Dynamene bifida Torelli, 1930

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 : 8

Dynamene bifida Torelli, 1930

Restricted synonymy.

Dynamene bifida : Torelli (1930).

Dynamene bifida : Holdich (1968, 1970).

Material examined.

Specimens were examined from seven locations in Spain, Greece, France, Italy and Turkey in the Mediterranean - 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 each arm of the bidentate process is large, tapering and with a well-developed, downwardly-directed accessory process a quarter of the way from the apex; the pleotelsonic boss is very small with raised pointed corners (Fig. 2 G–H). In stage 7 females the pleotelsonic dome is smoothly rounded in side view and the pleotelsonic foramen is at the end of short tube (Fig. 3 L–M).

Size.

Adult males (stage 8) typically 5.0 × 3.0 mm, although a specimen of 7.0 mm length has been seen; pre-ovigerous females (stage 7) typically 4.0 × 2.0 mm.

Life-history.

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

Habitat.

Adults, including stage 8 females, were found among Hydroides unicata colonies and other cryptic habitats in the Bay of Naples ( Torelli 1930, Holdich 1970). Ledoyer (1962) recorded it from Ulva lactuca at Endoume, southern France, and Holthuis (unpublished records) from rocky shores amongst algae at 0.0-1.0 m at Banyuls-sur-Mer. The latter record included stage 8 females.

Colour.

All specimens seen were a pale, sandy yellow. No polychromatism was observed.

Geographical distribution.

The distribution of this species shown in Holdich (1970) has been extended by the present study. It has a widespread distribution in the Mediterranean stretching from southern Spain to Turkey (Fig. 5C).

Remarks.

Originally described by Torelli (1930) from the Bay of Naples, males of this distinctive, and sometimes large, species has been infrequently recorded, and females even less so. The accessory process on each arm of the bidentate process is similar to that found in the Australian species, Dynamene ramuscula ( Holdich and Harrison 1980). The fact that ovigerous females were found amongst shallow-water algae raises questions about the life-history of this species, although in the Bay of Naples this stage has been recorded with males in more protective habitats.