Alicella

The genus name Alicella refers to the ship Princess Alice, which collected the first specimens in 1897. The ship itself is named after Alice Heine, who was the wife of Albert I, Prince of Monaco.

File:Alicella gigantea.png in 1899]]

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. These specimens were collected using triangular traps that were set at {{Convert|5285|m|abbr=out}} in depth.Chevreux, E. (1899). [https://www.marinespecies.org/aphia.php?p=sourcedetails&id=11475 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. 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.{{Cite web |title=WoRMS - World Register of Marine Species |url=https://www.marinespecies.org/aphia.php?p=specdetails&id=42933&tid=488208 |access-date=2025-05-17 |website=www.marinespecies.org}}{{Cite web |title=WoRMS - World Register of Marine Species |url=https://www.marinespecies.org/aphia.php?p=specdetails&id=42932&tid=488208 |access-date=2025-05-17 |website=www.marinespecies.org}} Chevreux placed this species in the family Lysianassidae. In 1906, the species description was revised by Thomas Roscoe Rede Stebbing, but little new information was provided.{{Cite book |last=Stebbing |first=Thomas R. R. |url=https://www.biodiversitylibrary.org/bibliography/1224 |title=Amphipoda I. Gammaridea |date=1906 |publisher=Friedländer |location=Berlin |doi=10.5962/bhl.title.1224}}

A second species was described as Alicella scotiae in 1912 by Charles Chilton from specimens collected during the Scottish National Antarctic Expedition.{{Cite journal |last=Ohilton |first=Chas |date=1912 |title=XXIII.—The Amphipoda of the Scottish National Antarctic Expedition |url=https://www.cambridge.org/core/product/identifier/S0080456800002957/type/journal_article |journal=Transactions of the Royal Society of Edinburgh |language=en |volume=48 |issue=2 |pages=455–520 |doi=10.1017/S0080456800002957 |issn=0080-4568}} However, this species was later recognized to actually be Eurythenes obesus, and therefore was synonymized with that species.{{Cite journal |last1=Barnard |first1=J. Laurens |last2=Shulenberger |first2=Eric |date=1976 |title=Clarification of the Abyssal Amphipod, Paralicella tenuipes Chevreux |url=https://www.jstor.org/stable/20103110 |journal=Crustaceana |volume=31 |issue=3 |pages=267–274 |doi=10.1163/156854076X00053 |jstor=20103110 |bibcode=1976Crust..31..267B |issn=0011-216X}}

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. In 2008, this genus 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.{{cite journal |author=J. K. Lowry & C. de Broyer |year=2008 |title=Alicellidae and Valettiopsidae, two new callynophorate families (Crustacea: Amphipoda) |url=http://www.mapress.com/zootaxa/2008/f/zt01843p066.pdf |journal=Zootaxa |volume=1843 |pages=57–66 |doi=10.11646/zootaxa.1843.1.5}}

{{multiple image

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| alt1 = A clump of landhoppers in the palm of a hand

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| alt2 = A giant amphipod bigger than a hand

| footer = Size comparison between a cluster of Americorchestia (left) and an Alicella gigantea (right). The former is a more typical size for amphipods.

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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).{{cite web |title=Why are so many deep-sea animals red in color? |url=https://oceanexplorer.noaa.gov/facts/red-color.html |website=oceanexplorer.noaa.gov |publisher=NOAA |access-date=22 May 2025}} Alicella gigantea however are uniformly white, which may reflect their lack of predators. Although there is very little sexual dimorphism, there are very small differences in the shape and size of antenna segments between males and females.

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.

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, one middle tooth and the rakers (blade like structures) absent. The mandible palp is attached distally to 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 medial edge (the surface pointed towards the middle of the body) 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.

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. 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 dactylus 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.

A. gigantea are the largest known amphipods in the world and can reach between {{convert|240|-|340|mm}} in length. There have been several suggested reasons and mechanisms for this gigantism.

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 size and life spans, which in turn leads to abnormally large body growth. One study found that genes related to “growth regulation” were overrepresented 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.

