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Alicella

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Alicella gigantea
Specimen collected from Japan Trench in 2022.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Amphipoda
Parvorder: Lysianassidira
Superfamily: Alicelloidea
Family: Alicellidae
Genus: Alicella
Chevreux, 1899
Species:
A. gigantea
Binomial name
Alicella gigantea
Chevreux, 1899 [1]

Alicella gigantea is an amphipod inhabiting the deep sea, the largest species ever observed, with some individuals reaching up to 34 centimetres (13 in) long; this species is an example of abyssal gigantism. The monotypic Alicella lives only at great depths; the first specimens were collected at the end of the 19th century from the Madeira Abyssal Plain, and subsequent specimens have been found on other abyssal plains of both the Atlantic and Pacific Oceans, as well within ocean trenches and fracture zones.

Taxonomy

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The genus name Alicella refers to the ship Princess Alice, which collected the first specimens. The ship itself is named after Alice Heine, who was the wife of Albert I, Prince of Monaco. The species name gigantea refers to the very large size of the species.[2]

This species was first described in 1899 by Édouard Chevreux from two specimens collected by the Princess Alice while on an expedition at the Madeira Abyssal Plain off the Canary Islands in 1897.[3] These specimens were collected using triangular traps that were set at 5,285 metres (17,339 ft) in depth.[2] The holotype and paratype specimens are a juvenile of indeterminate sex and a juvenile male respectively; they are currently deposited within the Oceanographic Museum of Monaco.[4][5] Chevreux placed this species in the family Lysianassidae.[2] In 1906, the species description was revised by Thomas Roscoe Rede Stebbing, but little new information was provided.[6]

Drawing of Alicella gigantea specimen by Édouard Chevreux in 1899.

A second species was described as Alicella scotiae in 1912 by Charles Chilton from specimens collected during the Scottish National Antarctic Expedition.[7] However, this species was later recognized to actually be Eurythenes obesus, so it was synonymized into that species.[8]

It underwent a taxonomic revision in 1987, where the authors redescribed both original type specimens and described new specimens collected during the SEABED 2 and DEMERABY abyssal campaigns.[3] In 2008, this species was moved from the Lysianassidae to a new family, the Alicellidae and was selected as the type genus. This family contains six other genera, all of which are deep sea scavengers.[9]

Description

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Many other amphipods possess either red to orange coloration, which is thought to help avoid predators (as the red wavelength of light is quickly absorbed by water, and never reaches the deep sea).[10] Alicella gigantea however are uniformly white, which may reflect their lack of predators.[11] Although there is very little sexual dimorphism, there are very small differences in the shape and size of antenna segments.[3]

The peduncle of the second antennae is short its first article strongly swollen. The mouthparts form a squarish bundle with the labrum and epistome being inconspicuous and blunt. The incisor edge is straight with some inner corner teeth, one middle tooth and the rakers absent. The mandible palp is attached distally to the molar, while the molar itself is rather large, simple and covered in small hairs. The first maxilla has an inner plate with many setae occupying the medial edge while the first maxilla palp is two jointed and is large. The second maxilla has a medial facial row of setae and the inner and outer plates of the maxilliped are strongly developed. The second maxilla palp is longer than the outer plate.[12]

The first coxa is expanded at the anterior end and is visible. The first gnathopod is small and simple. The third article of this gnathopod is elongated,  article five is longer than the sixth and the dactyl is large. For the second gnathopod, article six is slightly shorter than article (both of which are elongated and linear) and the seventh article is an overlapping obsolescent palm. The dactyls of the third to seventh periopods are quite short. The inner ramus of the second uropod is unnotched. The third uropod has a regular peduncle and the outer ramus is articulated. The telson is elongated and deeply cleft.[12]

Of these traits, A. gigantea can be best distinguished from other Alicellidae by the combination of having the first gnathopod simple in structure and the first urosomite with a rounded hump. [13]

A.gigantea are the largest known amphipods in the world and can reach between 240–340 millimetres (9.4–13.4 in) in length.[12][14] The size of this species of amphipod is hypothesized to be connected to oxygen availability. A. gigantea have gills on coxa 7 and tubuliform accessory lobes.[clarification needed] These additional structures allow for A. gigantea to absorb more oxygen, which is a known contributor to gigantism.[15]

Distribution and habitat

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Alicella gigantea is a marine species that has primarily been recorded in the lower abyssal and hadal depths between 4,850–7,000 metres (15,910–22,970 ft) in depth,[15] which would restrict them to oceanic trenches and fracture zones, such as the Kermadec Trench in the southwest Pacific.[16] However, there is a single record of a juvenile specimen at 1,720 metres (5,640 ft) in depth that was collected with a fish trap.[12] Similar to this, there is a record of a specimen being recovered from the stomach of a black-footed albatross in the Hawaiian Islands.[17] It has been suggested that this record may be due to the high lipid content of this species causing it to float upwards in the water column.[11] A 2025 study found A. gigantea's depth range to be 3,890–8,931 metres (12,762–29,301 ft), which suggests that 59% of the world's oceans (and all six major ocean bodies) is suitable habitat for this amphipod.[18][19]

