Cryptolithodes sitchensis
Encyclopedia
Cryptolithodes sitchensis, variously known as the umbrella crab, Sitka crab or turtle crab, is a species
of lithodid crustacean
native to coastal regions of the northeastern Pacific Ocean
, ranging from Sitka, Alaska to Point Loma, California. Its carapace
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 17 metres (55.8 ft).
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 my 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.
.
are whole. Male and female C. sitchensis have symmetrical abdomens, yet females have a greater number of accessory plates on the left side of the third tergite.
. This may be the reason for the diverse colorations of its carapace to camouflage with its surroundings.
A major threat to C. sitchensis in Southern California is deforestation and its effects on the giant kelp forests around the Channel Islands National Park
. The giant kelp forests of Macrocystis pyrifera
form a protective canopy, fostering the ideal temperature for various species that are temperature sensitive, such as C. sitchensis, and the growth of macroalgae and coralline algae needed for their survival.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of lithodid crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
native to coastal regions of the northeastern Pacific Ocean
Pacific 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...
, ranging from Sitka, Alaska to Point Loma, California. Its carapace
Carapace
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...
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 17 metres (55.8 ft).
Description
Cryptolithodes sitchensis has a half-moon shaped carapace that extends over all of its eight walking legs and two cheliped, giving them their common names of turtle crab, umbrella crab or helmet crab. The carapace can be 5–10 cm (2–3.9 ) at the adult stage and has scalloped edges. This carapace ranges from neutral sandy colors to bright oranges, reds, and purples. The rostrumRostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
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 my 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
Cryptolithodes sitchensis can be found from southern Alaska to southern California. They live within 18 metres (59.1 ft) of the intertidal zone along the exposed coasts of the Pacific Ocean. Intertidal species of Lithodidae prefer habitats of cooler temperatures ranging from 0–25 °C (32–77 F) and temperatures of 16 °C (60.8 °F) during larval development. This causes a restriction on their distribution as water temperatures change due to global warmingGlobal warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
.
Identification
The distinguishing characteristic between C. sitchensis and C. typicus is that C. sitchensis has a rostrum that 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 larval development of C. sitchensis is characteristic of having six tergites at the megalopal stage. Upon reaching the adult stage the first and second abdominal segments have fused and the sixth tergite and telsonTelson
The telson is the last division of the body of a crustacean. It is not considered a true segment because it does not arise in the embryo from teloblast areas as do real segments. It never carries any appendages, but a forked "tail" called the caudal furca is often present. Together with the...
are whole. Male and female C. sitchensis have symmetrical abdomens, yet females have a greater number of accessory plates on the left side of the third tergite.
Natural history
Cryptolithodes sitchensis may be hard to spot due to its rough, rock-like exterior, but is easily caught due to its slow movements. Found most commonly in the intertidal zone, C. sitchensis feeds on coralline algaeCoralline 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...
. This may be the reason for the diverse colorations of its carapace to camouflage with its surroundings.
Threats
Natural predators of C. sitchensis include larger marine invertebrates like octopus, as well as sea birds, and marine mammals like otters.A major threat to C. sitchensis in Southern California is deforestation and its effects on the giant kelp forests around the Channel Islands National Park
Channel Islands National Park
- External links :* Official site: * *...
. The giant kelp forests of Macrocystis pyrifera
Macrocystis pyrifera
Macrocystis pyrifera, commonly known as Giant kelp or Giant bladder kelp, is a species of kelp , and one of four species in the genus Macrocystis...
form a protective canopy, fostering the ideal temperature for various species that are temperature sensitive, such as C. sitchensis, and the growth of macroalgae and coralline algae needed for their survival.