Idaliadoris depressa

Idaliadoris depressa (Alder & Hancock, 1842)

Idaliadoris depressa @ L'Escala, Girona, Spain by Enric Madrenas

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. Furfaro et al.(2022) introduced a new genus Idaliadoris Furfaro & Trainito, 2022 (type species Idaliadoris neapolitana) grouping 8 species with finger-like more or less swollen dorsal papillae and with a common egg spawn shape. According to Furfaro et al (2022), the shape of the egg masses was revealed to be a useful diagnostic character allowing one to distinguish between genera in the Onchidorididae systematics.

Synonyms

• Doris depressa Alder & Hancock, 1842
• Onchidoris depressa (Alder & Hancock, 1842)
• Atalodoris depressa (Alder & Hancock, 1842)
• Knoutsodonta depressa (Alder & Hancock, 1842)

Description
This is a small, oval shaped, flattened nudibranch, reaching only 9mm in length. The body is translucent white with regular spots of red-brown pigment that are concentrated on the middle of the back. The spicules that are incorporated in the mantle are quite big so they can be distinguished with a hand lens. This species has distinctive long hairy transparent tubercles all over its back, shorter close to the mantle border. The rhinophores are colored light reddish brown, with a wide rachis and with small lamellae. Gills are located on the back of the dorsum, formed by up to 12 pinnate whitish leaves surrounding the anus.

Biology
This animal feeds on the encrusting bryozoan Schizomavella linearis. It is normally found under stones on the shore or in shallow water, between 5 to 40+ meters. The spawn is a very fine pink thread laid in a neat spiral. Its abundance is unknown as it is rarely recorded due to its small size and good camouflage.

Etymology

• Idaliadoris. The type species of the genus, Idaliadoris neapolitana, was described with the original combination Idalia neapolitana, but the generic epithet was not usable as it was previously assigned to another genus, Idalia (Leuckart, 1828). The union between the genus used in the original description with “doris” maintains a connection with the taxonomic history and the belonging to the suborder Doridina.
• Depressa. From Latin “depressus”, reduced, low, flattened.

Distribution
Found all around the British Isles, It has been recorded as far north as the Orkneys and Norway, and south to the Atlantic coast of France (Wimereux) and Spain (Oviñana, Cudillero, Asturias), also in the the Mediterranean coast of Spain (L’Escala, Girona) (Furfaro et al., 2022). A previous report from Huelva, Spain rendered a different species (Idaliadoris cervinoi) (Furfaro et al. 2022). Aparently, it has also been reported in Ghana (Western Africa) (Edmunds, 2013).

More pictures

Bibliography

1246567 Idaliadoris depressa 1 eunomia-revista-en-cultura-de-la-legalidad 50 creator asc 1 2473 https://opistobranquis.info/wp-content/plugins/zotpress/
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

• European Sea Slugs by Morddyn
• NCBI GenBank
• World Register of Marine Species

Cite this article as: