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Cephalopods


The cephalopods, which include the squid, octopus and cuttlefish are exclusively marine animals that are found from shallow water to the deepest parts of the oceans. The cephalopods belong to the Phylum Mollusca, which also includes the mussels, limpets, slugs and snails. The name cephalopod means head-foot, which reflects the evolution of the muscular foot of the ancestral mollusc into the head and arms of the modern cephalopod. In both squid and octopus a ring of eight muscular arms covered with suckers surrounds the mouth. Squid also have two extendible tentacles that are used to capture prey.

Cephalopods include the largest and probably most intelligent of the invertebrates, having well-developed senses and large brains. Captive octopuses have been shown to perform complex tasks and to possess short and long-term memory. Most cephalopods possess chromatophores, which are cells containing coloured pigments, that can be controlled by muscles to allow the squid or octopus to change colour for camouflage or communication. The majority of cephalopods also have an ink sac, which can be used to expel a cloud of dark ink to confuse predators.

Galiteuthis glacialis (27p stamp) is one of the most abundant and widely distributed of the Antarctic squids. It is a delicate mid-water (pelagic) species that lives from the surface down to around 1 km deep. The stamp depicts a juvenile squid (around 5 cm). Galiteuthis glacialis is eaten by many predators including light mantled sooty albatross, grey-headed albatross and white-chinned petrels.

The glacial squid Psychroteuthis glacialis (65p stamp) is an active, muscular species, which reaches a moderate size of 40 cm body length. The glacial squid is abundant throughout Antarctic waters and South Georgia is at the northern end of its range. This species is an important prey for many predators including elephant and Weddell seals, wandering and grey-headed albatross and emperor penguins.

The octopuses are divided into two groups, both of which are found in South Georgia waters. The incirrate octopods are the more familiar, shallow water forms and are represented by four species in South Georgia waters. These species are benthic (associated with the sea-floor) and feed on small invertebrates. Pareledone turqueti and Adelieledone polymorpha occur in shallow waters, whilst Thaumeledone gunteri (90p stamp) and Graneledone sp. are found deeper. Thaumeledone gunteri is a small species (less than 10 cm) living between 400 and 700 m all around South Georgia.

The cirrate octopuses are deep-water animals that possess numerous pairs of cirri (like thick hairs) on the arms and have large ear-like fins that have given them the name “Dumbo octopus”. In South Georgia waters the cirrates are represented by two species Stauroteuthis gilchristi and Opisthoteuthis hardyi. Stauroteuthis gilchristi (£1.10p stamp) is a mid-water species, living at depths of 700-1000 m around South Georgia. The arms of this species are connected by thin membranous tissue to form a web and the stamp depicts the octopus expanding the arms and web. This maybe a defensive posture, which makes the octopus appear bigger to possible predators.

Title: Cephalopods
Date of Issue: 7 April 2010
Country: Georgia
Denominations: 27p, 65p, 90p, £1.10

One comment

  1. Very, very nice issue…!!!!

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