''Petrolisthes elongatus'', known as the New Zealand half crab, elongated porcelain crab, blue half crab, blue false crab or simply as the half crab or false crab, 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 ...

porcelain crab Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They have flattened bodies as an adaptation for living in rock crevices. They are delicate, readily losing limbs when attack ...

native to

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

Description

The

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 ...

is flattened with smooth side and rear margins, width is up to , and long whip-like antennae grow from the front corners, with the short

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

extending beyond the large prominent eyes. The animal either filter feeds with long setae borne from the

maxilliped An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...

palps, or scavenges by chopping up flesh with the second maxilliped and further shredding with the mandibles. The large

cheliped A chela ()also called a claw, nipper, or pinceris a pincer-like organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through New Latin '. The plural form is chelae. Legs bearing a chela are called chelipeds. ...

s are generally smooth with no teeth or serrations, mainly used for territorial defense among males, who usually have one enlarged. Chelipeds and legs bear randomly located spines which can break off with wear, and these areas are dorsally coloured the same as the carapace, in black, blue, greenish or greyish, the ventral areas lighter. The last pair of legs are setose, reduced in size and carried folded under a large abdominal flap, which also allows the animal to swim backwards. Telson and uropods also setose. Studies in New Zealand from the 1960s and 1970s showed a difference in breeding biology from north to south, with ovigerous females found all year round in Auckland, and only in the summer months around Kaikoura. Females are assumed to brood two or three times during their lifespan, producing 500 - 1000 eggs.McLay, Colin L., “Brachyura and crab-like Anomura of New Zealand”, University of Auckland, Leigh Marine Laboratory, 1988

Distribution & Habitat

''P. elongatus'' is native to all areas of

but has also been introduced to

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

and

Victoria, Australia Victoria is a state in southeastern Australia. It is the second-smallest state with a land area of , the second most populated state (after New South Wales) with a population of over 6.5 million, and the most densely populated state in Au ...

. In New Zealand it habits mussel beds, wharf pilings, estuaries, and the intertidal zone on rocky shores, where it is abundant beneath boulders and stones.

References

Porcelain crabs Marine fauna of Tasmania Marine crustaceans of New Zealand Crustaceans described in 1837 Taxa named by Henri Milne-Edwards {{decapod-stub