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Alicella

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Alicella gigantea
Specimen collected from the 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 a giant species of amphipod that lives in the deep sea. Sometimes referred to as the "supergiant amphipod", the largest of these crustaceans reach up to 34 cm (13 in) in length. It is the only species within the genus Alicella. This species only lives in the deep sea at 4,850–7,000 m (15,910–22,970 ft) in depth. The species is pale in colour and is distinguished from other deep sea amphipods by minute anatomical differences, apart from size in the larger specimens. The large size of the species is often presented as an example of abyssal gigantism, though the specifics of this trait remain under investigation. Genetic studies into the species have found that it has an exceptionally large genome, which may be linked to its large body size.

It was first collected and described in the 1890s from the Madeira Abyssal Plain off the Canary Islands. Although it is rarely detected, A. gigantea is a cosmopolitan species and can potentially occur in 59% of the world's oceans. Their diet varies with age, but they are primarily scavengers of carrion. Like other amphipods, female A. gigantea brood their eggs in pouches. Individuals of the species are inferred to have an unusually long life span and can reach over 10 years in age. Despite their relative isolation from the surface, human pollutants such as DDT and chlordane have been detected in specimens.

Taxonomy

[edit]
Édouard Chevreux, 1899

The first two specimens of Alicella gigantea were collected by the Princess Alice, a ship named after Alice Heine, wife of Prince Albert I of Monaco.[2] These specimens were collected while on an expedition at the Madeira Abyssal Plain off the Canary Islands in 1897 using triangular traps that were set at 5,285 metres (17,339 ft) in depth.[3][2] The species was then subsequently described by Édouard Chevreux, who named the genus after the ship they were collected by. Chevreux placed this species in the family Lysianassidae. The holotype (a single specimen upon which a species description is made) and paratype (additional specimens on which a species description is made) specimens are a juvenile of indeterminate sex and a juvenile male respectively; they are currently deposited within the Oceanographic Museum of Monaco.[4][5] In 1906, the species description was revised by Thomas Roscoe Rede Stebbing, but little new information was provided.[6]

A second species was described as Alicella scotiae in 1912 by Charles Chilton from a specimen 20 mm (0.79 in) long collected during the Scottish National Antarctic Expedition. It was described as a new species because of subtle differences in the morphology of the mouthparts.[7] However, this species was later recognized to actually be Eurythenes obesus, a species described by Jeremy Barnard and Eric Shulenberger in 1976, and therefore was synonymized with that species, making A. gigantea the only species in its genus.[8]

Phylogeny[9]

A. gigantea 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 genus was moved from the Lysianassidae to a new family, the Alicellidae, and was selected as its type genus. This family contains six other genera, all of which are deep sea scavengers.[10]

Phylogeny

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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 (group of organisms that include all descendants of a common ancestor) with Tectovalopsis and Diatectonia.[9] In contrast to this, a 2015 study found that Alicella formed a clade with Cyclocaris and Tectovalopsis although Diatectonia sequences were not used in this study.[11]

Description

[edit]
Specimen measuring around 120 mm (4.7 in) in length.

Since red wavelengths of light are quickly absorbed by water and thus doesn't reach the deep sea, most amphipods have red to orange coloration, which helps them avoid predators. Alicella gigantea however are mostly pale, which may reflect their lack of predators.[12] Although there is very little sexual dimorphism, there are very small differences in the shape and size of antenna segments between males and females.[3]

A. gigantea can be best distinguished from other Alicellidae by the combination of having the first gnathopod (leg-like appendage modified for feeding) simple in structure and the first urosomite (segment that makes up part of the abdomen) with a rounded hump.[9]

The peduncle (the first three segments of the antennae) of the second antennae is short and its first article (segment) is strongly swollen. The mouthparts form a squarish bundle with the labrum and epistome (plate-like structures) being inconspicuous and blunt. The incisor edge (cutting edge of the mandible) is straight with some inner corner teeth. There is one middle tooth and the rakers (blade-like structures) are absent. The mandible palp is attached to the front end of the molar, while the molar (grinding section of the mandible) itself is rather large, simple and covered in small hairs. The first maxilla (mouthpart appendages) have an inner plate with many setae (hair-like structures) occupying the inner edge while the first maxilla palp (appendage sprouting off the maxilla) is two-jointed and large. The second maxilla has a medial facial row of setae and the inner and outer plates of the maxilliped (appendages modified for feeding) are strongly developed. The second maxilla palp is longer than the outer plate.[13]

The first coxa (first segment of the gnathopod) 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 dactylus (claw) is large. In the second gnathopod, article six is slightly shorter than article five (both of which are elongated and linear) and the seventh article is an overlapping obsolescent palm. The dactyli of the third to seventh pereopods (leg-like structures) are quite short. The inner ramus (branches at the end of an appendage) of the second uropod (appendages on the last segment of the body) is unnotched. The third uropod has a regular peduncle (segment at beginning of appendage) and the outer ramus is articulated. The telson (rearmost segment on the body) is elongated and deeply cleft.[13]

Gigantism

[edit]
A clump of landhoppers in the palm of a hand
A giant amphipod bigger than a hand
Size comparison between a cluster of Americorchestia (left) and an Alicella gigantea (right). The former is a more typical size for amphipods.

