The stalked crinoid fauna (Echinodermata) of the Molucca and Celebes Seas, Indonesia: taxonomic diversity and observations from remotely operated vehicle imagery
The seafloor of the Molucca and Celebes Seas, Indonesia, was investigated using a remotely operated vehicle with high-definition video during 18 dives to depths of 280 to 3200 m. Irregular slopes and rocky substrata supported abundant megabenthos, including stalked crinoids. Video zoomed on many individuals provided enough details to assign 770 stalked crinoids to major taxa and many to species level. These taxa included Guillecrinus neocaledonicus, Ptilocrinus cf. amezianeae, three species of Hyocrinus, an unknown phrynocrinid, Naumachocrinus hawaiiensis, Proisocrinus ruberrimus, Endoxocrinus alternicirrus, seven phenotypes in the Subfamily Metacrininae and one taxon of unknown affiliation. A novel observation of a juvenile Endoxocrinus included the attachment disk to a rocky surface. Taxa usually considered rare were well represented on hard substrata, thus expanding knowledge of their depth distributions. Mostly, stalked crinoids were sparsely distributed in low densities (to 186 individuals per km), except for occasional single-species clusters. Metacrinins and P. cf. amezianeae dominated at depths of 250–600 m, while E. alternicirrus and G. neocaledonicus were the most abundant species at a depth range of 1000–1400 m. The largest peak of species richness (with nine of the 17 taxa identified) occurred at 1000 to 2000 m. Many specimens altered their feeding posture with current intensity, but a balloon-like crown posture is common in low or non-existent currents. The postures of several mobile metacrinin individuals suggest an active role of arms and cirri in slow crawling movements. The possible origin of some taxa from either Gondwanaland or Eurasian margins is discussed using biogeographical and paleontological data. The location of the Wallace line cannot be delimited only using extant stalked crinoid distribution.