Tag: crab

A new crab is settling in the Mediterranean: early evidence of establishment of a Lessepsian species in the Ionian Sea

New research reveals the rapid expansion of the portunid crab, Gonioinfradens giardi, highlighting ongoing biological changes in the Mediterranean Sea.

Guest blog post by Francesco Tiralongo

The Mediterranean Sea is undergoing rapid ecological transformations driven by climate change and human-mediated species introductions. Among the most striking processes is the increasing arrival and establishment of non-indigenous species entering through the Suez Canal, a phenomenon known as Lessepsian migration.

A new study published in Acta Ichthyologica et Piscatoria documents the rapid expansion of the Indo-Pacific swimming crab Gonioinfradens giardi in the Ionian Sea, off the coast of Italy. Following the first confirmed Italian record – a single specimen collected at Portopalo di Capo Passero in November 2025 – researchers documented 11 additional individuals between November 2025 and January 2026, providing early evidence that the species has moved beyond sporadic occurrence and may already be establishing stable populations in the region.

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🦀A new study highlights the rapid expansion and early establishment of the non-indigenous Indo-Pacific swimming crab, Gonioinfradens giardi, along the Ionian coast of Sicily in the Mediterranean Sea The research was published in the open-access journal Acta Ichthyologica et Piscatoria. 👉Full article here: Tiralongo F, Leotta P, Accolla H, Tibullo D, Felici A (2026) Rapid expansion of a Lessepsian migrant crab, Gonioinfradens giardi (Crustacea, Brachyura, Portunidae), in the Ionian Sea: New records and early evidence of establishment. Acta Ichthyologica et Piscatoria 56: 145-149. https://doi.org/10.3897/aiep.56.185183 #invasivespecies #conservation #italy
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Our findings suggest that Gonioinfradens giardi is transitioning from occasional records to a more consistent presence in the central Mediterranean. This raises important questions about its potential ecological role and interactions with native species.
explains Francesco Tiralongo, lead author of the study

To reconstruct the current distribution of the species, the newly collected data integrates recent records with field observations obtained through a collaboration with local fishers utilizing standard artisanal fishing gears.

The haul of a dozen individuals within a two-month period indicates that environmental conditions are becoming more favorable for its persistence. Furthermore, these captures mark the westernmost presence of the species in the Mediterranean Sea to date.

Distribution map of *Gonioinfradens* *giardi*; new records along the Ionian coast of Sicily are shown in yellow (circles), while the red circle indicates the first published record. Credit to Tiralongo et al., 2026

The rapid emergence of this species highlights how dynamic and responsive Mediterranean ecosystems are to ongoing environmental changes. Documenting these early phases of establishment is crucial for understanding future ecological scenarios and supporting informed management decisions.
adds Alberto Felici, co-author of the study

The establishment of non-indigenous crustaceans may have cascading effects on local ecosystems, including competition with native species and potential implications for fisheries. While the long-term impacts of G. giardi remain uncertain, its rapid spread reflects broader changes already underway in Mediterranean marine biodiversity.

*Gonioinfradens giardi*, credit to Francesco Tiralongo.

This case adds to a growing list of species reshaping Mediterranean ecosystems. Continuous monitoring, including contributions from fishers and citizen scientists, will be essential to track these dynamics and support adaptive management strategies.
Tiralongo adds

A YouTube video by the study’s lead author, Francesco Tiralongo, in which he introduces Gonioinfradens giardi – a species relatively unknown in the Mediterranean – explains its origin, describes how it entered the ecosystem, and outlines its current distribution in Italian waters as well as its potential impacts on ecosystems and fisheries.

The study contributes to the expanding body of evidence that the Mediterranean Sea is becoming a hotspot for biological invasions, emphasizing the need for coordinated research and monitoring efforts at regional and basin-wide scales.

