Marrus orthocanna
Encyclopedia
Marrus orthocanna is a species
of pelagic
siphonophore, a colonial animal
composed of a complex arrangement of zooid
s, some of which are polyp
s and some medusae
. It lives in the Arctic
and other cold, deep waters, swimming independently in mid-ocean.
. Other zooids in this region undertake digestion and assimilation of food items. Reproductive medusae are found among the polyps in the siphosome and also various other specialised zooids. The various forms are all arranged in a repeating pattern.
in the mesopelagic zone of the Arctic Ocean
, the north west Pacific Ocean
, the Bering Sea
, the Sea of Okhotsk
, the north Atlantic Ocean
and the Mediterranean Sea
. It is found at depths ranging between 200 and 800 m (656.2 and 2,624.7 ft). The greatest depth at which it has been observed is about 2000 m (6,561.7 ft). At these depths the temperature is about 4 °C (39.2 °F), hardly any light penetrates from the surface and human observation is limited to what can be seen from submersible craft.
and its diet is thought to consist mainly of small crustacean
s such as decapods
, krill
, copepod
s and mysids.
This colonial animal arises from a single fertilised egg. The protozooid that develops from this subsequently bud
s to form the other members of the colony which are thus genetically identical. The protozooid first thins and elongates, the middle section becoming the stem of the colony. The pneumatophore forms at the opposite end to the mouth. Next a growth zone on the thin stem forms and budding occurs with the formation of the nectophores. As the stem continues lengthening, further zooids develop above these. Another growth zone sees the development of the siphosome and the continuing elongation of the stem carries these zooids down with it. The division of labour between the zooids is an evolutionary advance in the constant struggle for existence in the deep sea. Such organisms as Marrus orthocanna blur the boundaries between the individual polyp and the whole colonial organism. Each cannot exist without the other.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of pelagic
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
siphonophore, a colonial animal
Colony (biology)
In biology, a colony reference to several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defense or the ability to attack bigger prey. Some insects live only in colonies...
composed of a complex arrangement of zooid
Zooid
A zooid or zoöid is a single animal that is part of a colonial animal. The zooids can either be directly connected by tissue or share a common exoskeleton...
s, some of which are polyp
Polyp
A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are approximately cylindrical in shape and elongated at the axis of the body...
s and some medusae
Medusa (biology)
In biology, a medusa is a form of cnidarian in which the body is shaped like an umbrella, in contrast with polyps. Medusae vary from bell-shaped to the shape of a thin disk, scarcely convex above and only slightly concave below...
. It lives in the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
and other cold, deep waters, swimming independently in mid-ocean.
Description
Like other siphonophores, Marrus orthocanna is a colony composed of a number of specialised zooids linked together by a long stem. At the front is the pneumatophore, an orange-coloured, gas-filled float. Behind this is the nectosome, a region where there are a number of translucent nectophores with red, unlooped radial canals. These are bell-shaped medusae specialised for locomotion. When they contract, water is expelled which causes the colony to move. Their contractions are coordinated which enables the animal to swim forwards, sidewards or backwards. The remaining region is the siphosome. Most of the zooids here are polyps, specialised for collecting food. They do this for the whole colony, spreading their single long tentacles in the water to snare preyPredation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
. Other zooids in this region undertake digestion and assimilation of food items. Reproductive medusae are found among the polyps in the siphosome and also various other specialised zooids. The various forms are all arranged in a repeating pattern.
Distribution and habitat
Marrus orthocanna occurs pelagicallyPelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
in the mesopelagic zone of the Arctic Ocean
Arctic Ocean
The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...
, the north west Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, the Bering Sea
Bering Sea
The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves....
, the Sea of Okhotsk
Sea of Okhotsk
The Sea of Okhotsk is a marginal sea of the western Pacific Ocean, lying between the Kamchatka Peninsula on the east, the Kuril Islands on the southeast, the island of Hokkaidō to the far south, the island of Sakhalin along the west, and a long stretch of eastern Siberian coast along the west and...
, the north Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
and the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
. It is found at depths ranging between 200 and 800 m (656.2 and 2,624.7 ft). The greatest depth at which it has been observed is about 2000 m (6,561.7 ft). At these depths the temperature is about 4 °C (39.2 °F), hardly any light penetrates from the surface and human observation is limited to what can be seen from submersible craft.
Biology
Marrus orthocanna can be several metres long and the tentacles can extend fifty centimetres on either side. It moves forward intermittently before pausing to put out its "fishing lines", ready to ensnare passing creatures. It is a carnivoreCarnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
and its diet is thought to consist mainly of small crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s such as decapods
Decapoda
The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...
, krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
, copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s and mysids.
This colonial animal arises from a single fertilised egg. The protozooid that develops from this subsequently bud
Budding
Budding is a form of asexual reproduction in which a new organism grows on another one. The new organism remains attached as it grows, separating from the parent organism only when it is mature. Since the reproduction is asexual, the newly created organism is a clone and is genetically identical...
s to form the other members of the colony which are thus genetically identical. The protozooid first thins and elongates, the middle section becoming the stem of the colony. The pneumatophore forms at the opposite end to the mouth. Next a growth zone on the thin stem forms and budding occurs with the formation of the nectophores. As the stem continues lengthening, further zooids develop above these. Another growth zone sees the development of the siphosome and the continuing elongation of the stem carries these zooids down with it. The division of labour between the zooids is an evolutionary advance in the constant struggle for existence in the deep sea. Such organisms as Marrus orthocanna blur the boundaries between the individual polyp and the whole colonial organism. Each cannot exist without the other.
External links
- Physonect siphonophore poster, NOAA Office of Ocean Exploration