Ecuador has a high diversity of ecosystems in its coastal and marine territory with beaches, bays, estuaries, cliffs, coastal lagoons and rocky coasts being the most representative. So far, 1,859 marine species have been identified in Ecuador. Of these, 1380 species of non-commercial marine invertebrates and vertebrates, belonging to 8 Phyla and distributed in 25 groups or classes, occur along the coast of Ecuador. These are: Protozoans, 9 groups: Oceanic and estuarine Diatoms, Cyanophyta, Chlorophyta, Dinoflagellates, Coccolithophorida, Silicoflagellates, Euglenophyta, Tintinnids and planktonic and benthic Foraminifera; Cnidaria, 2 classes: Hydromedusae and Scyphomedusae; Mollusca, 5 classes: Wood-boring molluscs and rock-boring and benthic bivalves; Gasteropoda: (Thecosomatans, Pteropods, Heteropods and benthic species, Polyplacophora, Scaphopoda and Cephalopoda); Annelida, 1 group: benthic Polychaeta; Arthropoda, 1 class: Crustacea (Cirripedia, Anomura, Brachyuran, Euphausiids); Chaetognatha, 1 group; Echinodermata, 4 classes: Asteroidea, Ophiuroidea, Echinoidea and Holothuroidea; Chordata, 2 classes: Marine mammals and birds. Both the biodiversity of the meiobenthos of the Gulf of Guayaquil and that of the inter-tidal zone are presented. The 479 demersal species of commercial importance are grouped in 4 Phyla (Chordata, Arthropoda, Mollusca, and Echinodermata), 41 orders, 143 families and 258 genera. The phylum Chordata represented by fish is the most diverse group on the coast with 270 species from 142 genera, 63 families, and 22 orders, the order Perciformes being the best represented with 143 species. Molluscs form the next biggest group with 110 species. In general, the biggest biodiversity of species seems to be in the Gulf of Guayaquil, the main estuary of Ecuador. However, this may be because that area has been better studied than the others. The work presented is mainly the result of research carried out by Equatorians and thus cannot be claimed to include the whole of the current information about marine biodiversity in Ecuador.