Gorgonocephalus arcticus

Lore & Background

Gorgonocephalus arcticus was first discovered at 300 m depth in the Skagerrak by Mortensen. Five Gorgonocephalus species were discovered from European waters, with four occurring in Scandinavian waters. Technological advances, including remotely operated vehicles (ROVs), have allowed scientists to view this basket star in situ and conduct additional lab research. Its populations are distributed from the Arctic to Cape Cod, Massachusetts, and it commonly lives in areas of moderate to strong current flow. This species is found at varying depths from the sublittoral zone to a maximum of 1500 m. It has been observed living non-parasitically on the exterior of Boltenia ovifera, a tunicate found in a similar range.

Morphologically, G. arcticus has five arms extending from a central disc, though some individuals have as many as 20 arms. The arms branch into smaller subdivisions, and the calcified ossicle endoskeleton is covered by a fleshy skin giving a rubbery appearance. The disc is pentagonal, yellowish, and covered with scales. The mouth on the lower surface is framed by five jaws with spinelink teeth and papillae, leading to a saclike stomach that ends in a blind pouch; the species lacks intestines and an anus. Bursal slits on the oral side open to respiratory bursae for gas exchange. Movement is achieved by strong arm strokes that lift the disc and thrust the animal forward, using flexible articulated arms supported by an internal skeleton.

Reader's Guide

Gorgonocephalus arcticus is a suspension feeder that extends its arms vertically into the water column to capture planktonic organisms such as zooplankton and micronekton. Unlike other observed basket stars that feed only at night, G. arcticus has been observed feeding by day. It actively traps prey by waving the tips of its outstretched arms, which are covered in rings of hooks that entangle larger plankton. Upon contact, the arm coils inward, and nearby tendrils curve toward it to further ensnare the prey. The upper arm extensions are more flexible than the lower parts, aiding in prey capture. Tube feet extend only about 1 mm into the water column and are not involved in removing large plankton; instead, tube feet along with girdle hooks and spines move captured particles toward the mouth. Girdle hooks are curved ossicles attached by ligaments, hypothesized to be spines adapted to restrain prey. Lateral spines increase in size and number from the arm tip toward the base. The species is associated with hard substrates and creates islands of similar hard substrate fauna when surrounded by unsuitable sandy substrates, as observed in the fiords surrounding Baffin Island in Canada. Its feeding mechanism has been extensively studied in the wild and in captivity.

Did You Know?

• Gorgonocephalus arcticus can have up to 20 arms, though it usually has five.
• This species lacks intestines and an anus; its mouth leads to a blind pouch stomach.
• It has been observed feeding during the day, unlike other basket stars that feed only at night.
• The species lives non-parasitically on the exterior of the tunicate Boltenia ovifera.