The Socotra Archipelago (Yemen) is globally recognized for its outstanding biodiversity and endemism, designated on this basis a UNESCO World Heritage Site in 2008. The island underwent long geological and political isolation, ensuring preservation of unique ecosystems until the start of the new millennium. Now, Socotra Island is undergoing rapid development, out of balance with conservation. Major causes for biodiversity loss in other global insular ecosystems such as habitat fragmentation and degradation, pollution, invasive species and the impact of tourism, are becoming pressing issues that deserve close attention. Unsustainable resource use, the loss of traditional land management and illegal trade in biota are worrying phenomena that further increase the pressures on Socotra’s ecosystems. We provide the first comprehensive review of potential human impacts on Socotra before the 21^st century, an updated discussion of some of the principal threats to its biodiversity in recent times, discussing local examples within a historical context of known extinction processes on islands, and underline the importance of traditional knowledge in the protection of Socotran ecosystems.

We move the freshwater cladocerans Alona verrucosa Sars, 1901 and related species from the lump genus Alona Baird, 1843 (Anomopoda: Chydoridae: Aloninae) to Anthalona gen. n. We revise the group and describe five new taxa from tropics and subtropics: Anthalona simplex n. sp., DR Congo, A. harti n. sp., Africa (with two subspecies), A. acuta n. sp., Brazil and A. obtusa n. sp., Borneo. Anthalona is a genus of relatively small-sized, stenothermic Aloninae with specializations for scraping. Within the subfamily, the new genus is closest to Karualona and Coronatella. We discuss possible homoplasy of limb characters between latter and Anthalona. The genus can be considered an important case study in an evolutionary trend towards oligomerization of limb structures at low taxonomical levels and within an extant crustacean lineage. Composition of the genus reflects a complex history. Species with unusual morphologies (A. brandorffi, A. simplex n. sp.) appear basal in our phylogeny and may be relicts, in comparison to a pantropical A. verrucosa complex of similar forms. Several species may coexist in a single water body such as A. acuta n. sp. and A. verrucosa in the Neotropics, suggesting niche separation.

We investigate morphology and taxonomic rank of several Alona species related to A. rectangula Sars, 1861. Despite high morphological intraspecific variability, a number of synapomorphies shows that taxa related to A. rectangula are sufficiently different in external and internal morphology from “true” Alona Baird, 1843. These are removed from Alona into separate genera. The rare West-African A. holdeni Green 1962 is redescribed and we describe a new species from North Africa, Arabia and islands in the Western Indian Ocean. We reinstate the name Coronatella Dybowski & Grochowski to receive A. rectangula, A. holdeni, and a new species, C. anemae. Sharing several synapomorphies, the subantarctic species A. weinecki Studer appears related to A. meridionalis Sinev, 2006. We assign them to Ovalona gen.n., similar in morphology to Coronatella, but with less limb reductions. At a higher level, we discuss morphology and distribution of both genera and of the similar A. elegans-group. To situate Coronatella within the subfamily, we introduce a “Coronatella-branch”, a group of medium-sized Aloninae with limb reductions, comprising Coronatella, Leberis, Celsinotum, A. dentifera, A. monacantha and possibly Karualona and A. verrucosa-group, in comparison with a “Hexalonabranch” and Alona s.str. Adaptations to life in temporary pools and salinity tolerance may have played an important role in separation and radiation of a Coronatella-branch.

We discuss current progress with the revision of Alona Baird, 1843 (Crustacea: Cladocera: Chydoridae), the largest cladoceran lump genus. We present the first inventory of these Aloninae since the 1970’s and include an updated checklist of names, with comments on the current status and position of each taxon. We discuss validity, affinities and synonymy of ca. 240 names, including subspecies and varieties. Recent taxonomic shifts have lead to a better delineation of natural groups in the Aloninae but the Alona puzzle remains incomplete. The majority of taxa are grouped into species-complexes or separate genera. We count 14 Aloninae genera, now considered valid, that were split from Alona. The status of a significant portion remains unclear, due to poor original descriptions and/or loss of type material. Even with detailed morphological descriptions, the phylogenetic position of many Aloninae remains unsettled. Analysis of Alona taxonomy based on the checklist shows historical trends and long periods of instability in the systematics of these micro-crustaceans.