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The genus Beroe Browne, 1756 (Ctenophora, Beroidae) occurs worldwide, with 25 currentlydescribed species. Because the genus is poorly studied, the definitive number of species is uncertain. Recently, a possible new Beroe species was suggested based on internal transcribed spacer 1 (ITS1) sequences from samples collected in Svalbard, Norway. Another species, Beroe ovata, was introduced to Europe from North America, initially in the Black Sea and subsequently (and possibly secondarily) into the Mediterranean and Baltic Seas. In areas where ctenophores have been introduced, they have often had significant detrimental ecological effects. The potential for other cryptic and/or undescribed Beroe species and history of spread of some species in the genus give reason for additional study. When alive, morphological hallmarks may be challenging to spot and photograph owing to the animals' transparency and near-constant motion. We sampled and analyzed 109 putative Beroe specimens from Europe, using morphological and molecular approaches. DNA analyses were conducted using cytochrome oxidase 1 and internal transcribed spacer sequences and, together with published sequences from GenBank, phylogenetic relationships of the genus were explored. Our study suggests the presence of at least 5 genetic lineages of Beroe in Europe, of which 3 could be assigned to known species: Beroe gracilis Künne 1939; Beroe cucumis Fabricius, 1780; and Beroe ovata sensu Mayer, 1912. The other 2 lineages (here provisionally named Beroe "norvegica" and Beroe "anatoliensis") did not clearly coincide with any known species and might therefore reflect new species, but confirmation of this requires further study. [ABSTRACT FROM AUTHOR]

The fundamental object of this investigation were the muscle cells of Beroe, the results obtained were completed and verified on the muscle cells of Bollina, the observations "in vivo" having been the ground method and the differently stained sections of the fixed materials performing controlling functions. The gelatinous body of Beroe is abundant in muscle cells. Their structure is distinctly to be seen on thick cells, they are covered with sarcolemma, under which the author found a layer of a dark, intensively refracting light, plasma, whereas the medulla of the cell is filled with much more transparent plasma, on the sections there is to be seen its structure with large granular alveoles, with small vacuoles and characteristical granulosity. In this transparent medulla layer of the plasma lies the nucleus, on the preparations you can observe that long cells often contain several nuclei.

Not far behind: First record of Beroe ovata Mayer, 1912 (Ctenophora: Beroida: Beroidae) off the Mediterranean coast of Israel [ABSTRACT FROM AUTHOR]