Spirularia is an order of marine Cnidarians, tube-dwelling anemones, in the subclass Ceriantharia. It is one of the two orders making up Ceriantharia and includes two families, Botrucnidiferidae

and Cerianthidae, and around 99 species. The two orders differ in the makeup of their cnidome (the types of cnidocyte present), the relative sizes of the oral discs and the shape and structure of the mesenteries. These anemones dwell in parchment-like tubes immersed in soft sediment, and have two whorls of tentacles, the outer tentacles being much longer than the inner ones.

Spirularia. Retrieved November, 05 2021, from en.wikipedia.org/wiki/Spirularia.

Cerianthidae is a family of tube-dwelling anemones in the order Spirularia of the subclass Ceriantharia.

Cerianthidae. Retrieved November, 05 2021, from en.wikipedia.org/wiki/Cerianthidae.

Pachycerianthus fimbriatus is a cerianthid anemone that burrows in substrate and lives in a semi-rigid tube made of felted nematocysts. The anemone is often seen in bright orange to red.

Like most anemones, the tube-dwelling anemone contains stinging cells or nematocytes along its tentacles, however, the cells are not toxic to humans.

The ceriantharia possess two whorls of tentacles, one surrounding the mouth (labial tentacles) and one at the edge of the oral disc (marginal tentacles).

Pachycerianthus fimbriatus. Retrieved November, 05 2021, from en.wikipedia.org/wiki/Pachycerianthus_fimbriatus.