Phrikoceros cf. katoi  Newman & Cannon, 1996
top photo: Cory Pittman, collected off Ka`anapali, Maui. 25-45 ft.
middle photo: Ralph Turre, Makena Landing, Maui. (taken at night).
bottom photo: Rebecca Bicker, Kealia, Maui.

Body elongate oval with a few marginal ruffles, raised medially. Background color orange, lighter medially and more intense at margin; dorsum excluding margin covered with a multitude of minute white dots that tend to coalesce in irregular clusters; margin contains irregular white transverse streaks and spots, most of which do not reach to edge. Pseudotentacles square and laterally ruffled. Cerebral eyes in a circular cluster.

Three Phrikoceros species on the Newman & Cannon CD are orange with white microdots--Phrikoceros baibaiye, Phrikoceros sp. 3 and Phrikoceros katoi. The closest by far, to the Hawaiian worm, is katoi. The Hawaiian worm differs visually from katoi in two respects: 1) It lacks the two "regular and distinct clusters" of microdots characteristic of katoi (one behind the eyespots and one posteriorily), and 2) it has distinct white dots and bands in the margin. The original description specifically states that katoi lacks dots and bands in the margin.

UPDATE: The bottom photo shows a worm that Rebecca Bicker photographed in January 2024 at Kealia, Maui. This worm more closely resembles the photo on the Newman & Cannon CD in that it has the two distinct clusters of microdots and lacks white markings in the margin.

Photos of orange worms from Hastings Point, New South Wales, labeled "Phrikoceros katoi" closely resemble the Hawaiian worms. (Curiously, the third photo shows two orange worms apparently mating, but one of them looks more like Phrikoceros baibaiye. P. baibaiye was described from Hastings Point and is reported to be common there.)

A web search for Phrikoceros baibaiye yielded a photo from New Caledonia that is a good match for Phrikoceros katoi, including the two clusters of white microdots anteriorily and posteriorily and margins largely clear of white spots and streaks. Another photo of katoi, this one identified by Leslie Newman, is posted on Marine Flatworms of the World.

Although the two animals above seem distinct from the Hawai`i and Hastings Point worms, this intriguing photo from the Philippines shows the two together, perhaps ready to mate. The left worm matches the "classic" Phrikoceros katoi form (without marginal spots), and the right worm matches the Hawaiian form (with marginal spots). This certainly suggestive of one variable species, Phrikoceros katoi.

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