Psammechinus miliaris
Encyclopedia
Psammechinus miliaris is a species
of sea urchin
in the family
Parechinidae
. It is sometimes known as the green sea urchin or shore sea urchin. It is found in shallow areas of the eastern Atlantic Ocean
and the North Sea
.
is globular, somewhat flattened dorso-ventrally, and up to five centimetres in diameter. It is covered in short, equi-length robust spines. The test and spines of shallow water specimens are purplish-brown but specimens from deeper water have a greenish test and pale coloured spines with purple tips. If individuals are transferred from one depth range to another, they retain their original colouration in their new location. On each ambulacral plate there are three pairs of tubercles each with a spine attached, the central one being a primary spine. On the ventral side, the orifices are relatively small and the buccal membrane is closely packed with thick plates with many pedicellariae but no spines. The globiferous pedicellariae are numerous but small and the tridentate pedicellariae are stout with broad blades.
south to Morocco
, but not in the Mediterranean Sea
. It is particularly common in the North Sea. It is mostly a littoral species but can be found from low tide mark down to a depth of one hundred metres. It is often found on or under Saccharina latissima, a large brown seaweed with which it shares its range. It occurs in a range of other habitats including under boulders and rocks, among seaweed, on rough ground such as oyster
banks, in burrows in gravelly sediments and on the rhizome
s of Zostera marina
in seagrass
meadows. The larva
e often settle onto man-made structures such as ropes close to aquaculture
facilities.
and feeds on marine worms, hydroids
, small crustacean
s, molluscs
, diatom
s, macroalgae and detritus
. It eats both fresh and rotting kelp (S. latissima) but the former is more difficult to digest and takes longer to pass through the gut. It is effective at removing fouling organisms from salmon cages and oyster trays
.
Spawning
takes place in spring and early summer. The female releases a single batch of 80,000 to 2,500,000 eggs into the water column where they are fertilised. The echinopluteus larva
e form part of the zooplankton
for one to two months before settling on the sea bed and undergoing metamorphosis
.
P. miliaris is sometimes present in large numbers in suitable habitats. In a shallow Zostera marina
meadow off the west coast of Scotland
, they were recorded at 182 per square metre and 28 per square metre on the adjacent muddy sediment. In littoral habitats they can reach densities of 352 individuals per square metre. Their grazing and predation
have a considerable effect on the benthic
ecology
and if they are experimentally removed from an area, there is a significant change in the community of encrusting organisms. In one study it was found that the tube worm Pomatoceros
increased as did the more ephemeral algal
species. Another study found that an individual urchin could eat 8 to 12 barnacles (Semibalanus balanoides
) or 6 mussels (Mytilus edulis) in a day.
s of P. miliaris are sometimes eaten, particularly in Mediterranean cuisine. They are small in specimens caught in the wild but larger in individuals that have been eating prepared salmon food and the possibility of aquaculture
is being investigated.
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 sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Parechinidae
Parechinidae
Parechinidae is a family of sea urchins in the class Echinoidea.-Characteristics:All Camarodonts have imperforate tubercles and compound ambulacral plates. In addition, the characteristics of the Parechinids include the interambulacral plates being densely covered with tubercles with many subequal...
. It is sometimes known as the green sea urchin or shore sea urchin. It is found in shallow areas of the eastern 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 North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
.
Description
The testTest (biology)
A test is a term used to refer to the shell of sea urchins, and also the shell of certain microorganisms, such as testate foraminifera and testate amoebae....
is globular, somewhat flattened dorso-ventrally, and up to five centimetres in diameter. It is covered in short, equi-length robust spines. The test and spines of shallow water specimens are purplish-brown but specimens from deeper water have a greenish test and pale coloured spines with purple tips. If individuals are transferred from one depth range to another, they retain their original colouration in their new location. On each ambulacral plate there are three pairs of tubercles each with a spine attached, the central one being a primary spine. On the ventral side, the orifices are relatively small and the buccal membrane is closely packed with thick plates with many pedicellariae but no spines. The globiferous pedicellariae are numerous but small and the tridentate pedicellariae are stout with broad blades.
Distribution and habitat
P. miliaris occurs in the eastern Atlantic Ocean from ScandinaviaScandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
south to Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
, but not in 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 particularly common in the North Sea. It is mostly a littoral species but can be found from low tide mark down to a depth of one hundred metres. It is often found on or under Saccharina latissima, a large brown seaweed with which it shares its range. It occurs in a range of other habitats including under boulders and rocks, among seaweed, on rough ground such as oyster
Oyster
The word oyster is used as a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. The valves are highly calcified....
banks, in burrows in gravelly sediments and on the rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
s of Zostera marina
Zostera marina
Zostera marina is a species of seagrass known by the common names common eelgrass and seawrack. It is an aquatic plant native to marine environments on the coastlines of mostly northern sections of North America and Eurasia. It is the most wide-ranging marine flowering plant in the Northern...
in seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
meadows. The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e often settle onto man-made structures such as ropes close to aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
facilities.
Biology
P. miliaris is an omnivoreOmnivore
Omnivores are species that eat both plants and animals as their primary food source...
and feeds on marine worms, hydroids
Hydrozoa
Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...
, 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, molluscs
Mollusca
The Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...
, diatom
Diatom
Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons , fans , zigzags , or stellate colonies . Diatoms are producers within the food chain...
s, macroalgae and detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
. It eats both fresh and rotting kelp (S. latissima) but the former is more difficult to digest and takes longer to pass through the gut. It is effective at removing fouling organisms from salmon cages and oyster trays
Oyster farming
Oyster farming is an aquaculture practice in which oysters are raised for human consumption. Oyster farming most likely developed in tandem with pearl farming, a similar practice in which oysters are farmed for the purpose of developing pearls...
.
Spawning
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
takes place in spring and early summer. The female releases a single batch of 80,000 to 2,500,000 eggs into the water column where they are fertilised. The echinopluteus larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e form part of the zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
for one to two months before settling on the sea bed and undergoing metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
.
P. miliaris is sometimes present in large numbers in suitable habitats. In a shallow Zostera marina
Zostera marina
Zostera marina is a species of seagrass known by the common names common eelgrass and seawrack. It is an aquatic plant native to marine environments on the coastlines of mostly northern sections of North America and Eurasia. It is the most wide-ranging marine flowering plant in the Northern...
meadow off the west coast of Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, they were recorded at 182 per square metre and 28 per square metre on the adjacent muddy sediment. In littoral habitats they can reach densities of 352 individuals per square metre. Their grazing and predation
Predation
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...
have a considerable effect on the benthic
Benthos
Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.Many organisms...
ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
and if they are experimentally removed from an area, there is a significant change in the community of encrusting organisms. In one study it was found that the tube worm Pomatoceros
Pomatoceros triqueter
Pomatoceros triqueter is a species of tube-building annelid worm in the class Polychaeta. It is common on the north eastern coasts of the Atlantic Ocean and in the Mediterranean Sea....
increased as did the more ephemeral algal
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
species. Another study found that an individual urchin could eat 8 to 12 barnacles (Semibalanus balanoides
Semibalanus balanoides
Semibalanus balanoides is a common and widespread boreo-arctic species of acorn barnacle. It is common on rocks and other substrates in the intertidal zone of north-western Europe and both coasts of North America.-Description:...
) or 6 mussels (Mytilus edulis) in a day.
Use as food
The gonadGonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s of P. miliaris are sometimes eaten, particularly in Mediterranean cuisine. They are small in specimens caught in the wild but larger in individuals that have been eating prepared salmon food and the possibility of aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
is being investigated.