCBI GenBank
• OBIS - Search by Taxon
• World Register of Marine Species

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