Sensu Schmid, 1993 (possibly T. duodinaria Kieffer, 1922)
Body
Medium sized larvae. The body with stout setae about as long as the segment. The anterior and posterior parapods are separate and bear rows of claws (Schmid, 1993).
Head
Antenna
The antenna consists of five segments. The blade reaches the tip of the 3th antennal segment. Lauterborn organs are conspicuous (Schmid, 1993).
Mentum
The mentum has one median tooth and 5 pairs of lateral teeth Tvetenia sp-A mentum. The ventromental plates are weak. The beard is absent.
Labrum
The pecten epipharyngis consists of three scales, SI is plumose Tvet discolor S1 pict and the premandible has one apical tooth (Schmid, 1993).
Mandible
The mandible has an apical tooth and 5 pair of inner teeth. The mola with 3 spines (Schmid, 1993).
Differential characteristics
Tvetenia can be identified by the stout body setae Tvet discoloripes body setae, mentum with 5 pairs of lateral teeth Tvet discoloripes mentum, weak ventromental plates and SI plumose. Tvetenia differs from Eukiefferiella by having long stout body setae.
Tvetenia sp. a can be separated from the other Tvetenia species by the single median mental tooth Tvetenia sp-A mentum.