Unidentified Haminoeid #2
|Maximum size: 7 mm (excluding
a fragile, strongly inflated, transparent shell
without spiral striae. The animal is translucent cream with white
rosettes and irregular brown lines that often form "lightning bolt"
patterns. Occasional animals have much less brown and juveniles have
disproportionately large "lightning bolts." In some animals, the "tail" may have a dark dorsal band.
haminoeid #2 is a common sand-dwelling species found in protected to
moderately protected sand channels at depths of 1-3 m (3-10 ft) as well
as in silty Halimeda kanaloana
beds at depths of 8-11 m (26-36 ft). Rarely, juveniles may be found in
rocky habitats. In shallow sand channels, it appears to be an ephemeral
species with very large numbers of larvae settling after periods of low
surf have allowed the development of a micro-algal film on the sand's
surface (presumably their food). Such populations engage in
synchronized spawning, then appear to "spawn out" and die. (Note 1) More stable populations may occur in the H. kanaloana beds. (Note 2) The egg masses are greenish-yellow and
cylindrical. (Note 3) They are deposited in
dense patches, sometimes containing thousands of masses (though a few
dozen to a few hundred are more common). During spawning, the animals
can usually be found crawling among the
egg masses or concealed under a thin layer of sand near them. Fish
behavior suggests that the masses contain anti-feedant chemicals. (Note 4) Hatching occurs
in five to six days in the laboratory.
Maui and Midway: widely distributed in the Indo-Pacific.
It was first
Hawaii off Makena, Maui by PF in 1991.
Midway Atoll; May 30, 1993.
Observations and comments:
1: Over the years, populations of
this species have appeared several times in sand channels on the inner
reef flat at Hekili Point. In August, 1991 extensive patches of egg
masses were seen but no animals could be found in association with
them. Collected egg masses hatched in four days and all masses in the
field disappeared over the same period. On April 27, 1999 extensive
patches of egg masses were seen with associated animals. Several
collected animals kept in an aerated container with a sand bottom laid
two batches of egg masses on the mornings of the 28th and 30th (the
latter noticeably smaller). Most died shortly after laying the second
group of masses. The first eggs laid hatched in the evening on May 3rd.
Meanwhile, all but a couple egg masses disappeared in the field by May
5th and no animals could be found. In a second basin near Hekili Point,
additional patches of egg masses were seen by Darcey Kehler on April
29th but no animals could be found. On Oct. 28, 2007 several small
patches of egg masses were seen with no associated animals. Most had
disappeared by the 29th. Extensive patches of egg masses were seen on
May 27th, 2008 but no animals could be found. On the morning of
April 23, 2009, many small patches were found with associated animals.
The patches were less dense than usual with the animals evenly
distributed among the masses (suggesting that they may have laid their
first masses the night before). On April 27, 2014 very extensive patches
of egg masses were found at depths of 0.5-1 m just off the beach west
of Hekili Point. Patches were ultimately found in an area of about 200 m
by 20 m. Numerous animals were found on and between the patches of egg
masses (in sufficient numbers that their mucous trails altered the
texture of the bottom sediment). Many animals were also observed from
April 27 through April 29 drifting in the water column on mucous strings
(at slack low tide) with many appearing over an adjacent down-current
sand patch (with few eggs) on April 29. The animals had disappeared from
about 75% of the up-current patches by April 29 and from the remaining
patches by April 30 with only a few lingering in the adjacent
down-current sand patch. Hatching had probably started by May 2 and was
largely completed in the up-current portion of the area by May 3. In all
cases, the egg
masses appeared after a couple weeks of unusually calm water conditions
had permitted a noticeable micro-algal film to develop on the surface
of the sand. Also, no animals were found in adjacent rocky habitats
before, during or after the spawning events. These notes support the
suggestion that the larvae settle in such locations only when their
food algae becomes available, spawn synchronously, then die back. A
subjective estimate of the times between the most recent surf events
capable of stripping algal film from the sand channels and the
spawnings suggests that the species may have a post-larval life span of
as little as two weeks, perhaps less. The lower density of masses in
the patches observed on April 23, 2009 and the lack of "donut shaped"
patches during hatching suggest that the patches are "built up"
by animals laying multiple masses (perhaps 3-4 at 1-2 day intervals)
over their entire areas rather than by adding masses to their edges.
Note 2: On April 15th and 18th, 2007 innumerable patches of egg
masses were seen in silty Halimeda
beds in Maalaea Bay. The patches were smaller than those typically
found at Hekili Point (most only containing a few dozen masses) but
were scattered over the bottom every meter or so "as far as the eye
could see" during the entire duration of the dives. Some had
associated animals, some not.
Note 3: When several animals were held together in a dish on
April 27, 1999, they laid cylindrical egg masses comparable to those
seen in the field. However, when an animal collected on April 15, 1997
was held alone it laid a spherical egg mass similar to those laid by
other haminoeids. (see
photo) That suggested that egg laying in the field might be a truly "social"
behavior that required two or more animals to shape the mass during
deposition. However, three animals collected on April 28, 2014
and held in separate dishes laid typical egg masses demonstrating that
the previous observation was anomalous and that they do not require a
"helper" to form an elongate egg mass. Typical egg masses were also laid in two dishes containing multiple animals.
Note 4: On Oct. 29, 1999 foraging goatfish (Mulloidichthys flavolineatus?) were
changing direction to avoid patches of egg masses. In addition, black
durgon (Melichthys niger) and
juvenile parrotfish were observed "nibbling" the eggs, then backing
off. Similar observations have been made on other occasions. That
suggests the masses may contain fairly
powerful anti-feedant chemicals (perhaps obtained from cyanophytes in
the micro-algal film on which the animals appear to feed?).