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 photos copyright John P. Hoover unless otherwise credited

Eric Sanford

HORN-EYED GHOST CRAB Ocypode ceratophthalma (Pallas, 1772)
Family Ocypodidae
    A mostly nocturnal crab of sandy beaches named for its remarkable hornlike eyes.. Shelters in a burrow by day, identified by a conical pile of sand at the entrance. It grows to about 1.5 inches carapace width and is widespread in the Indo-Pacific.
    Eric Sanford took this rare photo. He writes: "The Horn-Eyed Ghost Crab was photographed at Kahuku Point on the north shore of O'ahu. Although we saw lots of big holes dug by this species, we only saw this single crab out foraging. It was first thing in the morning and the beach was quiet (in terms of human traffic), so perhaps we got lucky to see this individual out and about before it retreated to its burrow. But the large burrows from this crab seemed very common in Hawai'i, so it might be a helpful addition for readers to see a photo. I was impressed by their eyes and their speed!"

Pauline Fiene

HARLEQUIN CRAB Lissocarcinus laevis Miers, 1886
Family Portunidae
     Closely related to the common Sea Cucumber Crab Lissocarcinus orbicularis (p. 275 in my book), in Hawaii this crab is rarely encountered and seems to lack the bold "harlequin" pattern typical elsewhere in the Indo-Pacific, except perhaps on the claw-bearing limbs. It is commensal with large anemones, including tube anemones. Pauline Fiene photographed this individual with a Sand Anemone Heteractis malu in Ma`alaea Bay, Maui (see p. 39 of my book). Athough classified in the swimming crab family, Portunidae, it probably does not swim much, if at all, and remains with its host anemone for all its adult life. To about 1.5 inches carapace width. The species is widespread in the Indo-Pacific.

` ALAMIHI Metopograpsus thukuhar (Owen, 1839)
Family Grapsidae
     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 Ocean.

Pachygrapsus planifrons DeMan 1888
Family Grapsidae
     This is a small crab with a carapace less than an inch wide that is common in some tide pools. It has a slightly trapezoidal carapace with eyes at the front corners. Distinctive white spots on inner sides of claws are revealed when the crab is feeding, though not all individuals seem to show these spots. Perhaps they are related to the sex of the animal. Indo-Pacific. The more common Pachygrapsus plicatus is similar , but has numerous transverse ridges on carapace. Photos: Punaluu Beach Park, Hawaii.

John Earle

GREEN FLAT ROCK CRAB Percnon abbreviatum (Dana 1851)
Family Grapsidae
     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.

Paul Okumura

Spider crab in the genus Oncinopus.
Family Inachidae
       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.

Achaeus japonicus?
Family Inachidae
       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 with growths.

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SEA URCHIN CRAB
Echinoecus pentagonus (A. Milne Edwards, 1879)
Family Pilumnidae
       Although this crab is in my book on p. 270, the photo does not show the whole animal. Here are some additional pictures. This crab is a common parasite of the Banded Sea Urchin Echinothrix calamaris. 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. At top is a free-roaming male or small female on a Banded Urchin, as photographed by Alexia Benrezkellah. Dr. Peter Castro reports that while juveniles may occasionally settle on urchin species other than the Banded Urchin, the rectums of these other urchins are too small to house a mature female. The lower photo by John Earle shows a male or small female on a Pebble Collector Urchin Pseudoboletia indiana.

Rare observation of Dwarf Moray, Gymnothorax melatremus preying on E. pentagonus: On 01-26-2016 Alexia Benrezkellah wrote: "While on a dive ... this morning I saw one of the coolest things I've seen underwater. A dwarf moray rammed its head into the hole of an urchin and ripped out the crab and swallowed it whole. Unfortunately ... no photos."

HALIMEDA CRAB
Huenia heraldica (De Haan, 1837)
Family Epialtidae
     This little green crab mimics Halimeda algae, and often attaches a segment of Halimeda to the pointed end of its carapace (rostrum) to heighten the effect--see center and bottom photos. The species occurs from the shallows down to scuba depths and is found throughout most of the Indo-Pacific. It grows to about 3/4 in. carapace width. Another common name is Arrowhead Crab. Top photo by Cory Pittman, taken at Kapalua, Maui. Center and bottom photos by Katherine Shepherd taken off Sugar Beach, north Kihei, Maui. depth: about 20 ft.

GIANT ELBOW CRAB
Rhinolambrus contrarius (?)
Family Parthenopidae
     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 a bucket.
     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:

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.

I 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!.

Here is a link to my video, alas with only visible light…not so good at 130 ft.

http://www.veoh.com/videos/v1159909rJCYf7tD

KING KONG CRAB
Daldorfia rathbunae (De Man, 1902)
Family Parthenopidae
     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:

Like 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.

This 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.

However, Dr. 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 D. rathbunae.

Below is another photo, taken by John Earle at Makua, Oahu at a depth of 40 ft.

Ghost Crab juvenile
Ocypode sp.
       Ray 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."

Viaderiana taeniola (Rathbun, 1906)
family Pilumnidae
top photo: J.Hoover Wai`anae, O`ahu. 100 ft.
bottom photo: Tina Owens, Kona, Hawai`i.

Nucia speciosa Dana 1852
family Leucosiidae
O`ahu. collected by Darrell Takaoka

Crinitocinus alcocki (Borradaile, 1900)
family Goneplacidae
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)."