giant isopod

File:Bathynomus giganteus.jpg

File:giant isopod.jpg

Giant isopods are a good example of deep-sea gigantism (cf. giant squid), as they are far larger than the "typical" isopods that are up to {{convert|5|cm|abbr=on}}. Bathynomus can be divided into "giant" species where the adults generally are between {{convert|8|and|15|cm|abbr=on}} long and "supergiant" species where the adults are typically between {{convert|17|and|50|cm|abbr=on}}.{{cite journal |last1=McClain |first1=Craig R. |last2=Balk |first2=Meghan A. |last3=Benfield |first3=Mark C. |last4=Branch |first4=Trevor A. |last5=Chen |first5=Catherine |last6=Cosgrove |first6=James |last7=Dove |first7=Alistair D.M. |last8=Gaskins |first8=Lindsay C. |last9=Helm |first9=Rebecca R. |last10=Hochberg |first10=Frederick G. |last11=Lee |first11=Frank B. |last12=Marshall |first12=Andrea |last13=McMurray |first13=Steven E. |last14=Schanche |first14=Caroline |last15=Stone |first15=Shane N. |last16=Thaler |first16=Andrew D. |title=Sizing ocean giants: patterns of intraspecific size variation in marine megafauna |journal=PeerJ |date=13 January 2015 |volume=3 |pages=e715 |doi=10.7717/peerj.715 |pmid=25649000 |pmc=4304853 |doi-access=free }} One of the "supergiants", B. giganteus, reaches a typical length between {{convert|19|and|36|cm|abbr=on}}; an individual claimed to be {{convert|76|cm|abbr=on}} long has been reported by the popular press, but the largest confirmed was {{circa}} {{convert|50|cm|abbr=on}}.

Their morphology resembles that of their terrestrial relative, the woodlouse. Their bodies are dorsoventrally compressed, protected by a rigid, calcareous exoskeleton composed of overlapping segments. Like some woodlice, they can curl up into a "ball", where only the tough shell is exposed. This protects from predators trying to strike at the more vulnerable underside. The first shell segment is fused to the head; the most posterior segments are often fused, as well, forming a "caudal shield" over the shortened abdomen (pleon).

The large eyes are compound with nearly 4,000 facets, sessile, and spaced far apart on the head.{{cite journal |last1=Chamberlain |first1=Steven C. |last2=Meyer-Rochow |first2=V. Benno |last3=Dossert |first3=William P. |title=Morphology of the compound eye of the giant deep-sea isopod Bathynomus giganteus |journal=Journal of Morphology |date=August 1986 |volume=189 |issue=2 |pages=145–156 |doi=10.1002/jmor.1051890205 |pmid=3746916 |s2cid=37070286 }} They have two pairs of antennae. The uniramous thoracic legs or pereiopods are arranged in seven pairs, the first of which is modified into maxillipeds to manipulate and bring food to the four sets of jaws. The abdomen has five segments called pleonites, each with a pair of biramous pleopods. These are modified into swimming legs and rami, flat respiratory structures acting as gills. The isopods are a pale lilac or pinkish.

The individual species generally resemble each other but can be separated by various morphological features, notably the number (7–13) and shape (straight or upturned) of the spines on the pleotelson ("tail"), shape (simple or bifid) of the central spine on the pleotelson, and the shape and structure of the uropods and pereopods.{{cite journal |last1=Kou |first1=Qi |last2=Chen |first2=Jun |last3=Li |first3=Xinzheng |last4=He |first4=Lisheng |last5=Wang |first5=Yong |title=New species of the giant deep-sea isopod genus Bathynomus (Crustacea, Isopoda, Cirolanidae) from Hainan Island, South China Sea |journal=Integrative Zoology |date=July 2017 |volume=12 |issue=4 |pages=283–291 |doi=10.1111/1749-4877.12256 |pmid=28054459 |hdl=173321/20801 |hdl-access=free }}

