D 9; A 13; P110; P2 7; GR 8+1+10=19.
HL 29.9% of SL; ED 5.8; BD 53.6; SN 9.0; IO 2.5; UJ 24.9; P1L 20.8; P2L 4.8.
Body deep and extremely compressed; body depth 1.9 in SL. Mouth large and vertical. Posteriorly located teeth on maxilla pointed forward. Upper preopercular spine well developed. Short post-abdominal spine present. Supra-abdominal, preanal, anal and subcaudal groups of photophores nearly in a straight and continuous line; abdominal photophores 13; supra-abdominal + preanal + anal + subcaudal photophores 20; dorsal blade present and well developed in front of dorsal fin. Abdominal margin under supra-abdominal photophores keeled and semi-translucent. Formalin fixed specimen brownish black dorsally, pure black ventrally; upper part of photophores yellowish white, middle part bluish black.
Distribution:
Argentine Patagonia, found only in the Atlantic (Schultz, 1964), mesopelagic (Norman, 1930).
Remarks:
Distinguished from the closely related species. A. Affinis Garman, 1899 by the following characters: A. affinis has a rather slender body (body depth 2 1/4 to 2 1/3), dorsal blade lower than that of A. gigas (Schultz, 1964). It is somewhat curious that any fishes of Sternoptychidae have not been recorded from the waters off Argentina so far (Norman, 1937a; Ringuelet and Aramburu, 1960; Menni, Ringuelet and Aramburu, 1984). So, this is the first record of Argyropelecus gigas simultaneously as well as the family Sternoptychidae to the Argentine ichthyofauna. However, the eastern South Pacific survey by R/V Anton Brunn recorded 6 species of Argyropelecus; A. gigas, A. aculeatus, A. affinis, A. hemigymnus, A. sladeni, and A. olfersi (Craddock and Mead, 1970).