Umbraculum mediterraneum or Umbrella slug

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I saw this beautiful specimen of Umbraculum mediterraneum during a dive in a Mediterranean coral reef at a depth of over 70 meters. In many years of diving I had never come across this nudibranch. It is an adult specimen of rather large dimensions, in fact it is well over 20 cm in length. This leads me to think that, together with Aplysia depilans, it is among the largest nudibranchs present in the Mediterranean Sea.

Umbraculum mediterraneum - Umbraculum umbraculum - Umbracolo - Umbrella slug - www.intotheblue.it

Umbraculum mediterraneum – Umbraculum umbraculum – Umbracolo – Umbrella slug – www.intotheblue.it

 

The Umbraculum mediterraneum, common name the Umbrella slug,  belongs to the Phylum of Molluscs, to the Class Gastropods, to the Subclass Opisthobranchs, to the Order Notaspidi and to the Family Umbraculidae. The small shell present in the upper part is white. The color of the body, massive and rounded with a large foot, is brown-grey and has warts that are generally translucent white but which can vary depending on the diet. On the head there are two rhinophores under which there are two very small eyes. From the information acquired I can state that it is a nudibranch with predominantly nocturnal habits, but at that depth there is almost no sunlight and therefore, in my opinion, its habits last the whole day.

 

Umbraculum mediterraneum - Umbraculum umbraculum - Umbracolo - Umbrella slug - www.intotheblue.it

Umbraculum mediterraneum – Umbraculum umbraculum – Umbracolo – Umbrella slug – www.intotheblue.it

 

Opisthobranchs is a now informal name for a large and diverse group of specialized complex gastropods. The reduction or loss of the shell, the elaboration of the head, foot or mantle, and the acquisition of chemical defences are evolutionary trends shared by most opisthobranch taxa.   The loss of shell in the group is an example of parallel evolution and has occurred on multiple independent occasions.

 

There is no marked distinction between head and mantle. The tentacles, situated close to the mouth, are used for orientation. Behind them are the rhinophores, olfactory organs which often have complex forms. The middle part of the foot is the sole, used for locomotion. The sides of the foot have evolved into parapodia, fleshy winglike outgrowths. Principally soft-bodied marine creatures with a reduced or absent shell and no operculum, opisthobranchs use other methods for protection. The group has a diverse variety of highly specialized auxiliary defenses. Due to a combination of outstanding camouflage and aggressive toxicity they have few predators.

 

Umbraculum mediterraneum - Umbraculum umbraculum - Umbracolo - Umbrella slug - www.intotheblue.it

Umbraculum mediterraneum – Umbraculum umbraculum – Umbracolo – Umbrella slug – www.intotheblue.it

 

Opisthobranchs may be herbivores, detritivores or carnivores. Being slow, the carnivores hunt sedentary prey. They may eat bryozoans, Cnidaria or sponges absorbing the sponge toxin for defensive purposes. Opisthobranchs are hermaphrodites and have complex reproductive strategies, typically involving reciprocal sperm transfer and storage until the eggs are ready for fertilisation.

 

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Informazioni sull'autore / About the author:
Fanino Cirivasi Fanino Cirivasi ha scritto / wrote 223 articoli / Posts.
Questo articolo è stato scritto il / This article was written on 13/03/2024
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