S.Georgia : South Georgia and the South Sandwich Islands -Cephalopods
Submitted by Falkland Islands News Network (Juanita Brock) 13.03.2010 (Article Archived on 27.03.2010)
Dr Martin Collins writes about Cephalopods depicted on stamps.
South Georgia and the South Sandwich Islands -Cephalopods
Text by Dr Martin Collins.
Cephalopods - squid, octopus and cuttlefish, are exclusively marine animals that are found from shallow water to the deepest parts of the oceans.
Belonging to the Phylum Mollusca, including 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.
Including the largest and probably most intelligent of the invertebrates, Cephalopods have 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. Most cephalopods also have an ink sac, which can be used to expel a cloud of dark ink to confuse predators.
All cephalopods can move by jet propulsion, contracting the muscular body to expel water through the funnel, but as it is a rather inefficient mode of transport and most squid and octopus only utilise it when catching prey or escaping possible predators. Squid and cirrate octopods use their tail fins for more routine swimming.
Having short lives, most cephalopods, grow rapidly, reproducing once and then dying. In many tropical and temperate species the life cycle is completed within a year or less. In the cold waters of the Southern Ocean and the deep-sea, growth rates may be slower and longevity greater, but the majority of species spawn once and die. Eggs are either laid on the sea-floor (benthic) or drift in the ocean (planktonic) and hatch into small versions of the adult with no true larval stage.
Cephalopods usually eat small fish and crustaceans, which are caught by the arms and (in squid and cuttlefish) retractile tentacles. Prey needs to be thoroughly broken down before being swallowed, as the oesophagus passes through the middle of the brain. To achieve this the mouth includes a tough beak, similar in shape to that of a parrot, which is used to break up prey before it is swallowed.
Many larger animals, such as fish, seals, penguins, albatross and whales, eat cephalopods. The soft tissue of the squid or octopus is digested quickly, but the tough beaks are almost indigestible and accumulate in great numbers in the stomachs of predators such as sperm whales. Each species of squid or octopus has a unique shaped beak, so the beaks found in predator stomachs can be used to indicate which species was eaten.
Globally the cephalopods include around 650 species. The waters of South Georgia are home to 13 species of squid and 6 species of octopus. South Georgia squid range in size from small species such as Bathyteuthis abyssicola, which reach a maximum body size of 8 cm, to the Antarctic colossal squid (Mesonychoteuthis hamiltoni) (depicted on the sheetlet), which is thought to grow up to 3 m in body length and perhaps a tonne in weight.
The colossal squid is probably the largest living invertebrate and has the largest eyes, at around 30 cm in diameter, of all animals. Very few colossal squid have been caught. The largest specimen was caught in the RossSea in February 2007 and weighed 500 kgs, but the beak was considerably smaller than some that have been found in the stomachs of sperm whales, indicating that they can grow considerably bigger. A fishing vessel at South Georgia caught a specimen in July 2005, but only the head, arms and tentacles were recovered, which weighed 40 kgs, and are now preserved in the Natural History Museum in London. Colossal squid inhabit deep-waters throughout the Southern Ocean, where they are important prey of sperm whales. The colossal squid is a fearsome looking animal, not only because of its extremely large size, but the two long tentacles are armed with suckers and large rotating hooks that will grip prey. Scars from colossal squid hooks and suckers are frequently seen on the head and body of sperm whales, indicating that colossal squid put up quite a fight when attacked by a whale(£2 Souvenir Sheet). Little is known about the biology of the colossal squid, but they are thought to eat deep-sea fish and crustaceans.
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. The suckers of the closely related Stauroteuthis syrtensis can produce light (called bioluminescence) and it is likely that the suckers of S. gilchristi have similar capacity. This bioluminescence may function to attract prey or for communication with potential mates.
Text by Dr Martin Collins.
Designer Ross Watton
Printer BDT International
Process Stochastic lithography
Stamp size 36 x 36mm
Perforation Gauge 13.5 per 2 cms
Sheet layout 50 (2 x 25)
Souvenir Sheet Stamp size 51.46 x 51.7mm
Souvenir Sheet size 80 x 80mm
Perforation Gauge 13 per 2cm
Release date 7 April 2010
Production Co-ordination Creative Direction (Worldwide) Ltd
We acknowledge with thanks the help and assistance of Dr Martin Collins,
Dr Uwe Piatkowski and Dr Louise Allcock.
For additional information, please contact John Smith,
Pobjoy Mint Ltd, Tel: (44) 1737 818181 Fax: (44) 1737 818199