Pericelis hymanae (Poulter, 1974)
top photo: Cory Pittman, Kapalua Bay, Maui. under rock. < 18 ft.
bottom photo: Napili Bay, Maui. Under rock. 15 ft.

In theory, a thin brown median stripe distinguishes Pericelis hymanae from Pericelis 4. However, the stripe in P. hymanae appears to be quite variable, and it is likely that Pericelis 4 is actually P. hymanae. We are investigating further.

ID from Jean Poulter's chapter "Phylum Platyhelminthes" in Reef and Shore Fauna of Hawaii. Section 2. edited by Devaney and Eldredge (Bishop Museum Press, 1987).

Poulter's description reads: "Ovate to circular with a moderately ruffled margin. The ground color is off-white. Dorsally there is a median brown stripe that does not quite reach the anterior margin; the stripe is discontinuous through the cerebral region... These worms are usually found under rocks that harbor the bivalve mollusk Isognomon perna and often use the underside of the lower valve of Isognomon as a refuge." The bivalve shell at right of bottom photo (with thin brown lines!) is Isognomon perna.

The Newman & Cannon CD shows photos of a similar worm from the Great Barrier Reef and the Marshall Islands identified as Pericelis cf. hymanae. However, no explanation is given for the "cf." designation and there is no discussion, description, or photo of the true Pericelis hymanae. Adding to the confusion, the photo labeled Pericelis hymanae in the Newman & Cannon book is a duplicate of another photo on the same page and completely incorrect.

Pericelis hymanae was described from Hawaii specimens occurring in the same habitat as the worms pictured here. Although the CD states that the "cf." species occurs in Hawai`i, it seems reasonable to me to assume that the worms pictured here (both of which agree well with the color description given by Poulter and one of which is in apparent association with the bivalve Isognomon perna) are the true Pericelis hymanae.

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