A new species of mesopsammic polyclad, Theama mediterranea sp. nov., from lower intertidal habitats of the Mediterranean Sea, is described. The species differs from congeneres found in the tropical Pacific and the Atlantic coast of South America, in terms of size, structure of the male copulatory organ and number of eyes. T. mediterranea sp. nov. has a short pelagic juvenile phase, while adults are strictly interstitial; the life cycle is annual. Based on observation of the type material of Theama evelinae Marcus, 1949, the genus Eutheama Faubel, 1983 is synonymized with Theama Marcus, 1949.

Population structure of the sea urchin Paracentrotus lividus seems to vary depending on the habitat, as, on average, urchin density is higher on rocks, and size is larger in Posidonia oceanica seagrass. Here, we tested the hypothesis that P. lividus would choose P. oceanica rather than rocky habitat due to the greater availability of shelter and food in the seagrass. We conducted 2 experiments by using aquaria divided into 2 equal sections, each containing an array of 2 habitats: natural P. oceanica (P) and rocks (R) in the first experiment and natural (NP) and artificial (AP) P. oceanica in the second (to highlight the reason for preference). Each experiment included 2 experimental stages of no-choice (Stage 1) and choice (Stage 2): in the 2 no-choice treatments, sections were filled with the same habitat, and in the 2 choice treatments, sections were filled with P and R in Expt 1 and NP and AP in Expt 2. Under the null hypothesis that preference of habitat is random, the expected numbers of sea urchins that were distributed in the 2 sections of the habitat after 24 h were estimated by using formulae derived from maximal likelihood estimates. The results evidenced a preference by P. lividus for P. oceanica habitat rather than rocky habitat in the first experiment and for natural P. oceanica rather than artificial seagrass in the second experiment, thus suggesting that P. lividus individuals searched for a well-structured habitat where they could find both shelter and food.

Based on specimens collected in the Mediterranean and Red Sea coasts of Israel, the first lessepsian flatworm (Boninia neotethydis sp. nov.) is described. The genus Boninia includes cotylean polyclads characterized by the presence of multiple accessory (prostatoid) organs. The three species described are distributed in the western Pacific (B. mirabilis) and in the Caribbean (B. antillarum and B. divae). The new species differ from congenerics in the number and arrangement of the prostatoid organs, and in the number of marginal eyes. Specimens of the new species feed on mussels, and their possible effects on Mediterranean mussel cultures should be monitored.

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This paper deals with the diatoms from Upper Mustang Trans-Himalaya Region, Nepal.Key words: Algae, Diatoms, Upper Mustang Trans-Himalaya, NepalDOI: 10.3126/on.v7i1.2583Our Nature (2009) 7:243-247