Longosomatidae (= Heterospionidae) collected from abyssal depths of about 4150 m in the Peru Basin, eastern South Pacific, included 16 specimens of
Heterospio peruana sp. n., closely related to
H. sinica Wu & Chen, 1966, and one indeterminate specimen of another species. The species is characterized by a short branchiate thorax with 9 setigers with up to 4 or 5 pairs of branchiae, a midbody region with at least 7 strongly elongated setigers, and a short, inflated posterior region with 6 segments, first 5 of which setigerous. Setae of the thoracic region are exclusively capillaries; setae of elongated setigers form cinctures from setiger 10 and comprise aristate spines in addition to subuluncini-like capillaries from setiger 10 or 11; the last elongated setiger lacks aristate spines. The indeterminate specimen is an anterior fragment with 8 thoracic setigers and without modified setae (e.g., aciculars) or cinctures in midbody segments. Literature data on taxonomic characters of longosomatids are compiled.