Janolus cristatus (delle Chiaje, 1841)
Class: Gastropoda Cuvier, 1797
Subclass: Heterobranchia J.E. Gray, 1840
Clade: Euthyneura Spengel, 1881
Clade: Nudipleura Wägele & Willan, 2000
Order: Nudibranchia Cuvier, 1817
Suborder: Dexiarchia Schrödl, Wägele & Willan, 2001
Infraorder: Cladobranchia Willan and Morton, 1984
Parvorder: [unassigned] Cladobranchia Willan & Morton, 1984
Family: Proctonotidae J.E. Gray, 1853
Genus: Janolus Bergh, 1884
Species: Janolus cristatus (delle Chiaje, 1841) [Eolis]
- Antiopa splendida Alder & Hancock, 1848
- Antiopella cristata (Chiaje, 1841)
- Eolidia cristata Delle Chiaje, 1841
- Eolis cristata Delle Chiaje, 1841 (original)
- Janus spinolae Vérany, 1846
This nudibranch usually measures 25 mm in length but it has been cited with a maximum length of 80 mm. The body general coloration is translucent light brown, revealing some internal organs and the extensions of the digestive gland. The dorsum is crossed by a longitudinal white line (sometimes with a blu irisation) from the tail to the anterior part of the dorsum, where it splits into two. The side walls of the body may also get spots of the same hue. The rhinophores share the same color of the body and have very oblique lamellae, the apex is whitish. The bases of the rhinophores have no lamellae and join on the back of the head, between them there is a structure called “nuchal caruncle” with a brown and rough surface whose mission seems to be sensorial. The eyes are located at the base of each rhinophore. The most characteristic feature of this species is the existence of numerous papillae or cerata on the back that make it look like an aeolidacean nudibranch. However, these papillae grow from all around the body, including the anterior region of the head, and despite they have ramifications of the digestive gland inside, they lack the cnidosac of the aeolidaceans. The papillae are elongated, bulging somewhat in its central region, and they are translucent, with the apex of bluish-white color. They are contractile and can extend or shrink acquiring a rounded shape, according to the state of the animal. The papillae growing near the foot are much smaller than those located more dorsally. Within each papilla a branch of the digestive gland is visible as a straight brown cord, which ramifies at its apical end. The anus is at the end of a cylindrical, whitish and translucent anal papilla which is located in the back dorsal zone of the body; the top edge of the anal papilla is slightly lobed.
This species lives on well illuminated rocky walls between 10 and 25 m deep. It sometimes appears under stones. It is usually found in the vicinity or on different species of bryozoans of which it feeds. Several bryozoans have been cited as substrate or food for this species, like Alcyonidium gelatinosum, Bicellariella ciliata, different species of Bugula (B. avicularia, B. flabellata, B. neritina, B. turbinata) and Cellaria sp. The spawn consists of a long and thin string laid in a wavy way; the pink eggs have a size of about 80 microns, several eggs contained in each single ovigerous capsule. When animals are disturbed they are able to autotomize the papillae, which then continue shrinking and stretching after leaving the body, most probably as a defense mechanism. At times, specimens of J. cristatus are infested by the ectoparasitic copepod Doridicola agilis.
- Janolus is referred to the Greek god Janus, the one with two heads, god of beginnings and transitions (the month January is devoted to him), protector of homes (hence he’s represented with a key).
- Cristatus is referred to the crest, according to Bernard PICTON in his book “Nudibranchs of The British Isles”.
This species is distributed throughout the European coasts, from the North Sea to the Mediterranean, also in Canary islands and Madeira. In the Iberian Peninsula it has been cited in all coastal areas, both Atlantic and Mediterranean. In Catalonia it is relatively common in some locations of the Northern Costa Brava as Es Caials (Cadaqués).
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References for the species: Janolus cristatus
- Cantabria: Hidalgo (1916), Fernández-Ovies (1981, as Antiopella cristata).
Galicia: Urgorri and Besteiro (1983, 1984, both records as Antiopella).
Portugal: Nobre (1932, as Antiopa cristata), García-Gómez et al. (1991), Calado et al. (1999, 2003).
Andalucía (Atl.): Cervera and García (1986).
Gibraltar: García-Gómez (1983), García-Gómez et al. (1989).
Andalucía (Med.): Luque (1983, 1986, as Antiopella), Templado, Luque and Moreno (1988), Sánchez Tocino, Ocaña and García (2000a), Ocaña et al. (2000).
Levante: Fez (1974, as Janus cristatus), Templado, Talavera and Murillo (1987).
Catalunya: Theodor (1964), Ballesteros (1980, 1985), Ballesteros (datos no publicados) [Es Caials, Cap Falcó], M@re Nostrum [Es Caials 6/2000].
Canarias: Ortea et al. (2001), Moro et al. (2003), Wirtz and Debelius (2003).
Madeira: Wirtz (1995a, 1999).
General: Barletta, 1981:97; Brown & Picton, 1979:18; Eliot, 1906c:373; Farran, 1909:9; Hunnam & Brown, 1975:151; Jutting & Engel, 1936:56; Nordsieck, 1972:71; Pruvot-Fol, 1954b:375; Riedl, 1983:325; Schmekel, 1970:187; Thompson & Brown, 1976:138; Vicente, 1967:156; 1991a:[P] as Antiopella cristata; Bergh, 1873a:598; 1882:65; Costa, 1867:33; Fez Sanchez, 1974:106; Mazzarelli, 1903:286; Misuri, 1917:37; Tchang Si, 1931a:120; Tiberi, 1880:224; Trinchese, 1881:77; 1881a:77; Vayssiere, 1888d:29; 1913a:268 as Janus cristatus; Cattaneo-Vietti, Chemello, & Giannuzzi-Savelli, 1990:155[P]; Dekker, 1989:101; Hayward, Wigham, & Yonow, 1990:720; Marin & Ros, 1990:214; McMillan, 1968:70; Perrone, 1986a:31; Picton & Morrow, 1994:88[P]; Schmekel & Portmann, 1982:177[P]; Swennen, 1987:39; Templado, Talavera, & Murillo, 1987:94; Thompson, 1988:238[P]; Thompson & Brown, 1984:97[P] as Janolus cristatusSources: Cervera et al., 2004, Ballesteros, 2007 & 2016, McDonald, 2006 and other sources.
Janolus cristatus @ Keratea, Attica, Greece 16m 1-02-2017 by Leonidas Stavrou
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