WTF? (WHAT’S THAT FISH?) 14: ARROW CRABS

January 16, 2018 by Rolling Harbour

WTF? (WHAT’S THAT FISH?) 14: ARROW CRABS

It’s been a while since the last in the WTF? series, which is dedicated to the wilder, less conventionally fish-shaped side of reef life – those creatures that you may come across, blink into your face-mask, and silently mouth the words ‘What’s That Fish?’ (that’s what it looks like you are saying, anyway).

Let’s meet some Arrow Crabs Stenorhynchus seticornis, one of the very few creatures surely to have a triangular body plus a huge pointy nose (rostrum), supported on long skinny legs. To which add, they wear tiny blue gloves on their two front claws.

These crabs are coral reef dwellers and mostly stay concealed during the day. Their body is protected by a carapace, and the rostrum has serrated edges like a tiny rasp or file. I haven’t found a definitive reason for this gadget, but I suspect it is more for probing than for piercing or fighting.

There’s a considerable colour variation among these crabs, as these images show. The body may even have blue iridescent lines (#2, above). And those claws may be any of 50 shades of blue…

Arrow crabs are most active at night. They eat feather-duster worms (illus.) and similar invertebrates such as bristle worms.

Feather-duster worm (Melinda Riger / G B Scuba)

Arrow Crab Meal

Like certain types of shrimp, they also have a symbiotic relationship with anemones, whereby they make use of an anemone to benefit from the food it captures – and possibly for cover too. They are protected from anemone stings, whereas some of their predators are not.

This was the place where I was going to tell you about the arrow crab’s private life, but, well… “it’s complicated”. Briefly it is: male passes sperm-filled capsule to female; she uses it in some way whereby it fertilises her eggs; she then ‘broods’ the eggs in one of her ‘swimming legs’; the eggs hatch into larvae and swim off to eat plankton; each one then grows & moults, repeating the process until it has reached adult form. On balance, humans have arguably perfected a preferable method.

Arrow Crabs are apparently popular aquarium creatures, although they sound to me rather a disagreeable challenge. They can move quickly on those long legs, and it seems as if they inclined to be aggressive to other inhabitants of the tank. As far as I can make out, it’s best not to put 2 of them together: they certainly won’t be doing the sperm capsule thing described earlier…

Master of Disguise

Photo credits: Melinda Riger / G B Scuba (1, 3, 4, 5, 6); Adam Rees / Scuba Works (2, 8, 9); Nick Hopgood,Wiki (7); Chuck Elliot – video

“CRABACO?”: CRABBING ON ABACO, BAHAMAS

October 13, 2015 by Rolling Harbour

“CRABACO?”: CRABBING ON ABACO, BAHAMAS

It’s been a while since I was in a crabby mood, but autumn is here and there’s a sharp nip in the early morning air… What better time to visit a selection of the many crab species found on Abaco.

GHOST CRAB

I thought I had some good photos of these cute little guys with their ‘Carson the Downton Abbey Butler’ white gloves. However, Tom Sheley (header and below) has perfectly caught the tide-hanging that they enjoy, sometimes disappearing completely or perhaps leaving just their twin periscopes showing.

HERMIT CRAB

Many people’s favourite small crab, with their endearing house-moving habits as they grow. Excellent for racing, too (see HERE). Here’s one taking its mobile home up a tree; and another tucked safely into a ~~nerite~~ [Capt Rick Guest amends] Magpie Shell, Cittarium pica, (used to be Livona pica), the living animal of which is the 3rd most consumed animal behind Lobster & Conch in the Caribbean. They are Littoral around Shorelines and are also used as bait.

BLACK-BACKED LAND CRAB

Faithful guardians of my rod (there are 2 there)!

LAND CRAB

STONE CRAB

ARROW CRAB

CLINGING CRAB

BLUE CRAB

HORSESHOE CRAB (LIMULUS)

Credits: Tom Sheley (1, 2, 3); Keith Salvesen (4,7,8,9,15); Charlie Skinner (5,6); Melinda Riger (10,11,12,13); Leodec (14)

A BAHAMAS CRAB FEAST ON ABACO & BEYOND

July 15, 2013 by Rolling Harbour

A BAHAMAS CRAB FEAST ON ABACO & BEYOND

The photos below show a sample of the types of crab that may be found in and around the island of Abaco, both in the sea and on land. The wonderful underwater images were taken in adjacent waters by Melina Riger of Grand Bahama Scuba. The rest were taken by landlubbers at Rolling Harbour on the Delphi beach and rather closer to the building than one might expect. The last crab (and the header image) was a crab hooshed out of the coppice by Ricky Johnson to demonstrate its fighting prowess. I have put links to 2 posts featuring this fine specimen (including a video) at the end.

ARROW CRAB

HERMIT CRAB

HORSESHOE CRAB (LIMULUS)

COMMON GHOST CRAB (Ocypode quadrata), DELPHI BEACH

PET CRABS PROTECTING MY ROD OUTSIDE OUR ROOM (note second crab behind it) AND ADVERTISING HARDY PRODUCTS. Rick Guest has pointed out that the crab is not protecting my rod at all. As if! “The crab in the foreground is the male guarding “his” female, distinguished by the small, abdominal triangle. The wide margins of the female’s abdomen are evident.” So that’s how to tell the sex of a land crab.