including a few not in Hawaii's
two - crabs
other than xanthids
one, xanthids, is here)
Dr. Peter Castro's checklist
of all crabs known from the Hawaiian Islands
The Bishop Museum's unofficial list of all true crabs known
in Hawaii is here
Though not 100% accurate,
photos of many of Hawaii's small crabs can be found here
` ALAMIHI Metopograpsus
thukuhar (Owen, 1839)
Distinctive square carapace with eyes
at the front corners. Common in shallow protected areas clambering
about on exposed rocks at low tide. In other parts of the Indo-Pacific
found principally on mangrove roots. Tolerates brackish water and
can be seen in the mouths of streams. To well over 1 inch in carapace
width. Widely distributed throughout the tropical Indo-Pacific.
M. messor is similar, but restricted to the Western Indian
GREEN FLAT ROCK
CRAB Percnon abbreviatum (Dana 1851)
Closely related to the Flat Rock Crab
Percnon planissimum on p 209 of my book, this crab is greenish
with a faint light central stripe running back between the eyes.
The eyes are often reddish and there are often some indistinct yellow
spots on the legs. Crabs of this genus often have red or purplish
claw tips, faintly visible here. This is a still from video shot
by John Earle off Oahu. To about 1 inch carapace width. The species
is widespread in the Indo-Pacific. Identification tentative.
in the genus Oncinopus.
Paul Okumura of Kona Diving
Company photographed this unusual little crab at a depth of about
40 ft. at "Rabbi's Reef" a site off the Kona Coast of
Hawaii Island. Paul reports that he found it in rubble and that
it was about 1 inch across. I sent the photo Dr. Peter Ng of the
National University of Singapore who identified it as a spider crab
in the genus Oncinopus. Two species of Oncinopus are
known in Hawaii--O.araneus and O. neptunus-- but without
the actual crab in hand he could not determine which one it is.
I found this crab on a thick-spined
Chondrocidaris gigantea urchin at Ho'okena, Hawai'i at a depth
of about 30 ft. The urchin was out in the sand away from the reef,
which not its normal habitat. Dr. Peter Ng of the National University
of Singapore tentatively identified the crab as a member of the genus
Achaeus, possibly A. japonicus, although that species
has not been recorded from Hawaii. I temporarily placed the crab on
the sand for a photo (top). The lower photo shows it on one of the
urchin's thick spines, which, as usual with these urchins, was covered
SEA URCHIN CRAB
Echinoecus pentagonus (A. Milne Edwards, 1879)
The Sea Urchin Crab is common
on the Banded Urchin Echinothrix calamaris (see my book p
270). Large mature females inhabit the urchin's rectum (on the upper
part of the urchin) where they remain imprisoned, while males and
small females roam the surface of the urchin. This rare photo by
John Earle, however, shows a male or small female on a Pebble Collector
Urchin Pseudoboletia indiana. Dr. Peter Castro reports that
while juveniles may occasionally settle on other urchin species,
the rectums of these other urchins are too small to house a mature
Rhinolambrus contrarius (?)
John Earle spotted this amazing animal
sitting motionless in silty sand at a depth of about 60 ft. off
Kahe Point, O`ahu. He called me over then touched it lightly with
his wand whereupon it spread its arms menacingly in a span of at
least 12 in. Having never seen anything like it before, I decided
to collect it in case it was a species not known in Hawai`i. Picking
it up was easy but holding it for any length of time was not; it
seemed to be able to reach me with its pincers no matter where I
grasped it. Eventually we got it into a bag, and, once ashore, into
When I got home I put an airstone in the
bucket and started looking in books to see what it might be. Clearly,
it belonged to the crab family Parthenopidae, commonly known as
"elbow crabs." A 1965 book (long out of print) by Spencer
Wilkie Tinker got me pretty close to the answer. The book is titled
"Pacific Crustacea, an Illustrated Handbook of the Reef-Dwelling
Crustacea of Hawaii and the South Seas" and on p. 88 it shows
a photo of the crab, or something very much like it, under the name
Lambrus (Rhinolambrus) longispinis. Tinker called it the
Long-Spined Parthenopid Crab. Of it he says:
"The carapace of shell of this crab
is covered with tubercles and short spines. The front legs or chelipeds
are large and are also covered with tubercles and spines, of which
those along the angles of these legs are triangular in shape. The
walking legs are slender, quite smooth, and marked with encircling
bands of color. The carapace measures about two inches in width.
This is an Indo-Pacific species which extends from Hawaii southward
to Australia, westward to Japan, through the East Indies, and across
the Indian Ocean to the coast of Africa.
This rare crab has been retrieved
from rocky bottoms at depths of about one hundred feet."
I took photos
of the crab and sent them to the world's expert on parthenopids,
Dr. Swee Hee Tan of the National University of Singapore. However,
it was the weekend and I didn't expect Dr. Tan to answer for a couple
of days. Since the crab was in Tinker's book I figured it there
was no reason to keep it, so the following day John Earle and I
returned it to the spot where we had captured it.
