Calma glaucoides

Calma glaucoides (Alder & Hancock, 1854 )

Calma glaucoides by Enric Madrenas

Taxonomic note: The phylogenetic analyses performed by Cella et al. (2016) revealed that the traditional Tergipedidae family is polyphyletic and belongs to a larger monophyletic clade including members of the traditional families Eubranchidae, Fionidae and Calmidae; this was an unexpected result, since the validity of these taxa and their distinctness from the Tergipedidae was never questioned before. They proposed to join the families Tergipedidae, Eubranchidae, Calmidae and Fionidae under the name of Fionidae. This decision has been reinterpreted and completed in the paper by Korshunova et al. (2017) because it obviated evident morphological and molecular aspects.

Until a few years ago the only known species of the genus Calma in the world was C. glaucoides, described as Eolis glaucoides by Alder & Hancock in 1854. Another species of the same genus, C. gobioophaga was recently described thanks to specimens captured in the coasts Of Portugal (Calado & Urgorri, 2002). The study of the specimens of the Portuguese coasts has allowed to distinguish in the genus Calma two sympatric species that coexist in the same distribution area and live in the same habitat: C. glaucoides and C. gobioophaga.
Calado and Urgorri (2002) indicate the main differences between the two species, among which are the longest propodial tentacles in C. gobioophaga; the larger eyes located immediately behind the base of the rhinophores in C. gobioophaga, smaller and located behind the base of the rhinophores in C. glaucoides; kidney located between the second and last group of cerata in C. gobiophaga and between the second and fifth or sixth group of cerata in C. glaucoides; somewhat smaller egg size in C. gobioophaga; feeding on Gobius niger eggs in C. gobioophaga and eggs of Lepadogaster lepadogaster, L. purpurea, L. candollei, Parablennius gattorugine or P. pilicornis on C. glaucoides. Very recently Prkić et al. (2014) have performed a molecular study (COI and 16S genes) of Croatian specimens from different locations of C. glaucoides and C. gobioophaga confirming the separation of the two species.

Synonyms

• Eolis albicans Friele & Hansen, 1876
• Eolis glaucoides Alder & Hancock, 1854 (original)
• Forestia mirabilis Trinchese, 1881

Description
The specimens of this species are between 10 and 15 mm in length. The general color of the body is translucent yellowish white, allowing the internal organs to be visible by transparency, although it may also be dark yellow, purpuraceous or brown depending on the type of food. The head is quite short, as are the oral palps and the rhinophores. The rhinophores are smooth and semi-transparent and, like the oral palps, have an opaque tip due to whitish or yellowish pigmentation. The eyes are very small and are located right behind the base of the rhinophores. There are 7 to 10 groups of cerata well separated from each other and that begin very close to the rhinophores. The cerata are semitransparent, fairly long, thin and tappered. There are 3-4 cerata in each group. Within each cerata, the digestive gland is shaped like a thin, yellowish or creamy duct. In larger specimens there could be a fine bluish score on the cerata that makes the surface opaque and masks the digestive gland; the pointed apex of the cerata is yellowish. The cerata of the same group seem to grow from a common base. In most of the specimens the gonadal units are visible by transparency in the form of whitish structures of lobulated contour, located between the insertion zones of each group of cerata on each side of the back. The foot is wide and forms two short and sharp propodial tentacles. The tail is short and is usually covered by the rearmost cerata.

Biology
Animals of this species are usually found under stones from very shallow depths. Often the animals expand their cerata laterally resembling the tentacles of an anemone. It feeds on fish eggs such as Lepadogaster lepadogaster, L. purpurea, L. candollei, Parablennius gattorugine or P. pilicornis. The spawn is a sinuous cord, fine and very irregularly arranged with white eggs that are inside capsules of about 138 microns in diameter (Calado & Urgorri, 2002).

Etymology

• Glaucoides. Derives from Latin “glaucus”, white. Meaning “whitish”.

Distribution
Until year 2002 the sympatric species C. gobioophaga, with which it can be easily confused, was not described. Because of this it is possible that reports of C. glaucoides in many geographical areas may also include C. gobioophaga specimens. C. glaucoides is a species that has been found in European waters, from Norway, British Isles, French Atlantic and Mediterranean coasts, Tenerife (Canary Islands) and Gulf of Naples (Prkić et al., 2014). In the Iberian Peninsula it has been found and confirmed in Galicia and Portugal (Calado & Urgorri, 2002), in the Andalusian coasts and in Catalonia, where it has been reported at Cadaqués, Begur, Calella de Palafrugell, Palamós, Sant Feliu de Guixols and L’Ametlla de Mar.

Similar species
Calma gobioophaga, with longer propodial tentacles, larger eyes located immediately behind the base of the rhinophores, longer digestive gland, smaller eggs and feeds on fish eggs of the genus Gobius.

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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

• AsturNatura
• Biodiversity Heritage Library
• BiologiaMarina.org
• CIB - Club Immersio Biologia
• El Litoral de Granada
• Encyclopedia of Marine Life of Britain and Ireland
• Flickr pictures
• GROC
• 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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