An international team has formally described a new species of trapdoor spider that lives along ocean shorelines and withstands total submersion during high tide.

The Mauritian tidal trapdoor spider, *Idioctis marevallum*, belongs to the brush-footed trapdoor spider family Barychelidae within the mygalomorph lineage — the primitive branch of spiders that includes tarantulas.

Clarin reports the species was found on Ilot Vacoas, a protected one-hectare islet off Mauritius's southeast coast, during nighttime ecological surveys.

Detailed in the journal Arachnology, the discovery highlights specialized endemic fauna surviving in fragile coastal microhabitats — a striking find for readers used to trapdoor spiders of forest floors, not crashing surf.

Instead of digging burrows in soil, this spider inhabits narrow tubular cavities embedded in exposed coralline algae bedrock, which biologists believe marine mollusks and worms bored out millennia ago.

Its defense is architectural: Clarin reports the spider crafts a tightly fitted, hinged trapdoor from dense silk, coarse sand grains and dried marine algae.

When the tide rises, it retreats into its tunnel and seals the door, forming a watertight, air-trapping barrier that keeps the chamber dry while blending so seamlessly into the rock it is virtually invisible to shorebirds and predatory crabs.

The species name *marevallum* translates from Latin as "sea wall." Once the tide recedes, it opens the door under darkness to ambush small invertebrates.

The first sighting came in 2023 during field operations of the Mauritius Island Restoration Programme, uniting the Durrell Wildlife Conservation Trust, the Mauritian Wildlife Foundation, the National Parks and Conservation Service and the Forestry Service.

According to Clarin, entomologist Dr. Max Tercel, scanning crevices with a headlamp, spotted hairy spider legs protruding from a miniature trapdoor — "it felt like uncovering a hidden treasure," he recalled.

Durrell's Mauritius Country Manager Nik Cole said: "I couldn't believe something from the same group as tarantulas could be living in a place like this." The crew first thought it might be *Tigidia mauriciana*, described in 1892 and detected only once.

A second population was later confirmed on Ile aux Fouquets.

The formal description was led by arachnologist Danniella Sherwood with specialists from the Natural History Museum in London, Cardiff University, Wildlife Preservation Canada and Mauritian institutions.

Clarin reports the wider research identified several spider species never before documented in Mauritius, raising the island nation's known spider diversity by more than 25 percent.

Vikash Tatayah of the Mauritian Wildlife Foundation said that despite Mauritius being considered one of the countries with the most significant loss of native biodiversity, it is "unbelievable" to find species new to science in the most unexpected spots — supporting the need to preserve every nook and cranny that may still harbour unknown species.

The spider is part of a broader run of species discoveries this week.

bioengineer.org reports botanists have formally described *Ormosia viridiflora*, a green-flowered shrubby legume from Rongan County, Guangxi, China, distinguished by light green flowers and just five fertile stamens; it is known only from its type locality and, per bioengineer.org, meets IUCN thresholds for a tentative Critically Endangered assessment, with fewer than 50 mature individuals.

Meanwhile, CGTN reports researchers identified two new sage species — *Salvia zayuensis* and *Salvia toxantha* — in China's Hengduan Mountains, raising China's native *Salvia* count to 94. Together, the finds underscore how targeted surveys keep turning up life science has never catalogued.