Original source:

Tiralongo F, Leotta P, Accolla H, Tibullo D, Felici A (2026) Rapid expansion of a Lessepsian migrant crab, Gonioinfradens giardi (Crustacea, Brachyura, Portunidae), in the Ionian Sea: New records and early evidence of establishment. Acta Ichthyologica et Piscatoria 56: 145-149. https://doi.org/10.3897/aiep.56.185183

Notice me! Neglected for over a century, Black sea spider crab re-described

After the revision of available type specimens from all available collections in the Russian museums and the Senckenberg Museum in Frankfurt-on-Main, as well as newly collected material in the Black Sea and the North-East Atlantic, a research team of scientists, led by Dr Vassily Spiridonov from Shirshov Institute of Oceanology of Russian Academy of Sciences, re-described Macropodia czernjawskii and provided the new data on its records and updated its ecological characteristics.

Even though recognised in the Mediterranean Sea, the Macropodia czernjawskii spider crab was ignored by scientists (even by its namesake Vladimir Czernyavsky) in the regional faunal accounts of the Black Sea for more than a century. At the same time, although other species of the genus have been listed as Black sea fauna, those listings are mostly wrong and occurred either due to historical circumstances or misidentifications.Now, scientists re-describe this, most likely, only species of the genus occurring in the Black Sea in the open-access journal Zoosystematics and Evolution.

The studied spirder crab species *Macropodia czernjawskii* in the wild, Tuaphat (near Gelendzhik), Caucasus, Black Sea.
Photo by Sergey Anosov

The spider crab genus Macropodia was discovered in 1814 and currently includes 18 species, mostly occurring in the Atlantic and the Mediterranean. The marine fauna of the Black Sea is predominantly of Mediterranean origin and Macropodia czernjawskii was firstly discovered in the Black Sea in 1880, but afterwards, its presence there was largely ignored by the scientists.

After the revision of available type specimens from all available collections in the Russian museums and the Senckenberg Museum in Frankfurt-on-Main, as well as newly collected material in the Black Sea and the North-East Atlantic, a research team of scientists, led by Dr Vassily Spiridonov from Shirshov Institute of Oceanology of Russian Academy of Sciences, re-described Macropodia czernjawskii and provided the new data on its records and updated its ecological characteristics.

“The analysis of the molecular genetic barcode (COI) of the available material of Macropodia species indicated that M. czernjawskii is a very distinct species while M. parva should be synonimised with M. rostrata, and M. longipes is a synonym of M. tenuirostris”,
states Dr Spiridonov sharing the details of the genus analysis.

All Macropodia species have epibiosis and M. czernjawskii is no exception: almost all examined crabs in 2008-2018 collections had significant epibiosis. It normally consists of algae and cyanobacteria and, particularly, a non-indigenous species of red alga Bonnemaisonia hamifera, officially reported in 2015 at the Caucasian coast of the Black Sea, was found in the epibiosis of M. czernjawskii four years earlier.

“It improves our understanding of its invasion history. Museum and monitoring collections of species with abundant epibiosis (in particular inachid crabs) can be used as an additional tool to record and monitor introduction and establishments of sessile non-indigenous species,”
suggests Dr Spiridonov.

The spider crab species *Macropodia czernjawskii* in the wild, Tuaphat (near Gelendzhik), Caucasus, Black Sea.
Photo by Sergey Anosov

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Original source:

Spiridonov VA, Simakova UV, Anosov SE, Zalota AK, Timofeev VA (2020) Review of Macropodia in the Black Sea supported by molecular barcoding data; with the redescription of the type material, observations on ecology and epibiosis of Macropodia czernjawskii (Brandt, 1880) and notes on other Atlanto-Mediterranean species of Macropodia Leach, 1814 (Crustacea, Decapoda, Inachidae). Zoosystematics and Evolution 96(2): 609-635. https://doi.org/10.3897/zse.96.48342

Behind Green Eyes: New species of deep-water hermit crab finds itself unusual shelters

‘Green-eyed hermit crab’ is the common name for a new species recently discovered off the West Coast of South Africa. Apart from its magnetic stare, however, there is a number of characteristic morphological traits and an unusual home preference that all make the crustacean unique.

