Squat lobsters are not lobsters in the culinary sense. They are decapod crustaceans of the infraorder Anomura, the same group that includes hermit crabs and king crabs, and most species are small, laterally compressed animals that shelter in crevices or perch on hard substrates, waving their elongated claws in the current to feed. The family Munidopsidae, to which the new species belongs, is dominated by deep-water lineages, many of which are associated with seamounts, canyons, and other hard-bottom habitats far below the reach of sunlight-driven photosynthesis. Because these environments are geographically isolated from continental shelves and exhibit complex topographic and oceanographic patterns, they often harbor distinctive benthic communities, including endemic species found nowhere else.

The specimens that led to the new species were collected in late March 2024, during FORV Sagar Sampada cruise 404, using a chain bag dredge deployed at a station located at 8.54 degrees North, 73.26 degrees East, on what the team designated seamount 4 off Minicoy. Four individuals were recovered: an ovigerous female designated as the holotype, one male and two females designated as paratypes. All four came from the same dredge haul at 360 meters depth, collected by R. Ravinesh and his shipboard colleagues. The animals are small even by squat lobster standards, with postorbital carapace lengths ranging from about 4.5 to 5.2 millimeters and carapace widths between 3.7 and 4.4 millimeters.

Back in the laboratory, the team cleaned, photographed, and examined the specimens under a Leica M80 stereo-zoom microscope fitted with a high-definition camera, taking measurements with calibrated imaging software. The morphological analysis followed the descriptive terminology established in a 2019 revision of the genus by Rodríguez-Flores, Macpherson, and Machordom, which had itself described fifteen new species and remains the taxonomic backbone for Leiogalathea. Every appendage was scrutinized: the spination of the third maxillipeds, the proportions of the first pereopods, the armature of the walking legs, the shape of the rostrum, and the pattern of ridges sculpting the carapace, the armored plate that covers the head and thorax.

That ridge pattern proved decisive. Leiogalathea samudragiri shares with three of its closest relatives, L. achates, L. evander, and L. laevirostris, an unarmed hepatic margin on the carapace, a feature that initially groups them together. But the new species stands apart in two consistent characters: its mesogastric and mid-transverse ridges on the carapace are uninterrupted, running continuously across the midline, and the posterior half of the carapace bears six transverse ridges. In the three related species, the mid-transverse ridge is interrupted medially or submedially, and only four or five ridges follow it. Additional differences reinforce the split. Unlike L. achates, the new species lacks a spine on the posterior branchial margin and has subequal rather than unequal distal spines on the second antennal article. Unlike L. evander, it carries three well-developed rostral teeth rather than four to six rudimentary ones, and its abdominal tergite 3 bears a single elevated ridge rather than two. Unlike L. laevirostris, the basal antennular article is unarmed at its distomesial corner, and the mesial margin of the first pereopod’s carpus carries one spine rather than three.

The detailed anatomy is a study in miniature engineering. The rostrum, the pointed projection between the eyes, is slightly downturned and flattened dorsally, about 1.5 times as long as broad, with serrated lateral margins bearing three small teeth and three progressively smaller rudimentary teeth. The first pereopods, the elongated claws that give squat lobsters their characteristic silhouette, extend to nearly three times the carapace length and are clothed in uniramous stiff setae, with the merus segment alone slightly exceeding the carapace length and bristling with strong spines arranged along its mesial, dorsal, lateral, and ventral surfaces. The walking legs are moderately slender and laterally compressed, with propodi more than five times as long as broad and dactyli armed with rows of small, proximally diminishing teeth, each tipped with a slender movable spinule. The third maxilliped’s ischium terminates in a strong spine on its flexor margin and carries a crista dentata of twenty-two corneous denticles.

Even the coloration, recorded from freshly collected material, is distinctive and unexpectedly vivid for an animal living in near darkness. The rostrum and the anterior two-thirds of the carapace are bright orange, with light yellow patches on the posterior gastric region; the posterior carapace and anterior abdominal segments are pale orange, and the pereopods are bright orange marked with white patches. The species name itself is a nod to its habitat, combining the Sanskrit words samudra, meaning ocean, and giri, meaning mountain, a direct reference to the seamount where the animals were found. The holotype female was ovigerous, carrying eggs, which suggests the population was reproductively active at the time of collection.

The broader context makes the find more significant than a single addition to a checklist. The genus Leiogathea, established by Keiji Baba in 1969, is dominated by the Pacific Ocean, which hosts fourteen of its species, while the Atlantic and Indian Oceans had only two each before this description. The munidopsid fauna of the Northern Indian Ocean, the authors note, remains relatively unexplored compared with neighboring regions. A previous expedition had already yielded an unresolved Leiogalathea specimen from the Andaman Sea, reported as Leiogalathea sp. because it was damaged, hinting that the region harbors more diversity than the formal record reflects. The authors also point out that overlapping morphological characters among congeners probably indicate the existence of pseudocryptic species within the genus, externally near-identical lineages that only careful comparison of fine structural details, or genetic analysis, can separate.

