Polycerella emertoni

Polycerella emertoni  A.E.Verrill, 1880

Polycerella emertoni @ Delta de l'Ebre by Manuel Ballesteros
















































Polycerella emertoni  A. E. Verrill, 1880

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 140839).

  • Polycerella comyna Marcus Er., 1957
  • Polycerella conyna Er. Marcus, 1957
  • Polycerella davenportii Balch, 1899
  • Polycerella recondita Schmekel, 1965

Body as high as wide, with a maximum observed length of 5-6 mm approximately, although most animals measure 3-4 mm in length. The body is translucent with bright yellowish tones and small dark brown or green spots scattered throughout the body. This coloration makes the animals very cryptic on the bryozoan they are living. The anterior part of the head is rounded, with no prolonged elongations but sometimes with small warts. Rhinophores are smooth (not laminated) and they are contractile. There are three small bipinnate gills located in the middle of the back, the one in the center is usually the largest. The anal papilla is located behind the middle gill. Some conical tubercles can be observed on the back, the most developed being the rearmost ones, in particular a symmetrical pair that are located behind the gills. The front of the foot has a pair of small triangular extensions. Moro et al. (2017) provide good pictures and drawings of the species.

This species lives in the Mediterranean and eastern Atlantic on soft bryozoans such as Amathia verticillata, until recently identified as Zoobotryon verticillatum (Waeschenbach et al., 2015), where it is perfectly cryptic because of its small size, shape and color. In the western Atlantic coasts it has been reported living on and feeding on the bryozoans Amathia gracilis (until recently known as Bowerbankia gracilis), Amathia distans and Bugula neritina (Clark, 1975; Valdés et al., 2006). The animals lays the spawn on the same bryozoan it feeds on; it is cylindrical and slightly curved, has a size of about 3 mm and contains about 100 eggs, each of which is enclosed by a capsule of about 100 microns (García-Gómez & Bobo, 1986) while eggs measure between 45 and 60 microns (Schmekel & Portmann, 1982). In the laboratory it has been observed that animals shrink down to a ball when they are disturbed (original data of the authors). Franz & Clark (1972) provide interesting information on the systematics, reproductive biology and zoogeography of the species.


  • Polycerella. Diminutive of Polycera.
  • Polycera, derives from Greek Polys, many and Keras, horn
  • Emertoni, in honor to James Henry Emerton (1847-1930), US arachnologist honoured to name several species of copepods, polychaete and gastropods.

Polycerella emertoni was originally described by the Atlantic coast of North America (Verrill, 1980). Since then it has been reported in different parts of the western Atlantic such as Cuba (Moro et al., 2017), Venezuela and Brazil (Tamsouri et al., 2014), as well as the eastern Atlantic coasts as Ghana (Edmunds, 1977 ), Canary Islands (Moro et al., 2017) and the Iberian Peninsula, where it is known from Portugal and the coast of Càdiz (Cervera et al., 2004). In the Mediterranean it was first seen observed in 1964 in Lake Fusaro (Italy) (Schmekel, 1965) and then reported in Malta, Greece and Tunisia coasts (Tamsouri et al., 2014). On the Catalan coasts, it was cited for the first time at the Coves of Cala Maset, in Sant Feliu de Guíxols (GROC, 2017). In the Delta de l’Ebre, an abundant population of P. emertoni has been found recently on the colonies of Amathia verticillata that grow at a very shallow depth on wooden or iron pylons or even on the shells of  the pen shell  Pinna nobilis. Numerous spawns have been observed on the colonies of A. verticillata in August 2018. It is possible that the wide distribution of the species is related to the almost cosmopolitan distribution (in warm and temperate seas) of the bryozoans that are their substrate and food. P. emertoni is considered as an invasive species in the Mediterranean (Zenetos et al., 2004) more than an amphyatlantic species.

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


    Western Mediterranean:1 out of 5 stars
    Eastern Mediterranean:0 out of 5 stars
    Atlantic Ocean:1 out of 5 stars
[wpbi_chart type="bar" id="1" height="250" /]

This chart displays the monthly observation probability for Polycerella emertoni based on our own records.


Polycerella emertoni on Amathia verticillata, by Judith Camps © 2018


More pictures


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Further reading

Cite this article as:

Camps, Judith; Manuel Ballesteros; Enric Madrenas; Miquel Pontes (2021) "Polycerella emertoni" in OPK-Opistobranquis. Published: 11/09/2014. Accessed: 19/10/2021. Available at (https://opistobranquis.info/en/iPa0u)

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