A new amphiboreal gamasid mite genus, Thalassogamasus gen. n. is described, characterised by two distinct dorsal shields (opisthonotum hypotrichous, usually with ten pairs of setae); peritrematal shield reduced and posteriorly free; setae al1, al2 on palp genu and al on palp femur entire; dorsal chaetome homogenous; opisthosoma laterocaudally hypertrichous; in female, epigynium whip-like anteriorly, endogynium with two thick sclerotic masss; in male, tritosternum fully lost, hypostome deeply cleft, cheliceral arthrodial membrane fringelike. The new genus includes T. sidortschukae sp. nov. (Chukotka and Okhotsk coast), T. kurilensis sp. nov. (Kuril Islands) and T. lindrothi (Sellnick, 1974) (Iceland) comb. nov. The female of T. lindrothi (Sellnick, 1974) is considered conspecific with the male of Parasitus (Neogamasus) anderssoni Sellnick, 1974, comb. nov., syn. nov. All three Thalassogamasus species are seaside dwellers, inhabiting sandy beaches, salt marshes, and seaweed accumulations. Keys to the species (females and males) are presented. Peculiar morphological aspects of the dorsal shields, peritremes, and leg tarsi of the new genus are discussed. For another littoral species of Parasitidae, Parasitus kempersi Oudemans, 1902, a new combination is established, Phorytocarpais kempersi (Oudemans, 1902) comb. nov. Three littoral species of Uropoda (Phaulodinychus) Berlese, 1903 are first recorded from Russia: U. (P.) japanorepleta Hiramatsu, 1980 (northern and eastern Chukotka, Magadan Region, Kuril Islands), U. (P.) maritima Hiramatsu, 1977, and U. (P.) marihirschmanni Hiramatsu, 1977 (Kuril Islands).