It is a cosmopolitan species and has been recorded in North Atlantic Ocean, North Pacific Ocean, and the South West Pacific Ocean, though there are numerous gaps in their distribution that are likely due to the scarcity of this species.[15] A 2025 study sampling Alicella specimens worldwide confirmed low genetic divergence; all specimens sampled are to be considered the same species, though most collection sites for this study were in Pacific ocean trenches, which may skew the results.[18]

Genetics

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There have been few studies into the genetics of Alicella gigantea. In 2020, a study examined the relationships of deep sea amphipod species; sequences of 16S, COI, Histone 3, and 28S found that A. gigantea formed a clade with Tectovalopsis and Diatectonia.[13] However, in contrast to this, a 2015 study found that Alicella formed a clade with just Cyclocaris and Tectovalopsis (but Diatectonia sequences were not used in this study), which conflicts with the 2020 study.[20]

Phylogeny[13]

Most recently, a 2025 study examined the population genetics of A. gigantea over its entire known range. One of the key genetics findings of this study was that most populations shared a single haplotype for each gene, which indicates that this species distribution is a widespread and connected one.[18]

Genome

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In 2013, the size of the whole genome has been estimated to be about 34.79 gigabase pairs in length, which is considerably larger than genome size estimates for other species of deep amphipods in the same study. Because of the large size of the genome when compared to other deep sea amphipods, it has been shown that A. gigantea has a notably faster genome size diversification rate. It was hypothesized that this could be due to a whole genome duplication, but the authors cautioned this would require further study to prove.[15]

In 2019, the complete mitochondrial genome of Alicella gigantea was sequenced with a total length of 16,851 base pairs.[21][22] The study found that the genome had 13 protein-coding genes, 2 ribosomal genes, 22 transfer RNA genes and 2 noncoding gene regions.[22]

Alicella gigantea feeding at a bait station.

Biology

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Like many other amphipods, adult Alicella gigantea are primarily scavengers and feed on carrion.[3] Because of this behaviour, they are most frequently caught using baited traps.[15] Due to their dependence on carrion as a food source, the species may be susceptible to changes occurring at the ocean's surface.[23]

Alicella gigantea feeding on dead fish bait

The gut microbiome of A. gigantea is dominated by Candidatus Hepatoplasma.[24][25] One study compared the gut microbiome of A. gigantea with that of two other hadal amphipods and found that the particular gut assemblage was unique to each species.[25] It has also been discovered that hadal amphipods such as A. gigantea have large amounts of probiotic gut microbiota. It was suggested that this could support this species ability to survive in the deep sea.[26] Presently, it is unknown if these amphipods gut microbes are inherited from their parents or picked up from the surrounding environment.[11]

Although its size is thought to give it some protection from most deep sea predators, A. gigantea are known to be preyed upon by Coryphaenoides yaquinae.[12][11]

Life cycle

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Like all amphipods, female A. gigantea brood their eggs in a pouch. It has been suggested that females probably have several broods over their lifetimes.[12] The eggs are oval in shape and are 6.95 to 14.88 millimetres (0.274 to 0.586 in) in length. The shell of the eggs is composed of two chorion layers: the exochorion which is fibrillar in structure, and the endochorion layer which has a porous structure where the pores are on average less than 10 μm.[27]

As juveniles, their diet has been inferred to be mostly bacteria and zooplankton debris and then transitions into carrion and algae as they mature.[23] Alicella gigantea grows at a much faster rate compared to other amphipods.[14] The size of A. gigantea also allows them to avoid being preyed on by predators such as Notoliparis kermadecensis, a liparid snailfish that preys on smaller amphipods.[15] Analysis of 14C signatures indicates that hadal amphipods such as Alicella gigantea are unusually long lived and can reach over 10 years in age.[28]

Human impact

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Despite their apparently isolation from the surface, chemical contamination caused by humans has been detected in Alicella gigantea.[11] In one study, pesticides such as DDT and Chlordane were detected in A. gigantea specimens, whilst in another study trace elements such as cadmium and chromium were detected in high concentrations.[29][30]

