The majority of the almost 1,000 species of Palaemonidae, the most speciose family of caridean shrimp, largely live in symbioses with marine invertebrates of different phyla. These associations range from weak epibiosis to obligatory endosymbiosis and from restricted commensalism to semi-parasitism, with the specialisation to particular hosts likely playing a role in the diversification of this shrimp group. Our study elucidates the evolutionary history of symbiotic palaemonids based on a phylogenetic analysis of 87 species belonging to 43 genera from the Indo-West Pacific and the Atlantic using two nuclear and two mitochondrial markers. A complementary three-marker analysis including taxa from GenBank raises this number to 107 species from 48 genera. Seven larger clades were recovered in the molecular phylogeny; the basal-most one includes mostly free-living shrimp, albeit with a few symbiotic species. Ancestral state reconstruction revealed that free-living forms likely colonised cnidarian hosts initially, and switching between different host phyla occurred multiple times in palaemonid evolutionary history. In some cases this was likely facilitated by the availability of analogous microhabitats in unrelated but morphologically similar host groups. Host switching and adaptations to newly colonised host groups must have played an important role in the evolution of this diverse shrimp group.

The American spiny-cheek crayfish, Orconectes limosus, was first introduced into European waters in 1890. The first literature record about the occurrence of O. limosus on the territory of the Czech Republic was published almost 100 years later -in 1989. The presence of this species in Czechia, however, was first recorded already in the 1960s, when crayfish were observed in the dead arms and pools adjacent to the river Elbe (Labe) in Central Bohemia. In the following few decades the spiny-cheek crayfish has spread into several larger rivers of the Elbe watershed and some of their smaller tributaries. The eastern part of the country (mostly belonging to the watershed of the river Morava) has not yet been colonised by this species. O. limosus can be found in lower reaches of a number of watercourses of a low stream order, but does not seem to penetrate far upstream in such localities. Its distribution in standing waters is largely the result of intentional humanmediated translocations. The long-term coexistence of Orconectes and native crayfish species has not yet been recorded, although both introduced and native crayfish at least occasionally come into contact. As O. limosus is a major carrier of the crayfish plague on the Czech territory, and crayfish plague outbreaks have been recently recorded, the dynamics of Orconectes invasion deserves careful monitoring in the future. Key-words:Orconectes limosus, spiny cheek crayfish, invasive species, distribution, crayfish plague, Czech Republic. DISTRIBUTION DE L'ÉCREVISSE INVASIVE (ORCONECTES LIMOSUS) EN RÉPUBLIQUE TCHÈQUE. PASSÉ ET PRÉSENT RÉSUMÉL'écrevisse américaine, Orconectes limosus, a été introduite en Europe en 1890. Les premiers écrits relatant la présence d'O. limosus sur le territoire de la République tchèque ont été publié presque 100 ans plus tard, en 1989. Cette espèce a déjà été observée en Tchéchie cependant, dans les années 60, dans les bras morts et les plans d'eau adjacents à la rivière Elbe (Labe) en Bohème centrale. Dans les décennies suivantes, l'écrevisse américaine a colonisé d'autres grands cours d'eau du bassin de l'Elbe, et quelques-uns de leurs plus petits affluents. La partie orientale du pays (correspondant principalement au bassin de la rivière Morava) n'a pas encore été colonisée par cette espèce. O. limosus est présente dans les parties les plus basses d'un certain nombre de cours d'eau d'ordre hydrographique faible, mais elle ne semble pas remonter très en amont des cours d'eau. Sa répartition dans les eaux calmes est largement le résultat des transports effectués par l'homme. La coexistence au long-terme d'Orconectes et des espèces natives d'écrevisse n'a pas encore été établie, bien que les écrevisses natives et les écrevisses introduites se retrouvent au moins occasionnellement en contact. L'écrevisse O. limosus étant le principal vecteur de la peste de l'écrevisse sur le territoire tchèque, et des cas de peste de l'écrevisse ayant été récemment enregistrés, la dynamique de l'invasion de l'Orconectes doit être soigneuseme...

Marine sponges are frequently inhabited by a wide range of associated invertebrates, including caridean shrimps. Symbiotic shrimps are often considered to be commensals; however, in most cases, the relationship with sponge hosts remains unclear. Here we demonstrate that sponge-inhabiting shrimps are often parasites adapted to consumption of sponge tissues. First, we provide detailed examination of morphology and stomach contents of Typton carneus (Decapoda: Palaemonidae: Pontoniinae), a West Atlantic tropical shrimp living in fire sponges of the genus Tedania. Remarkable shear-like claws of T. carneus show evidence of intensive shearing, likely the result of crushing siliceous sponge spicules. Examination of stomach contents revealed that the host sponge tissue is a major source of food for T. carneus. A parasitic mode of life is also reflected in adaptations of mouth appendages, in the reproduction strategy, and in apparent sequestration of host pigments by shrimp. Consistent results were obtained also for congeneric species T. distinctus (Western Atlantic) and T. spongicola (Mediterranean). The distribution of shrimps among sponge hosts (mostly solitary individuals or heterosexual pairs) suggests that Typton shrimps actively prevent colonisation of their sponge by additional conspecifics, thus protecting their resource and reducing the damage to the hosts. We also demonstrate feeding on host tissues by sponge-associated shrimps of the genera Onycocaris, Periclimenaeus, and Thaumastocaris (Pontoniinae) and Synalpheus (Alpheidae). The parasitic mode of life appears to be widely distributed among sponge-inhabiting shrimps. However, it is possible that under some circumstances, the shrimps provide a service to the host sponge by preventing a penetration by potentially more damaging associated animals. The overall nature of interspecific shrimp-sponge relationships thus warrants further investigation.