Formally named after the University of Cape Town (UCT) alumnus Dr Lara Atkinson, the new hermit crab Paragiopagurus atkinsonaeis described by PhD candidate Jannes Landschoff, UCT, and Dr Rafael Lemaitre, Smithsonian Institution, USA, in the open access journal ZooKeys.

The Green-eyed hermit crab measures merely 70 mm in length and sports a coloration of mottled orange nuanced with cream to white. Among its distinct traits is the significant sexual dimorphism, where the males grow much larger right chelipeds in comparison to females.

Much like other hermit crabs in its family (Parapaguridae), the little crustacean does not use the shells of other molluscs to shelter its vulnerable body, but rather finds a home in the soft, polypy masses built from sand and material created by sea anemones which go on to live on the backs of these crabs in an amazing symbiosis.

“So, when you hold it [the hermit crab], it’s just organic material glued together with some sand,” explains Jannes in the UCT’s announcement about their discovery.

“Even more curiously, parapagurids start off in the usual way, occupying a tiny gastropod shell. But these eventually become deposited within this non-calcified ‘amalgam’ created by the anemones. As the hermit crab grows, its live ‘shell’, or carcinoecia, grows with it.”

The new species was discovered during a three-week survey back in 2013, conducted by the Department of Forestry and Fisheries and the South African Environmental Observation Network in the shallower deep waters (199 m to 277 m) off the West Coast of South Africa. Lara was on board one of the vessels when an unusual green-eyed crab turned up among the numerous specimens collected in one of the trawls. It was at that moment that she noticed that there was something peculiar about it and sent it for identification.

Restricted to a surprisingly small area for no obvious reason, the new species might be just bringing up some very important conservation messages.

“The area isn’t noticeably biologically or oceanographically distinct, but more detailed sampling from the area will tell us more about the habitat conditions. Future studies need to take this into account and give the area more research attention. If there’s something unusual about the site, you’d want to be careful, especially with mining operations along the West Coast,” says Jannes.

“Incidents like these are flags for future protection. The bottom line is we know so little about these offshore habitats from an ecological point of view. And if you’re planning for a marine protected area, you have to know what it is you’re protecting in that area.”

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Original source:

Landschoff J, Lemaitre R (2017) Differentiation of three common deep-water hermit crabs (Crustacea, Decapoda, Anomura, Parapaguridae) from the South African demersal abundance surveys, including the description of a new species of Paragiopagurus Lemaitre, 1996. ZooKeys676: 21-45. https://doi.org/10.3897/zookeys.676.12987

Caught red-handed: The ‘Candy striped hermit crab’ is a new species from the Caribbean

Recent underwater photographs and video obtained using scuba equipment by underwater photographer Ellen Muller at dive sites in the National Marine Park of the southern Caribbean island of Bonaire revealed the presence of a small, secretive and brightly colored red-striped hermit crab that proved to represent a species new to science. The new few-millimeter species is described in the open access journal ZooKeys.

The color pattern reminded author Dr. Rafael Lemaitre, Smithsonian Institution, USA, of traditional candy cane, and thus he assigned the common name “Candy striped hermit crab”. Meanwhile, the scientific name of the new species is Pylopaguropsis mollymullerae after Ellen Muller’s young granddaughter Molly Muller. The underwater photographer believes that the honor would “inspire her to continue the tradition of protecting the amazing and fragile diversity of marine life in Bonaire”.

The unusual hermit crab was first photographed inadvertently alongside a “flaming reef lobster”, while observing invertebrates that aggregate in crevices under a large coral ledge. Subsequently, more hermit crabs were photographed in various crevices shared with moray eels such as the “broad banded moray”, “spotted moray”, and “green moray”. When permits were obtained from the Government of the Island Territory of Bonaire, a few specimens were collected and brought for study to the Smithsonian Institution. The formal description was then prepared for publication and specimens were deposited in the collections of the National Museum of Natural History, as required by scientific rules when naming new species.

