Hemioniscus balani

Hemioniscus balani, a species of isopod crustacean, is a widespread parasitic castrator of barnacle in the northern Atlantic Ocean. Its range extends from Norway to the Atlantic coast of France, and as far west as Massachusetts.[2] It is also commonly found on the Pacific coast of North America; it is not known if the Pacific and Atlantic populations are the same species, or if the Pacific population exists following human-assisted introduction.

Hemioniscus balani
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Subphylum:
Crustacea
Class:
Malacostraca
Order:
Isopoda
Suborder:
Cymothoida
Family:
Hemioniscidae
Genus:
Hemioniscus
Species:
H. balani
Binomial name
Hemioniscus balani
Buchholtz, 1866[1]

Life history

H. balani parasitically castrates adults of several species of barnacles, including Semibalanus balanoides,[2] Chthamalus fissus, Chthamalus dalli, and Balanus glandula. Rarely does more than one H. balani parasitize the same host,[3] but under conditions of heavy infestation, a single barnacle may contain as many as seven H. balani individuals.[2]

Both the isopod parasite and its barnacle host are hermaphroditic crustaceans with a free-swimming larva and a sessile adult. H. balani is a protandrous hermaphrodite that develops into a female only after attaching to its adult host. While in its male swimming form, it resembles a typical isopod with antennae, jointed limbs, and a segmented exoskeleton.[4] When fully mature, the adult female form of H. balani is reduced to a bloated, star-shaped egg sac,[2] up to 8 mm in length inhabiting the mantle cavity of its barnacle host.[4]

The barnacle host species are simultaneous hermaphrodites, with both male and female gonads in each adult. H. balani feeds on its host's ovarian fluid, so the barnacle loses female reproductive ability, but can still produce sperm.[3]

References
  1. Christopher Boyko & Marilyn Schotte (2011). M. Schotte; C. B. Boyko; N. L. Bruce; G. C. B. Poore; S. Taiti & G. D. F. Wilson (eds.). "Hemioniscus balani Buchholtz, 1866". World Marine, Freshwater and Terrestrial Isopod Crustaceans database. World Register of Marine Species. Retrieved February 13, 2011.
  2. Nicola White (2008). "An acorn barnacle - Semibalanus balanoides - General biology". Marine Life Information Network: biology and sensitivity key information sub-programme. Marine Biological Association of the United Kingdom.
  3. S. M. Blower & J. Roughgarden (1988). "Parasitic castration: host species preferences, size-selectivity and spatial heterogeneity" (PDF). Oecologia. 75 (4): 512–515. doi:10.1007/BF00776413. Archived from the original (PDF) on 2016-03-04. Retrieved 2011-02-13.
  4. "Macrobenthos of the North Sea - Crustacea - Hemioniscus balani". Marine Species Identification Portal. Retrieved 14 February 2011.
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