Giant isopods like Bathynomus giganteus store substantial organic reserves in their midgut gland and fat body, with lipids forming a significant component, particularly in the fat body where triacylglycerols make up 88% of total lipids.{{Cite journal |last=Biesiot |first=Patricia M. |last2=Wang |first2=Shiao Y. |last3=Perry |first3=Harriet M. |last4=Trigg |first4=Christine |date=1999-07-01 |title=Organic Reserves in the Midgut Gland and Fat Body of the Giant Deep-sea Isopod Bathynomus Giganteus |url=https://academic.oup.com/jcb/article-lookup/doi/10.2307/1549253 |journal=Journal of Crustacean Biology |language=en |volume=19 |issue=3 |pages=450–458 |doi=10.2307/1549253 |issn=0278-0372}}

Giant isopods have been recorded in the West Atlantic from the US state of Georgia to Brazil, including the Gulf of Mexico and the Caribbean. The four known Atlantic species are B. obtusus, B. miyarei, B. maxeyorum, and B. giganteus, and the last of these is the only species recorded off the United States.{{cite journal |last1=Shipley |first1=Oliver N. |last2=Bruce |first2=Niel L. |last3=Violich |first3=Mackellar |last4=Baco |first4=Amy |last5=Morgan |first5=Nicole |last6=Rawlins |first6=Scott |last7=Brooks |first7=Edward J. |title=A new species of Bathynomus Milne Edwards, 1879 (Isopoda: Cirolanidae) from The Bahamas, Western Atlantic |journal=Zootaxa |date=2 August 2016 |volume=4147 |issue=1 |pages=82–88 |doi=10.11646/zootaxa.4147.1.6 |pmid=27515606 }} The remaining Bathynomus species are all restricted to the Indo-Pacific.

No species occur in both the Atlantic and Indo-Pacific. Previous records of B. giganteus from the Indo-Pacific are now considered misidentifications of other species. Giant isopods are unknown from the East Atlantic or East Pacific. The greatest species richness (five species) is found off eastern Australia, but it is possible other regions that are not as well-sampled match this figure. In general, the distributions of giant isopods are imperfectly known, and undescribed species may exist.

File:Laika ac Deep sea creatures (7472073020).jpg

Giant isopods are important scavengers in the deep-sea benthic environment. They are mainly found from the gloomy sublittoral zone at a depth of {{convert|170|m|abbr=on}} to the pitch darkness of the bathyal zone at {{convert|2140|m|abbr=on}}, where pressures are high and temperatures are very low.{{Cite thesis |first=B. T. |last=Cocke |year=1987 |title=Morphological variation in the giant isopod Bathynomus giganteus (suborder Flabellifera: family Cirolanidae) with notes on the genus |degree=Master's |publisher=Texas A&M University |page=129 pp}} A few species from this genus have been reported from shallower depths, notably B. miyarei between {{convert|22|and|280|m|abbr=on}},{{cite web |publisher=SeaLifeBase |date=23 March 2010 |url=http://www.sealifebase.org/Summary/speciesSummary.php?ID=10710&genusname=Bathynomus&speciesname=miyarei |title=Bathynomus miyarei |access-date=26 February 2012 }} the poorly known B. decemspinosus between {{convert|70|and|80|m|abbr=on}}, and B. doederleini as shallow as {{convert|100|m|abbr=on}}.

The depth record for any giant isopod is {{convert|2500|m|abbr=on}} for B. kensleyi, but this species also occurs as shallow as {{convert|300|m|abbr=on}}. Over 80% of B. giganteus are found at a depth between {{convert|365|and|730|m|abbr=on}}.{{Cite journal |author-link1=Lipke Holthuis |first1=L. B. |last1=Holthuis |first2=W. R. |last2=Mikulka |year=1972 |title=Notes on the deep-sea isopods of the genus Bathynomus A. Milne-Edwards, 1879 |journal=Bulletin of Marine Science |volume=22 |pages=575–591}} In regions with both "giant" and "supergiant" species, the former mainly live on the continental slope, while the latter mainly live on the bathyal plain. Although Bathynomus have been recorded in water as warm as {{convert|20|C|F|abbr=on}}, they are primarily found in much colder places.{{cite web |first1=L. |last1=Helgering |first2=H. |last2=Niele |first3=R. |last3=Mulders |first4=P. |last4=Smid |url=http://dare.uva.nl/cgi/arno/show.cgi?fid=544405 |title=Bathynomus giganteus' gigantisme |publisher=University of Amsterdam |date=10 February 2014 |access-date=14 January 2016}} For example, during a survey of the deep-sea fauna of Exuma Sound in the Bahamas, B. giganteus was found to be common in water between {{convert|3.25|and|13|C|F|abbr=on|1}}, but more abundant towards the lower temperature.{{cite web |first1=W. |last1=Hill |first2=M. |last2=Kelly |first3=I. |last3=Mauck |first4=S. |last4=Meggit |first5=W. |last5=Swanson |first6=H. |last6=Taft |first7=N. |last7=Violich |url=http://www.fishconserve.org/arcel/admin/uploads/FPLP198.pdf |title=The assessment of deep-sea distribution and abundance of scavenging fauna in the Exuma Sound |publisher=Fisheries Conservation Foundation |date=10 February 2014 |access-date=14 January 2016}}

