Spent females of deepwater squid Galiteuthis glacialis under the ice at the surface of the Weddell Sea (Antarctic)

Abstract

Two large (dorsal mantle length 42.5 and 47.5 cm), mated spent females of circum-Antarctic bathypelagic cranchiid squid Galiteuthis glacialis were caught early in March 1992 at the surface of the ice hole in the western Weddell Sea over depths 1915-1920 m by the team of the U.S.A.-Russian Ice Station Weddell-I. The structure of the reproductive system of adult females is described for the first time in detail.

Both were gelatinous, devoid of tentacles, with empty or almost empty stomachs. The empty spermatangia (sperm reservoirs of spermatophores) 30-35 mm in length were distributed in the mantle tissues parallel to the mantle surface and to each other in the dorso-anterior part of the mantle: 13 in one female, parallel to the body axis, and 20 in the other, parallel (13) or perpendicular (7) to the body axis. In the latter case, they represented probably two mating events. The spermatangia lay nearer to the inner than the outer mantle side and opened by a round window on the inner side; the skin with chromatophores above them remained intact. The spermatozoa had one flagellum and rod-like heads, length 5.0-5.3 μm, width 1.2-1.5 μm. The most characteristic features are: a very simple type of blood vessel branching making each micro-gonad currant-like, not grape-like; a very compact disposition of oviducal, nidamental glands and gill, forming a united complex located on both sides of the mantle cavity; and an ovary connected by mesentery along all its length with the continuation of the stomach from the caecum to the end of the gastrogenital ligament. Only immature degenerating trophoplasmatic oocytes, length 0.9-1.4, av. 1.0-1.2 mm, were contained in ovaries; only one mature egg (length 3.3 mm, width 2.4-2.5 mm) was found in each female. The absence of oocytes <0.9 mm and 1.5-3.2 mm indicates that the maturation of oocytes proceeds rather synchronously, one large portion of eggs (some tens of thousands) matures in a short time while others degenerate. The residual fecundity is assessed to be approximately 20,000 eggs.

It is hypothesized that mating occurs shortly before spawning and that mature males do not undergo gelatinous degeneration and do not lose tentacles. Spermatophores are placed on the inner side of the female's mantle with the aid of the male's tentacles and/or arms (less probably by the penis), but the exact mode of implantation is unclear. Spawning probably occurs at depths of adult habitat (approx. 500±2500m), may be multiportional but short; the exhausted female loses neutral buoyancy, rises to the surface and dies. Rising to the surface after spawning is a common feature of females of many meso- and bathypelagic squids undergoing gelatinous degeneration during maturation (Onychoteuthidae, Gonatidae, Histio-teuthidae, Cranchiidae, etc.) and may explain the common occurrence of large deep-water squids in the stomachs of seabirds, including those incapable of diving, and marine mammals.