Stenorhynchus

Lamarck, 1818

arrow crabs

Species Guides

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Stenorhynchus is a of marine spider crabs ( Inachoididae) commonly known as arrow crabs. These crabs are characterized by extremely long, slender legs and a narrow, often triangular or isosceles-shaped . Several are popular in the ornamental aquarium trade, including the yellowline arrow crab (S. seticornis) and red arrow crab (S. yangi). The genus exhibits notable morphological adaptations for life in structurally complex marine such as coral reefs.

Stenorhynchus seticornis by (c) Pauline Walsh Jacobson, some rights reserved (CC BY), uploaded by Pauline Walsh Jacobson. Used under a CC-BY license.Stenorhynchus seticornis by (c) Pauline Walsh Jacobson, some rights reserved (CC BY), uploaded by Pauline Walsh Jacobson. Used under a CC-BY license.Stenorhynchus seticornis by (c) Pauline Walsh Jacobson, some rights reserved (CC BY), uploaded by Pauline Walsh Jacobson. Used under a CC-BY license.

Pronunciation

How to pronounce Stenorhynchus: //ˌstɛnoʊˈrɪŋkəs//

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Identification

Arrow crabs are distinguished from other majoid crabs by their exceptionally elongated, thin legs and narrow, often or triangular . The rostrum is typically long and pointed, extending forward between the . is present: males possess significantly longer chelipeds than females. within the may be differentiated by coloration patterns, such as the yellow longitudinal stripe of S. seticornis versus the red coloration of S. yangi.

Images

Habitat

Marine environments, primarily coral reef on fore-reef slopes at depths of 3–15 meters. occupy crevices and complex structural refugia during daylight hours. S. debilis has been documented in bivalve mariculture devices in the Gulf of California.

Distribution

Tropical and subtropical western Atlantic Ocean (including Caribbean Sea: Barbados); eastern Pacific Ocean (Gulf of California, Mexico). Specific distribution varies by .

Diet

suspension feeding on planktonic organisms captured from water currents using elongated chelipeds while positioned on elevated substrates.

Life Cycle

Females carry masses attached to pleopods. S. debilis likely completes three maturation/ cycles within 3–4 months after the first crab instar, with step-wise growth patterns correlated with shape.

Behavior

Strong diel activity pattern: cryptic in reef crevices during daylight, emerging at dusk to assume exposed positions on coral . Exhibits pronounced site fidelity, returning to the same daytime shelter after foraging. Anti- includes rapid withdrawal into crevices and camouflage through body posture and coloration matching surrounding corals. Uses long legs for movement through complex coral structures.

Ecological Role

planktivore on coral reefs; prey for reef ; structural association with coral reef framework.

Human Relevance

Popular ornamental marine in the aquarium trade worldwide. S. seticornis and S. yangi are particularly sought after. S. debilis is collected from the southwestern Gulf of California for this trade.

Sources and further reading