Echinoderms

Echinoderms have complex water circulation systems, a body cavity, are capable of sensing their environment and moving around with tube feet. They have a calcareous endoskeleton. They are animals characterised by five-point radial symmetry. Most can reproduce asexually and can repair and regenerate organs and limbs. Their name means hedgehog skin. They thrive in all oceans, from the deep sea to shallow coastal areas.

Echinoderms include sea cucumbers, sea urchins, starfishes, brittlestars, and others. The first two groups were presented in the previous report. No new species or changes in ranks have occurred since 2016. Many of the common names have been updated to match names used across Canada. Starfishes are presented in the list below for the first time. Additional groups will be included in future reports.

A total of nine species of sea cucumbers, three sea urchins, and 15 starfishes are known to occur in the NWT’s portion of the western Arctic Ocean. One additional species of starfish is expected to be present, but an unknown number of additional species may be discovered with more monitoring.

Sea cucumbers

Sea cucumbers (subclass Holothuroidea) have leathery skin, a cylindrical body, tube feet, and a mouth equipped with tentacles. Some sea cucumbers have feet, long pipe-like projections that can be inflated by pumping water into them to enable movement. Some species are feetless but will move using muscle undulations. The type of oral tentacles will also vary. All sea cucumbers have a ring of calcareous plates that form the only substantial “endoskeletal” structure in the animal. This structure acts as an anchor for major muscles and also allows the cucumber to retract its tentacles into its body for protection.

Sea cucumbers are typically found in lower depths where they tend to sift through sediment in search of food. Their diet consists largely of plankton, detritus, and organic debris. Some species filter such a significant amount of sand that they play important ecological roles in maintaining healthy seabed ecosystems.

Sea urchins

Sea urchins (subclass Echinoidea) are the spiniest echninoderms. They are usually small with a spherical appearance. Their bodies consist of a shell (called test) with a protective spiny camouflage. They also have a central toothy month and can be quite mobile. They are highly effective at grasping, scraping, pulling, and tearing food off hard surfaces. They will feed on algae, plankton, kelp, barnacles, and molluscs. Urchins are such effective grazers that in some areas they can play a key role in preventing algae outbreaks. However, if urchin populations become abundant, they may also have negative impacts on coral growth and sea floor biomass coverage.

Starfishes

Starfishes (subclass Asteroidea) have five-point symmetry typically of echinoderms. Their body consist of central disc, plates, and five arms with surface that can be spiny, bumpy, or smooth, granular, or spiny. They have a central mouth and will feed on anything they can find on the bottom of oceans or even on coastal areas. Starfishes can reproduce both sexually and asexually and can regenerate damaged body parts.