Mytilus galloprovincialis is dark blue or brown to almost black. The two shells are equal and nearly quadrangular. The outside is black-violet coloured; on one side the rim of the shell ends with a pointed and slightly bent umbo while the other side is rounded, although shell shape varies by region. It also tends to grow larger than its cousins, up to 15cm, although typically only 5-8cm.

Adult mussels spawn gametes, after which fertilization of an egg occurs. The egg undergoes gametogenesis, forming a larvae. The larva forms into a juvenile which settles and attaches itself using byssal threads after 2 to 4 weeks (Matson 2000).

Mytilus galloprovincialis is widely cultivated in Japan and China (Morton 1996).

In its native range, M. galloprovincialis can be found from exposed rocky outer coasts to sandy bottoms (Ceccherelli and Rossi 1984). As an invader it typically requires rocky coastlines with a high rate of water flow. In fact, unlike the other 26 Asian and Atlantic molluscs introduced into Pacific regions only one introduced species, the Mediterranean mussel M. galloprovincialis, occurs in open coast, high energy environments on the Pacific coast; all remaining species are restricted to bays and estuaries (Carlton 1992).

Gonochoristic reproduction where males and females spawn simultaneously. M. galloprovincialis also has high fecundity and spawns at the time of year with the highest water temperature (Bayne 1976).

A filter-feeding bivalve that eats a wide range of planktotrophic organisms. This species prefers fast moving water that is free of sediment and thrives in regions where nutrient-rich upwelling occurs.

Shipping is held to be the most probable original mode of introduction of M. galloprovincialis to South Africa (Grant et al. 1984, in Branch and Stephanni 2004) and to Mexico (Carlton 1992).Late twentieth century distribution od M. galloprovincialis was probably enhanced by ballast water transport as well as ship fouling (Carlton 1992).M. galloprovincialis is sometimes transferred through mariculture as a food source and because it is confused with other Mytilus species

The alteration of benthic community dynamics by introduced bivalves on the Pacific coast remains largely uninvestigated including the impact of such invasives as M. galloprovincialis, but also Geukensia demissa, Musculista senhousia, Mya arenaria, Crassostrea virginica, Venerupis philippinarum, and Gemma gemma. It is known that M. galloprovincialis is able to outcompete and displace native mussels and become the dominant mussel species in certain localities. This is because M. galloprovincialis may grow faster than native mussels, be more tolerant to air exposure and have a reproductive output of between 20% and 200% greater than that of indigenous species (Van Erkom Schurink and Griffiths 1993, in Branch and Stephanni 2004). In a experiment to test the tolerance of the three native South African species to aerial exposure (in comparison to M. galloprovincialis) mussels were held for 42 weeks at the high-tide level where they experienced up to 7 days of continuous exposure to air. Under these conditions, survivorship of M. galloprovincialis was 92%, but 78% for Perna perna, 37–46% for Choromytilus meridionalis and 0–10% for Aulacomya ater (Hockey and van Erkom Schurink 1992, in Branch and Stephanni 2004). In South Africa the indigenous ribbed mussel A. ater was progressively displaced from semiexposed and exposed shores as the cover of M. galloprovincialis rose there. At sites where M. galloprovincialis was experimentally removed, there were no declines of A. ater (G.M. Branch Unpub. Data, in Branch and Stephanni 2004). Similarly, in southern California the introduction of M. galloprovincialis has been associated with a decline in the closely related native mussel M. trossulus (Geller 1999).
Since the 1980s the introduced Mediterranean mussel (M. galloprovincialis) has successfully invaded the southern African coastline and has become the dominant species on rocky intertidal shores of the west coast. A comparative study by Robinson and Griffiths (2002) to investigate differences between M. galloprovincialis invaded areas and non-invaded areas was conducted in Langebaan Lagoon, South Africa, and highlighted the affect M. galloprovincialis has on naturally-occurring communities. Communities in invaded areas differed significantly from non-invaded areas with figures indicating that naturally-occurring sandbank communities were being replaced with communities more typical of rocky shores. To conserve the natural biota of the centre banks, which lie within a national park, the mussel beds should to be removed (Robinson and Griffiths 2002).

Ballast water management could stop the spread of its larvae.

A new technique used in the aquaculture industry is the production of triploid and tetraploid mussels, which are functionally sterile, thereby eliminating the risk of wild populations establishing (McEnnulty et al. 2001).