Branchinecta gigas explained

Branchinecta gigas is a species of fairy shrimp that lives in western Canada and the United States. It is the largest species of fairy shrimp, growing up to 86mm long. It is known commonly as the giant fairy shrimp.

Description

Females reach sexual maturity when they are 45- long, and grow up to 86mm long; males reach only 66mm.[1] Unpublished records exist of individuals up to 180mm long. Despite being the largest species, B. gigas has the proportionally smallest eyes of any species in the family, and possibly in all Anostraca.[2]

Distribution

Branchinecta gigas has been found in Alberta, Saskatchewan, Washington, Montana, Oregon, North Dakota, Utah, Nevada and California.[3] A related species, B. raptor, occurs in Idaho.[4]

Ecology and behaviour

B. gigas lives in hypersaline lakes and rivers, with salinity ranging from 1.8 to 5.8‰.[3] These waters often have high turbidity (low visibility), and so B. gigas hunts by touch rather than by sight.[2] When feeding, B. gigas adopts a "hunting posture", with the body bent double. The animal swims dorsal side down, with the abdomen nearly parallel with the thorax, so that the sensitive antennae and caudal rami all extends forwards. The thoracic limbs are held wide open, ready to close on any prey which enters.[5] This response appears to be entirely by touch, which correlates with the turbidity of the waters where B. gigas and its prey live.[5] The prey taken by B. gigas is chiefly other species of fairy shrimp,[6] especially B. mackini,[2] although it also eats copepods, cladocerans and sometimes green algae.[4]

Taxonomy

In 1935, J. F. Clark collected two specimens of a large branchiopod near Coulee City, Washington. These specimens were sent to James E. Lynch of the University of Washington in Seattle, who visited sites between Coulee City and the Grand Coulee Dam in 1936, and discovered further specimens. Lynch described the species as Branchinecta gigas in 1937.[7]

Notes and References

  1. Graham R. Daborn . 1975 . Life history and energy relations of the giant fairy shrimp Branchinecta gigas Lynch 1937 (Crustacea: Anostraca) . . 56 . 5 . 1025–1039 . 1936144 . 10.2307/1936144.
  2. Michel A. Boudrias . Jammieson Pires . amp . 2002 . Unusual sensory setae of the raptorial Branchinecta gigas (Branchiopoda: Anostraca) . . 486 . 1 . 19–27 . 10.1023/A:1021317927643.
  3. Book: Ulrich Theodore Hammer . 1986 . Saline Lake Ecosystems of the World . Volume 59 of Monographiae Biologicae . . 978-90-6193-535-3 . The plankton communities of saline lakes . 171–336 . https://books.google.com/books?id=NOdvPFm6SyoC&pg=PA280.
  4. D. Christopher Rogers . Dana L. Quinney . James Weaver . Jørgen Olesen . amp . 2006 . A new giant species of predatory fairy shrimp from Idaho, USA (Branchiopoda: Anostraca) . . 26 . 1 . 1–12 . 10.1651/C-2509.1 . free .
  5. G. E. White . G. Fabris . R. Hartland-Rowe . amp . 1969 . The method of prey capture by Branchinecta gigas Lynch, 1937 (Anostraca) . . 16 . 2 . 158–160 . 20101576 . 10.1163/156854069X00411.
  6. Geoffrey Fryer . 1966 . Branchinecta gigas Lynch, a non-filter-feeding raptatory anostracan, with notes on the feeding habits of certain other anostracans . . 177 . 1 . 19–34 . 10.1111/j.1095-8312.1966.tb00948.x.
  7. James E. Lynch . 1937 . A giant new species of fairy shrimp of the genus Branchinecta from the state of Washington . . 84 . 3205 . 555–562, pls. 77–80 . 10.5479/si.00963801.84-3025.555.