A. gigantea is the largest known amphipod and can reach between 240–340 mm (9.4–13.4 in) in length.[13][14] As such, it is sometimes referred to as the "supergiant amphipod".[12][15] For comparison, other deep sea amphipods such as Eurythenes gryllus and Tectovalopsis wegeneri have been recorded at 126 mm (5.0 in) and 33.9 mm (1.33 in) in length respectively.[16][17] There have been several suggested reasons and mechanisms for this gigantism.[14][18]

Deep sea habitats have reduced temperatures and very high levels of hydrostatic pressure. To counteract these pressures, A. gigantea and other deep sea amphipods are hypothesized to have increased cell sizes and lifespans, which in turn lead to abnormally large body growth. One study in 2021 found that genes related to "growth regulation" were over-represented in A. gigantea when compared to smaller amphipods. This indicates that size control or growth regulation mechanisms may be responsible for the large size of the species.[14]

One study reported that A. gigantea had a high level of selenium in its leg muscles. This trace element is linked with growth and metabolic activity and therefore might partly explain why this species grows so large.[19] Another potential reason for the large size of A. gigantea was suggested by a 2013 study: It could have undergone a whole genome duplication, which could potentially increase the size of the species and explain its large genome size.[18]

Genome

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In 2013, the size of the whole genome was 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 faster rate at which the genome size changes. It was hypothesized that this could be due to a whole genome duplication, but the authors cautioned this would require further study to prove.[18]

In 2019, the complete mitochondrial genome of A. gigantea was sequenced with a total length of 16,851 base pairs.[20][21] The study found that the genome had 13 protein-coding genes, 2 ribosomal genes, 22 transfer RNA genes and 2 noncoding gene regions.[21]

Distribution and habitat

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Possible maximal range of A. gigantea; Black dots represent localities where Alicella have been collected, whereas blue sections indicate areas of seafloor within adequate depth for the species

Alicella gigantea is a rarely encountered marine species that has primarily been recorded in the lower abyssal and hadal depths between 4,850–7,000 metres (16,000–23,000 ft) in depth,[18][15] which would restrict them to oceanic trenches and fracture zones, such as the Kermadec Trench in the southwest Pacific.[22] 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.[13] There also is a record of a specimen from the stomach of a black-footed albatross in the Hawaiian Islands.[23] 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.[12] A 2025 study of 195 collections found that A. gigantea occur in depths between 3,890–8,931 m (12,760–29,300 ft), which suggests that 59% of the world's oceans (and all six major ocean bodies) is suitable habitat for this amphipod.[15][24]

It is a cosmopolitan species and has been recorded in the North Atlantic, North Pacific, and South West Pacific oceans, though there are numerous gaps in their distribution that are likely due to incomplete sampling of this species.[18] A 2025 study examined the genetics of A. gigantea populations over its entire known range, showing that most populations shared a single haplotype (group of genes that are inherited from a parent) for each gene. This indicates that there is significant gene flow between populations. However, most collection sites for this study were in Pacific ocean trenches, which may have skewed the results.[15]

Biology

[edit]
Swarms of Alicella feeding from BRUVs. The fish in the first photo are grenadiers

Marine amphipods such as Alicella gigantea swim using their pleopods, which are pulsated more quickly to increase their speed. They are also capable of walking on solid surfaces using their pereopods, but this method is not as fast.[25]

Feeding ecology

[edit]

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.[18]

The gut microbiome of A. gigantea is dominated by Candidatus Hepatoplasma.[26][27] One study in 2022 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.[27] It has also been discovered that hadal amphipods such as A. gigantea have large amounts of "probiotic" gut microbiota (microorganisms that are beneficial to the host).[28] Presently, it is unknown if these amphipod's gut microbes are inherited from their parents or picked up from the environment.[12]

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.[18] However, A. gigantea ranging from 40 to 100 mm (1.6 to 3.9 in) in length have been recorded from stomach contents of the Coryphaenoides yaquinae, the rough abyssal grenadier.[13][12]

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.[13] The eggs are oval in shape and are 6.95 to 14.88 mm (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, which has a porous structure with pores averaging less than 10 μm in diameter.[29]

Their diet consists mostly of bacteria and zooplankton debris as juveniles, transitioning into carrion and algae as they mature.[30] Analysis of 14C signatures indicates that hadal amphipods such as Alicella gigantea have an unusually long lifespan of over 10 years.[31]

Human impact

[edit]

Despite their apparent isolation from the ocean's surface, manmade pollutants have been detected in Alicella gigantea.[12] In one study in 2020, pesticides such as DDT and chlordane were detected in A. gigantea specimens, whilst in a 2022 study trace elements such as cadmium and chromium were detected in high concentrations which were suggested to be linked to human activity.[32][19] Due to their dependence on carrion as a food source, the species may be susceptible to changes occurring at the surface such as chemical pollution and overfishing.[30]

