probable egg mass
Dermatobranchus rubidus Gould, 1852
|Maximum size: 60 mm. (Kay,
This is an elongate, translucent rust-red animal with white ridges and darker red rhinophores.
We've never seen Dermatobranchus rubidus, personally.
Kay (1979) lists it as seasonally abundant on Oahu's fringing reefs. An
animal referenced in Gosliner &. Fahey, 2011 was collected from
the intertidal in Kihei, Maui by S. Jazwinski in 1979. However, in 2020-2021 numerous Maui animals where found on sand at 6-8 m
(20-26 ft) by Rebecca Bicker and others. It's primarily nocturnal and, unlike most arminaceans,
appears to feed on a small, sand-dwelling ceriantharian anemone (probably Arachnanthus sp.). (Note 1) It probably lays a one to two whorl white egg mass secured in the sand with an anchor of hardened mucus.
Maui and Oahu: widely distributed in the western & central Pacific.
It is listed in Kay as Dermatobranchus
rubida and was first reported from Hawaii in Gould, 1852 (as Diphyllidia rubida).
Photo: Kelly McCaffrey: 50 mm: Maalaea Bay, Maui: June 5, 2022.
Observations and comments:
1: Rebecca Bicker reported that
"Right after I shot the anemone picture, the Dermatobranchus dove into
the sand" and "I honestly did not see the anemone until I looked at the
photos on my computer." So, perhaps the feeding sequence goes: animal
bites anemone, anemone retracts puling animal into its hole, animal gets
one good bite then "resurfaces" and moves on to the next anemone?
Later, Jenna Szerlag and Kelly McCaffrey observed one feeding on
multiple anemones over a two minute period and Jenna said "After it'd gobble up the
anemone it would just go on to the next. I did not see it get sucked down
into the tube like Rebecca did." However, the anemones in her photos
were proportionately smaller than the one in Rebecca's. Perhaps, they
were "overpowered" by the D. rubida? (see photos) Lloyd Johnson also photographed one attacking an anemone.