- Arms and Web
- Length 220-290% of ML; formula II=III=IV>I except in late mature males where arms I are longest.
- Arm sucker rings with about 6-14 rounded or truncate teeth on distal and lateral margins, except in mature males where teeth are sharply pointed.
- Inner web virtually absent, outer web 3-8% length of longest arm.
- Club with suckers in 5-7 irregular rows on manus. Median suckers greatly enlarged, more than 4 times size of minute marginal suckers.
- Median, enlarged manus suckers with about 50-60 sharp, pointed teeth around entire margins.
- Buccal crown
- Buccal crown with 7 supports.
- Funnel organ
- Dorsal pad with strong, median ridge on each lateral arm, expanding posteriorly into broad flaps.
- Mantle and Skin
- Mantle skin and skin elsewhere covered with low, fleshy pads, giving overall rough appearance in large squid.
- Tubercules absent.
- Length 30-40% of ML; width 50-70% of ML.
- Compound photophores of large, uniform size on anterior 1/3 of ventral mantle.
- Compound photophores number usually 17 (rarely 16) around right eyelid.
- Arms IV with 3 longitudinal series on arm base.
- Reproductive system
- Males with paired genitalia and spermatophore organs.
- Length 5-6.1% of ML; sperm mass 35-46% of spermatophore length (SpL), cement body 10-21% of SpL, ejaculatory apparatus 34-49% of SpL with numerous loops.
- Mature males with each arm I modified as hectocotylus. Median 1/3-1/2 with greatly increased thickness, greatly expanded with large aboral keels and high protective membranes. Dorsal surfaces smooth, ventral surfaces papillated (see below). Distal half with pedicels of small suckers elongated to form palisades along arm margins. Only suckers on midportions of arms show noticeable enlargement.
- Ventral surface of modified arm I (hectocotylus) densely papillated.
Figure. Oral-lateral view of hectocotylus of S arcturi, arm I, 106 mm ML, 31° 51'N, 63° 44'W. Lateral view of papillated hectocotylus skin, same specimen. Drawing of papillation is from region indicated by arrow on drawing of hectocotylus above. Drawings from Voss et al. (1998).
The above information is from Voss (1969) and Voss, et al . (1998).