Telmessus cheiragonus (Tilesius, 1812 or 1815)
Common name(s): Helmet crab, Horse crab, Bristly crab
|Synonyms: Cancer cheiragonus, Telmessus serratus|
Infraorder Brachyura (true crabs)
|Telmessus cheiragonus male, 9.5 cm carapace width, from Padilla Bay.|
|(Photo by: Dave Cowles July 2005)|
How to Distinguish from Similar Species: This is the only member of Family Atelecyclidae in this area, and the only local species with a 5-sided carapace.
Geographical Range: Bering Sea to California, and to Siberia, Japan, and Korea. Not common on our coast south of Washington.
Depth Range: Intertidal to 110 meters. Mostly subtidal.
Habitat: Eelgrass, algae, soft bottoms, sometimes on rocky bottoms.
Biology/Natural History: This species is mostly subtidal but can be found in the eelgrass at very low tides at Padilla Bay. It can bury itself in the sediment. Eats a variety of food, such as eelgrass, eelgrass detritus, snails, algae, worms, and bivalves. Predators include sea otters and fur seals, the rosylip sculpin (Aschelichthys rhodorus), and gulls, which catch them in eelgrass beds at low tide, flip them over, and eat their insides. Comes to intertidal algae-covered rocks in spring or early summer for mating, which occurs just after the female molts. In Hokkaido, Japan, mating occurs in May and June (Nagao and Munehara, 2003). Nagao and Munehara (2007) found that in Japan adult females of this species store sperm from one mating season to the next. Females isolated from males during a mating season nevertheless laid fertile eggs by fertilizing them with sperm stored from the previous season.
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Gotshall and Laurent, 1979
Johnson and Snook, 1955
McConnaughey and McConnaughey, 1986
O'Clair and O'Clair, 1998
Kamio, M., Araki, M., Nagayama, T., Matsunaga, S. & Fusetani, N. 2005. The Antennular Outer Flagellum is the Site of Pheromone Reception in the Male Helmet Crab Telmessus cheiragonus. Biol. Bull. 208: 12-19.
Kamio, M., Matsunaga, S. & Fusetani, N. 2003. Observation on the Mating Behaviors of the Helmet Crab Telmessus cheiragonus (Brachyura: Cheiragonidae). J. Mar. Biol. Assoc. U.K. 83: 1007-1013.
Kamio, M., Matsunaga, S. & Fusetani, N. 2000. Studies on sex pheromones of the helmet crab, Telmessus cheiragonus 1. An assay based on precopulatory mate-guarding. Zool. Sci. 17: 731-733.
Kamio, M., S. Matsunaga, and N. Fusetani, 2002. Copulation pheromone in the crab Telmessus cheiragonus (Brachyura: Decapoda). Marine Ecology Progress Series 234: 183-190
Nagao, J., 1999. Growth and reproduction of the helmet crab Telmessus cheiragonus. Ph.D. dissertation, Hokkaido University, Hakodate, Japan
Nagao, J. and H. Munehara, 2001. Annual reproductive cycle of the helmet crab Telmessus cheiragonus on the sublittoral zones in Usujiri, southern Hokkaido, Japan. Crustacean Research 30: 72-81
Nagao, J. and H. Munehara, 2003. Annual cycle of testicular maturation in the helmet crab Telmessus cheiragonus. Fisheries Science 69: 1200-1208
Nagao, Jiro and Hiroyuki Munehara, 2007. Characteristics of broods fertilized with fresh or stored sperm in the helmet crab Telmessus cheiragonus. Journal of Crustacean Biology 27:4 565-569
Vincent, T.L.S., D. Scheel, and K.R. Hough, 1998. Some aspects of diet and foraging behavior of Octopus dofleini (Wulker, 1910) in its northernmost range. Marine Ecology 19: 13-29
Although this species is said to come to shallow water in the spring and summer primarily to mate, my experience is that single individuals are more commonly encountered in shallow waters near Rosario than are pairs. Furthermore, it is not uncommon to find smaller individuals perhaps half the size of the largest adults, which I presume may be juveniles. What they are doing in shallow water here near Rosario merits further investigation.
This species has no rostrum but has four teeth between the eyes and six on the anterolateral margin of the carapace. It has many stiff setae.
Photo by Dave Cowles, July 2005
This crab is able to extend its long legs farther dorsally than can most crabs, so that it can rake the hands of someone holding it across the back of the carapace.
This crab is common subtidally among the algae in Sharpe's Cove of Bowman's Bay, and among the eelgrass in Padilla Bay. We rarely if ever find it in the more exposed Rosario Bay or at Sares Head.
This juvenile has a carapace width of 1.2 cm. Photographed by
Dave Cowles at Rosario, July 2010.