Ram's Horn Squid
Occurs in open ocean at tropical and temperate latitudes world-wide (WA, NT, QLD, NSW, VIC, TAS).Features:
This small squid reaches sizes of around 6 cm long. Its most distinctive feature is the coiled internal shell (known as a Ram's Horn shell) that commonly washes ashore after storms in east, west and northern Australia. The shell is around 2 cm in diameter and is a loose coil in a single plane. It contains internal chambers joined by a tube that contains a living strand of tissue known as the siphuncle. The whole squid has the shape of a short cylinder with two short fins on the tip of the body on either side of the internal shell. There are eight arms and two retractable feeding tentacles. The arms and clubs at the tips of the feeding tentacles have numerous tiny suckers, each armed with a horny, toothed rim. The live animal would hang down from the shell, the fins being parallel to the seafloor. The very tip of the body has a large light organ situated between the fins. Colour in life is blood red but this skin is often scraped off during capture in fishing nets, exposing the white muscle underneath.Ecology/Way of Life:
Ram's Horn Squids are little known creatures of open ocean. During the day, they concentrate in large schools at depths of around 600-700 metres. At night, they join the many planktonic creatures that undergo vertical migration, rising into shallower waters to feed under the cover of darkness. The internal shell is used for buoyancy control, functioning in the same way as the external shell of the chambered nautiluses. The internal chambers of the shell contain gas at low pressures and the volume of water in the chambers is adjusted to cancel out body weight. This squid is the only living cephalopod with an internal coiled shell. Its fossil relatives have provided insights into the many cephalopods that evolved from nautilus-like ancestors (with an external shell) to the cuttlefish and squid that have internal shells.
Little is known of the biology of this squid and none have ever been observed live in their natural environment. The light organ on the tip of the body is unusual in that it points upwards in the living animal. All other bioluminescent midwater creatures of the open ocean produce downward light to cancel out their silhouette from predators below.
The two lower arms of mature males have strangely spiked arm tips that may be used to transfer spermatophores to the female. The youngest animals captured were at depths of between 1000 and 1750 metres, leading some researchers to suggest that the females may lay their eggs in deep water, at the bottom of the continental slope. At these depths, the pressure on the shell is more than half a tonne.Interaction with Humans/Threats:
There is no known human harvest of this squid.Further Reading:
Norman, M.D. 2000. Cephalopods: A world guide. ConchBooks, Hackenheim, Germany.
Text and map by Mark Norman; photographs by David Paul.Sponsorship welcomed:
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