References

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  1. ^ "Alicella gigantea Chevreux, 1899". Integrated Taxonomic Information System. Retrieved January 10, 2012.
  2. ^ a b c Chevreux, E. (1899). Sur deux espèces géantes d'amphipodes provenant des campagnes du yacht Princesse Alice. Bulletin de la Société Zoologique de France. 24, 152-158; figs. 1-6.
  3. ^ a b c d Claude de Broyer & Michael H. Thurston (1987). "New Atlantic material and redescription of the type specimens of the giant abyssal amphipod Alicella gigantea Chevreux (Crustacea)". Zoologica Scripta. 16 (4): 335–350. doi:10.1111/j.1463-6409.1987.tb00079.x. S2CID 86306559.
  4. ^ "WoRMS - World Register of Marine Species". www.marinespecies.org. Retrieved 2025-05-17.
  5. ^ "WoRMS - World Register of Marine Species". www.marinespecies.org. Retrieved 2025-05-17.
  6. ^ Stebbing, Thomas R. R. (1906). Amphipoda I. Gammaridea. Berlin: Friedländer. doi:10.5962/bhl.title.1224.
  7. ^ Ohilton, Chas (1912). "XXIII.—The Amphipoda of the Scottish National Antarctic Expedition". Transactions of the Royal Society of Edinburgh. 48 (2): 455–520. doi:10.1017/S0080456800002957. ISSN 0080-4568.
  8. ^ Barnard, J. Laurens; Shulenberger, Eric (1976). "Clarification of the Abyssal Amphipod, Paralicella tenuipes Chevreux". Crustaceana. 31 (3): 267–274. Bibcode:1976Crust..31..267B. doi:10.1163/156854076X00053. ISSN 0011-216X. JSTOR 20103110.
  9. ^ J. K. Lowry & C. de Broyer (2008). "Alicellidae and Valettiopsidae, two new callynophorate families (Crustacea: Amphipoda)" (PDF). Zootaxa. 1843: 57–66. doi:10.11646/zootaxa.1843.1.5.
  10. ^ "Why are so many deep-sea animals red in color?". oceanexplorer.noaa.gov. NOAA. Retrieved 22 May 2025.
  11. ^ a b c d e Jamieson, Alan J; Weston, Johanna N J (2023-06-01). "Amphipoda from depths exceeding 6,000 meters revisited 60 years on". Journal of Crustacean Biology. 43 (2): ruad020. doi:10.1093/jcbiol/ruad020. ISSN 0278-0372.
  12. ^ a b c d e f J. L. Barnard & Camilla L. Ingram (1986). "The supergiant amphipod Alicella gigantea Chevreux from the North Pacific Gyre". Journal of Crustacean Biology. 6 (4): 825–839. Bibcode:1986JCBio...6..825B. JSTOR 1548395.
  13. ^ a b c Weston, Johanna N. J.; Peart, Rachael A.; Jamieson, Alan J. (2020-01-02). "Amphipods from the Wallaby-Zenith Fracture Zone, Indian Ocean: new genus and two new species identified by integrative taxonomy". Systematics and Biodiversity. 18 (1): 57–78. Bibcode:2020SyBio..18...57W. doi:10.1080/14772000.2020.1729891. ISSN 1477-2000.
  14. ^ a b Li, Wenhao; Wang, Faxiang; Jiang, Shouwen; Pan, Binbin; Chan, Jiulin; Xu, Qianghua (Oct 2021). "The Adaptive Evolution and Gigantism Mechanisms of the Hadal "Supergiant" Amphipod Alicella gigantea". Frontiers in Marine Science. 8. Bibcode:2021FrMaS...843663L. doi:10.3389/fmars.2021.743663.
  15. ^ a b c d e f Jamieson, A. J.; Lacey, N. C.; Lörz, A. -N.; Rowden, A. A.; Piertney, S. B. (2013-08-01). "The supergiant amphipod Alicella gigantea (Crustacea: Alicellidae) from hadal depths in the Kermadec Trench, SW Pacific Ocean". Deep Sea Research Part II: Topical Studies in Oceanography. Deep-Sea Biodiversity and Life History Processes. 92: 107–113. Bibcode:2013DSRII..92..107J. doi:10.1016/j.dsr2.2012.12.002. ISSN 0967-0645.
  16. ^ Rebecca Morelle (2 February 2012). "'Supergiant' crustacean found in deepest ocean". BBC News. Retrieved 4 February 2012.
  17. ^ Harrison, Craig S.; Hida, Thomas S.; Seki, Michael P. (1983). "Hawaiian Seabird Feeding Ecology". Wildlife Monographs (85): 3–71. ISSN 0084-0173. JSTOR 3830593.
  18. ^ a b c Maroni, Paige J.; Niyazi, Yakufu; Jamieson, Alan (21 May 2025). "The supergiant amphipod Alicella gigantea may inhabit over half of the world's oceans". Royal Society. 12 (5). doi:10.1098/rsos.241635. ISSN 2054-5703. Retrieved 22 May 2025.
