Dynamene bicolor (Rathke, 1837)

Vieira, Pedro E., Queiroga, Henrique, Costa, Filipe O. & Holdich, David M., 2016, Distribution and species identification in the crustacean isopod genus Dynamene Leach, 1814 along the North East Atlantic-Black Sea axis, ZooKeys 635, pp. 1-29 : 6-7

Dynamene bicolor (Rathke, 1837)

Restricted synonymy.

Campecopea bicolor : Rathke (1837).

Dynamene bidentata : Torelli (1930); Omer-Cooper and Rawson (1934); Pauli (1954); Holthuis (1956); Barrett and Yonge (1964); [not Dynamene bidentata of Adams (1800)].

Dynamene torelliae : Holdich (1968, 1970).

Dynamene bicolor : Kussakin (1979); Maggiore and Fresi (1984).

Material examined.

Specimens have been examined from 48 locations in 12 countries in the Mediterranean and Black Seas - see the Suppl. materials 1 and 2. A number of literature records have been included where the diagrams clearly indicate this species.

Key morphological characters.

In stage 8 males the pleotelsonic boss is comprised of two right-angled triangular structures separated by a deep groove (however, the boss may be very low lying in some specimens, e.g., those from the Black Sea); the arms of bidentate process taper to a point and are rugose dorsally (Fig. 2 J–K). In stage 7 females the pleotelsonic dome is keeled in side view and the pleotelsonic foramen is flush with the edge of the pleotelson (Fig. 3H, I). The females of this species are very difficult to separate from those of Dynamene magnitorata . Maggiore and Fresi (1984) provide a complete description of Dynamene bicolor .

Size.

Adult males (stage 8) typically 3.5 × 1.5 mm, pre-ovigerous females (stage 7) typically 3.0 × 1.3 mm.

Life-history.

Nothing is known of the life-history, other than the fact that sexual dimorphism occurs with males developing the bidentate process characteristic of the genus.

Habitat.

Juveniles are usually found in shallow water on a variety of algae down to 3.0 m and adults in empty Balanus tests, in mussel beds, in rock crevices, within sponges, and under rocks throughout the Mediterranean. However, occasionally they have been found in deeper water, e.g., off the island of Chios (Greece) specimens were collected from Cystoseira at depths from 0.5 - 30 m (see Suppl. material 1).

Colour.

As with Dynamene bidentata , some degree of camouflage in the algal habitat is given by yellow or dull green ‘uniformis’ phenotypic varieties, and this is enhanced by the development in some individuals of patterns of white or red, dorsal, non-adaptable chromatophores ( Holdich 1969).

Geographical distribution.

The distribution of this species shown in Holdich (1970) has been extended by the present study. It is the most commonly recorded Dynamene species in the Mediterranean, occurring from the Balearic Islands in the west to the coast of Israel in the east, although there are only a few records for the North African coast (Fig. 5B). It has been frequently recorded around the Greek islands and mainland coast of both Greece and Turkey. The most northerly record is for Croatia in the Aegean Sea. It has also been recorded for a number of countries around the Black Sea (Bulgaria, Romania, Turkey and Georgia) (Fig. 5B). Most records in the literature refer to Dynamene torelliae , which is now considered synonymous with Dynamene bicolor .

Remarks.

Many records exist, both published and unpublished, for Dynamene bicolor (usually as ' Dynamene torelliae ') in the Mediterranean Sea, particularly from the coasts of Spain, France, Italy and Greece ( Holdich 1970, Bakir et al. 2014). However, its presence in Egypt and Israel was unreported until now. Previous observations indicated its presence in the Black Sea ( Kussakin 1979), where it was thought to be the only Dynamene species present ( Gönlügür-Demirci and Katağan 2004). On comparing specimens from the Black and Mediterranean Seas the current authors have accepted the decision of Kussakin (1979) that Dynamene torelliae and Dynamene bicolor are synonymous. However, it is clear that some of the specimens from the Black Sea have a reduced pleotelsonic boss, and the two may eventually turn out to be separate species when more material is examined. Kirkim et al. (2006) commented on the form of the pleotelsonic boss, stating that this can vary from two small projections to a well-formed boss in specimens of ' Dynamene torelliae ' from the Aegean Sea. Rathke’s (1837) drawings of Dynamene bicolor show the posterior halves of a female and a stage 7 male. The male has two joined hemispherical pleotelsonic bosses, which are similar to those found in the same stage of ' Dynamene torelliae ' and unlike that of Dynamene edwardsi the other species in the region, which is single.