Soon afterwards I got an answer from Dr.
Tan. He thought it looked like Rhinolambrus contrarius but
of course couldn't be sure without a specimen. I notified Dr. Peter
Castro, who is working on crabs at the Bishop Museum; he said that
Rhinolambrus contrarius is not presently known from the Hawaiian
Islands. So, it looks like it's at least possible that it's a different
species than the one pictured in Tinker's book, which, come to think
of it, did seem to have thicker chelae (pincers). Also, Tinker's
animal came from rocky bottom whereas this crab was in soft silty
sand and nowhere near rocks. On the other hand, Tinker's description
of the banded legs was perfect. So in the end we don't know what
it is. It could well be a new record for Hawai`i but we won't know
until another is found and collected as a specimen. I have here
proposed the common name Giant Elbow Crab, just in case it is not
the same as Tinker's animal. Dr. Tan, however, says that in terms
of leg span there are probably larger elbow crab species in Japan
and the Mediterranean.
July 15, 2007
update: Kent Backman writes from Kaua`i:
saw a odd looking horned helmet in the sand at 130 ft, which turned
out to be odd because it was (temporarily?) cohabitating with this
strange looking crab. With its two large arms folded, it was about
the breadth of the horned helmet
14 inches or so. But when
I approached with my video camera to get a macro shot, the arms
popped out and it attacked in a very quick defensive maneuver.
am quite positive I have not seen this guy before. I would have
liked to collect it, but my hour+ deco in ripping current was hard
enough as it was. I would have had to somehow kill that crab in
order to bring it up safely. He was very defensive!.
is a link to my video, alas with only visible light
good at 130 ft.
KING KONG CRAB
Daldorfia rathbunae (De Man, 1902)
I photographed this crab at Makua,
Oahu, in about 30 ft. In the original ed. of Hawaii's Sea Creatures
I showed a similar but smaller crab which I erroneously called the
Horrid Elbow Crab with the scientific name Daldorfia horrida,
but it has turned out to be the recently-named Daldorfia dimorpha
(Tan & Ng, 2007). In the revised edition I kept the photo but
called it "Holcom's Elbow Crab" (Daldorfia sp.)
after diver Ron Holcom, who collected the animal and showed it to
me. However, Tinker's 1965 book "Pacific Crustacea..."
lists Daldorfia horrida as occurring in Hawaii and mentions
that it grows to a width of 4 in. I suspect the crab above is the
same species that Tinker shows in his book. He calls it the "Horrid
Parthenopid Crab" and writes:
most parthenopid crabs, the surface of this species is rough. It
is covered with rough elevations and depressions and with smaller
tubercles and pits. The chelipeds (claws) are usually unequal in
size, and the walking legs bear spines which grow in such a way
that they form a perforated margin along the upper edge of the leg.
The carapace is somewhat five-sided and is four inches in width.
crab is an Indo-Pacific species... (and) is reported to live on
bottoms of mud or broken shells from shallow water to depths in
excess of three hundred feet.
Swee Hee Tan of the National University of Singapore says that as
far as he knows the true D. horrida does not occur in Hawai`i
and the crab which Tinker illustrates and describes is actually
Below is another
photo, taken by John Earle at Makua, Oahu at a depth of 40 ft.
Ghost Crab juvenile
Farm took this wonderful picture of a small crab on a beach near
Honokohau Harbor, on the Kona Coast of the Big Island; Dr. Peter
Ng of the National University of Singapore identified it as a small
ghost crab. Two species of ghost crabs are known in Hawai`i but
it's not clear which one this represents. Ray writes: "It is
a very small crab (less than 1 inch across including the legs) with
some of the most amazing camouflage that I have ever seen. I'm not
sure whether it truly matches the mixture of white, black, and beige
sand particles or if it is somewhat transparent and you actually
see the sand particles through the body and legs. Whatever the case,
nature certainly is protecting the little guy from predators. We
could see him when he moved, but he disappeared when he stopped.
I just took a picture of the area where I thought he had stopped
and found him in the picture."
top photo: J.Hoover Wai`anae, O`ahu. 100 ft.
bottom photo: Tina Owens, Kona, Hawai`i.
O`ahu. collected by Darrell Takaoka
About 9-10 years ago Tina Owens sent me these crab photos which
she took in Kona, Hawai`i. Tina called it the "Crusader Crab"
because of the red cross on its back. I sent the photos to Dr. Peter
Ng in Singapore who replied. "Your crusader crab is interesting!!!
It may well be a rather rare animal called Parapilumnus."
Peter has a long memory. In Dec. 2013 he wrote: "Finishing
up loose ends all over
. Had this old picture sent by you.
It was an unidentified crab which I said may be Parapilumnus
was from a lady called "Tina" I know what it is now
A new genus allied to Parapilumnus which I calling Crinitocinus
. Species is Crinitocinus alcocki (Borradaile, 1900)."