A.蟲(chóng)體長(zhǎng)管形,由頭及若干形狀相似的體節(jié)組成。頭部有觸角l對(duì),體節(jié)除前3節(jié)外,每節(jié)有足2對(duì)
B.蟲(chóng)體分頭、胸、腹三部,有觸角l對(duì),足3對(duì),有翅或無(wú)翅
C.蟲(chóng)體分頭胸部及腹部,或頭胸腹融合為一體,有足4對(duì),無(wú)觸角,無(wú)翅
D.蟲(chóng)體分頭胸部和腹部,有觸角2對(duì),步足5對(duì),多數(shù)種類水生
E.蟲(chóng)體窄長(zhǎng),背腹扁,由頭及若干形狀相似的體節(jié)組成。頭部有觸角l對(duì)。體節(jié)除后2節(jié)外,每節(jié)有足1對(duì)。第1對(duì)足變形為毒爪