Placida dendritica (Alder & Hancock, 1843)
Placida dendritica by Enric MadrenasTaxonomy
Class: Gastropoda Cuvier, 1797
Subclass: Heterobranchia J.E. Gray, 1840
Clade: Euthyneura Spengel, 1881
Clade: Panpulmonata Jörger et al., 2010
Clade: Sacoglossa von Ihering, 1876
Superfamily: Limapontioidea J.E. Gray, 1847
Family: Limapontiidae J.E. Gray, 1847
Genus: Placida Trinchese, 1877-79
Species: Placida dendritica (Alder & Hancock, 1843) [Calliopaea]
- Calliopaea dendritica Alder & Hancock, 1843 (original)
- Hermaea aoteana Powell, 1937
- Hermaea brevicornis Costa A., 1867
- Hermaea capensis Macnae, 1954
- Hermaea dendritica (Alder & Hancock, 1843)
- Hermaea lutescens Costa A., 1866
- Hermaea orbicularis Costa A., 1866
- Hermaea ornata MacFarland, 1966
- Hermaea venosa Lovén, 1844
- Placida aoteana (Powell, 1937)
- Placida babai Ev. Marcus, 1982
The size of this species is small, between 5 and 8 mm, although there are cites of animals reaching 20 mm in length. The background color of the animal is white but it is decorated by the many dark green dendritic branches of the digestive gland, that spreads throughout the body, including cerata, rhinophores, head and foot, and make it acquire this tone and the ability to go unnoticed on Chlorophycean seaweeds like those of the genus Codium. The relatively short rhinophores are auriculate; the eyes can be seen just behind the base of the rhinophores. The cerata are numerous and distributed up into 8 groups on both sides, although in small specimens they show no clear appearance of grouping. The olive green digestive gland extends inside of the cerata, where it is profusely branched. The anal papilla is long and narrow and it is located in the anterior dorsal position; the cardiac region is located right behind. The foot is wide, semitransparent, and rounded in its front part, while in the back part it ends in a tapered tail, also infiltrated by hepatic branches.
The white and green color of this species is a perfect camouflage on the algae Codium fragile ssp tomentosoides, Codium tomentosum and Bryopsis plumosa, among other seaweed species. P. dendritica feeds on the apical part of these algae. This species is able to retain the living chloroplasts of algae in its tissues. These organules remain active for about 24 h, so it is not certain that they provide any kind of organic food to the sacoglossan. Juveniles are also found between different algae and even among Posidonia oceanica rhizomes. From this species there have been isolated certain chemical compounds called “placidenes” that might be involved in the defense mechanisms of the animal, as they are abundant in secreted mucus when disturbed. The spawn is a spiral about 3 mm in diameter, composed by about two turns of a white egg cord.
- Placida. From Latin “placeō”, please, satisfy. Also means placid, gentle, quiet, still, calm, mild, peaceful.
- Dendritica. From Greek “Dendron”, tree. Resembling or having a branching treelike figure.
Apparently this is an almost cosmopolitan species as there are cites in temperate and cold temperate almost everywhere: Atlantic (from Norway to Madeira and the British Isles), South Africa, Australia, New Zealand, Japan and the Western Mediterranean. It is doubted whether these remote findings respond to a complex of different species than the Mediterranean specimens. In the Iberian Peninsula it has been collected all along its coastline and it has also been observed in the Balearic islands. This species is widespread throughout the Catalan coast, but because of its small size and, especially, because its crypsis on Chlorophycean algae makes it go unnoticed for most divers.
|: OBIS||: OPK|
|: GROC 2010-2011||: VIMAR|
|: Enric Madrenas||: Manuel Ballesteros.|
|: João Pedro Silva||: M@re Nostrum|
|: Bernard Picton||: Other sources|
|: GBIF.ORG||: Marine Regions|
References for the species: Placida dendritica
Cantabria: Ortea (1977a,c, as Hermaea). Galicia: Urgorri and Besteiro (1983, as Hermaea), Trigo and Otero (1987, as Hermaea). Portugal: García-Gómez et al. (1991). Andalucía (Med.): García Raso et al. (1992). Levante: Fez (1974, as Hermaea), Templado, Talavera and Murillo (1983), Templado et al. (2002), Ballesteros et al. (1986), Marín and Ros (1987, 1988). Catalunya: Ros (1975, 1978b, 1985a), Ros & Altimira (1977), Ballesteros (1980, 1985), Pereira & Ballesteros (1982). Baleares: Ballesteros and Templado (unpubl. data). Madeira: Wirtz (1999, as P. cf. dendritica).
Sources: Cervera et al., 2004, Ballesteros, 2007, McDonald, 2006 and other sources.
This chart displays the observation probability for Placida dendritica
based on our own records.
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.