The successful settlement of the African pea crab Afropinnotheres monodi in the Bay of Cadiz was analysed to get new insights into the evolution of pea crab parasite life history traits. The pea crab lives symbiotically and with high prevalence in the bivalves Cerastoderma glaucum and Mytilus galloprovincialis, and with low prevalence in Scrobicularia plana. A remarkable monopolisation of host (one crab/bivalve) occurred irrespective of host species and crab demographic categories (males, hard females, soft females), probably as an optimisation of resources in smallsize hosts. However, there was a clear asymmetry in host use by the different crab 2 categories. A 1:1 sex ratio was found in crabs harboured by C. glaucum and S. plana, with most of the female crabs being small and hard specimens, whereas crabs inhabiting M. galloprovincialis were primarily large reproductive females. Ovigerous females were found throughout the year in M. galloprovincialis and there was a strong correlation between female size and fecundity, suggesting that the females harboured by this host were the major contributors to the reproductive effort of the studied population. Conversely, most of the new crabs recruiting to the population were harboured by the remaining two host species. We hypothesise that such a generalist but asymmetrical usage of bivalve hosts by pea crabs may have clear benefits for species in geographical expansion as A. monodi, facilitating its dispersal to new locations and its successful settlement in sheltered systems, as the Bay of Cadiz.

The complete larval series (zoea I, zoea II and megalopa) of the crab Ergasticus clouei is described and illustrated based on plankton samples from Mediterranean waters. The zoea II and megalopal stages, previously unknown, are described here for the first time. Nucleotide sequence analysis of two gene regions (16S rDNA and Cox1 genes) confirmed the assignment of these larvae to Ergasticus clouei. The molecular analyses and the morphology of the larval stages revealed large differences between Ergasticus and Inachus, the type genus of the family Inachidae. In fact, E. clouei larvae presented a series of morphological characters, such as antennal shape and mouthparts setation pattern that placed them closer to the family Oregoniidae. The phylogenetic analyses also showed significant support for the monophyly of the Oregoniidae + Ergasticus group. The data argue for removal of Ergasticus and the related genera (Bothromaia, Pleisticanthoides, Parapleisticantha and Pleistacantha) from the Inachidae and their placement within the Oregoniidae as a separate subfamily, Pleistacanthinae Števčić, 2005. Our results demonstrate that larval stages provide reliable morphological traits, independent from those of adults, to help resolving relationships among Majoidea genera.

After the recent detection, by both morphology and DNA barcodes, of the larval stages of an unknown species of pea crab (Pinnotheres sp.) in European waters, adults of this crab are herein reported and described as a new species. The current known geographic distribution of the species comprises the Gulf of Cádiz in the eastern Atlantic and the adjacent Mediterranean waters of the south of the Iberian Peninsula (Alboran Sea), where this crab is well-established inside the anomiid bivalve Anomia ephippium. In the Gulf of Cádiz, the species displayed a relatively high prevalence: on average, 55.6–77.7%, in A. ephippium samples. The dominant demographic categories of the new species were soft females (61.8–77.0%) with fewer males (17.7–21.10%). Most of the host bivalves carried only one crab; in bivalves harbouring two crabs, heterosexual pairs were collected more frequently than expected by chance, which suggests that they could be mated pairs. A strong correlation between host size and soft female size was found (r = 0.73, P < 0.01) indicating that space availability within hosts seems to be relevant in determining the size of the sedentary phase of the new crab species.

Summary: Almost 50 years have passed since a group of reputed carcinologists (viz. Lipke B. Holthuis, Isabella Gordon and Jacques Forest) finished the posthumous work of Ricardo Zariquiey Álvarez (1968) on decapod crustaceans of the Iberian Peninsula. No lists of decapod fauna specifically covering this area have been published since then, and an update is needed. The current list of brachyuran crabs of the Iberian Peninsula comprises 140 species, which is 35 species more than the 105 valid species listed in Zariquiey Álvarez (1968). Systematic changes have affected the original classification, so now there are 20 superfamilies, 36 families and 77 genera. Additional species have been recorded in Iberian waters due to natural range expansions from nearby areas (Mediterranean and Atlantic), introductions by anthropogenic activities, and description of new taxa. Also, two species were synonymized. Several of these changes, based on evidence from larval morphology and/ or molecular data, are detailed in this review. Although descriptions of crab species new to science are not expected to occur at a significant rate, an increase in the number of species in the Iberian Peninsula is expected to result from the introduction of alien species.Keywords: checklist; Brachyura; Crustacea; Decapoda; crab; Iberian Peninsula. Lista comentada de los cangrejos braquiuros (Crustacea: Decapoda) de la península Ibérica (SO Europa)Resumen: Han pasado casi 50 años desde que un grupo de reputados carcinólogos (viz. Lipke B. Holthuis, Isabella Gordon y Jacques Forest) finalizaran la obra póstuma de Ricardo Zariquiey Álvarez (1968), "Crustáceos decápodos de la Península Ibérica". Desde entonces no se ha publicado una lista de la fauna de decápodos que cubra específicamente este área, y era necesaria una actualización. La lista actual de braquiuros de la Península Ibérica consta de un total de 140 especies, 35 especies más de las 105 especies válidas enumeradas en Zariquiey Álvarez (1968). Los cambios en la sistemática han afectado la clasificación original, por lo que ahora hay 20 superfamilias, 36 familias y 77 géneros. Otras especies han sido citadas en aguas ibéricas debido a expansiones naturales de su rango de distribución desde áreas cercanas (Mediterráneo y Atlántico), a las introducciones mediadas por las actividades antropogénicas y a la descripción de nuevas especies. Además, se han sinonimizado dos especies. Varios de estos cambios, basados en evidencias de la morfología de las larvas y/o datos moleculares, se detallan en esta revisión. Aunque no se espera que las descripciones de nuevas especies de cangrejos para la ciencia se produzcan a un ritmo significativo, si es esperable un incremento en el número de especies en la Península Ibérica como resultado de la introducción de especies exóticas.