''Cryptolithodes sitchensis'', variously known as the umbrella crab, Sitka crab or turtle crab, is a

species In biology, a species is the basic unit of Taxonomy (biology), 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 ...

of lithodid

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...

native to coastal regions of the northeastern

Pacific Ocean 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 definition, to Antarctica) in the south, and is bounded by the contine ...

, ranging from

Sitka, Alaska russian: Ситка , native_name_lang = tli , settlement_type = Consolidated city-borough , image_skyline = File:Sitka 84 Elev 135.jpg , image_caption = Downtown Sitka in 1984 , image_size ...

to Point Loma, California. Its

carapace A carapace is a 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 tortoises, the und ...

extends over its legs such that when it pulls in its legs, it resembles a small stone. It lives in rocky areas from the low intertidal to depths of .

Description

''Cryptolithodes sitchensis'' has a half-moon shaped carapace extending over all of its eight walking legs and two chelipeds, giving them their common names of turtle crab, umbrella crab or helmet crab. The carapace can be at the adult stage and has scalloped edges. This carapace ranges from neutral sandy colors to bright oranges, reds, and purples. The rostrum extends forwards from the carapace, gradually widening before ending abruptly. From above, only the eyes and second antennae are visible. The ventral side is commonly white in color, and the abdomen is protected by multiple hard plates that lack raised margins. The chelipeds are smooth. The fifth pair of walking legs are located at the posterior and are difficult to distinguish.

Range

''C. sitchensis'' can be found from southern Alaska to southern California, where they are common. They live within of the

intertidal zone 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 habitats with various species ...

along the exposed coasts of the Pacific Ocean. Intertidal species of Lithodidae prefer habitats of cooler temperatures ranging from and temperatures of during larval development. This causes a restriction on their distribution as water temperatures change due to

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate variability and change, Climate change in a broader sense also includes ...

Identification

The distinguishing characteristic between ''C. sitchensis'' and '' C. typicus'' is that the rostrum of ''C. sitchensis'' is wider distally than proximally, while the opposite is found in ''C. typicus''. Also, ''C. typicus'' has raised margins of the abdominal segments, while ''C. sitchensis'' does not.

Life history

The larvae of ''C. sitchensis'' have six tergites at the megalopal stage. Upon reaching the adult stage, the first and second abdominal segments have fused and the sixth tergite and

telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...

are whole. ''C. sitchensis'' males and females have symmetrical abdomens, yet females have a greater number of accessory plates on the left side of the third tergite.

Natural history

''C. sitchensis'' may be hard to spot due to its rough, rock-like exterior, but it is easily caught due to its slow movements. Found most commonly in the intertidal zone, this species feeds on

coralline algae Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of r ...

. The reason for the diverse colorations of its carapace may be camouflage with its surroundings.

Threats

Natural predators of ''C. sitchensis'' include larger marine invertebrates, such as

octopuses An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefis ...

seabirds Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environ ...

, and marine mammals, such as

otters Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic, or marine, with diets based on fish and invertebrates. Lutrinae is a branch of the Mustelidae family, which also includes ...

. A major threat to ''C. sitchensis'' in

Southern California Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban ...

deforestation Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then land conversion, converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban area, urban ...

and its effects on the giant kelp forests around the Channel Islands National Park. The forests of ''

Macrocystis pyrifera ''Macrocystis pyrifera'', commonly known as giant kelp or bladder kelp, is a species of kelp (large brown algae), and one of four species in the genus '' Macrocystis''. Despite its appearance, it is not a plant; it is a heterokont. Giant kelp ...

'' form a protective

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an ...

, fostering the ideal temperature for various species that are temperature-sensitive, such as ''C. sitchensis'', and the growth of

macroalgae Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of ''Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ke ...

and coralline algae needed for their survival.

References

External links

CalPhotosVideo of ''C. sitchensis''
{{Taxonbar, from=Q3932839 King crabs Crustaceans of the eastern Pacific Ocean Crustaceans described in 1853 Taxa named by Johann Friedrich von Brandt