An overview of the specific diversity in the genus Cystiscus Stimpson, 1865 and the description of 27 new Cystiscus species (Muricoidea: Cystiscidae) from the Walters Shoal, southwestern Indian Ocean

Abstract

The Cystiscus fauna collected on the Walters Shoal by the 2017 MNHN/IRD Expedition is revised on the ground of shell morphology. Twenty-nine different species are recognized, 27 of them being formally described as Cystiscus subcylindricus, sp. nov., C. triplicatus sp. nov., C. herberti sp. nov., C. inflatus sp. nov., C. stimpsoni sp. nov., C. pyriformis sp. nov., C. harpaeformis sp. nov., C. laurae sp. nov., C. robustus sp. nov., C. minimus sp. nov., C. ovoides sp. nov., C. mamillatus sp. nov., C. angustus sp. nov., C. profundus sp. nov., C. granum sp. nov., C. dentiferus sp. nov., C. alatus sp. nov., C. apertus sp. nov., C. contortus sp. nov., C. sinuosus sp. nov., C. pupoides sp. nov., C. lussii sp. nov., C. smithi sp. nov., C. serratus sp. nov., C. lachrymaformis sp. nov., and C. quinqueplicatus sp. nov. Among the 27 described species, 25 of them are only known from their holotype, one paratype from the type station is reported for C. subcylindricus, and two conspecific specimens collected from a non-type station are reported for C. lussii. Eight morphs represented by one or two shells are tentatively ascribed to some of the 27 recognized species. Among the 29 recognized species, 28 of them are found at bathyal levels, and only one of them (C. quinqueplicatus) was collected at a reef level, so the Cystiscus fauna of the Walters Shoal is characterized as bathyal fauna. From the fact that any other Cystiscus assemblage was ever studied from the bathyal of the Indo-Pacific Province, no direct comparison is made with external items, and the Cystiscus species of the Walters Shoal are only compared to each other.