Wise Old Octopus & Jellyfish

The common octopus is an extraordinary creature. It’s a molluscs – a relative of the slugs and snails you find in your garden, and along with the cuttlefish, squid and nautilus, belongs to a group of marine molluscs known as cephalopods. Literally translated the name means “head-footed”, and the bizarre-looking cephalopods certainly look as if their tentacle-like arms sprout straight from their large heads.

The common octopus has a worldwide distribution in tropical, sub-tropical and temperate seas. Here in Ireland it is approaching the north-eastern limits of it’s Atlantic range, and occures off the south and south-west coasts, and up the east coast as far north as Dublin Bay. The species may be extending its range northward as water temperatures rise through the effects of climate change.

Common octopuses live in coastal waters and the upper part of the continental shelf up to a maximum depth of about 150 metres (492 foot). Small specimens are sometimes found in deep rock-pools on the extreme low-shore, although they can be very difficult to spot given their exceptional ability to blend in with their surroundings.

This is a medium to large octopus that can reach lengths of over 1 metre (3.3 foot), but which is generally nearer the 60cm (c. 2 foot) mark when fully grown. It has a well developed head, large, complex eyes that give it excellent colour vision, beak-like jaws and eight muscular arms each lined with a double row of suckers. Although it can change both the texture and colour of its skin at will, it tends to be a mottled yellowish or greenish brown, and the skin of the body is generally covered in raised bumps or warts.

Octopuses are predatory, and actively hunt crustaceans and bivalve molluscs. They are mainly nocturnal, although they do occasionally emerge from their lairs for a daylight hunting sortie. To get about over short distances octopuses crawl along using their arms and suckers, but when they need to cover greater distances, or when speed is of the essence they use jet-propulsion. By contracting the muscular mantle an octopus can expel a jet of water in any direction it chooses through its funnel-like siphon, conveniently thrusting its body in the opposite direction.

Credit: Irelands Wildlife

This widespread jellyfish species is found in the Atlantic, Indian and Pacific oceans across a variety of climate zones. Optimum water temperature for the species is between 9 and 19 degrees Celsius, but it can tolerate a much wider temperature range from -6 degrees Celsius to as high as 31 degrees Celsius. Also known as the moon jelly and saucer jelly, this is the most common species of jellyfish in Irish waters. It mainly occurs near the coast, sometimes in massive numbers, and occasionally washes up on beaches.

The adult jellyfish consists of a translucent disc or saucer that is normally up to 250mm (10 inches) across, but which can reach a diameter of up to 400mm (16 inches). A variety of colourful body parts are visible through the disc, including four very prominent circular gonads arranged around the centre – these are typically mauve, violet, reddish, pink or yellowish in colour.

The disc itself is relatively thick at the centre, thinning markedly towards the outer edge, and is fringed by a ring of relatively short, hollow tentacles at the margins. These tentacles are used as a filtration net to snare small prey animals, and are armed with stinging cells called nematocysts. The four oral “arms”, that radiate from the mouth out towards the disc margins along the animal’s underside also carry a payload of stinging cells.

Credit: Irelands Wildlife