Kalmar "nematode" tana nufin nau'in tsutsotsin tsutsa da ke cikin phylum Nematoda. Wadannan tsutsotsi suna da siffar dogayen su, siriri, siffa mai siffar siliki, tare da madaidaicin ƙarshen kai da wutsiya. Ana samun su a wurare daban-daban, ciki har da ƙasa, ruwa, da tsire-tsire, kuma yawancin nau'in nau'in parasitic ne, suna zaune a ciki ko a jikin wasu kwayoyin halitta. kowane nau'in tsutsotsi na phylum Nematoda. Wadannan tsutsotsi suna da mahimmanci a fannoni da yawa, ciki har da aikin noma, inda za su iya zama masu amfani (misali, a matsayin magungunan ƙwayoyin cuta na halitta) da kuma cutarwa (misali, a matsayin tsire-tsire). Ana kuma nazarinsu a fannin binciken likitanci da na halitta, domin wasu nau'in na iya haifar da cututtuka ga mutane da sauran dabbobi, yayin da wasu kuma suna da siffofi na musamman na halitta wanda ke sanya su kima ga binciken kimiyya.