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Edit [01 December 2020]: Urticina crassicornis does not occur in North Pacific, a smooth-walled species of Urticina from North Pacific identified previously as Urticina crassicornis is now separated into a distinct species, see Urticina timuri

Many photos in the Internet labeled Urticina crassicornis (or Tealia crassicornis) are wrongly identified and show another Pacific species: Urticina grebelnyi (known also as Christmas anemone or Painted anemone). Two species have nothing in common and it is hard to understand why and how they can be confused.

The most important distinguishing features of Urticina crassicornis are: 1) viviparity - juveniles are developed in the coelenteron of parent anemone to a polypoid stage and 2) smooth column (body) - see photos below: is shows no any traces of large tubercles or vesicles we see on many photos labeled Christmas anemone or Painted anemone. Christmas or Painted anemone is covered by numerous vesicles, vesicles are especially clearly visible on contracted specimens. These two species have different color pattern. Christmas anemone is NOT an Urticina crassicornis, but belongs to another species: Urticina grebelnyi. The only other Urticina species which has absolutely smooth column is Urticina timuri from Pacific, but it is oviparous (releases eggs to water column rather than incubates juvenile anemones).

The typical specimens of Urticina crassicornis are up to 10 cm high and with a tentacular crown up to 10 cm diameter and the column about 6-7 cm diameter. The color is variable, although most specimens range from plain reddish-brown to pale orange. The column is smooth, without traces of verrucae or vesicles, always clear, without attached sand or other foreign particles. The oral disk is much paler than the column, usually yellowish or whitish. Short thin red radial bands outline the tentacle bases; the region around the mouth may be reddish, otherwise the colour of the oral disk is plain. The tentacles are encircled with the wide white and red bands in the middle.