Another potential reason for the large size of A. gigantea is that it could have undergone a whole genome duplication, which could potentially increase the size of the species (and explain their large genome size).{{Cite journal |last1=Jamieson |first1=A. J. |last2=Lacey |first2=N. C. |last3=Lörz |first3=A. -N. |last4=Rowden |first4=A. A. |last5=Piertney |first5=S. B. |date=2013-08-01 |title=The supergiant amphipod Alicella gigantea (Crustacea: Alicellidae) from hadal depths in the Kermadec Trench, SW Pacific Ocean |url=https://www.sciencedirect.com/science/article/pii/S0967064512001932 |journal=Deep Sea Research Part II: Topical Studies in Oceanography |series=Deep-Sea Biodiversity and Life History Processes |language=en |volume=92 |pages=107–113 |bibcode=2013DSRII..92..107J |doi=10.1016/j.dsr2.2012.12.002 |issn=0967-0645}}

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 so might partly explain why this species grows so large.

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.{{Cite journal |last1=Weston |first1=Johanna N. J. |last2=Peart |first2=Rachael A. |last3=Jamieson |first3=Alan J. |date=2020-01-02 |title=Amphipods from the Wallaby-Zenith Fracture Zone, Indian Ocean: new genus and two new species identified by integrative taxonomy |url=https://www.tandfonline.com/doi/full/10.1080/14772000.2020.1729891 |journal=Systematics and Biodiversity |volume=18 |issue=1 |pages=57–78 |doi=10.1080/14772000.2020.1729891 |bibcode=2020SyBio..18...57W |issn=1477-2000}} 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.{{Cite journal |last1=Ritchie |first1=H. |last2=Jamieson |first2=A. J. |last3=Piertney |first3=S. B. |date=2015-11-01 |title=Phylogenetic relationships among hadal amphipods of the Superfamily Lysianassoidea: Implications for taxonomy and biogeography |url=https://linkinghub.elsevier.com/retrieve/pii/S0967063715001491 |journal=Deep Sea Research Part I: Oceanographic Research Papers |volume=105 |pages=119–131 |doi=10.1016/j.dsr.2015.08.014 |bibcode=2015DSRI..105..119R |issn=0967-0637}}{{cladogram|title=Phylogeny|clades=

{{cladeR |reverse=yes|style=font-size:66%;line-height:66%;

|1={{cladeR

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|1=

{{cladeR

|label1=

|1=Cyclocaris franki

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|2={{cladeR

|label1=

|1=Paralicella caperseca

|label2=

|2=Eurythenes gryllus

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|label2=

|2={{cladeR

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|1=Civifractura serendipia

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|2={{cladeR

|label1=

|1=Alicella gigantea

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|2={{cladeR

|label1=

|1={{cladeR

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|1=Tectovalopsis sp.

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|2=Tectovalopsis sp.

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|label2=

|2={{cladeR

|label1=

|1=Tectovalopsis wegeneri

|label2=

|2={{cladeR

|label1=

|1=Tectovalopsis wegeneri

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|2={{cladeR

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|1=cf. Diatectonia

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|2=Diatectonia sp.

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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.{{cite journal |last1=Maroni |first1=Paige J. |last2=Niyazi |first2=Yakufu |last3=Jamieson |first3=Alan |date=21 May 2025 |title=The supergiant amphipod Alicella gigantea may inhabit over half of the world's oceans |url=https://royalsocietypublishing.org/doi/10.1098/rsos.241635#d1e426 |journal=Royal Society |volume=12 |issue=5 |doi=10.1098/rsos.241635 |issn=2054-5703 |access-date=22 May 2025}}

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.

