Practice question

Monoplacophora is small class of deep-sea molluscs considered living fossil because single dredged living species Neopilina galatheae recovered in 1952 off Costa Rica, previously known only from Cambrian-Devonian fossils. Exhibits cap-shaped single shell, serially repeated gills with five to six ctenidia, eight pairs of foot retractor muscles, two atria and nephridia suggesting traces of metamerism bridging annelid segmentation and molluscan organization, intermediate between polyplacophorans and conchiferans. Gastropoda snails sluggish crawl, Polyplacophora eight plates, Cephalopoda advanced brains. Neopilina survival demonstrates evolutionary stasis and primitive molluscan body plan persistence over geological time.