Subgenus (Cydippina) W. H. Dall, 1900
(3-4-4-0-24-14-1-24-2-0-0-0-0) Ref. Abbott, 1974 p 508 [see also as Genus] extenuata W. H. Dall, 1900 (3-4-4-0-24-14-1-24-2-1-0-0-0) Slender Macoma Ref. Abbott, 1974 p 508 Amer. Fish. Soc., 1988 p 41
(3-4-4-0-24-14-1-24-2-0-0-0-0) Ref. Abbott, 1974 p 508 [see also as Genus]
extenuata W. H. Dall, 1900 (3-4-4-0-24-14-1-24-2-1-0-0-0) Slender Macoma Ref. Abbott, 1974 p 508 Amer. Fish. Soc., 1988 p 41