The lugworms of the cold temperate waters of the Southern Hemisphere all belong to the genus Abarenicola. This genus falls naturally into two sections, whose members respectively possess and lack statocysts.
The cysted section is confined to the Southern Hemisphere. Its component forms have hitherto been described either as assimilis (Ehlers) or as assimilis var. affinis (Ashworth). This, however, is an oversimplification; the so-called variety includes in fact a number of distinct forms.
The characters which are useful in separating the forms are described and discussed. In particular, it is argued, contrary to the views of previous authorities, that valuable taxonomic information can be got from the nature of the statoliths in the cysted forms.
According to the revised classification here presented, there are three species of cysted Abarenicola:
(1) Abarenicola assirnilis (Ehlers) with five subspecies, assirnilis from Magellan Strait, Beagle Channel and South Georgia, brevior subsp. n. from Magellan Strait, Beagle Channel and the Falkland Islands, insularurn subsp. n. from Kerguelen, Macquarie, Auckland and Campbell Islands, devia subsp. n. from Victoria, Australia and New Zealand and haswelli subsp. n. from Tasmania. There are indications that additional local forms of this widely distributed species could be defined, given larger supplies of material.
(2) Abarenicola affinis (Ashworth) with four subspecies, affinis from New Zealand, clarki subsp. n. from Tasmania, africana subsp. n. from South Africa, and chiliensis subsp. n. from central Chile.
(3) Abarenicola gilchristi sp. n. from South Africa.
The cystless section of the genus is confined to the Northern Hemisphere. except for the species pusilla (Quatrefages) from central Chile. The only two available specimens of this species are redescribed, and reasons are given to explain why representatives of several other species have been incorrectly recorded as pusilla from time to time.
The distributions of the forms are correlated with those of two of the coastal water types recently defined by Knox. Three nearly related forms (Abarenicola assirnilis assirnilis, A. a. brevior, and A. a. insularurn) occur in Sub?antarctic Cold Temperate water, except for a single aberrant individual of A. a. assirnilis from Antarctic water. The other forms occur in the rather warmer and more saline Cold Temperate Mixed water.
Temperature appears to be the most important factor controlling the geographical distribution of the caudate Arenicolidae.
Southern Ocean: Antarctic and Subantarctic marine regions together (= E+W+S+M(+T))