A new genus of the subfamily Pontoniinae, Ancylomenes gen. nov. is established for the ‘Periclimenes aesopius species group’ of the genus Periclimenes Costa. The new genus is distinguished from other genera of Pontoniinae on account of the strongly produced inferior orbital margin with reflected inner flange, and the basicerite of the antenna armed with an angular dorsal process. Fourteen species have been previously recognized as belonging to the ‘P. aesopius species group’. One Eastern Pacific species (P. lucasi Chace), and two Atlantic species (P. anthophilus Holthuis & EiblEibesfeldt, and P. pedersoni Chace) are now also placed in Ancylomenes gen. nov. A further new species associated with a cerianthid sea anemone, A. luteomaculatus sp. nov. is described and illustrated on the basis of specimens from the Ryukyu Islands, southern Japan, and Philippines. A key for their identification, and a checklist of the species of Ancylomenes gen. nov. are provided.

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A new genus, Manipontonia, is designated to include Periclimenes psamathe (De Man, 1902), on account of its peculiar morphology, with the combination of a long and slender rostrum with ventral margin unarmed, the proximal rostral dorsal teeth and epigastric tooth having fine ventral denticulations and endopod of male first pleopod with the appendix interna terminally with few terminal cincinnuli, which distinguishes this genus from all other species of Periclimenes, and the other genera of the Pontoniinae. The report includes some new host records: Acabaria robusta (Shann) [Gorgonacea]; Dendronephthya cf. decussata Utinomi [Alcyonacea].

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Sexual dimorphism in body size and weaponry was examined in two Cinetorhynchus shrimp species in order to formulate hypotheses on their sexual and mating systems. Collections of Cinetorhynchus sp. A and Cinetorhynchus sp. B were made in March, 2011 on Coconut Island, Hawaii, by hand dipnetting and minnow traps in coral rubble bottom in shallow water. Although there is overlap in male and female size, some males are much larger than females. The major (pereopod 1) chelipeds of males are significantly larger and longer than those of females. In these two Cinetorhynchus species, males and females have third maxillipeds of similar relative size, i.e., those of males are not hypertrophied and probably not used as spear-like weapons as in some other rhynchocinetid (Rhynchocinetes) species. Major chelae of males vary with size, changing from typical female-like chelae tipped with black corneous stout setae to subchelate or prehensile appendages in larger males. Puncture wounds or regenerating major chelipeds were observed in 26.1 % of males examined (N = 38 including both species). We interpret this evidence on sexual dimorphism as an indication of a temporary male mate guarding or “neighborhoods of dominance” mating system, in which larger dominant robustus males defend females and have greater mating success than smaller males. Fecundity of females increased with female size, as in most caridean species (500–800 in Cinetorhynchus sp. A; 300–3800 in Cinetorhynchus sp. B). Based on the sample examined, we conclude that these two species have a gonochoric sexual system (separate sexes) like most but not all other rhynchocinetid species in which the sexual system has been investigated.