In 2019, the complete mitochondrial genome of A. gigantea was sequenced with a total length of 16,851 base pairs.{{Cite web |last=Li |first=Jun-Yuan |last2=Song |first2=Zeng-Lei |last3=Yan |first3=Guo-Yong |last4=He |first4=Li-Sheng |date=2019 |title="Alicella gigantea mitochondrion, complete genome" |url=https://www.ncbi.nlm.nih.gov/nuccore/MK215211.1 |website= |publisher=National Center for Biotechnology Information}}{{Cite journal |last1=Li |first1=Jun-yuan |last2=Song |first2=Zeng-lei |last3=Yan |first3=Guo-yong |last4=He |first4=Li-sheng |date=2019-12-01 |title=The complete mitochondrial genome of the largest amphipod, Alicella gigantea: Insight into its phylogenetic relationships and deep sea adaptive characters |url=https://linkinghub.elsevier.com/retrieve/pii/S014181301934961X |journal=International Journal of Biological Macromolecules |volume=141 |pages=570–577 |doi=10.1016/j.ijbiomac.2019.09.050 |issn=0141-8130 |pmid=31505211}} The study found that the genome had 13 protein-coding genes, 2 ribosomal genes, 22 transfer RNA genes and 2 noncoding gene regions.

Alicella gigantea is a marine species that has primarily been recorded in the lower abyssal and hadal depths between {{Convert|4850|–|7000|m|abbr=out}} in depth, which would restrict them to oceanic trenches and fracture zones, such as the Kermadec Trench in the southwest Pacific.{{cite web |author=Rebecca Morelle |author-link=Rebecca Morelle |date=2 February 2012 |title='Supergiant' crustacean found in deepest ocean |url=https://www.bbc.co.uk/news/science-environment-16834913 |accessdate=4 February 2012 |publisher=BBC News}} However, there is a single record of a juvenile specimen at {{Convert|1720|m|abbr=out}} in depth that was collected with a fish trap. Similar to this, there is a record of a specimen being recovered from the stomach of a black-footed albatross in the Hawaiian Islands.{{Cite journal |last1=Harrison |first1=Craig S. |last2=Hida |first2=Thomas S. |last3=Seki |first3=Michael P. |date=1983 |title=Hawaiian Seabird Feeding Ecology |url=https://www.jstor.org/stable/3830593 |journal=Wildlife Monographs |issue=85 |pages=3–71 |issn=0084-0173 |jstor=3830593}} 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. A 2025 study found A. gigantea's depth range to be {{Convert|3890|–|8931|m|abbr=out}}, which suggests that 59% of the world's oceans (and all six major ocean bodies) is suitable habitat for this amphipod.{{cite web |last1=Sankaran |first1=Vishwam |title=Rarely seen 'supergiant' deep-sea cousin of woodlice is actually quite common, study finds |url=https://ca.news.yahoo.com/rarely-seen-supergiant-deep-sea-092259427.html |access-date=22 May 2025 |website=ca.news.yahoo.com |publisher=The Independent}}

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. 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.

File:Alicella gigantea from 6700m deep.jpg. Alongside them are grenadiers]]

Like many other amphipods, adult Alicella gigantea are primarily scavengers and feed on carrion.{{cite journal |author=Claude de Broyer & Michael H. Thurston |year=1987 |title=New Atlantic material and redescription of the type specimens of the giant abyssal amphipod Alicella gigantea Chevreux (Crustacea) |journal=Zoologica Scripta |volume=16 |issue=4 |pages=335–350 |doi=10.1111/j.1463-6409.1987.tb00079.x|s2cid=86306559 }} Because of this behaviour, they are most frequently caught using baited traps. Due to their dependence on carrion as a food source, the species may be susceptible to changes occurring at the ocean's surface.