The shape of the right, or major, pincer of this new hermit crab species is remarkable and unique with its shape and massive size when compared to the body. The underside of the claw of this pincer is deeply excavated, scoop-like. The function of the pincer and claw, however, is at present unknown, although a video shows that it is used by the hermit crab to push itself while crawling along the bottom.

The behavior of this new hermit crab is intriguing. Is there an ecological association of this new species with moray eels? Could this new hermit crab species function as a “cleaner” or a “den commensal”? At least in one instance, an individual was observed crawling on the body of a “broad banded moray”, perhaps feeding on mucus or materials present on it. These observations could be interpreted as evidence of some kind of symbiotic association, or den commensalism, between the two animals. The brightly colored pattern of the hermit crab with red stripes and very long, hairy antennae are also typical for most crustaceans considered fish “cleaners”.

“Cleaning” parasites or fouling organisms from the body of many cooperating fish, or removal of undesired food particles by certain small and colorful shrimps has been known for nearly 60 years, but never has a hermit crab been documented to engage in such type of ecological association. Further studies are needed in order to confirm the true ecological role of this fascinating hermit crab.

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Original source:

Lemaitre R (2017) Discovery of a new species of hermit crab of the genus Pylopaguropsis Alcock, 1905 from the Caribbean: “den commensal” or “cleaner”? (Crustacea, Anomura, Paguridae). ZooKeys 646: 139-158, https://doi.org/10.3897/zookeys.646.11132

New crab species shares name with 2 ‘Harry Potter’ characters and a hero researcher

While not much is known about the animals living around coral reefs, ex-Marine turned researcher Harry Conley would often take to the island of Guam, western Pacific Ocean, and dig deep into the rubble to find fascinating critters as if by magic learnt at Hogwarts. Almost 20 years after his discoveries and his death, a secret is revealed on the pages of the open access journal ZooKeys – a new species and genus of crab, Harryplax severus.

Having dug as deep as 30 m into Guam’s coral reef rubble, Harry Conley collected many specimens which stayed in his personal collection until the early 2000’s when Dr. Gustav Paulay, currently affiliated with the University of Florida, handed the specimens to the second author of the present study, Dr. Peter Ng, National University of Singapore, which resulted in many discoveries and publications. Among the lot, however, were two unusual specimens which were not studied until much later. Only recently did Dr. Peter Ng and his colleague at the National University of Singapore and lead author of the paper, Dr. Jose Christopher E. Mendoza, discover that they represent not only a new species, but also a new genus.

Having chosen the name Harryplax for the new genus, the two authors pay tribute to the crab’s original collector Harry Conley, who they describe as a “soft-spoken ex-Marine with a steely determination and a heart of gold,” and whose endeavours “have substantially advanced the cause of marine science”. The name is also meant to allude to the main protagonist in J. K. Rowling’s famous fantasy novel series, whose magical abilities the scientists liken to Conley’s knack for finding rare or new species. Of the two authors, Dr. Mendoza is the self-confessed ‘Potterhead’, who was not about to pass up the chance of naming a new crab after his favourite fictional characters. In his turn, Dr. Ng, who knew Harry Conley personally, was quite amused and happy to agree.

The crab’s species name, severus, is inspired by another ‘Harry Potter’ character – Professor Severus Snape, who despite being a central character in the series, keeps his background and agenda mysterious until the very end, when he reveals a key secret. Showing his real identity, the character, to the authors, is “just like the present new species which has eluded discovery until now, nearly 20 years after it was first collected”.

The new species is a tiny crab measuring less than a centimeter in both length and width and can be found deep in coral rubble or under subtidal rocks, perhaps also in cavities. To survive in the dark depths, the species has evolved with reduced eyes, well developed antennae, and long, slender legs. For the time being it is known only from the island of Guam.