In contrast, preliminary studies indicate that B. doederleinii stops feeding when the temperature falls below {{convert|3|C|F|abbr=on}}.{{Cite journal|first1= R. |last1=Wetzer |year=1986 |title=Bathynomus, A living Sea monster |journal=Terra |volume=25 |issue=2 |pages=26–29}}{{cite journal |last1=Sekiguchi |first1=Hideo |last2=Yamaguchi |first2=Yuichiro |last3=Kobayashi |first3=Hiroshi |title=Geographical distribution of scavenging giant isopods bathynomids in the Northwestern Pacific |journal=Nippon Suisan Gakkaishi |date=1982 |volume=48 |issue=4 |pages=499–504 |doi=10.2331/suisan.48.499 |doi-access=free }} This lower temperature limit may explain their absence from temperate and frigid regions where seas at the depth preferred by Bathynomus often are colder. They are thought to prefer a muddy or clay substrate and lead solitary lives.

Although generalist scavengers, these isopods are mostly carnivorous and feed on dead whales, fish, and squid. They may also prey on slow-moving animals such as sea cucumbers, sponges, radiolarians, nematodes, and other zoobenthos, and perhaps even live fish. They are known to attack trawl catches. One giant isopod was filmed attacking a larger dogfish shark in a deepwater trap by latching onto and eating its face.{{cite episode |title=Alien Sharks: Close Encounters |series=Shark Week |network=Discovery Channel |date=6 July 2015}}

As food is scarce in the deep-ocean biome, giant isopods must take advantage of whatever food they have available. They are adapted to long periods of famine and have been known to survive over 5 years without food in captivity.{{cite news |last=Gallagher |first=Jack |url=http://www.japantimes.co.jp/news/2013/02/26/national/tanks-deep-sea-isopod-hasnt-eaten-for-over-four-years |title=Aquarium's deep-sea isopod hasn't eaten for over four years |newspaper=The Japan Times |date=2013-02-26 |access-date=2013-05-21}}{{cite web |url=https://www.npr.org/blogs/krulwich/2014/02/22/280249001/i-wont-eat-you-cant-make-me-and-they-couldnt |title=I Won't Eat, You Can't Make Me! (And They Couldn't) |publisher=NPR |date=February 22, 2014 |access-date=February 23, 2014}} When a significant source of food is encountered, giant isopods gorge themselves to the point that they could barely move. A study examining the digestive system contents of 1651 specimens of B. giganteus found that fish were most commonly eaten, followed by cephalopods and decapods, particularly carideans and galatheids.{{cite journal |last1=Briones-Fourzán |first1=Patricia |last2=Lozano-Alvarez |first2=Enrique |title=Aspects of the biology of the giant isopod Bathynomus giganteus A. Milne Edwards, 1879 (Flabellifera: Cirolanidae), off the Yucatan Peninsula |journal=Journal of Crustacean Biology |date=1 July 1991 |volume=11 |issue=3 |pages=375–385 |doi=10.2307/1548464 |jstor=1548464 |doi-access=free }}

