Ehlers, 1864
The main diagnostic character of the members of this family is a single pair of large and complex eyes. Prostomium small with four, five or six antennae. Three, four or five pairs of tentacular cirri and an eversible proboscis, with short papillae or long terminal horns. Body slender and elongate with numerous segments, almost always broken into fragments in zooplankton samples. Parapodial glands are present, laterally, dorsally or ventrally between the parapodial lobes on most body segments; these are referred to as "segmental glands". The glands range in size from small oval projections in some species to elongated kidney-shaped structures extending from the dorsal to the ventral cirrophore. A pair of anal cirri is present, but it is usually difficult to see due to body damage. It is assumed by the presence of the eversible muscular proboscis, sometimes provided with a pair of lateral projections for grasping prey, that alciopid polychaetes are predators; however, the nature of the prey is unknown (Day, 1967). By the presence of this structure, their complex eyes, and their behavior, Uschakov (1972) suggested they are active predators. Rice (1987) describes the behavior, in situ, of some species of this family from the Bahama Islands in the Western Atlantic Ocean, and gives new information on morphology using electron microscopy and discusses aspects of reproduction, and systematics. He added two new taxonomic characteristics (sperm type and body transparency), and constructed an evolutionary tree of the alciopid polychaetes. In general, he agrees with Støp-Bowitz (1949) in the generic relationships, dividing the genera of this family into two somewhat distinct groups on the base of the type of setae.
In addition to those included in the key, alciopids reported from the South Atlantic include three more species described recently from the Gulf of Guinea by Dr. Støp-Bowitz (1991), most of them with only one specimen: Pseudalciopa modesta Støp-Bowitz, 1991, Rhynchonerella longicirrata Støp-Bowitz, 1991, and Vanadis brevirostris Støp-Bowitz, 1991.
Ten genera:
Genus Alciopa Audouin and Milne Edwards, 1833
Alciopa reynaudi
Genus Alciopina Claparède and Panceri, 1867
Alciopina parasitica
Genus Krohnia Quatrefages, 1866
Krohnia lepidota
Genus Naiades Delle Chiaje, 1830
Naiades cantraini
Genus Plotohelmis Chamberlin, 1919
Plotohelmis alata
Plotohelmis capitata
Plotohelmis tenuis
Genus Pseudalciopa Støp-Bowitz, 1991
Genus Rhynchonerella Costa, 1864
Rhynchonerella angelini
Rhynchonerella bongraini
Rhynchonerella gracilis
Rhynchonerella moebii
Rhynchonerella petersi
Genus Torrea Quatrefages, 1850
Torrea candida
Genus Vanadis Claparède, 1870
Vanadis antarctica
Vanadis crystallina
Vanadis formosa
Vanadis longissima
Vanadis minuta
Vanadis studeri
Vanadis tagensis
Vanadis violacea
Genus Watelio Støp-Bowitz, 1948
Watelio gravieri