Aldisa smaragdina

Aldisa smaragdina (Ortea, Perez & Llera, 1982)

Aldisa smaragdina by Enric Madrenas

Taxonomic note: In the last revision of the genus (Millen & Gosliner, 1985) the authors indicate that the situation is unclear. Aldisa smaragdina is believed to be a synonymous with the former Aldisa binotata Pruvot-Fol, 1953. The problem is that the original description of A. binotata is poor, with no information of its anatomy. The unique specimen on which the description was based is lost, so it can not be studied. So European researchers use the name Aldisa smaragdina, as there is no consensus on whether Aldisa binotata can be recognized.

Description
The body is dorso-ventrally flattened, up to 30 mm of length and deep red colored. The mantle is covered with small tubercles. There are two large dark oval spots located between the rhinophores and the gill. There is also a quite faded whitish band on each side, located right behind the first dorsal spot. It has two lamellated rhinophores, with few lamellae arranged almost vertically, protected by tuberculated rhinophoral sheaths. The gill consists of 5 reddish, white tipped gill leaves, protected by a crenulated sheath (with a series of crested mantle projections). The oral tentacles are short and blunt, slightly rolled.

It can be confused with Aldisa banyulensis Pruvot-Fol, 1951, that despite it is also red with two dark spots on the back, it is smaller (with a maximum of 15 mm), has the white dorsal band located right before the second dorsal spot, it has 8 completely translucent red (without white tips) gill leaves, rhinophores with more numerous lamellae that are horizontally arranged, the rhinophoric sheaths and gill sheath with smooth edges, with flattened and triangular, pointy, oral tentacles, it feeds on another sponge: Hemymicale columella, and put less eggs that are larger (200μm in diameter). There is another species with which could be confused, Aldisa expleta Ortea, Perez & Llera, 1982, but it lacks the dark dorsal spots.

Biology
Lives on rocky bottoms, from 3 m depth, where it feeds sponge Phorbas fictitius (Bowerbank, 1866) and is usually found on it, as it has the same coloration as the sponge and the dark spots on the dorsum mimic the inhalent openings, called pore-sieves (cribri), of the sponge, in what is known as crypsis by homocromy. For this reason it is a difficult to see species, and is considered rare. The spawn is a single turn of 1 cm diameter with capsules containing relatively small red eggs (130μm in diameter) each. Skin produces certain substances similar to progesterone.

Etymology

• Aldisa. Probably referred to an Iceland viking saga of the same name.
• Smaragdina. From Greek “smaragdos”, meaning “emerald”, because of the colour of the gills, often greenish white.

Distribution
This species was described in 1982 with specimens collected in the Canary Islands and Asturias (Spain). It has subsequently been cited in the waters of Galicia (Spain), Portugal, including the Azores and Madeira, in Morocco and Cape Verde, as well as in the Mediterranean, in Gibraltar and Granada on the Andalusian coast, also in the Levant and the Balearic Islands. There are recent reports in Catalonia, at Golf de Sant Jordi (Roig, 2019 [in] GROC) and L’Escala (Madrenas, 2022 [in] OPK).

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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

• Acta Naturalis Scientia
• AsturNatura
• Biodiversity Heritage Library
• El Litoral de Granada
• Flickr pictures
• Fotosub Jacobo Alonso
• Interim Register of Marine and Nonmarine Genera
• NCBI GenBank
• OBIS - Search by Taxon
• Sea Slug Forum
• The SlugSite
• World Register of Marine Species

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