  19. ^ Sankaran, Vishwam. "Rarely seen 'supergiant' deep-sea cousin of woodlice is actually quite common, study finds". ca.news.yahoo.com. The Independent. Retrieved 22 May 2025.
  20. ^ Ritchie, H.; Jamieson, A. J.; Piertney, S. B. (2015-11-01). "Phylogenetic relationships among hadal amphipods of the Superfamily Lysianassoidea: Implications for taxonomy and biogeography". Deep Sea Research Part I: Oceanographic Research Papers. 105: 119–131. Bibcode:2015DSRI..105..119R. doi:10.1016/j.dsr.2015.08.014. ISSN 0967-0637.
  21. ^ ""Alicella gigantea mitochondrion, complete genome"". 2019.
  22. ^ a b Li, Jun-yuan; Song, Zeng-lei; Yan, Guo-yong; He, Li-sheng (2019-12-01). "The complete mitochondrial genome of the largest amphipod, Alicella gigantea: Insight into its phylogenetic relationships and deep sea adaptive characters". International Journal of Biological Macromolecules. 141: 570–577. doi:10.1016/j.ijbiomac.2019.09.050. ISSN 0141-8130. PMID 31505211.
  23. ^ a b Shi, Linlin; Xiao, Wenjie; Liu, Zhiguo; Pan, Binbin; Xu, Yunping (2018-11-01). "Diet change of hadal amphipods revealed by fatty acid profile: A close relationship with surface ocean". Marine Environmental Research. 142: 250–256. Bibcode:2018MarER.142..250S. doi:10.1016/j.marenvres.2018.10.012. ISSN 0141-1136. PMID 30389235.
  24. ^ Wei, Taoshu; Liao, Yanwen; Wang, Yong; Li, Junyuan; He, Lisheng (2023-11-18). "Comparably Characterizing the Gut Microbial Communities of Amphipods from Littoral to Hadal Zones". Journal of Marine Science and Engineering. 11 (11): 2197. Bibcode:2023JMSE...11.2197W. doi:10.3390/jmse11112197. ISSN 2077-1312.
  25. ^ a b Chan, Jiulin; Geng, Daoqiang; Pan, Binbin; Zhang, Qiming; Xu, Qianghua (August 2022). "Gut Microbial Divergence Between Three Hadal Amphipod Species from the Isolated Hadal Trenches". Microbial Ecology. 84 (2): 627–637. Bibcode:2022MicEc..84..627C. doi:10.1007/s00248-021-01851-3. ISSN 0095-3628. PMID 34545412.
  26. ^ Chan, Jiulin; Geng, Daoqiang; Pan, Binbin; Zhang, Qiming; Xu, Qianghua (2021). "Metagenomic Insights Into the Structure and Function of Intestinal Microbiota of the Hadal Amphipods". Frontiers in Microbiology. 12. doi:10.3389/fmicb.2021.668989. ISSN 1664-302X. PMC 8216301. PMID 34163447.
  27. ^ Li, Wenhao; Wang, Faxiang; Jiang, Shouwen; Pan, Binbin; Liu, Qi; Xu, Qianghua (2022-09-12). "Morphological and molecular evolution of hadal amphipod's eggs provides insights into embryogenesis under high hydrostatic pressure". Frontiers in Cell and Developmental Biology. 10. doi:10.3389/fcell.2022.987409. ISSN 2296-634X. PMC 9511220. PMID 36172273.
  28. ^ Wang, Ning; Shen, Chengde; Sun, Weidong; Ding, Ping; Zhu, Sanyuan; Yi, Weixi; Yu, Zhiqiang; Sha, Zhongli; Mi, Mei; He, Lisheng; Fang, Jiasong; Liu, Kexin; Xu, Xiaomei; Druffel, Ellen R.M. (2019-05-28). "Penetration of Bomb 14 C Into the Deepest Ocean Trench". Geophysical Research Letters. 46 (10): 5413–5419. doi:10.1029/2018GL081514. ISSN 0094-8276.
  29. ^ Cui, Juntao; Yu, Zhiqiang; Mi, Mei; He, Lisheng; Sha, Zhongli; Yao, Peng; Fang, Jiasong; Sun, Weidong (2020-12-15). "Occurrence of Halogenated Organic Pollutants in Hadal Trenches of the Western Pacific Ocean". Environmental Science & Technology. 54 (24): 15821–15828. Bibcode:2020EnST...5415821C. doi:10.1021/acs.est.0c04995. ISSN 0013-936X. PMID 33211967.
  30. ^ Zhu, Lingyue; Geng, Daoqiang; Pan, Bingbing; Li, Wenhao; Jiang, Shouwen; Xu, Qianghua (2022-03-01). "Trace Elemental Analysis of the Exoskeleton, Leg Muscle, and Gut of Three Hadal Amphipods". Biological Trace Element Research. 200 (3): 1395–1407. doi:10.1007/s12011-021-02728-9. ISSN 1559-0720.
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