(Fig. 17 a–d.)
Non-type specimens. USA: California, Pioneer Seamount, 7.ii.1950, 37.35000°N, 123.41666°W, 1097–822.96 m: 1 F 20.6 mm (CAS-IZ 190354). — USA: California, Pioneer Seamount, 7.ii.1950, 37.349957°N, 123.430026°W, 805.–988 m: 1 M 10.5 mm (CAS-IZ 190356). — USA: Forty Mile Bank, off San Diego, California, leg. Greg Rouse and Nicolas Mongiardino Koch, R/V Falkor, ROV SuBastian dive S0446, SCB-172, 31.vii.2021, 32.6029°N, 118.02571°W, 1035 m: 1 F 13.4 mm (SIO-BIC C14546). — USA: California, leg. Robert C. Vrijenhoek, R /V Western Flyer, ROV Tiburon dive T665, 2.v.2004, 33.10070°N, 120.96000°W, 870 m, 1 specimen not sexed, not measured (USNM 1463979).
Bering Sea (Piip submarine volcano) at 984-m depth, California, from 805- to 1097-m depth.
COI, 16S rRNA and 28S rRNA.
Newly recorded for the East Pacific. Munidopsis piipa belongs to a group of species with a rostral spine short and spiniform, frontal margin of the carapace straight and telson with 10–12 plates. This group includes Munidopsis ariadne Macpherson, 2011 from the eastern Mediterranean, Munidopsis goodridgii Alcock & Anderson, 1899, Munidopsis karukera Macpherson, Beuck & Freiwald, 2016 from the Caribbean Sea, Munidopsis maunga Schnabel & Bruce, 2006, Munidopsis milleri Henderson, 1885 from the Philippines, Munidopsis polymorpha from shallow caves in the Canary Islands, Munidopsis spinipes MacGilchrist, 1905 from the Bay of Bengal and Munidopsis kexueae Dong, Gan & Li, 2021 from seamounts near the Yap Trench, West Pacific.
Munidopsis piipa closely resembles M. kexueae both morphologically and genetically. The descriptions of these species almost overlapped during the time of revisions and publication, therefore the species were not compared before our work. Phylogenetic and some species delimitation analyses do not support these species hypotheses, considering M. piipa and M. kexueae as a single taxon. However, haplotype networks demonstrate large genetic distances between the two species, with up to 4% of divergence for COI or 19 mutational steps (Fig. 4). The percentage of divergence between these species is low compared to other squat lobsters in the family, (e.g. Rodríguez-Flores et al. 2019 b, Leiogalathea); although some species of the abyssal clade have been delimited based on similar genetic distance values (Jones and Macpherson 2007; Dong et al. 2019). According to the original species descriptions (Marin 2020; Dong et al. 2021), spinulation on the carapace margins and relative width of the rostrum are different in both taxa. However, these morphological and genetic differences could be part of intraspecific variation and population genetic structure, as very few specimens have been analysed to date. More data, including the analyses of more specimens, would be desirable to solve this taxonomic problem.