The gut microbiome of A. gigantea is dominated by Candidatus Hepatoplasma.{{Cite journal |last1=Wei |first1=Taoshu |last2=Liao |first2=Yanwen |last3=Wang |first3=Yong |last4=Li |first4=Junyuan |last5=He |first5=Lisheng |date=2023-11-18 |title=Comparably Characterizing the Gut Microbial Communities of Amphipods from Littoral to Hadal Zones |journal=Journal of Marine Science and Engineering |language=en |volume=11 |issue=11 |pages=2197 |doi=10.3390/jmse11112197 |doi-access=free |bibcode=2023JMSE...11.2197W |issn=2077-1312}}{{Cite journal |last1=Chan |first1=Jiulin |last2=Geng |first2=Daoqiang |last3=Pan |first3=Binbin |last4=Zhang |first4=Qiming |last5=Xu |first5=Qianghua |date=August 2022 |title=Gut Microbial Divergence Between Three Hadal Amphipod Species from the Isolated Hadal Trenches |url=https://link.springer.com/10.1007/s00248-021-01851-3 |journal=Microbial Ecology |language=en |volume=84 |issue=2 |pages=627–637 |doi=10.1007/s00248-021-01851-3 |pmid=34545412 |bibcode=2022MicEc..84..627C |issn=0095-3628}} 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. 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.{{Cite journal |last1=Chan |first1=Jiulin |last2=Geng |first2=Daoqiang |last3=Pan |first3=Binbin |last4=Zhang |first4=Qiming |last5=Xu |first5=Qianghua |date=2021 |title=Metagenomic Insights Into the Structure and Function of Intestinal Microbiota of the Hadal Amphipods |journal=Frontiers in Microbiology |language=English |volume=12 |doi=10.3389/fmicb.2021.668989 |doi-access=free |issn=1664-302X |pmc=8216301 |pmid=34163447}} Presently, it is unknown if these amphipods gut microbes are inherited from their parents or picked up from the surrounding environment.{{Cite journal |last1=Jamieson |first1=Alan J |last2=Weston |first2=Johanna N J |date=2023-06-01 |title=Amphipoda from depths exceeding 6,000 meters revisited 60 years on |url=https://academic.oup.com/jcb/article/43/2/ruad020/7162648 |journal=Journal of Crustacean Biology |volume=43 |issue=2 |pages=ruad020 |doi=10.1093/jcbiol/ruad020 |issn=0278-0372|doi-access=free }}

Although its size is thought to give it protection from most deep sea predators, A. gigantea are known to be preyed upon by the rough abyssal grenadier (Coryphaenoides yaquinae).{{Clarify|reason=How large were these grenadiers? How big were the specimens eaten?|date=June 2025}}

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.{{cite journal |author=J. L. Barnard & Camilla L. Ingram |title=The supergiant amphipod Alicella gigantea Chevreux from the North Pacific Gyre |journal=Journal of Crustacean Biology |volume=6 |issue=4 |year=1986 |pages=825–839 |jstor=1548395 |bibcode=1986JCBio...6..825B }} The eggs are oval in shape and are {{convert|6.95|to|14.88|mm}} 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.{{Cite journal |last1=Li |first1=Wenhao |last2=Wang |first2=Faxiang |last3=Jiang |first3=Shouwen |last4=Pan |first4=Binbin |last5=Liu |first5=Qi |last6=Xu |first6=Qianghua |date=2022-09-12 |title=Morphological and molecular evolution of hadal amphipod's eggs provides insights into embryogenesis under high hydrostatic pressure |journal=Frontiers in Cell and Developmental Biology |language=English |volume=10 |doi=10.3389/fcell.2022.987409 |doi-access=free |issn=2296-634X |pmc=9511220 |pmid=36172273}}

