Type species: Nais picta Dujardin, 1839, by subsequent designation.
Diagnosis. Body elongated, not divided into distinct regions; ventral groove and two lateral grooves present. Segments indistinctly annulated. Prostomium broadly rounded, palpode absent; subdermal eyespots; a pair of large, eversible nuchal organs divided into a ventral and a dorsal region. Branchiae entirely absent. Segmental lateral eyes present between parapodia. Parapodial lobes reduced, notopodial and neuropodial capillaries emerging from body wall. Interparapodial ciliated sensory pits present and a ventral lobe may be present. Noto- and neuropodial lappets absent. Noto- and neuropodial small fascicles of simple capillary chaetae. Pygidium with short anal funnel bearing marginal papillae and a pair of basal papillae.
Remarks. Hartman (1959) synonymized thirteen Polyophthalmus species with P. pictus (Dujardin, 1839). The author only considered P. striatus Kükenthal, 1887 as a valid and distinct species from P. pictus. Michaelsen (1892) described P. longisetosus based on a specimen collected in the pelagic environment with long capillaries on last five segments and it was most likely an epitoke. The species P. qingdaoensis Purschke, Ding & Müller, 1995 was recently described and distinguished from P. pictus mostly on the basis of the ultrastructure, size, position and number of the segmental eyes (ocelli), and number of anal papillae. Sene Silva (2007), in an unpublished Ph.D. dissertation, examined the type material of P. translucens Hartman, 1960 and suggested it should be synonymized with Ophelina abranchiata Stop-Bowitz, 1948. Purschke, Ding & Müller (1995) described Polyophthalmus qingdaoensis based on ultrastructural differences of the segmental eyes and discussed that several Polyophthalmus species synonymized with P. pictus could actually be valid. Until now, three species are considered as valid: P. pictus, P. qingdaoensis, and P. translucens (Blake & Maciolek 2016a). A taxonomic revision of the P. pictus species complex would be desirable including intra- and interspecific variability but also molecular data, whenever possible. There are very few morphological features and body pigmentation has been the main character used to separate species. However, this feature seems to be variable among populations and the pigmentation can also fade in preserved material. The segmental origin of the lateral eyes and its extent in segments, length of capillaries on anterior and posterior end, number and types of capillaries per parapodium, parapodial structures, and number of pygidial papillae should also be comparatively examined.