The expedition itself is part of a larger national effort. The samples were gathered under India’s Deep Ocean Mission, specifically the Samudrayaan program, coordinated through the Ministry of Earth Sciences, with CMLRE in Kochi leading the faunal exploration aboard the research vessel Sagar Sampada. Seamounts have been recognized as ecological hotspots since faunal explorations began in the 1940s, yet only a handful of Indian Ocean seamounts have ever been surveyed, leaving vast tracts of undersea topography biologically uncharted. Voucher specimens of the new species, registered under the catalog numbers IO/SS/ANO/00195 through 00197, are deposited in the Bhavasagara Referral Centre at CMLRE, which serves as the regional node of the Ocean Biodiversity Information System for the Indian Ocean, and the associated occurrence data will be made publicly available through the OBIS portal.

For now, Leiogalathea samudragiri is known only from its type locality in the Lakshadweep Sea off Kerala, at 360 meters depth, a single seamount station in an ocean basin where deep-water sampling effort remains sparse. Whether the species is a narrow endemic restricted to one undersea mountain, as many seamount-associated invertebrates appear to be, or simply under-collected across a wider range, will only be resolved by further expeditions. What the discovery does demonstrate is that even a single dredge haul, examined with the right taxonomic expertise, can reveal a lineage new to science in one of the most heavily trafficked yet least explored marine regions on Earth, and that the census of life on the Indian Ocean’s seamounts has barely begun.

Subject of Research: Taxonomic description of a new deep-sea squat lobster species from an Arabian Sea seamount

Article Title: A new deep-sea munidopsid squat lobster of the genus Leiogalathea Baba, 1969 (Decapoda: Anomura) from the southeastern Arabian Sea, India

Article References: Tiwari, S., Padate, V. P., & Cubelio, S. S. (2026). A new deep-sea munidopsid squat lobster of the genus Leiogalathea Baba, 1969 (Decapoda: Anomura) from the southeastern Arabian Sea, India. Discover Oceans, 3(1), Article 6. https://doi.org/10.1007/s44289-026-00117-5

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00117-5

Keywords: squat lobster, Leiogalathea samudragiri, seamount, Arabian Sea, deep sea, taxonomy, new species, Munidopsidae, Decapoda, Anomura, Deep Ocean Mission, marine biodiversity

The specimens came to light during deep-sea exploratory surveys conducted by the fisheries oceanographic research vessel FORV Sagar Sampada, operating under India’s Deep Ocean Mission through the Centre for Marine Living Resources and Ecology (CMLRE) of the Ministry of Earth Sciences. Using a Challenger dredge towed at roughly 2.5 knots across seamount summits and slopes, the team retrieved crabs from two separate locations. One female was collected at Sandhayak seamount off Alappuzha, Kerala, at a depth of 283 metres, while a male and a second female were recovered from Investigator Bank near Minicoy Island at 220 metres. The two sites lie hundreds of kilometres apart, suggesting the species may be more widely established on these submerged elevations than the sparse record implies.

Sphenomerides trapezioides is no ordinary crab. It belongs to the Trapeziidae, a family of small, obligate symbiotic brachyurans that spend their entire lives in intimate association with corals and other cnidarians. Most trapeziids, such as the familiar guard crabs of the genus Trapezia, shelter among the branches of reef corals, feeding on coral mucus and repaying their hosts by aggressively deterring predators, including the notorious crown-of-thorns starfish Acanthaster planci. This defensive partnership is ancient: the tropical to subtropical distribution of modern trapeziids, together with their fossils preserved in coral-bearing rocks, indicates that the symbiosis had already been established by the Eocene epoch, tens of millions of years ago.

What sets Sphenomerides apart from its reef-dwelling relatives is both its taxonomy and its choice of partner. The genus is monotypic, meaning it contains just this single species, and it is placed in its own subfamily, Sphenomeridinae. Unlike most trapeziids, which associate with hermatypic, zooxanthellate corals of shallow sunlit reefs, S. trapezioides is usually found with siliceous sponges and azooxanthellate corals in deeper water. In the Lakshadweep material, the crabs were found associated with a solitary coral identified as Paracyathus sp., an ahermatypic coral that builds no reefs and hosts no symbiotic algae. The finding doubles as a biogeographic milestone, marking the first record of this coral genus from the seamounts of the Lakshadweep Sea.

The species has a fragmented and intriguing distribution history. It was originally described from a male specimen measuring 8.5 by 11 millimetres, collected off the west coast of the Andaman Islands at depths of 403 to 439 metres during the pioneering deep-sea dredging expeditions of the survey steamer Investigator in the late nineteenth century. Subsequent records came from the Nicobar Islands at 271 metres, with additional Andaman Sea material extending the depth range to between 238 and 531 metres. Beyond Indian waters, the crab has been reported from Haruku Island in Indonesia at 138 to 152 metres and from off Madagascar at 220 to 362 metres, and more recently it was documented off Visakhapatnam on India’s southeast coast in the northwestern Bay of Bengal. The new Lakshadweep records now bridge the gap between these scattered Indo-West Pacific populations.

