Munidopsid squat lobsters are among the most abundant decapods at abyssal depths and the most diverse squat lobster group in the East Pacific region. During recent cruises along the East Pacific, many deep-sea squat lobsters were collected. Among these, we described five new munidopsid species supported both by morphological characters and molecular phylogenetics: Munidopsis girguisi sp. nov., M. nautilus sp. nov., M. testuda sp. nov., M. cortesi sp. nov. and M. hendrickxi sp. nov. We also report new records of several Munidopsis species across the East Pacific that increase the species distribution ranges. Here, we reconstructed the phylogenetic relationships of the East Pacific species in relation to other Galatheoidea using one nuclear and two mitochondrial gene fragment(s); we also performed single locus species delimitation analyses to explore the species status of various East Pacific munidopsid taxa. The new taxa were photographed, illustrated and imaged with micro-computed tomography. The phylogenetic results show that: (1) Janetogalathea californiensis, previously included in the family Galatheidae, nests within Munidopsidae; (2) the phylogenetic position of Phylladiorhynchus and Coralliogalathea as belonging in Galatheidae is not supported; and (3) Munidopsis is paraphyletic, agreeing with recent systematic hypotheses. Short genetic distances and species delimitation analyses suggested that a clade mostly constituted by abyssal species might include fewer species than currently considered, as species show a wider geographic range than previously considered, conforming with traditional hypotheses of cosmopolitanisms in abyssal species. ZooBank: urn:lsid:zoobank.org:pub:CED9EB18-7061-47A7-B2FF-7F1DAFCC7B12.

Benthic assemblages of the Antarctic continental shelf are dominated by sessile and slow-moving, epifaunal invertebrates. This community structure persists because shell-crushing (durophagous) predators are absent or ecologically insignificant in shelf habitats. Durophagous teleosts, elasmobranchs, and crustaceans have been excluded by cold waters over the Antarctic shelf for millions of years. Now, as shallow waters warm rapidly, predatory king crabs (Lithodidae) living in the upper bathyal zone could emerge onto the shelf and into nearshore habitats. To assess the potential for a bathymetric expansion, we genetically inferred the historical demography of a population of the most abundant durophagous predator found in deep water off the western Antarctic Peninsula: the lithodid Paralomis birsteini Macpherson. Analysis of mitochondrial DNA sequences from crabs sampled at 1200–1400 m depth on the slope off Marguerite Bay suggests this population has expanded twice over the past 132,000 years. Those expansions were possibly coincident with episodes of climatic warming in Antarctica and elsewhere, raising the possibility of a third expansion in response to anthropogenic climate change.