Goniobranchus annulatus (Eliot, 1904)
Goniobranchus annulatus @ Alternatives (North Red Sea) 21/02/2007 by Miquel PontesTaxonomy
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: Doridoidea Rafinesque, 1815
Family: Chromodorididae Bergh, 1891
Genus: Goniobranchus Pease, 1866
Species: Goniobranchus annulatus (Eliot, 1904) [Chromodoris]
- Chromodoris annulata Eliot, 1904 (original)
- Glossodoris annulata (Eliot, 1904)
Maximum size cited for this species is 100mm, although it usually measures between 40 and 60 mm. It has a translucent white body with round orange spots, absent in some specimens (van Rinj, 27/11/2007 in Sea Slug Forum; van Belle, 7/02/2002 in Sea Slug Forum). The rhinophores and gills are surrounded by a purple to red circle each, the circles rarely incomplete and sometimes joined together by a purple line (Neal, 4/05/2010 in Sea Slug Forum). The mantle border is purple, while the lower part is white but for the anterior part which is completely purple (except in some cases cited by Yonow in 2008), this is a trait very easy to observe because the animal is constantly waving the edge of the mantle up and down when moving. The rhinophores have two colors, the basal part is white, as is most of the lamellar area, while the distal part of the stem and the lamellae are purple. The branchial plume is well developed, the animal keeps it quite vertical and is also bicolored: it has up to a dozen gill leaves of triangular section colored in white with purple borders. The gills form an open circle surrounding the anus, and the animal moves them in a rhythmic, vibratile way. On the rear part of the body, the foot is white with orange dots with the same pattern as the dorsum, protruding behind the mantle, so it is visible.
Goniobranchus annulatus feeds on sponges of the genus Chelonaplysilla, although it seems to have a preference for the species Chelonaplysilla violacea. The spawn consists of a gelatinous ribbon of about 10 mm high coloured yellowish-white or pink, wound in a spiral and attached to the substrate by one of its sides. The free edge is not undulated as in other similar species. It inhabits the hard bottoms and rocky walls between the surface and about 40 meters deep, both in calm and current beaten environments. It is believed to obtain certain antidepredating chemicals (complex terpenes) from the sponges it feeds on, storing them in the opaque white glands located around the edge of the mantle. Its colorful design (aposematic coloration) is intended to warn potential predators of its bad taste or toxicity, to prevent attacks. The animal usually moves around waving the mantle edge up and down, especially evident in its anterior part, and with a constant vibration of the gills. There are two other dorid species that partially share the distribution range of this species and that can be easily confused with it: Hypselodoris pulchella and Hypselodoris ghardaqana. Gohar & Aboul-Ela (1957) give some simple keys to distinguish them synthesized in the following table:
|Dorsum color||creamy white w/yellow spots, purple difuse reticula||translucent white w/yellow spots, purple circles||white w/yellow spots|
|Max.size||110 x 30 mm||64 x 20 mm||55 x 13 mm|
|Rhinophores||long, dark blue w/white axis||long, conical, deep purple||short, reddish purple w/pink red axis|
|Gills||20-30, branched, kept vertical, vibratile||9-12, not branched, kept vertical, vibratile||9-11, not branched, kept horizontal, non-vibratile|
|Egg-Ribbon||reddish orange, free edge wavy||creamy white, free edge not wavy||white, free edge slightly wavy, single layer of eggs|
|Photo||Erwin Köhler ©||Miquel Pontes ©||Brian Mayes ©|
- Goniobranchus, from Greek “gonios”, angle and “brangchia”, gills.
- Annulatus, from Latin “annulatus”, bearing a ring, for the characteristic rings surrounding the rhinophores and gills in this species.
Originally described in Zanzibar by Eliot in 1904, this species lives mainly in the Indian Ocean, where it has been cited from southern Africa (Mayotte, Reunion, Madagascar, etc.) to the Persian Gulf, also in the Red Sea and the Western tropical Pacific Ocean, where it has been cited in Myanmar and Thailand. As curious cases, there is a report from Table Cape, Tasmania (Close, G., 14/07/1984 in GBIF.ORG, 2016) and another in the Gulf of California (Bertsch and Kerstitch, 1984). It is also present in the Mediterranean Sea, where it is considered a lessepsian invasive species, as it is believed to have entered through the Suez Canal from the Red Sea, and seems to be successfully established in Israel, Lebanon, Turkey and Greece.
|: OBIS||: OPK|
|: GROC 2010-2011||: VIMAR|
|: Enric Madrenas||: Manuel Ballesteros.|
|: João Pedro Silva||: M@re Nostrum|
|: Bernard Picton||: Other sources|
|: GBIF.ORG||: Marine Regions|
This chart displays the observation probability for Goniobranchus annulatus
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.