Cryptolithodes sitchensis

Cryptolithodes sitchensis
An umbrella crab from the intertidal at Bean Hollow State Beach, Pescadero, CA, USA.
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Infraorder: Anomura
Family: Lithodidae
Genus: Cryptolithodes
Species: C. sitchensis
Binomial name
Cryptolithodes sitchensis
Brandt, 1853 [1]

Cryptolithodes sitchensis, variously known as the umbrella crab, Sitka crab or turtle crab,[2] is a species of lithodid crustacean native to coastal regions of the northeastern Pacific Ocean, ranging from Sitka, Alaska to Point Loma, California.[3] 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 m (56 ft).[3]

Description

Red specimen
Ventral view

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 5–10 cm (2.0–3.9 in) at the adult stage and has scalloped edges. This carapace ranges from neutral sandy colors to bright oranges, reds, and purples.[4]:192, 255 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 my multiple hard plates that lack raised margins.[4]:407 The chelipeds are smooth. The fifth pair of walking legs are located at the posterior, and are difficult to distinguish.[5]

Range

C. sitchensis can be found from southern Alaska to southern California. They live within 18 m (59 ft) of the intertidal zone along the exposed coasts of the Pacific Ocean.[5] Intertidal species of Lithodidae prefer habitats of cooler temperatures ranging from 0–25 °C (32–77 °F) and temperatures of 16 °C (61 °F) during larval development. This causes a restriction on their distribution, as water temperatures change due to global warming.[6]

Identification

The distinguishing characteristic between C. sitchensis and C. typicus is 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.[4]:407

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 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.[7]

Natural history

C. 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, this species feeds on coralline algae. The reason for the diverse colorations of its carapace may be camouflage with its surroundings.[8]

Threats

Natural predators of C. sitchensis include larger marine invertebrates, such as octopuses, sea birds, and marine mammals, such as 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. The 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.[9]

References

  1. ↑ WoRMS (2011). "Cryptolithodes sitchensis Brandt, 1853". World Register of Marine Species. Retrieved January 10, 2012.
  2. ↑ "Cryptolithodes sitchensis". ZipCode Zoo. Retrieved November 14, 2009.
  3. 1 2 Gregory C. Jensen (1995). Pacific Coast Crabs and Shrimps. Sea Challengers. ISBN 0-930118-20-0.
  4. 1 2 3 Eugene N. Kozloff (1993). Seashore Life of the Northern Pacific Coast. Seattle, WA: University of Washington Press.
  5. 1 2 Andy Lamb & Bernard Hanby (2005). Marine Life of the Pacific Northwest: A Photographic Encyclopedia of Invertebrates, Seaweeds and Selected Fishes. Harbour Publishing. p. 313. ISBN 1-55017-361-8.
  6. ↑ Sally Hall & Sven Thatje (2009). "Global bottlenecks in the distribution of marine Crustacea: temperature constraints in the family Lithodidae". Journal of Biogeography. 36 (11): 2125–2135. doi:10.1111/j.1365-2699.2009.02153.x.
  7. ↑ Patsy A. McLaughlin & Rafael Lemaitre (2000). "Aspects of evolution in the anomuran superfamily Paguroidea: one larval prospective" (PDF). Invertebrate Reproduction and Development. 38 (3): 159–169.
  8. ↑ Dave Cowles (2005). "Cryptolithodes sitchensis Brandt, 1853". Walla Walla University. Retrieved May 11, 2010.
  9. ↑ Michael H. Graham (2004). "Effects of Local Deforestation on the Diversity and Structure of Southern California Giant Kelp Forest Food Webs". Ecosystems. 7 (4): 341–357. doi:10.1007/s10021-003-0245-6. JSTOR 3658821.
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