References

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  1. ^ "Alicella gigantea Chevreux, 1899". Integrated Taxonomic Information System. Retrieved 10 January 2012.
  2. ^ a b Chevreux, Édouard (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 17 May 2025.
  5. ^ "WoRMS - World Register of Marine Species". www.marinespecies.org. Retrieved 17 May 2025.
  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, Jerry L; 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. ^ a b c Weston, Johanna N J; Peart, Rachael A; Jamieson, Alan J (2 January 2020). "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.
  10. ^ Lowry, James K; de Broyer, Claude (2008). "Alicellidae and Valettiopsidae, two new callynophorate families (Crustacea: Amphipoda)" (PDF). Zootaxa. 1843: 57–66. doi:10.11646/zootaxa.1843.1.5.
  11. ^ Ritchie, Heather; Jamieson, Alan J; Piertney, Stuart B (1 November 2015). "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.
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  13. ^ a b c d e f Barnard, Jerry L; Ingram, Camilla L (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.
  14. ^ a b c Li, Wenhao; Wang, Faxiang; Jiang, Shouwen; Pan, Binbin; Chan, Jiulin; Xu, Qianghua (October 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 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). Bibcode:2025RSOS...1241635M. doi:10.1098/rsos.241635. ISSN 2054-5703. PMC 12092127. PMID 40400524.
  16. ^ D’Acoz, Cédric d’Udekem; Havermans, Charlotte (10 June 2015). "Contribution to the systematics of the genus Eurythenes S.I. Smith in Scudder, 1882 (Crustacea: Amphipoda: Lysianassoidea: Eurytheneidae)". Zootaxa. 3971 (1). doi:10.11646/zootaxa.3971.1.1. ISSN 1175-5334.
  17. ^ Barnard, Jerry L; Ingram, C L (1990). Lysianassoid Amphipoda (Crustacea) from deep-sea thermal vents. Smithsonian Contributions to Zoology. (499), 1-80. https://doi.org/10.5479/si.00810282.499
  18. ^ a b c d e f g Jamieson, A J; Lacey, Nicholas C; Lörz, Anne -N; Rowden, Ashley A; Piertney, Stuart B (1 August 2013). "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.
  19. ^ a b Zhu, Lingyue; Geng, Daoqiang; Pan, Bingbing; Li, Wenhao; Jiang, Shouwen; Xu, Qianghua (1 March 2022). "Trace elemental analysis of the exoskeleton, leg muscle, and gut of three hadal amphipods". Biological Trace Element Research. 200 (3): 1395–1407. Bibcode:2022BTER..200.1395Z. doi:10.1007/s12011-021-02728-9. ISSN 1559-0720. PMID 34018124.
  20. ^ Li, Jun-Yuan; Song, Zeng-Lei; Yan, Guo-Yong; He, Li-Sheng (2019). "Alicella gigantea mitochondrion, complete genome". National Center for Biotechnology Information.
  21. ^ a b Li, Jun-yuan; Song, Zeng-lei; Yan, Guo-yong; He, Li-sheng (1 December 2019). "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.
  22. ^ Rebecca Morelle (2 February 2012). "'Supergiant' crustacean found in deepest ocean". BBC News. Retrieved 4 February 2012.
  23. ^ Harrison, Craig S; Hida, Thomas S; Seki, Michael P (1983). "Hawaiian seabird feeding ecology". Wildlife Monographs (85): 3–71. ISSN 0084-0173. JSTOR 3830593.
  24. ^ Sankaran, Vishwam (21 May 2025). "Rarely seen 'supergiant' deep-sea cousin of woodlice is actually quite common, study finds". ca.news.yahoo.com. The Independent. Retrieved 22 May 2025.
  25. ^ Steele, Derek H (1988). "What is the amphipod life style?". Crustaceana. Supplement (13): 134–142. ISSN 0167-6563. JSTOR 25027759.
  26. ^ Wei, Taoshu; Liao, Yanwen; Wang, Yong; Li, Junyuan; He, Lisheng (18 November 2023). "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.
  27. ^ 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.
  28. ^ 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.
  29. ^ Li, Wenhao; Wang, Faxiang; Jiang, Shouwen; Pan, Binbin; Liu, Qi; Xu, Qianghua (12 September 2022). "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.
  30. ^ a b Shi, Linlin; Xiao, Wenjie; Liu, Zhiguo; Pan, Binbin; Xu, Yunping (1 November 2018). "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.
  31. ^ 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. (28 May 2019). "Penetration of bomb 14C into the deepest ocean trench". Geophysical Research Letters. 46 (10): 5413–5419. doi:10.1029/2018GL081514. ISSN 0094-8276.
  32. ^ Cui, Juntao; Yu, Zhiqiang; Mi, Mei; He, Lisheng; Sha, Zhongli; Yao, Peng; Fang, Jiasong; Sun, Weidong (15 December 2020). "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.
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