Brooding of egg masses by a squid in Japan is described. Brooding females were photographed in situ, and the females, their eggs, and their hatchlings were collected. The squid had all undergone gelatinous degeneration and swam slowly and continuously by undulating the fins and expelling water sporadically through the funnel. Eggs were held together by a dark, viscous material that formed a single-layer, sheet-like mass, from which hatchlings were seen to emerge. The annual appearance of brooding females in surface waters during spring suggests that they transport their egg masses from deep water to the surface before the eggs hatch. Genetic analyses identified the squid as Gonatus madokai (family Gonatidae), now the second gonatid and third squid known to brood.

Until 1991, squids were thought to spawn either by attaching egg capsules to solid substrates (nearshore species) or releasing free-floating eggs or egg masses (oceanic species). But that year, a diver off Rausu, Hokkaido, in northern Japan noticed something extraordinary--squid brooding egg masses attached to their arms (1). The squid measured about 60 cm in mantle length (ML) and were not identified to species level, but appeared to belong to the family Gonatidae, which comprises 16 known species in the North Pacific (2). Since then, the brooding squid have been observed annually in shallow waters off Rausu during mid-April to mid-June (K. Seki, pers. obs.). but have remained unidentified.

In 2005, similar brooding behavior was reported in squid off California (3). They were identified as Gonatus onyx Young, 1972, making this species the first documented to brood. Gonatus onyx, however, reaches a maximum ML of 15 cm (2), suggesting that the Japanese squid belong to a different species. Here we describe brooding by the squid in Japan and identify them as G. madokai Kubodera and Okutani, 1977, now the second gonatid squid known to brood.

A scuba diver, with a supporting crew in an outboard skiff, conducted a search for brooding squid during 17-21 May 2010 in nearshore waters off Rausu (44[degrees]00'45" N, 145[degrees]12'15" E). During the nearly 10 h of total dive time, five females (ML range: 38-43 cm) were observed at 5-20-m depth with eggs attached to their arms (Fig. 1A). Each squid was photographed in situ, and the squid and its eggs were collected by hand. Seawater temperature in the collection area ranged from 0 to 4 [degrees]C. Brooding females were also photographed and videotaped in the same area in May 2006 and April--May 2010 at 1-20-m depth.

Frozen tissue samples from two of the collected females were analyzed to identify the species. A 658-bp sequence of the mitochondrial cytochrome c...