# Umbraculida Umbraculida is a small order of marine heterobranch sea slugs, comprising about ten species worldwide, in which the animal carries an external limpet-shaped (patelliform or calyptraeiform) shell on its back.[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) The group contains the superfamily Umbraculoidea and the family Umbraculidae.[2](https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=78121) *[Umbraculum umbraculum](https://www.edgepedia.org/umbraculum-umbraculum)* (Lightfoot, 1786), the Atlantic umbrella slug, is a species within Umbraculidae[2](https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=78121) and a sponge predator.[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) | Key fact | Detail | |---|---| | Rank and size of group | Order Umbraculida, superfamily Umbraculoidea, family Umbraculidae; about ten species worldwide[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) • [2](https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=78121) | | Species | *Umbraculum umbraculum* (Lightfoot, 1786), the Atlantic umbrella slug, a species within Umbraculidae[2](https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=78121) | | Habitat | Sciaphilous (shade-loving) rocky substrates rich in sponges, at depths of about 5–36 m in the Sicily survey[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) | | Shell dependence | Shell loss is not rare; umbraculids can survive, and even breed, without a shell[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) | ## Limpet-form anatomy of a sea slug Umbraculids are heterobranch sea slugs, yet they look like limpets because a single external shell sits on the dorsal surface. The shell is not essential. Observations compiled from several authors (Lochore 2004, Limouzin 2006, Rudman 2006), and from the Sicily survey show that *U. umbraculum* and *Tylodina perversa* do not seem to have an absolute need for the shell to live. In the Sicily study one breeding specimen of *U. umbraculum* lacked a shell entirely, and another lost its shell under light pressure without apparent damage; loss of the shell in umbraculids is described as not rare.[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) ## Sponge feeding and diet Umbraculids feed on sponges by rasping tissue with the radula, the toothed ribbon characteristic of molluscs. Recorded sponge prey include *Tethya* spp., *Aaptos aaptos*, *Ancorina alata*, and *Plakina trilopha*.[3](http://www.seaslugforum.net/find/umbrumbr) Predation leaves visible marks. In the Sicily survey *U. umbraculum* was often documented beneath the sponge *Crambe crambe*, a previously unrecorded prey item, and the sponges showed lacerations and missing parts; the species is described as a predator that tends to cause considerable damage to its prey.[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) *Tylodina perversa* shows a different pattern. In the study area it was never found on *Aplysina* sponges, always on algal substrates, supporting the hypothesis that where *Aplysina* is scarce this species feeds exclusively on cyanobacteria.[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) ## Where they live and by the numbers The Sicily survey of the central-eastern coast gives concrete habitat and depth figures. A total of 23 *U. umbraculum* individuals were found: 14 at Santa Maria La Scala, 6 at Santa Tecla, and 3 at Catania, observable year-round.[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) Depths were 13–36 m at Santa Maria La Scala, 5.1–23 m at Santa Tecla, and 6.4–14 m at Catania, on sciaphilous rocky substrates rich in sponges, red calcareous algae, *Peyssonnelia* spp., and *Jania* turf.[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) Size varies strikingly in *T. perversa*. The specimens measured in Sicily were 8–15 mm, with 15 mm the maximum, against a reported Mediterranean maximum of 70 mm (Trainito and Doneddu 2014, cited in the study). The authors suggest these are dwarf populations in environments where *Aplysina* sponges are scarce, rather than a conflicting size record.[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) ## Life cycle and breeding Detailed breeding activity of *U. umbraculum* was documented for the first time in May 2022, in the Sicily study; such behavior had never previously been reported in detail.[1](https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf) ## Taxonomic history and phylogenetic position In current registries Umbraculida sits within [Heterobranchia](https://www.edgepedia.org/heterobranchia) as order Umbraculida, superfamily Umbraculoidea Dall, 1889, and family Umbraculidae Dall, 1889, with *Umbraculum umbraculum* (Lightfoot, 1786) listed as the Atlantic umbrella slug.[2](https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=78121) This placement is apart from the keyhole limpets (Fissurellidae) that the limpet-like shell resembles. ## References 1. New observations on two umbraculid molluscs: *Tylodina perversa* and *Umbraculum umbraculum* along the central-eastern coast of Sicily. https://www.iris.unict.it/retrieve/cde5a2b7-3435-4b5c-82be-0ae73805df45/TRAVAUX_article_91185_en_1.pdf 2. Integrated Taxonomic Information System – Report (Umbraculidae). https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=78121 3. [Umbraculum umbraculum, The Sea Slug Forum](http://www.seaslugforum.net/find/umbrumbr) --- *Topic: Encyclopedia › Life and health › Animals › Invertebrates › Molluscs › Gastropods › Heterobranchia › Other opisthobranchs › Umbrella shells and keyhole limpet slugs (Umbraculida, Tylodinoidea)* *Initially written Sep 17, 2026 · Edited: Oct 11, 2026; Oct 15, 2026; Oct 25, 2026* *Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.* License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license