Giant isopods collected along the east coast of Australia by setting traps exhibit a variation in diversity with water depth. The deeper the water, the fewer number of species found, and the larger the species tended to be. The giant isopods found in very deep waters off Australia were compared to those found off Mexico and India. From the fossil record, Bathynomus is thought to have existed more than 160 million years ago, so it did not evolve independently in all three locations, but since then Bathynomus likely would show divergent evolution in the various locations. However, the giant isopods in all three locations are almost identical in appearance (although some differences are seen, and they are separate species). This reduced phenotypic divergence is linked to the extremely low light levels of their habitat.{{Cite book |first=A. |last=Parker |title=In the Blink of an Eye: How Vision Kick-started the Big Bang of Evolution |pages=121–132 |year=2003 |publisher=The Free Press |isbn=0-7432-5733-2}}

A study of the seasonal abundance of B. giganteus juveniles and adults suggests a peak in reproductive capacity in the spring and winter. This is observed to be due to a shortage of food during the summer. Mature females develop a brood pouch or marsupium when sexually active, the pouch being formed by overlapping oostegites or brood plates grown from the medial border of the pereiopods. The young isopods emerge from the marsupium as miniatures of the adults, known as mancae. This is not a larval stage; the mancae are fully developed, lacking only the last pair of pereiopods.

There have been occasional attempts at utilizing giant isopods as novelty food, such as prepared in East Asian cuisine like ramen. Relative to total size, there is not very much "meat" to be harvested. The meat is sometimes described as resembling lobster and/or crab in taste, with a somewhat firmer, chewier texture.{{cite news |last1=Everington |first1=Keoni |title=Taipei eatery features giant isopod ramen {{!}} Taiwan News {{!}} 2023-05-23 15:19:00 |url=https://www.taiwannews.com.tw/en/news/4899689 |work=Taiwan News |date=23 May 2023}}

The genus currently contains the following species:{{Cite WoRMS|id=248508|db=isopoda|title=Bathynomus A. Milne-Edwards, 1879}}

{{Div col|colwidth=25em}}

• Bathynomus affinis
• Bathynomus brucei
• Bathynomus bruscai
• †Bathynomus civisi
• Bathynomus crosnieri
• Bathynomus decemspinosus
• Bathynomus doederleini
• Bathynomus giganteus
• Bathynomus immanis
• Bathynomus jamesi
• Bathynomus kapala
• Bathynomus keablei
• Bathynomus kensleyi
• †Bathynomus kominatoensis
• Bathynomus lowryi
• Bathynomus maxeyorum
• Bathynomus miyarei
• Bathynomus obtusus
• Bathynomus pelor
• Bathynomus propinquus (nomen dubium)
• Bathynomus raksasa
• Bathynomus richeri
• †Bathynomus sismondai
• †Bathynomus steatopigia
• †Bathynomus undecimspinosus
• Bathynomus yucatanensis
• Bathynomus vaderi{{Div col end}}

Fossilized specimens of Bathynomus are known extending back to at least the Early Oligocene (Rupelian) of Italy, with other fossils being known from Japan and Spain.{{Cite journal |last1=Hyžný |first1=Matúš |last2=Campos |first2=Ildefonso Bajo |last3=Carretero |first3=Joaquín Cárdenas |date=2020-07-22 |title=A new species of Bathynomus A. Milne-Edwards, 1879 (Malacostraca: Peracarida: Isopoda: Cirolanidae) from the upper Miocene of the Guadalquivir Basin (Spain) |url=https://www.biotaxa.org/Zootaxa/article/view/zootaxa.4819.1.8 |journal=Zootaxa |volume=4819 |issue=1 |pages=159–169 |doi=10.11646/zootaxa.4819.1.8 |pmid=33055675 |s2cid=222839202 |issn=1175-5334}}

{{Reflist}}

{{Commons category|Bathynomus}}

• {{Cite news |title=Trapping for Predators, Diving for Prey |date=October 13, 2002 |first=Bob |last=Carney |publisher=NOAA Ocean Explorer |url=http://oceanexplorer.noaa.gov/explorations/02mexico/logs/oct13/oct13.html}}
• {{cite web |url=http://www.whozoo.org/Anlife2001/chelsy/clh_Bathynomus.htm |title=Deep Sea Isopod |first=Chelsy |last=Plott |publisher=WhoZoo.org |access-date=February 21, 2009}}

{{Taxonbar|from=Q14746702}}

{{DEFAULTSORT:Giant Isopod}}

Category:Cymothoida

Category:Extant Miocene first appearances

Category:Taxa named by Alphonse Milne-Edwards