Query: keyword: "SEM"
|Authors||Jean-Paul Henry, Guy Magniez|
|Title||Nouvelles données sur les Asellidae épigés d’Extrême-Orient (Crustacea, Isopoda, Asellota)|
|Journal||Contributions to Zoology|
|Keywords||Asellus (Asellus) levanidovorum n. sp.; ; gen. Asellus n. def.; ; Sakhalin and Kunashir Islands; ; SEM; ; structure of copulatory pleopods; ; subgen. Asellus; subgen. Arctasellus nov|
|Abstract||Numerous samples of oculate Asellus from eastern Siberia and the Japanese Islands, one from southern China, and one from Alaska, have been studied. The epigean fresh waters of this large Asiatic region generally harbour populations identified as Asellus (Asellus) hilgendorfii Bovallius, 1886, or some of its geographical forms previously considered as species, subspecies, or not yet named. The “hilgendorfii” complex seems to possess the dimension of a superspecies.|
A new pigmented-oculate species, Asellus (Asellus) levanidovorum is sympatric with A. (A.) hilgendorfii in the lake Bolon region (lower part of the Amur River basin) and is present also in the Sakhalin and Kunashir Islands. Its copulatory organ (endopodite of male 2nd pleopod) shows a large cannula and study with SEM allows us to understand the organizational pattern of this organ in all species belonging to the true genus Asellus, including the type-species Asellus (A.) aquaticus (Linnaeus, 1758) where the cannula is small and deeply hidden. Strong relationship between these species points to the existence of a subgenus Asellus inside the genus Asellus auct.
The three Arctic species, A. latifrons Birstein, 1947, A. alaskensis Bowman & Holmquist, 1975 and A. birsteini Levanidov, 1976, represent a second subgenus, Arctasellus nov., inside the genus Asellus car. emend., characterized by their onisciform aspect, the reduction of the coxopodites of all pereiopods, and the structure of the different parts of the copulatory appendages, homologous with those of the subgenus Asellus, but simpler and exposed.
The Asellidae appear to be a heterogeneous family, having taken origin from several marine ancestors, and having colonized independently the fresh waters of several remote continental sites. These separate elements evolved independently in the North Pacific (Japan Sea region), Baikal, the Mediterranean and Paratethys, southwestern Atlantic Europe, and Atlantic North America.
All species of the far-eastern group (genera Asellus, Calasellus, Mesoasellus, Nipponasellus, Phreatoasellus, Sibirasellus, and Uenasellus) show a common general architecture of the copulatory appendages, with homologous elements (“Asellus pattern”) in each of them. This multigeneric group represents a distinct unit inside the family Asellidae. The presence of its main member, Asellus (A.) aquaticus, in Europe is the result of a recent and long-range migration westward inside the natural area of the autochthonous Mediterranean forms.
|Download paper|| http://www.repository.naturalis.nl/document/547598 |