Thordisa azmanii

Thordisa azmanii Cervera & García-Gómez, 1989

Thordisa azmanii @ L'Escala by Enric Madrenas

Nota taxonómica: Ortea & Martínez (1991) consider that this species is the same as Thordisa diuda Marcus, 1955 but this proposal has been rebutted by Cervera et al (2004) and by Alvim & Dias-Pimenta (2013).

Description
The oval shaped body can reach a maximum size of about 15mm. It is coloured from orange to dark brown, with a convex notum and a spiculous texture. The mantle, whose edges have small white dots, is covered with spiculated conical shaped tubercles of different sizes, the largest ones are stained in white at the tips, and the smaller ones appear aligned at the edges of the mantle and rhinophoric and gill sheaths, giving them an irregular appearance. The lower part of the mantle shows the radial arrangement of the spicules in the tissue, as well as branched spiculous groups. The foot, coloured light yellow, has two lobes and is spiculous, and occasionally extends behind the mantle when the animal is in movement. The rear edge of the foot has tiny white spots. The oral tentacles are short and have a cylindrical shape. The dark brown rhinophores have between 9 and 11 lamellae, the tips of the 3 or 4 more distal are stained white. The branchial plume has 5 to 7 bipinnate leaves, coloured dark brown in its basal part and white in the distal part, surrounding the anal papilla.

Biology
The specimens found in Galicia (Almón et al., 2011) lived on sponges of the Raspailia genus: specifically Raspailia hispida (Montagu, 1818), Raspailia (Raspailia) ramosa (Montagu, 1818) and Raspailia (Raspailia) cf. viminalis (Schmidt, 1862) and they are supposed to feed on them, but this point has not been proven. The spawn consists of a light yellow ribbon, fixed by one of its sides to the substrate -generally on the sponge-, wound in a spiral of between one and two turns, with eggs of about 100 microns in diameter, arranged transversely in rows of about 25 in two overlapping layers (Ortea et Martínez, 1990). Observed at a certain distance, the general appearance of this nudibranch is similar to that of the bryozoan Cellepora pumicosa, which could be understood as a form of camouflage in which the animal adopts the appearance of a species unattractive for predators. The spiculous notum facilitates the retention of marine debris in the same way Raspailia sponges do, so they can pass unadverted to predators.

Etymology

• Thordisa. Woman name of Old Norse origin, cited in the Sagas. A fair woman to look on, high-minded, and rather hard of heart.
• Azmanii, in honor of Dr. J. Azmani (M.D.), “who eliminated a chronic ailment of one of us” (Cervera et García-Gómez, 1989).

Distribution
This species has been cited on the Atlantic coasts of the Iberian Peninsula: in Cádiz (Cervera & García Gómez, 1989), in Portugal (García Gómez, 1991), in the Ría de Arousa, Galicia (Almon et al., 2011) and in Cudillero, Asturias (Ortea & Martínez, 1990 as T.diuda). The specimens from Asturias and Cádiz were collected in the intertidal, while those from Galicia were found at 20 meters of depth, so its bathymetric distribution is not clear. It has also been found off the coast of St. Agnes, Cornwall, Great Britain (Picton, 1978 [in] Medslugs) and at Ouessant, French Brittany (Roche, F. [in] NE Atlantic Nudibranchs, 2018), also at the Azores (Chan & Gosliner, 2007). There is a report from Cape Verde (Ortea & Cabrera, 1999) as T.diuda which probably corresponds to T.azmanii, as the authors assimilate it to the findings from Northern Spain, although Alvim & Pimenta (2013) indicate that is not T.diuda. There are very few records of this species in the Mediterranean Sea: so far it has only been found in Granada (Sánchez Tocino et al., 2000) and at L’Escala, Girona, Spain (Madrenas, E. pers. comm.). Federico Betti’s find in Numana, Italy in 2010, has verified that it does not belong to the genus Thordisa, but to the genus Doris.

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

• AsturNatura
• Biodiversity Heritage Library
• El Litoral de Granada
• Flickr pictures
• Forum Natura Mediterraneo
• iNaturalist
• Interim Register of Marine and Nonmarine Genera
• NCBI GenBank
• OBIS - Search by Taxon
• Sea Slug Forum
• World Register of Marine Species

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