a class of Annelida or in former classifications an order of Chaetopoda that comprises chiefly marine annelid worms usually having paired setate appendages on most segments, a differentiated head with eyes, tactile processes and bristles, and chitinous jaws and being distinguished from the related oligochaete worms by possession of separate sexes and by a complex life history with a free-swimming trochophore larva, hrl eristunud pea-, kere- ja sabapiirkonnaga ning paljudest segmentidest koosneva (metameerse) saleda kehaga rõngusside klass; üle 6000 liigi... Enamik hulkharjasusse elutseb meredes., classe d'annélides marines ? nombreuses soies latérales, comprenant notamment la néréide, l'arénicole