(Edwards, 1929)
Body
The anterior and posterior parapods are separate and bear rows of claws. Anterior parapods without subapical combs and at most with small teeth Parapha cf. impensus ant pp 8. The anal segment is placed ventrally on the preanal segment, thus forming a more or less right angle with the body axis. The procercus is very small. (Wiederholm, 1983; Moller Pillot, 1984b; Saether and Wang, 1995).
Head
The head length is 0.25 - 0.27 mm. The smaller sickel shaped eye is placed ventrally of the larger one instead of distally Paraphaenocladius eye.
Antenna
The antenna consists of five segments, segment 1 is twice as long as wide and 2 x as long as the second segment.
Mentum
The mentum has two median teeth and 5 pairs of lateral teeth. The ventromental plates are lobed and do not cover teeth of the mentum. The beard is absent. The setae submenti are close to the mentum.
Labrum
The pecten epipharyngis consists of three short spines, SI is plumose and the labral lamellae are fused to form a plate with a smooth of serrated tip. The premandible has three apical teeth (Wiederholm, 1983; Moller Pillot, 1984b).
Mandible
The mandible has an apical tooth and 3 inner teeth. (Wiederholm, 1983).
Differential characteristics
The combination of two eyes on top of each other and the more or less right angle between the anal segment and the body axis are distinctive.
P. penerasus can be separated from the other Paraphaenocladius by 1st antennal segment 2x as long as the second and no additional combs on the anterior parapods.