Thecacera pennigera (Montagu, 1815)
Class: Gastropoda Cuvier, 1797
Subclass: Heterobranchia J.E. Gray, 1840
Clade: Euthyneura Spengel, 1881
Clade: Nudipleura Wägele & Willan, 2000
Order: Nudibranchia Cuvier, 1817
Suborder: Euctenidiacea Tardy, 1970
Infraorder: Doridacea Thiele, 1931
Superfamily: Polyceroidea Alder & Hancock, 1845
Subfamily:Polycerinae Alder & Hancock, 1845
Genus: Thecacera Fleming, 1828
Species: Thecacera pennigera (Montagu, 1815) [Doris]
- Doris pennigera Montagu, 1815 (original)
- Thecacera lamellata Barnard, 1933
- Thecacera maculata Eliot, 1905
This species can reach up to 30 mm in length. The body color is translucent white and it is completely covered with small irregular patches of orange and yellow, sprayed with black dots of varying density. The black dots are smaller but appear in greater numbers. Atlantic individuals differ from Pacific ones in color, density and size of the spots. Individuals occasionally appear with orange spots larger than normal. The anterior side of the body is wider than the rear side, converging into a thin and long foot with a keel on each side. The head is short, blunt and wide, without digitations or oral tentacles on its anterior edge. The rhinophores are lamellate and have the same colour pattern as the rest of the body; they are surrounded by a flared sheath that does not cover them completely. The gill consists of 3-5 bipinnate or tripinnate leaves, not retractile, and laid in a horseshoe shape around the anal papilla. Gill is located in the middle of the dorsum, right ahead of two elongated protuberances, coloured similar to the rest of the body, that Picton & Morrow (1994) considered glandular and of defensive mission. The foot has two propodial tentacles of sensory character, used for locating and orienting at short distances.
This nudibranch is very cryptic on the substrate, and has nocturnal habits. It can live from the intertidal down to 36 m (Swennen 1961; Willan & Coleman, 1984). It is a highly specialized carnivorous species that feeds exclusively on certain species of colonial bryozoans such as Crisularia (=Bugula) plumularia, C. turrita, Bugula neritina, Bugulina (=Bugula) flabellata, B. turrita and B. stolinifera (McDonald & Nybakken, 2009). It appears closely associated with these populations of bryozoans. Their narrow, white, ribbon-like spawn are laid on the bryozoans, and they are often the best indicator of its presence (Willan & Coleman 1984, Dekker 1986). Usually they are found in low densities among the bryozoans, until favorable environmental conditions trigger massive recruitment episodes with lots of new individuals.
- Thecacera. From Greek “theke” (θήκη), a receptacle, a scabbard or sheath + “kērós” (κηρός), horn, for the shielded rhinophores.
- Pennigera. From Latin “penna”, feather + “gerere”, bearing. Overall meaning is “feathered” or “winged”.
The distribution of this species, that prefers temperate climate but has a wide thermal tolerance, is cosmopolitan (Thompson, 1976). It can be found from the south and west of the British Isles, Ireland’s west coast, the west coast of Europe, the Mediterranean Sea, the macaronesic region (Wirtz, 1999), West Africa, South Africa, Brazil coasts, the eastern United States (from Massachusetts to Florida, possibly discontinuous), Pakistan, Japan, Korea, eastern and southern Australia and New Zealand (Willan 1976; Gosliner 1987; Picton and Morrow 1994; Valles et al, 2000). Willan (1976) suggested that the species has spread beyond its original range of distribution due to transport marine. One reason to assert this claim could be the fact that it feeds on colonial bryozoans, and these species are often part of the “fouling”, the epibiont fauna that can grow on the hull of ships. Several specimens of various world populations have been studied, and there have been found no significant morphological differences between samples from the different countries but the size and number of spots on the mantle (Jung et al., 2013). In the Iberian Peninsula it has been observed in the Cantabrian coast, in Portugal and in the Andalusian Atlantic coast. It has not been found yet in the Catalan coast.
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