Inachidae

Distinguished from other majoid crab families by combination of: long, slender walking legs; carapace typically longer than broad with prominent rostrum; orbits usually incomplete or with reduced supraorbital margin; male abdomen with narrow, triangular pleon. Differs from Majidae by generally more slender build and different gonopod structure. Separation from Epialtidae requires examination of sternal and gonopod characters. Genus-level identification relies on rostrum shape, carapace tuberculation patterns, and leg proportions.

Spider crabs with elongated, often triangular or pear-shaped carapaces. Legs are notably long and slender relative to body size, giving the characteristic spider-like appearance. Carapace surface typically bears tubercles, spines, or other ornamentation. Chelipeds (claws) are usually slender and elongated. Body size varies considerably among genera. Many species have reduced or modified fifth pereiopods tucked beneath the carapace.

Exclusively marine. Found from intertidal zones to mesophotic depths exceeding 100 meters. Habitats include soft bottoms, rocky substrates, and areas with sessile invertebrate cover such as gorgonians, antipatharians, sponges, and sea anemones. Some species occupy specialized niches including association with specific host organisms.

Primarily Atlantic Ocean (including NE Atlantic and Mediterranean), with significant representation in Indo-Pacific region. Records from Black Sea, Canary Islands, Korean waters, Colombian Caribbean, and South African coasts. Distribution is genus-specific; no single species spans entire family range.

• sea anemones - symbiotic associationInachus phalangium and Macropodia czernjawskii observed in association with sea anemones; specific nature of relationship not fully characterized
• sponges - habitat associationPodochela curvirostris found associated with sponges at 107m depth
• gorgonians and antipatharians - habitat associationAchaeus cranchii collected from soft bottoms with gorgonians and antipatharians

Self-decoration with epibiosis is well-documented in multiple genera, particularly Macropodia. Crabs actively place algae, sponges, and other materials on hooked setae covering the carapace and legs, providing camouflage and possibly chemical protection. Defensive behaviors include the 'stockade' posture (legs extended to appear larger) and swimming escape responses observed in Metoporhaphis calcarata. Some species exhibit specialized associations with sessile invertebrates, using them as elevated perches or refuge.

Epibiotic species serve as mobile substrate for diverse algal and invertebrate communities, potentially facilitating dispersal of sessile organisms. Association with sea anemones and other cnidarians may involve cleaning behaviors or protection, though mutualistic benefits remain poorly characterized. As predators and scavengers, they contribute to benthic food web dynamics.

Limited direct economic importance. Some species may be incidentally captured in fisheries. Museum collections of epibiotic species have been proposed as monitoring tools for tracking introductions of non-indigenous sessile species, as the crab's epibiosis records local community composition at time of collection.

• MajidaeSimilar spider crab morphology; distinguished by more robust body form, complete orbits, and different male pleon shape
• EpialtidaeOverlapping habitat preferences and camouflage behaviors; distinguished by sternal morphology and gonopod structure

• crustacean
• marine
• spider crab
• decapod
• epibiosis
• camouflage

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Notice me! Neglected for over a century, Black sea spider crab re-described | Blog
• Swimming and the Stockade: Defensive Behaviors in the False Arrow Crab, Metoporhaphis calcarata (Brachyura: Inachidae)
• New records of Decapod Crustaceans (Decapoda: Pontoniinae and Inachidae) associated with sea anemones in Turkish waters
• First record of three brachyuran decapods (Inachidae, Polybiidae, Thiidae) from the Canary Islands (NE Atlantic)
• Taxonomy and ecology of the Cape Town Spider Crab, Macropodia falcifera (Stimpson, 1858) (Crustacea: Decapoda: Brachyura: Inachidae)
• Supplementary Data on the Distribution of Inachus Parvirostris (Risso, 1816) (Decapoda, Brachyura, Inachidae) from Turkey
• First records of Paratymolus pubescens Miers, 1879 and Litosus sexspinosus (Miers, 1884) (Decapoda, Brachyura, Inachidae) from Korean waters
• Phalangipus somnathensis Sureandiran, Karuppasamy & Suyani, 2024—a junior synonym of Encephaloides armstrongi Wood-Mason in Wood-Mason & Alcock, 1891 (Crustacea, Brachyura, Inachidae)
• FIRST RECORD OF THE CRAB PODOCHELA CURVIROSTRIS (A. MILNE EDWARDS, 1979) (BRACHYURA: INACHIDAE) FROM THE COLOMBIAN CARIBBEAN
• A new cryptic species of Inachus (Decapoda: Brachyura: Inachidae) from European waters and an updated identification key to the species of Inachus with two protogastric tubercles
• 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)
• Supplementary material 1 from: 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
• Figure 2 from: 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
• Figure 1 from: 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
• Figure 8 from: 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
• Figure 12 from: 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