unknown B - Cycloporus ?
photos: top: Kevin Roe, Maalaea Bay, Maui. 25 ft. in Halimeda at night; bottom: David Prutow, Kawaihae, Hawaii. 15 ft.

Kevin Roe found this unusual worm in early February 2021 while diving Maalaea Bay at night. He estimates it was about 12 mm long. It appears to have a translucent body filled with an irregular network of fine white threads--possibly channels in its digestive system. If so, the color might change depending on what it happens to feed on. It has marginal tentacles, which would place it in one of four families: Pseudocerotidae, Euryleptidae, Pericelididae or Bonniidae. More photos of this rare worm would be welcome.

Update: Cory Pittman suggests it might be in the genus Cycloporus, family Euryleptidae. See below for his observations.

Update May 18 2023: David Prutow photographed another during the day at Kawaihae, Hawaii. It was small, about 6-8 mm long. Here's some video he shot, showing how transparent the body is.

BACK to streaks / lines
BACK to mottled / speckled

There's a large patch of tentacular eyes running up the inner sides of the marginal tentacles but the cerebral eyes are very weakly developed--only three little black flecks where I'd expect to find them.

The upper surface is reticulated in lines of cream pigment. I don't think the lines are channels of the digestive system (not enough symmetry...). But, the animal's tissues are nearly transparent. And, the
reticulations probably extend to the underside. So, they show through behind the dorsal ones (in thinner areas) creating the apparent "depth."

There are small tubercles coincident with the major junctions of the dorsal reticulations.

There's a broken, mid-dorsal line of brown pigment and random, diffuse brown spots.

There's a narrow, translucent-orange submarginal line.

Some on-line photos of Cycloporus spp. show similar features though not in exactly that combination and not with the weird ridges on the marginal tentacles...