A Redescription and Biological Characteristics of Octopus longispadiceus (Sasaki, 1917) in the Western Part of the Sea of Japan

Abstract

An octopus collected by a bottom trawl survey off Tajima Region in the western part of the Sea of Japan, was identified as Octopus longispadiceus (Sasaki, 1917). A total of 506 specimens were examined either in raw, defrosted or formalin fixed conditions. Both females and males were collected from depths of 175 m to 300 m, and mature individuals appeared all year round. The sex ratio is nearly 50 %. The maximum size is 458 mm in TL(total length) in males and 485 mm in females in raw condition. This species is mediumsized and mature at 240 mm in TL in males and 265 mm in females. The mantle surface is generally smooth. The dorsal mantle length is about 25 % of TL. The mantle opening extends about half of the body circumference. The funnel organ is thickly W-shaped with a long central ramus in formalin fixed condition. The total number of gill lamellae is 20-23. The arms are slender, with a formula of I>II>III>IV, and the longest arm is about 75 % of TL. Suckers are biserial, about 130 in number on arm I of a male specimen of 300 mm in TL. Males have enlarged suckers at 15-30th from the base on all arms. The right third arm in mature males is hectocotylized and longer than the left third arm. The hectocotylus is slenderly conical and of about 6 % of TL. The terminal organ is crescent-shaped in raw condition. The maximum length and diameter of the spermatophore are 90 mm and 1.4 mm, and those of the egg are 22 mm and 9 mm, respectively. An ovary posesses 30 to 50 eggs. Judging from egg size, newly hatched juveniles crawl on the seabed, with no planktonic phase.