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Cranchia scabra (Family Cranchiidae)

Glass Squid

Distribution:

Tropical and subtropical waters of the world (WA, NT, QLD, NSW, VIC).

Features:

A soft-bodied jelly-like squid of open ocean with a body that reaches around 15 cm long. It has a spherical to oval body with a small head and short arms. The whole animal is completely transparent except for the eyes and the vertical cylindrical liver. Up to 14 small light organs are present on the underside of the eyes. Mature females have light organs on the tips of the arms. Small rounded fins are present at the rear of the body. There is no shell. There are eight arms and two extendable feeding tentacles. The arms and tips of the feeding tentacles have suckers armed with horny, toothed rims. The distinctive feature of this squid is the numerous small cartilage tubercles covering the body.

Ecology/Way of Life:

This sluggish transparent squid lives hanging midwater in open ocean. It maintains buoyancy by holding a special jelly-like layer of skin on the outside of its body, using the cartilage tubercles to attach this skin. This skin layer contains ammonia solution making it lighter than seawater and providing enough lift to allow this animal to be suspended inactive in the water. Other glass squids obtain neutral buoyancy by having a special bladder of ammonia solution within the gill cavity (see photo of Megalocranchia fisheri from Hawaii).

This squid has a unique defence. If threatened it pulls its head, arms and feeding tentacles inside its gill cavity and inflates itself into a ball. This may be a similar strategy to that used by pufferfishes, making it harder to eat for small-mouthed predators.

The light organs on the underside of the eyes are fuelled by chemical reactions. The light is used to hide the silhouette of the eyes from predators below.

Little is known of reproduction. Adult females have light organs on the ends of their arms that may be used to attract males. Males attach sperm packets to the outside of the female's body. Females probably release transparent jelly-like masses of eggs that float midwater.

Members of this squid family are eaten by toothed whales, lancetfish, tuna, seabirds, sharks and dolphins. Some species get very large, greater than two metres long.

Interaction with Humans/Threats:

There are no commercial harvests of this deep-sea squid. Its soft flesh and high ammonia content makes it unsuitable for human consumption.

Further Reading:

Tree of Life website

Norman, M.D. 2000. Cephalopods: A world guide. ConchBooks, Hackenheim, Germany.

Acknowledgments:

Text by Mark Norman, photographs by Dick Young.

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