Studi sui Crostacei Anfipodi 74. Contributo alla revisione del genere Bogidiella Hertzog (Crustacea, Amphipoda, Gammaridae)

At least 18 species of Europe, Africa, Asia, Middle and South America, belong to the genus Bogidiella Hertzog 1933 (= Jugocrangonyx S. Karaman 1933). This paper gives a catalog of all the species well known today, with their bibliographical data and their occurrence. The Authors then examine the systematic position of the genus Bogidiella which has been classified in a special family (Bogidiellidae) by some authors, and which is considered to belong to the Gammaridae by others. The analysis of the features of this genus made us decide to include it in the Gammaridae family, of which it forms a particular group, in any case (Bogidiella group). Pseudingolfiella Noodt and, probably, Parancrangonyx Stebbing and Kerguelenella Ruffo also belong to this group which is characterized by the pleopods reduction. We have studied the specific characters of all the species of Bogidiella, and their relationship with the taxonomy of the genus; those characters have been included in the tables (see table I) and discussed individually. We have concluded that the majority of the described species are valid; doubts are expressed on the B. glacialis S. Karaman, which is probably synonimous of B. albertimagni Hertzog and on B. ruffoi Birstein and Ljovuschkin, which is very similar to the B. lindbergi Ruffo. Considering current knowledge on the subject, it is not possible to recognize groups of similar species within the genus; as a matter of fact, the species known today show a range of diverging characters which are combined differently in different geographical areas. A table is shown to classify, using the more evident morphological characters, the different species of Bogidiella. From an ecological point of view the Bogidiella is divided into four different groups: a) mesopsammic marine species, b) litoral interstitial species, c) hyporheic interstitial species, d) troglobitic species. Two morphologically distinct types correspond to those four ecological groups: the mesopsammic interstitial type, which characterizes the first, second and third group, and the troglobitic type. From a biogeographical and evolutionary point of view, it seems evident that the Bogidiella come from the sea and their spreading to fresh water occurred in two different ways: the first was through the litoral interstitial habitat to the hyporrheic interstitial habitat, and the second by colonization, directly or indirectly, of large underground water basins. This population of the fresh water certainly occurred during different periods; as a matter of fact it is possible to find, even today, litoral interstitial species moving to the fresh water, while on the other hand species localized in regions corresponding to tertiary seas far from the actual coastal lines have been described (Central Asia, the Dead Sea, Danubian Region). With regard to this latter case, the transition to fresh water certainly occurred during the prequaternary period.