Arachnactidae

The Arachnactidae are a family of deep-sea sea stars, belonging to the order Brisingida. These unusual sea stars are characterized by their exceptionally long, slender arms that often resemble the legs of a spider, hence their common name, “spider stars”. They are widely distributed in all oceans, typically residing in the deep sea, where they find food in the benthic zone.

Banded Tube Dwelling Anemone – Isarachnanthus maderensis

Sera Anemone – Arachnanthus lilith

Common Names

Arachnactidae are commonly known as "spider stars", due to their long, thin arms that resemble spider legs.

Characteristics

Arachnactidae are distinguished by their unique morphology, which includes:

  • Long, slender arms: The defining feature of arachnactids, their arms are typically many times longer than their central disc. This allows them to reach out and forage for food in the sediment, capturing prey in the benthic zone.
  • Small, central disc: The central disc is comparatively small compared to the size of their arms. It houses the mouth, anus, and other vital organs.
  • Multiple arms: Arachnactids typically have 6 to 15 arms, with some species having even more. The number of arms is species-specific.
  • Minute spines: The arms are covered in minute, delicate spines that aid in locomotion and sensory perception.
  • Tube feet: Like other sea stars, arachnactids have tube feet that assist in movement and feeding. However, their tube feet are relatively small and sparsely distributed due to the thinness of their arms.
  • Coloration: While most arachnactids are typically pale, some species exhibit bright colors, including reds, oranges, and yellows. These vibrant hues may serve as camouflage against the darker depths of the sea.

Environments

Arachnactidae are primarily deep-sea dwellers, inhabiting the benthic zone, the seafloor, at depths ranging from a few hundred meters to several thousand meters. This environment is characterized by high pressure, low temperatures, and limited light penetration. The specialized morphology of these sea stars, including their long arms and sensitive spines, allows them to navigate and find food in this challenging habitat.

References