Micromelo undatus

Micromelo undatus (Bruguière, 1792)

Micromelo undatus @ Gran Canaria by Aketza Herrero

































Micromelo undatus  (Bruguière, 1792)

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 140121).
Taxonomic note: the genus Micromelo (family Aplustridae) is found in almost all the tropical and subtropical seas of the world, with the exception of the American Pacific. Until recently, most authors considered the species Micromelo undatus (Bruguière, 1792) as the only valid in this genus. The study by Feliciano et al. (2021) Molecular and morphological analyzes reveal pseudocryptic diversity in Micromelo undatus (Bruguière, 1792) (Gastropoda: Heterobranchia: Aplustridae) examines the populations of specimens identified as M. undatus throughout their geographic range by using molecular techniques. The results revealed that M. undatus is a complex of four species with consistent genetic and anatomical differences. A review of the literature and an evaluation of the type material allowed three of the four species to be named: Micromelo guamensis (from the Western Pacific), M. undatus (from the Atlantic) and M. scriptus (from the Indo-Pacific). A new name is introduced for the fourth species, found in Philippine waters: Micromelo barbarae Feliciano, Malaquias, Stout, Brenzinger, Gosliner & Valdés, 2021.


  • Bulla elegans Menke, 1830
  • Bulla nitidula Dillwyn, 1817
  • Bulla undata Bruguière, 1792
  • Bullina elegans Menke, 1830
  • Micromelo undata [sic]

Body very flat, of up to 40mm long, shape oval to elongate. Base color is white to translucent grey, covered with large, oval opaque white spots, densely arranged. Distance between spots about same size as the spots themselves. Mantle, rhinophores, and foot with a marginal yellow-orange band followed by a pale blue or green diffuse area. Headshield as long as wide, prominently narrower mid-length. White shell, ovalled but nearly round, almost as long as wide, coloured with red to brown lines forming a quite regular pattern. Rear side of  the shell aperture forming a smooth rounded edge with apex, while the outer edge of the aperture is curved.

Found in shallow water (0-10 meters) on sandy or rocky ground, preferably on algal turf areas, and are common in rocky pools of the lower intertidal zone. Feeds on polychaete worms (Gosliner, 1987). This species is active both at day and night. Although it can retract into the shell, it does so very rarely. Under UV light the shell looks red while the body looks green.


  • Undatus, from Latin “undatus”, ondulated.

Ascension Island (Padula et al., 2017), Cape Verde (Valdés, 2005), Canary Islands (Moro et al., 2003), Azores (Nordsieck, 1972), the Caribbean coast of Costa Rica, St. Lucia (Valdés et al., 2006), Jamaica (Feliciano et al., 2021), Curaçao (Feliciano et al., 2021), and Brazil (Padula et al., 2012).

Known georeferenced records of the species: Micromelo undatus
: GROC 2010-2011
: Enric Madrenas
: João Pedro Silva
: Bernard Picton
: Manuel Ballesteros.
: M@re Nostrum
: Altres fonts
: Marine Regions


    Western Mediterranean: ☆☆☆☆☆
    Eastern Mediterranean: ☆☆☆☆☆
    Atlantic Ocean: ★☆☆☆☆

This chart displays the monthly observation probability for Micromelo undatus based on our own records.

More pictures


    Ballesteros, M., E. Madrenas, and M. Pontes. 2023. OPK - Opistobranquis. (https://opistobranquis.info/).
    Bruguière, J. G. 1789. Encyclopdie méthodique ou par ordre de matières. Histoire naturelle des vers. Pancoucke, Paris. Vol. 1, part 1, p. 1-344 [june 1789]; Vol. 1, part 2, p. 345-758 [13 Feb. 1792; dates after N. EVENHUIS, 2003, Zootaxa, 166: 37; Zootaxa, 207]; Atlas pl. 1-189 [1791]; pl. 190-286 [1797] pl. 287-390 [1798] pl. 391-488 [1816: edited by Deshayes].
    Cervera, J. L., G. Calado, C. Gavaia, M. A. E. Malaquías, J. Templado, M. Ballesteros, J. C. García-Gómez, and C. Megina. 2004. An annotated and updated checklist of the opisthobranchs (Mollusca: Gastropoda) from Spain and Portugal (including islands and archipelagos). Boletín Instituto Español de Oceanografía, 20 (1-4): 1-111. L.
    Feliciano, K., M. A. E. Malaquías, C. Stout, B. Brenzinger, T. M. Gosliner, and Á. Valdés. n.d. Molecular and morphological analyses reveal pseudocryptic diversity in Micromelo undatus (Bruguière, 1792) (Gastropoda: Heterobranchia: Aplustridae). Systematics and Biodiversity. 0: 1–25.
    Frank, B. et al. 1998. Micromelo undatus accessed through: JaxShells.org on 2014-12-14. (http://www.jaxshells.org/micmo.htm).
    Long, S. J. 2006. Bibliography of Opisthobranchia 1554-2000. Bayside Books & Press, Tustin, CA, U.S.A. 672p.
    Malaquias, M. A. E., J. Mackenzie-Dodds, P. Bouchet, T. M. Gosliner, and D. G. Reid. 2009. A molecular phylogeny of the Cephalaspidea sensu lato (Gastropoda: Euthyneura): Architectibranchia redefined and Runcinacea reinstated. Zoologica Scripta 38(1): 23-41.
    McDonald, G. 2009. Bibliographia Nudibranchia. 2nd Online Edition, Annotated. 1072 pp  Institute of Marine Sciences, University of California, Santa Cruz. (http://escholarship.org/uc/item/8115h0wz).
    Moro, L., J. L. Martín Esquivel, M. J. Garrido Sanahuja, and I. Izquierdo Zamora. 2003. Lista de especies marinas de Canarias (algas, hongos, plantas y animales). Consejería de Política Territorial y Medio Ambiente del Gobierno de Canarias.
    Ortea, J., and L. Moro. 2019. Las babosas marinas de las islas de Cabo Verde en el tiempo: Cronología de su descubrimiento. Avicennia. 25: 1–36.
    Ortea, J., J. Espinosa, M. Caballer, and Y. Buske. 2012. Initial inventory of the seaslugs (Opisthobranchia and Sacoglossa) from the expedition Karubentos, held in May 2012 in Guadeloupe (Lesser Antilles, Caribbean Sea). Revista de la Academia Canaria de Ciencias 24: 153-182.
    Oskars, T. R., P. Bouchet, and M. A. E. Malaquias. 2015. A new phylogeny of the Cephalaspidea (Gastropoda: Heterobranchia)based on expanded taxon sampling and gene markers. Molecular Phylogenetics and Evolution 89 (2015) 130–150.
    Schaefer, F. 1990. Sea secrets: Micromelo undatus. Sea Frontiers 36(2): 56.
    Toll, L., and M. Ballesteros. 2017. “Opistobranquios” (Mollusca: Gastropoda) de la colección malacológica Lluís Dantart. Spira 6 (2017): 171–184.
    Valdés, A., J. Hamann, D. W. Behrens, and A. DuPont. 2006. Caribbean sea slugs: a field guide to the opisthobranch mollusks from the tropical northwestern Atlantic. Washington: Sea Challengers Natural History Books. 289 pp.
    WoRMS Editorial Board. 2023. World Register of Marine Species. WoRMS. (http://www.marinespecies.org).

    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.

Further reading

Cite this article as:

Ballesteros, M., Madrenas, E. & Pontes, M. (2023) "Micromelo undatus" in OPK-Opistobranquis. Published: 20/02/2015. Accessed: 27/02/2024. Available at (https://opistobranquis.info/en/?p=18215)

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