Family: Circumferential paratene of mono- or dikinetids; not cirral or bristle-like.
Genus: Paratene makes nearly closed circle around body; ventral kinety often present (Illustrated Guide, 1985).
Ovoid to spherical; adoral zone very conspicuous two to four conspicuous sickle-form frontal membranellae, adoral membranellae extend down cytopharynx; no body bristles or cirri (Kudo, 1966). Body conical, ovoid or elongate posteriorly; somatic cilia absent; AZM composed of large membranelles which emerge from the peristome and encircle the apex of the cell; polysaccharide plates or platelets may conver and strengthen the posterior portion of the body (Carey, 1992).
Strombidium sulcatum Claparède and Lachmann, 1858: Ovoid, 60 μm long; anterior bluntly pointed; AZM extends 1/3 the body length; posterior rounded; the region of cortical platelets from the equatorial cleft to posterior end; a band of trichites presents in this region (Carey, 1992).
Strombidium viridae Stein, 1867 (Syn. Strombidium nasutum Smith, 1897): Conical, with a well-developed peristomial collar; rounded posterior; 80 μm long; bundles of trichites make an equatorial band; posterior covered with polygonal cortical platelets; macronucleus vermiform (Carey, 1992).