''Ligia exotica'', also called sea roach or wharf roach, is a

woodlouse Woodlice are terrestrial isopods in the suborder Oniscidea. Their name is derived from being often found in old wood, and from louse, a parasitic insect, although woodlice are neither parasitic nor insects. Woodlice evolved from marine isopods ...

sea slater ''Ligia'' is a genus of isopods, commonly known as rock lice or sea slaters. Most ''Ligia'' species live in tidal zone cliffs and rocky beaches, but there are several fully terrestrial species which occur in high-humidity environments. Ecolog ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Ligiidae Ligiidae is a family of woodlice, the only family in the infraorder Diplocheta. Its members are common on rocky shores, in similar habitats to those inhabited by species of the bristletail '' Petrobius'' and the crab '' Cyclograpsus''. The famil ...

. It is found in various parts of the world living on rocky coasts and harbour walls just above high water mark.

Description

''Ligia exotica'' can grow to in length, with the males being rather bigger than the females. The general colour is dark grey, sometimes with brown flecks, and the

appendage An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...

s are pale brown. The head has a pair of long antennae which exceed the length of the body, and two unstalked, bulging eyes. The body is flattened dorsally and has seven

thoracic The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main ...

segments, each with a pair of legs, and six abdominal segments. The first five of these bear flat, membranous

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

s and the sixth bears a pair of long, forked

uropod Uropods are posterior appendages found on a wide variety of crustaceans. They typically have functions in locomotion. Definition Uropods are often defined as the appendages of the last body segment of a crustacean. An alternative definition sugge ...

s.''Ligia exotica'': Wharf roach
Smithsonian Marine Station. Retrieved December 3, 2011.

Distribution and habitat

''Ligia exotica'' is believed to be

native Native may refer to: People * '' Jus sanguinis'', nationality by blood * '' Jus soli'', nationality by location of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Nat ...

to the coasts of

Western Europe Western Europe is the western region of Europe. The region's extent varies depending on context. The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the Western half of the ancient Mediterranean ...

and the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

. Other authorities suggest it originated in the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

and

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

s. The fact that Roux gave it the specific name "'" when he first described the species in 1828 from near

Marseilles Marseille (; ; see below) is a city in southern France, the prefecture of the department of Bouches-du-Rhône and of the Provence-Alpes-Côte d'Azur region. Situated in the Provence region, it is located on the coast of the Mediterranean S ...

, may indicate that it was not previously known in that locality. It has spread to many other temperate and subtropical parts of the world including the

Red Sea The Red Sea is a sea inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab-el-Mandeb Strait and the Gulf of Aden. To its north lie the Sinai Peninsula, the Gulf of Aqaba, and th ...

, the eastern seaboard of the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

and

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

. It is thought that the spread occurred unintentionally via shipping, either in ballast or between the planks of timber ships. Its natural habitat is rocks and cliffs in the splash zone just above high water mark where it lives in damp crevices. It is also found, sometimes in large numbers, on jetties and harbour walls.

Biology

''Ligia exotica'' is both a grazer on

microalgae Microalgae or microphytes are microscopic scale, microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine life, marine systems, living in both the water column and sediment. They are unicellul ...

and

diatom A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...

s and a scavenger on plant remains and

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

. In the eastern United States, where it is considered to be invasive, it seems to be the dominant invertebrate in its habitat. The impact of this on competing organisms and its contribution to the diet of

predators Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

has not been properly evaluated, however the NEMESIS database suggests it is not likely to be of much significance. Individual ''Ligia exotica'' are either male or female. Fertilization is internal and eggs are laid in batches of about eighty in moist cracks and fissures. Females often carry their eggs around with them using specially adapted appendages. The larvae develop into juveniles which go through a number of moults before becoming adult. ''Ligia exotica'' has a passive

water transportation Water transportation is the international movement of water over large distances. Methods of transportation fall into three categories: * Aqueducts, which include pipelines, canals, tunnels and bridges A bridge is a structure built to span ...

system through open

capillaries A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the in ...

in its legs.

References

External links

* {{Taxonbar, from=Q1049222 Woodlice Crustaceans described in 1828