Umbraculida

The Umbraculida have a fairly homogeneous body organization which is highlighted by the presence of a voluminous bipectinate gill to the right of the body, between the foot and the dorsal mantle .

Umbraculum umbraculum by Enric Madrenas

Animals are medium to large size, with a a pair of rolled rhinophores on the head, and a flat frontal veil that usually differentiates short oral tentacles. The dorsal mantle is well developed and completely covers the body and can be smooth or covered with tubercules. In genera Tylodina and Umbraculum there is an outer patelliform, slightly calcified shell that does not cover the entire animal. In some species there are microscopic spicules embedded in the mantle tissues. The buccal bulb has a lip with independent masticatory elements. There is always a Radula but it lacks of rachidian or medium teeth. The mantle cavity is located between the mantle and the foot, below the shell, to the right side of the body, and houses the gill . The foot is very broad and often there is an apparent metapodial mucus-secreting gland in the back.

Biology
Some species of Umbraculida are big sized (about 20 cm in the largest specimens of Umbraculum umbraculum) and fairly visible on the coastal bottoms where they live. Usually they are very sedentary. The Umbraculida, like most other opisthobranchs, are hermaphrodites, have internal fertilization and copula is reciprocal. Shortly after mating, the animals lay an irregular shaped egg ribbon. Veliger larvae that hatch from the eggs are planktonic and planktotrophic. They are basically carnivores, they may feed on sponges, colonial or solitary tunicate and other invertebrates, but the case of Tylodina perversa looks different; apparently it could feed on the green algae living in the sponge tissues, despite it is also known of its ability to incorporate into its own tissues the pigments of the sponge it feeds on, and thus have homocromy (same colour) with the substrate.

Distribution
Most umbraculid species live in temperate and tropical waters of all oceans. All families have representatives in European waters.

Classification
This group belonged, until recently, to the traditional order of Notaspideans, within Opisthobranchia, which is no longer accepted. This is because, as it has been recently demostrated, comparative morphological analysis and recent molecular studies, the two included families (Pleurobranchidae and Umbraculidae) represent two different lineages that may not share common ancestors. Phylogenetic analysis conducted in recent years tend to place the Umbraculidae in a clade (referred as Euopisthobranchia in the work by Jörger et al., 2010 ) that also holds the Runcinacea, the Anaspidea and Cephalaspidea ss, among others.

The taxonomy of this group according to WoRMS is as follows:

  • Order Umbraculida Odhner, 1939
    • Superfamily Umbraculoidea  Dall, 1889 (1827)
      • Family Tylodinidae Gray, 1847
        • Genus Anidolyta Willan, 1987
        • Genus Tylodina Rafinesque, 1814
      • Family Umbraculidae Dall, 1889
        • Genus Spiricella Rang, 1828
        • Genus Umbraculum Schumacher, 1817

There are only about 10 species known worldwide.

Umbraculida species cited in the Mediterranean or around the Iberian Peninsula:

Tylodina perversa by Enric Madrenas

Tylodina perversa

Umbraculum umbraculum per Enric Madrenas

Umbraculum umbraculum

Bibliography

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.

Cite this article as:

Ballesteros, Manuel, Enric Madrenas, Miquel Pontes et al. (2012-2017) "Umbraculida" in OPK-Opistobranquis, Published: 10/09/2013, Accessed: 26/05/2017 at (http://opistobranquis.info/en/94oIo)

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