with egg mass
Costasiella sp. #2
|Maximum size: about 12 mm.
species has an opaque-white body. The cerata are mottled-green basally
grading to opaque-white with a few translucent spots (elevated?)
The tips of the lateral cerata are tinged with blue. The rhinophores
tips and bases. There is a translucent-cream patch in front of the eye
spots and an oval black patch behind them. Some animals may have a few
flecks of brown in front of the eye spots and a few white flecks on the
translucent rhinophore tips. Young animals may have less white pigment. The rhinophores may show a central bulge
Costasiella sp. #2
is known from numerous animals found on its host algae (Avrainvillea amadelpha)
at 5-30 m (15-100 ft), sometimes in association with Costasiella kuroshimae and/or Costasiella sp. #3.
(see photos) It lays a compact, spiral, translucent egg mass
and may bury itself partially in sand when not on its food algae. (Note 1) (Note 2)
Distribution: Big Island, Maui and Oahu: probably widely distributed in the Indo-Pacific.
It may have been first recorded in Hawaii from Honokohau Harbor, Big Island by Rachel Schackne in Oct., 2019. (Note 3) It may turn out to be
"Costasiella sp. 1" as illustrated in Gosliner, et. al. 2018. Since its food algae, Avrainvillea amadelpha, is thought to be introduced there's some chance that this species is, as well. (Note 4)
Photo: Marketa Murray: about 5 mm: found by Christian Hamilton & Marketa Murray; Honokohau Harbor, Big Island; May 17, 2020.
Observations and comments:
1: Marketa Murray reported that she found about 6 different blades of Avrainvillea amadelpha about 2 m apart in an area of about 20 square meters on each of two dives in a low density Halimeda kanaloana
bed. She found 5-8 animals on each blade at around 9:00 AM and 3-5
animals on each blade at around 12:00 PM. It was a sunny day with 50-100 ft
Note 2: Rich Neely found two large animals in a patch of Halophila decipiens
at 15 m (49 ft). Rich reports that they were "...motionless with their
heads buried in the sand. I thought I was seeing things so I gave one a
gentle lift and it started to move around, very camera shy as I followed
its circles until it decided to bury its head again and become
motionless again. This happened several times." There was no Avrainvillea amadelpha in the vicinity. Perhaps, they had exhausted available food and were searching for more. Perhaps, they drifted into the Halophila patch...
Note 3: Pam Madden, Marketa Murray and Christian Hamilton
were the first to send us photos and data for this species. Subsequent
to uploading the page, Marc Hughes sent us his photos, some predating
theirs (earliest, Oct. 31, 2019). However, he
said that he was shown the animals by Rachel Schackne in October and
may be other photos that predate his. He also forwarded one
of Rachel's photos indicating that she knew the animal. But, it
lacked a "date taken" tag so we're giving her a tentative credit pending
confirmation with a securely dated photo (we usually use a "first clear
evidence" standard for determining priority). If we receive any
photos that predate Marc's and Rachel's, (it appears to be a popular
dive site...) we'll change the credit, accordingly. Please let us know
if you have any.
Note 4: Costasiella sp. #2 is very similar to Costasiella sp. #1
in it's head markings. It differs from that species in having few or no
iridescent flecks, largely continuous white pigment rather than white
flecks, larger central cerata with translucent spots (pustulate?) and bluish cerata
tips confined to the lateral cerata. We opted to split the two based on
those differences. Costasiella sp. #1 is found in shallow rocky habitats where it almost certainly isn't eating Avrainvillea amadelpha and is probably exposed to more surge. This
may reinforce the evidence for the split. But, it can't be ruled out
that the two
represent different forms that a single species assumes in response to
differences in diet and habitat. Hence, the split will really require DNA
work for final confirmation. Most "black mask" photos from
elsewhere in the Indo-Pacific seem closer to this species than to C. sp. #1.