Oregonia bifurca

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Oregonia bifurca
Male
Female
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Brachyura
Family: Oregoniidae
Genus: Oregonia
Species:
O. bifurca
Binomial name
Oregonia bifurca
Rathbun, 1902

Oregonia bifurca, commonly known as the split-nose crab or the split-nose decorator crab, is a species of crabs belonging to the family Oregoniidae. It is a rare deep-water species that inhabits the tops of seamounts and guyots in the northeastern Pacific Ocean; from the Aleutian Islands, the Bering Sea, the Hawaiian–Emperor seamount chain, to the waters off British Columbia. It is closely related to the more common shallow-water species Oregonia gracilis, the graceful decorator crab.

Like other

sexually dimorphic, with males larger than the females. The carapace
length is about 33.7 millimetres (1.33 in) in males and 29 mm (1.1 in) in females. The entire body and the long and slender legs are covered densely with curving yellow hair.

Taxonomy

Oregonia bifurca is one of the two extant

type specimen (a female) was collected from a depth of about 500 metres (1,600 ft) in the waters north of the Rat Islands of the Aleutian island chain (USS Albatross station 3785).[2]

Description

Oregonia bifurca are relatively small crabs. Like other members of Majoidea, they are

sexually dimorphic.[3] Adult males grow to an approximate carapace length of 33.7 millimetres (1.33 in) with a carapace width of about 25 mm (0.98 in).[4] Adult females grow to an approximate carapace length of 29 mm (1.1 in) with a carapace width of about 20 mm (0.79 in).[3][5]

Abdomen of male

The carapace is somewhat oblong in shape, about three-fourths as wide as it is long. It is slightly narrower at the anterior end. Two small spines are present at the posterior margin of eye

pleon) is composed of seven distinct segments.[3]

The appendages of males are slender and covered with dense long yellow curving hairs interspersed with shorter and finer hairs. The claw-bearing legs (

pleopods of the males are also enlarged at the tips and possess rows of long filaments.[3][4]

The appendages of females are also covered in dense long yellow curving hairs interspersed with shorter and finer hairs. Female chelipeds are much shorter than in males, only growing to about 37 mm (1.5 in). They are about one and a half times as long as the carapace. The arm of the chelipeds has a row of short blunt spines on the inner edge. The palm of the claws are about the same length as the fingers, and is slightly longer than the arm. The fixed finger and the moveable finger fit closely together and possess small teeth. Unlike in males, the cheliped is shorter than the first walking leg which is about 50 mm (2.0 in) in length. The rest of the walking legs also decrease in length front-to-back, as in males.[3]

Oregonia bifurca can be readily distinguished from O. gracilis in having shorter rostral horns that curve away from each other, triangular postorbital spines closer to the eyes and pointing more forward, a wider front end of the carapace, and long and slender dactyli on their walking legs.[3] The tuberculation in O. bifurca is finer than in O. gracilis.[4]

Distribution and habitat

Oregonia bifurca is a

foraminiferous mud. Their habitat is mutually exclusive with that of O. gracilis, which is found in shallow water to only about 400 m (1,300 ft).[3][6]

O. bifurca is a rare species. Aside from the waters around the Aleutian Islands, it has also been documented in the Bowers Bank of the western Bering Sea,[7] the Nintoku Seamount of the central Pacific Hawaiian–Emperor seamount chain,[6] and off the coast of British Columbia in North America.[8][9]

References

  1. ^ Davie, P. (2012). "Oregonia bifurca Rathbun, 1902". WoRMS. World Register of Marine Species. Retrieved September 7, 2012.
  2. doi:10.5479/si.00963801.1272.885
    .
  3. ^ a b c d e f g Garth, John S. (1958). Brachyura of the Pacific Coast of America, Oxyrhyncha (PDF). Allan Hancock Pacific Expeditions. Volume 21, Part 1. Los Angeles: The University of Southern California Press. pp. 135–141.
  4. ^ a b c d Rathbun, Mary J. (1925). The Spider Crabs of America (PDF). Bulletin (United States National Museum) 129. Washington: Government Printing Office. pp. 71–79.
  5. ^
    Cole, Leon J. (1910). Harriman Alaska Expedition. Volume X: Crustacea. Harriman Alaska Series. Washington: Smithsonian Institution. pp. 171
    –172, pl. VI.
  6. ^ a b Sakai, Tsune (1978). Decapod Crustacea from the Emperor Seamount Chain (PDF). Researches on Crustacea, 8 (Suppl.). Tokyo: Carcinological Society of Japan. pp. 1–39.
  7. ^ Takeda, Masatsune (1987). "Oregonia mutsuensis Yokoya, 1928, as a synonym of O. gracilis Dana, 1851" (PDF). Zoology, National Science Museum, Tokyo. 20: 133–136.
  8. doi:10.1139/z80-109
    .
  9. ISBN 9789251054024
    .

External links
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