Allopetrolisthes spinifrons
Encyclopedia
Allopetrolisthes spinifrons is a species of porcelain crab
. It displays "hypercarcinisation", whereby the resemblance to a true crab
is enhanced by sexual dimorphism
of the abdomen. It lives along the Pacific coast of Peru and Chile, as a symbiont of a sea anemone
.
length of around 20 millimetre (0.78740157480315 in). It displays an extreme form of carcinisation
– evolution
of a crab-like form – referred to as "hypercarcinisation". In contrast to other porcelain crabs, A. spinifrons shows sexual dimorphism
of the pleon
(abdomen), closely resembling the situation in true crabs
. Females have a large pleon, similar to that of other porcelain crabs, covering almost all of the sternum. Males have a short, triangular pleon that only covers a small part of the sternum. A. spinifrons also differs from its relatives in having many fewer and smaller spines
on its legs. These morphological differences are thought to be a consequence of the species' ecology, living in close association with a sea anemone
, where the ability to escape by swimming is not needed.
, from Isla San Lorenzo
, Peru
to San Vicente, Chile
, at depths of up to 12 fathoms (21.9 m).
A. spinifrons lives symbiotically
on the sea anemone
Phymactis papillosa, chiefly in the lower intertidal zone
. In common with other porcellain crabs, A. spinifrons is a filter feeder
, but will also feed on faeces and mucus
produced by the sea anemone. The porcelain crab benefits from the protection afforded by the sea anemone's stinging cells.
in 1837 by Henri Milne-Edwards
, under the name Porcellana spinifrons. It was placed in the genus Petrolisthes
by Giuseppe Nobili in 1901, and moved to the new genus Allopetrolisthes
by Janet Haig in 1960, alongside two other species formerly placed in Petrolisthes
Porcelain crab
Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They are typically less than wide, and have flattened bodies as an adaptation for living in rock crevices...
. It displays "hypercarcinisation", whereby the resemblance to a true crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
is enhanced by sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
of the abdomen. It lives along the Pacific coast of Peru and Chile, as a symbiont of a sea anemone
Sea anemone
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...
.
Description
Allopetrolisthes spinifrons grows to a maximum carapaceCarapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
length of around 20 millimetre (0.78740157480315 in). It displays an extreme form of carcinisation
Carcinisation
In evolutionary biology, carcinisation is a hypothesised process whereby a crustacean evolves into a crab-like form from a non-crab-like form. The term was introduced by L. A...
– evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
of a crab-like form – referred to as "hypercarcinisation". In contrast to other porcelain crabs, A. spinifrons shows sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
of the pleon
Pleon
Pleon is a Europe based Public Relations and communications consultancy. It is part of the Brodeur Pleon Worldwide network and a subsidiary of BBDO Worldwide. Pleon belongs to the Omnicom Group. Pleon is headquartered in Düsseldorf, Germany.- Overview :...
(abdomen), closely resembling the situation in true crabs
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
. Females have a large pleon, similar to that of other porcelain crabs, covering almost all of the sternum. Males have a short, triangular pleon that only covers a small part of the sternum. A. spinifrons also differs from its relatives in having many fewer and smaller spines
Spine (zoology)
A spine is a hard, thorny or needle-like structure which occurs on various animals. Animals such as porcupines and sea urchins grow spines as a self-defense mechanism. Spines are often formed of keratin...
on its legs. These morphological differences are thought to be a consequence of the species' ecology, living in close association with a sea anemone
Sea anemone
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...
, where the ability to escape by swimming is not needed.
Distribution and ecology
Allopetrolisthes spinifrons is found in the eastern Pacific OceanPacific 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...
, from Isla San Lorenzo
San Lorenzo Island, Peru
San Lorenzo Island is the largest island of Peru. The island is in the Pacific Ocean near the port of Callao and measures .-Access:As of 2011, San Lorenzo is not open to the public...
, Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
to San Vicente, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, at depths of up to 12 fathoms (21.9 m).
A. spinifrons lives symbiotically
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
on the sea anemone
Sea anemone
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...
Phymactis papillosa, chiefly in the lower intertidal zone
Intertidal zone
The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...
. In common with other porcellain crabs, A. spinifrons is a filter feeder
Filter feeder
Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
, but will also feed on faeces and mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
produced by the sea anemone. The porcelain crab benefits from the protection afforded by the sea anemone's stinging cells.
Taxonomy
Allopetrolisthes spinifrons was first describedAlpha taxonomy
Alpha taxonomy is the discipline concerned with finding, describing and naming species of living or fossil organisms. This field is supported by institutions holding collections of these organisms, with relevant data, carefully curated: such institutes include natural history museums, herbaria and...
in 1837 by Henri Milne-Edwards
Henri Milne-Edwards
Henri Milne-Edwards was an eminent French zoologist.Henri Milne-Edwards was the 27th child of William Edwards, an English planter and militia colonel in Jamaica and Elisabeth Vaux, a French. He was born in Bruges, Belgium, where his parents had retired. At that time, Bruges was a part of the...
, under the name Porcellana spinifrons. It was placed in the genus Petrolisthes
Petrolisthes
Petrolisthes is a genus of marine porcelain crabs, containing the following extant species:*Petrolisthes aegyptiacus Werding & Hiller, 2007*Petrolisthes agassizii Faxon, 1893*Petrolisthes amoenus...
by Giuseppe Nobili in 1901, and moved to the new genus Allopetrolisthes
Allopetrolisthes
Allopetrolisthes is a genus of porcelain crabs, comprising three species:*Allopetrolisthes angulosus *Allopetrolisthes punctatus *Allopetrolisthes spinifrons...
by Janet Haig in 1960, alongside two other species formerly placed in Petrolisthes