As juveniles, their diet has been inferred to be mostly bacteria and zooplankton debris and then transitions into carrion and algae as they mature.{{Cite journal |last1=Shi |first1=Linlin |last2=Xiao |first2=Wenjie |last3=Liu |first3=Zhiguo |last4=Pan |first4=Binbin |last5=Xu |first5=Yunping |date=2018-11-01 |title=Diet change of hadal amphipods revealed by fatty acid profile: A close relationship with surface ocean |url=https://linkinghub.elsevier.com/retrieve/pii/S0141113618306093 |journal=Marine Environmental Research |volume=142 |pages=250–256 |doi=10.1016/j.marenvres.2018.10.012 |pmid=30389235 |bibcode=2018MarER.142..250S |issn=0141-1136}} Alicella gigantea grows at a much faster rate compared to other amphipods.{{cite journal |last1=Li |first1=Wenhao |last2=Wang |first2=Faxiang |last3=Jiang |first3=Shouwen |last4=Pan |first4=Binbin |last5=Chan |first5=Jiulin |last6=Xu |first6=Qianghua |date=Oct 2021 |title=The Adaptive Evolution and Gigantism Mechanisms of the Hadal "Supergiant" Amphipod Alicella gigantea |url=https://www.researchgate.net/publication/355199453 |journal=Frontiers in Marine Science |volume=8 |bibcode=2021FrMaS...843663L |doi=10.3389/fmars.2021.743663 |doi-access=free}} 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.

Analysis of ¹⁴C signatures indicates that hadal amphipods such as Alicella gigantea have an unusually long life span of over 10 years.{{Cite journal |last1=Wang |first1=Ning |last2=Shen |first2=Chengde |last3=Sun |first3=Weidong |last4=Ding |first4=Ping |last5=Zhu |first5=Sanyuan |last6=Yi |first6=Weixi |last7=Yu |first7=Zhiqiang |last8=Sha |first8=Zhongli |last9=Mi |first9=Mei |last10=He |first10=Lisheng |last11=Fang |first11=Jiasong |last12=Liu |first12=Kexin |last13=Xu |first13=Xiaomei |last14=Druffel |first14=Ellen R.M. |date=2019-05-28 |title=Penetration of Bomb 14 C Into the Deepest Ocean Trench |journal=Geophysical Research Letters |language=en |volume=46 |issue=10 |pages=5413–5419 |doi=10.1029/2018GL081514 |issn=0094-8276|doi-access=free }}

Despite their apparently isolation from the surface, chemical contamination caused by humans has been detected in Alicella gigantea. 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 which were suggested to be linked to human activity.{{Cite journal |last1=Cui |first1=Juntao |last2=Yu |first2=Zhiqiang |last3=Mi |first3=Mei |last4=He |first4=Lisheng |last5=Sha |first5=Zhongli |last6=Yao |first6=Peng |last7=Fang |first7=Jiasong |last8=Sun |first8=Weidong |date=2020-12-15 |title=Occurrence of Halogenated Organic Pollutants in Hadal Trenches of the Western Pacific Ocean |url=https://pubs.acs.org/doi/10.1021/acs.est.0c04995 |journal=Environmental Science & Technology |volume=54 |issue=24 |pages=15821–15828 |doi=10.1021/acs.est.0c04995 |pmid=33211967 |bibcode=2020EnST...5415821C |issn=0013-936X}}{{Cite journal |last=Zhu |first=Lingyue |last2=Geng |first2=Daoqiang |last3=Pan |first3=Bingbing |last4=Li |first4=Wenhao |last5=Jiang |first5=Shouwen |last6=Xu |first6=Qianghua |date=2022-03-01 |title=Trace Elemental Analysis of the Exoskeleton, Leg Muscle, and Gut of Three Hadal Amphipods |url=https://link.springer.com/article/10.1007/s12011-021-02728-9 |journal=Biological Trace Element Research |language=en |volume=200 |issue=3 |pages=1395–1407 |doi=10.1007/s12011-021-02728-9 |issn=1559-0720}}

File:7000m Super-G in hand.jpg|Specimen

File:Alicella gigantea specimen.png|ditto

File:Alicella gigantea from 6200m.jpg|ditto, from {{Convert|6200|m|abbr=out}} depth

File:Alicella gigantea feeding.jpg|Feeding at a bait station

File:Live Alicella gigantea feeding.jpg|ditto

{{Reflist|32em}}

{{Taxonbar|from=Q18091951|from2=Q2836751}}

Category:Amphilochidea

Category:Monotypic amphipod genera

Category:Amphipods of the Pacific Ocean

Category:Amphipods of the Atlantic Ocean

Category:Crustaceans described in 1899