Dynamene edwardsi (Lucas, 1849)

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 : 9-10

Dynamene edwardsi (Lucas, 1849)

Restricted synonymy.

Naesa edwardsi : Lucas (1849).

Dynamene hanseni : Monod (1923).

Dynamene edwardsi : Holdich (1968a, 1970); Harrison (1982).

Dynamene bidentata : Picker and Griffiths (2011).

An extensive synonymy was given by Holdich (1968a, c) for citations prior to 1968.

Material examined.

Specimens were examined from 89 locations in NE Atlantic, Mediterranean, Adriatic, Aegean and Red Seas - see Suppl. materials 1 and 2. A number of literature records, e.g., the Suez Canal, have been included where the diagrams clearly indicate this species.

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.

Key morphological characters.

Body convex; in stage 8 males the apices of arms of the bidentate process are swollen, each with a short, downwardly-directed spur; the pleotelsonic boss is plate-like with two forward-facing pegs; the body exhibits various degree of setation (Fig. 2 E–F), e.g., specimens examined from the Balearic Islands (Spain) and the island of Chios (Greece) are somewhat different from other Dynamene edwardsi seen by us in being very hirsute, with a pronounced developing boss and respiratory tube in the stage 7 males. In stage 7 females the pleotelsonic dome is keeled in side view, with a median protuberance; the pleotelsonic foramen is at the end of a short tube (Fig. 3 E–G). Further details are provided by the scanning electron microscope pictures of the posterior body of a stage 8 male and a stage 7 female in Holdich (1976). See keys to stage 8 males and stage 7 females.

Size.

Adult males (Stage 8) typically 5.5 × 2.25 mm; pre-ovigerous females (stage 7) typically 3.0 × 1.1 mm, specimens of 4.4 × 2.3 mm have been seen from the Venice Lagoon, Italy.

Habitat.

Juveniles and adults have been found amongst a variety brown, green and red algae in the littoral and sublittoral zones, sometimes in conjunction with Dynamene bicolor in the Mediterranean, and with Dynamene bidentata and Dynamene magnitorata on Atlantic coasts. Adults have also been recorded from amongst mussels and tube worm colonies and barnacle tests in the Bay of Naples ( Torelli 1930, Holdich 1970), and elsewhere in the Mediterranean (e.g., Rivosecchi 1961, Bellan-Santini 1962). It has been found associated with encrusting matter on solid surfaces in some harbours and canals. On occasions it has been found amongst the ‘trottoir’ on steep-sided cliffs as deep as 10 m. Monod (1932) recorded it from coralline and fucoid algae on the coast of NW Africa. In the Azores, adults have been recorded from empty Chthamalus stellatus tests attached to lower shore cobbles, along with Campecopea lusitanica . In West Portugal (Buarcos) it is present with Dynamene bidentata and Dynamene magnitorata . However, while Dynamene bidentata adults were present in barnacles, no Dynamene edwardsi were found inside barnacles, only among intertidal algae and on a few ‘small’ algae in shaded crevices at 0-1 m. Also, they were not present among mussels. Unusually, adults, including stage 8 females, were found in upper shore sandstone crevices, along with Campecopea hirsuta , in southern Portugal.

Colour.

The general body colour is a dull grey-green, individuals sometimes exhibit polychromatism caused by patterns of white, dorsal, non-adaptable chromatophores as seen in some of the other species ( Holdich 1969).

Geographical distribution.

The distribution of this species shown in Holdich (1970) has been extended by the present study. It is the most meridional of the Atlantic species, occurring from Galicia in north-western Spain to Nouadhibou in Mauritania (Fig. 5D). This is the currently known southern limit of Dynamene species of the NE Atlantic-Black Sea axis. It is widespread in the Macaronesian islands and in the eastern and western Mediterranean (Fig. 5D). The most northerly record comes from the Venice Lagoon in the Adriatic Sea. It is also the only Dynamene species recorded from the Red Sea, in the Gulf of Aqaba (Fig. 5D). Glynn (1972) recorded a species that is clearly Dynamene edwardsi from the Suez Canal. Picker and Griffiths (2011) have recorded this species (as Dynamene bidentata ) from South Africa.

Remarks.

Dynamene edwardsi occupies a wide vertical range in the littoral zone on NE Atlantic shores, and from the littoral zone down to 10 m in the Mediterranean. In recent field work, it was found to be very abundant in the Canary Islands and Madeira archipelago, whereas Dynamene magnitorata was more common in the Azores and Dynamene edwardsi rare. It is the most southerly of the Dynamene species extending down the West African coast to Mauritania and the only record for tropical waters. Glynn (1972) suggested that Dynamene edwardsi has migrated from the Mediterranean throughout the whole length of the canal. Our study has shown that it has now reached the Gulf of Aqaba in the Red Sea

The records for the Suez Canal and Red Sea are interesting as they show movement from the Mediterranean Sea into the Red Sea, whilst many marine species are moving in the opposite direction ( Galil et al. 2014). No Dynamene species have yet been recorded from the Indian Ocean ( Schotte and Kensley 2005). However, a stage 8 male has been recorded from Port Elizabeth harbour in South Africa by Picker and Griffiths (2011). They suggest that it may have been introduced as a fouling organism or in ballast water. It is known that this species can be transported amongst fouling organisms on ships, as evidenced by the finding a stage 8 male on a ship in Tangiers harbour (Morocco) (see Suppl. material 1).

This species is variable in its morphology and particularly in the degree of hirsuteness. It may be that some of the specimens collected from the Balearic and Greek islands are in fact a new species, but more material is needed to prove this. Ideally, a molecular genetic analysis needs to be carried out on Mediterranean and Adriatic specimens. Such a technique applied to specimens from some NE Atlantic coasts and Macaronesian islands has shown that a number of cryptic species may be present ( Vieira et al. 2015).