Morphological details recorded from the fresh specimens add valuable diagnostic information. The carapace is hexagonal, convex, smooth and glabrous, with a carapace width to length ratio of about 1.4 and poorly defined regions. The frontal margin is moderately wide and deflexed, divided into two truncated, rounded lobes by a shallow median notch, while the anterolateral margins carry three small teeth, the first sitting at the external orbital angle. The orbits are incomplete, each supraorbital margin bearing a single suture, and the inner suborbital angle carries a small spine. The ocular peduncles are short and thick with lightly pigmented terminal corneas, and the antennules fold transversely within transverse fossae. The female from Sandhayak seamount measured 5.3 millimetres in carapace length and 7.1 millimetres in width; the male from Investigator Bank measured 5.8 by 7.6 millimetres.

Perhaps the most striking contribution of the new study is the documentation of live coloration, which is rarely captured for deep-water crabs. Freshly collected animals were narcotised with menthol pellets, photographed alive, and then preserved in 90 percent ethanol, following the standardised survey protocols developed by the CMLRE team. In life, the carapace is uniformly pale pinkish-orange with slightly deeper orange margins. The chelipeds match the carapace in colour, with translucent proximal segments and slightly lighter distal segments, while the tips of the fingers are distinctly white, creating a sharp contrast against the surrounding orange-pink. The walking legs are semi-translucent orange-pink with faint darker orange tinges at the joints, and the ocular peduncles are pale orange with darker corneal regions. Photographs were captured with a Fujifilm GFX 100S mirrorless camera fitted with a 120 millimetre macro lens, producing archival-quality images of a species few living researchers had seen intact.

All voucher specimens have been deposited in the reference collections of CMLRE in Kochi, Kerala, ensuring that future researchers can verify the identification and apply modern techniques such as DNA barcoding. The authors, Raveendhiran Ravinesh, Nosad Sahu and Narayanane Saravanae, note that establishing reliable taxonomic records from bathyal and seamount habitats is essential for long-term biodiversity monitoring, particularly as climate change and mounting anthropogenic pressures bear down on deep-sea ecosystems. Seamounts are increasingly recognised as biodiversity hotspots and potential stepping stones for larval dispersal, yet the fauna of Indian seamounts remains only patchily catalogued, making every verified record a building block for conservation planning.

The biogeographic implications reach well beyond a single crab. The Lakshadweep Sea occupies a strategic position between the Arabian Sea and the broader Indo-West Pacific region, and the authors suggest it may function as a dispersal corridor, a transition zone, or even a partially isolated biogeographic unit. Comparative analyses with adjacent basins and seamount systems can help scientists evaluate species distribution patterns, larval dispersal pathways, habitat-driven morphological variation, and the influence of deep-water circulation on regional biodiversity. In other words, a crab measuring barely six millimetres across its carapace may hold clues to how marine life moves across one of the planet’s largest ocean basins.

The work also aligns directly with the objectives of India’s Deep Ocean Mission, a flagship national programme aimed at building baseline knowledge of the country’s vast exclusive economic zone, including its little-explored seamount ecosystems. Cruises 402 and 404 of FORV Sagar Sampada, during which the crabs were collected, form part of a systematic effort to sample deep-sea benthic habitats using standardised collection, preservation and documentation methods. As dredges continue to bring up unfamiliar organisms from these submerged mountains, records like this one underscore how much of the deep Indian Ocean remains unmapped at the species level, and how a single dredge haul can connect the present-day fauna to specimens collected aboard a nineteenth-century steamship more than 135 years ago.

Subject of Research: New distribution record of the symbiotic trapeziid crab Sphenomerides trapezioides from Lakshadweep Sea seamounts

Article Title: A new record of the trapeziid crab Sphenomerides trapezioides (Wood-Mason in Wood-Mason & Alcock, 1891) (Decapoda: Brachyura: Trapezioidea) from the seamounts of the Lakshadweep Sea, Northern Indian Ocean

Article References: Ravinesh, R., Sahu, N., & Saravanae, N. (2026). A new record of the trapeziid crab Sphenomerides trapezioides (Wood-Mason in Wood-Mason & Alcock, 1891) (Decapoda: Brachyura: Trapezioidea) from the seamounts of the Lakshadweep Sea, Northern Indian Ocean. Discover Oceans, 3(1), Article 42. https://doi.org/10.1007/s44289-026-00149-x

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00149-x

Keywords: Sphenomerides trapezioides, Trapeziidae, seamounts, Lakshadweep Sea, deep-sea biodiversity, Indian Ocean, coral symbiosis, Paracyathus, Deep Ocean Mission, FORV Sagar Sampada, brachyuran crabs, biogeography