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Original source:

Mendoza JCE, Ng PKL (2017) Harryplax severus, a new genus and species of an unusual coral rubble-inhabiting crab from Guam (Crustacea, Brachyura, Christmaplacidae). ZooKeys 647: 23-35. https://doi.org/10.3897/zookeys.647.11455

New species of pea-size crab parasitizing a date mussel has a name of a Roman god

Tiny crabs, the size of a pea, dwell inside the mantles of various bivalves, living off the food filtered by their hosts. A new species of these curious crustaceans has recently been reported from the Solomon Islands, where an individual was found to parasitise a large date mussel.

Because of the new pea crab’s characteristic large additional plate, covering its upper carapace, giving it the illusion of having two faces, it has been named after Janus, the Roman two-faced god. Discoverers Dr Peter Ng, National University of Singapore, and Dr Christopher Meyer, U.S. National Museum of Natural History, Smithsonian Institution, have their findings published in the open access journal ZooKeys.

Being only the second species in the genus (the first was from Malaysia), the new pea crab Serenotheres janus can be distinguished by its broader carapace and other features. It is cream-yellow in colour. oo_106009

Both representatives of the genus are unique in having an additional large plate covering the upper side of the carapace. However, its purpose is still unknown. The two pea crabs are also the only known parasites of the rock-boring bivalves of the mytilid subfamily Lithophaginae.

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Original source:

Ng PKL, Meyer C (2016) A new species of pea crab of the genus Serenotheres Ahyong & Ng, 2005 (Crustacea, Brachyura, Pinnotheridae) from the date mussel Leiosolenus Carpenter, 1857 (Mollusca, Bivalvia, Mytilidae, Lithophaginae) from the Solomon Islands. ZooKeys 623: 31-41. doi: 10.3897/zookeys.623.10272

Crab from the Chinese pet market turns out to be a new species of a new genus

Shimmering carapaces and rattling claws make colourful freshwater crabs attractive to pet keepers. To answer the demand, fishermen are busy collecting and trading with the crustaceans, often not knowing what exactly they have handed over to their client.

Luckily for science and nature alike, however, such ‘stock’ sometimes ends up in the hands of scientists, who recognise their peculiarities and readily dig into them to make the next amazing discovery. Such is the case of three researchers from University of New South Wales, Australia, The Australian Museum, Sun Yat-sen University, China, and National Chung Hsing University, Taiwan, who have found a new species and even a new genus of freshwater crab, and now have it published in the open access journal ZooKeys.

Knowing about the growing demand for eye-catching freshwater crabs from southern China, the authors took a look at the ornamental fish market to eventually identify an individual with unusually structured male gonopod, which in crustaceans is a swimming appendage modified to serve as a reproductive organ. Having their interest drawn by the peculiar crab, lead author Chao Huang managed to persuade the fish dealer to let them survey the collection site located in northern Guangdong, southern China.

Despite superficial resemblance to an already existing freshwater crab genus, at second glance, the crab turned out to be quite distinct thanks to a unique set of features including the carapace, the gonopod and the relatively long and slender legs. Once the molecular analyses’ results were also in, the authors had enough evidence to assign the freshwater crab as a species and even a genus new to science.

Being a primarily aquatic species, the new crab prefers the pools of limestone hillstreams, therefore its name Yuebeipotamon calciatile, where calciatile means ‘living on limestone’. To adapt to the habitat, the species seems to have developed its characteristic slender legs, which make it easier for the crab to climb and move around whenever the short-lived limestone hillstreams make it search for a new home.

The carapace of the new crab is usually coloured in maroon to dark brown, while the claws and legs are reddish to purplish. Interestingly, the adults are much more vivid compared to the juveniles.

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Original source:

Citation: Huang C, Shih H-T, Mao SY (2016) Yuebeipotamon calciatile, a new genus and new species of freshwater crab from southern China (Crustacea, Decapoda, Brachyura, Potamidae). ZooKeys 615: 61-72. doi: 10.3897/zookeys.615.9964