''Heloecius cordiformis'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of semiterrestrial

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

found in

mangrove swamps A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in severa ...

and

mudflat Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal fl ...

s along the east coast of

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

. Adults are around wide, with males being larger and having larger and more conspicuously coloured claws. The males wave their claws to communicate with other crabs, giving them their

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...

of semaphore crab. They can breathe both in air and under water, and feed at low tide on detritus in the sediment. ''H. cordiformis'' is the only species in the genus ''Heloecius'' and the family Heloeciidae.

Description

Adults of ''H. cordiformis'' are around wide, with a dark purple,

mottle Mottle is a pattern of irregular marks, spots, streaks, blotches or patches of different shades or colours. It is commonly used to describe the surface of plants or the skin of animals. In plants, mottling usually consists of yellowish spots o ...

carapace A carapace is a Dorsum (biology), dorsal (upper) 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 tor ...

. The

compound eye A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which disti ...

s are on long eyestalks. The

claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tarsus ...

s are

sexually dimorphic Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

, with males' claws showing positive

allometry Allometry is the study of the relationship of body size to shape, anatomy, physiology and finally behaviour, first outlined by Otto Snell in 1892, by D'Arcy Thompson in 1917 in ''On Growth and Form'' and by Julian Huxley in 1932. Overview Allom ...

, while females' claws grow isometrically; a male's claws thus become proportionally larger as the crab grows, becoming much larger than those of females. The colour of the

s is correlated with both sex and size. The smallest crabs have green claws, followed by orange and pink, with the largest male crabs having purple claws; females with purple claws have small claws. The purple colour is the easiest of the four to distinguish against the reflectance spectrum of the mudflats on which the crabs live.

Distribution

''H. cordiformis'' lives from

Brisbane Brisbane ( ) is the capital and most populous city of the states and territories of Australia, Australian state of Queensland, and the list of cities in Australia by population, third-most populous city in Australia and Oceania, with a populati ...

(

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...

), along the coast of

New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...

Port Philip Bay Port Phillip ( Kulin: ''Narm-Narm'') or Port Phillip Bay is a horsehead-shaped enclosed bay on the central coast of southern Victoria, Australia. The bay opens into the Bass Strait via a short, narrow channel known as The Rip, and is comp ...

(

Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...

), as well as eastern parts of

Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...

Ecology and behaviour

''H. cordiformis'' lives in

intertidal The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of Marine habitat, habitats with var ...

mangrove A mangrove is a shrub or tree that grows in coastal saline water, saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evoluti ...

s, and in

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

, where it is the most abundant crab species, usually living among the roots of the mangroves. ''H. cordiformis'' can breathe both in air and in water. While out of the water, ''H. cordiformis'' moves its carapace up and down; this capability allows the crab to breathe air without losing the water held in the gill chamber under the carapace. ''H. cordiformis'' is primarily a deposit feeder, sifting through the

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

for

organic matter Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...

and the

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

from

s, but also has large

mandibles In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

that it uses to eat larger pieces of plants and animals. Both males and females use their claws alternately; while one is transferring food to the mouthparts, the other claw is collecting more material. Predators of ''H. cordiformis'' include a variety of

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

s and

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

. Males signal to other crabs by waving their brightly coloured claws, which gives the species its

of "

semaphore Semaphore (; ) is the use of an apparatus to create a visual signal transmitted over distance. A semaphore can be performed with devices including: fire, lights, flags, sunlight, and moving arms. Semaphores can be used for telegraphy when arra ...

crab".

Systematics

''Heloecius cordiformis'' was first described as ''Gelasimus cordiformis'' by

Henri Milne-Edwards Henri Milne-Edwards (23 October 1800 – 29 July 1885) was an eminent French zoologist. Biography Henri Milne-Edwards was the 27th child of William Edwards, an English planter and colonel of the militia in Jamaica and Elisabeth Vaux, a Frenchw ...

, in the family

Ocypodidae The Ocypodidae are a family of semiterrestrial crabs that includes the ghost crabs and fiddler crabs. They are found on tropical and temperate shorelines around the world. Some genera previously included in the family are now treated as members o ...

(''Gelasimus'' is now a

subgenus In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between t ...

of ''

Uca The fiddler crab or calling crab may be any of more than one hundred species of semiterrestrial marine crabs in the family Ocypodidae, well known for their sexually dimorphic claws; the males' major claw is much larger than the minor claw, whil ...

''). It was transferred to a new genus by

James Dwight Dana James Dwight Dana Royal Society of London, FRS FRSE (February 12, 1813 – April 14, 1895) was an American geologist, mineralogist, volcanologist, and zoologist. He made pioneering studies of mountain-building, volcano, volcanic activity, and the ...

in 1851, alongside a newly described species, ''H. inornatus''. A 1983 study concluded that ''Heloecius'' was the most primitive of the crabs in the family Ocypodidae, and erected a new subfamily for the genus, which was later raised to the

rank Rank is the relative position, value, worth, complexity, power, importance, authority, level, etc. of a person or object within a ranking, such as: Level or position in a hierarchical organization * Academic rank * Diplomatic rank * Hierarchy * H ...

of family, as Heloeciidae. Dana's ''H. inornatus'' and other species described in the genus are all considered taxonomic synonyms of ''H. cordiformis''.

References

{{Taxonbar, from=Q2523176 Ocypodoidea Crustaceans of Australia Monotypic arthropod genera Taxa named by Henri Milne-Edwards

Description

Distribution

Ecology and behaviour

Systematics

See also

References