Defenses
 
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Invertebrates
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The topic considered here reating to defenses of invertebrates deals withbehaviour. Other invertebrate defenses are accessible via the icons.
 
 

Invertebrate defenses: behaviour

hot buttons for behavioral part of BCCR

Behavioural defenses in Caribbean invertebrates are many and varied, but are generally encompassed in the icon-topics shown.

This part of behavioral defenses includes bite back and autotomy.

NOTE lit. "self cut" Gr., is a strategy of casting off part of the body, such as a tail or claw, when under attack by a predator

 
 

Invertebrate defenses: behaviour: bite back

 
 

seahorse dive leader for Biology of Caribbean Coral Reefs website

photograph of hermit crab Coenobita sp. taken from a video

"We're not exactly on a dive right now, but these back-reef hermit crabs are always fun to watch. You wouldn't want to get bitten by one of them, though. They may be slow and ponderous, but their large crushing claws are quite powerful." - Cayman Brac, 2004

NOTE also known as soldier crabs Coenobita sp.

 
 

photograph of Caribbean duppy crab Cardisoma guanhumi
In addition to the hermit crab shown in the preceding video, there are several species of semiterrestrial crabs living in the Caribbean area. These species are mostly constrained to areas that provide either direct contact with seawater, via deep burrows, or access to standing water, in order to irrigate the gills for gas exchange. Most of the crabs are active at night and it's not uncommon to see large duppy crabs and other species wandering along paths and roads during their feeding and reproductive excursions. All are bound to the sea for reproduction, specifically, in that when their eggs are ready to hatch, ovigerous females have to release the larvae directly into the sea. Following several weeks or months in the plankton, the settling stage arrives back on shore and the juveniles take up the adult mode of life.

The Caribbean duppy crab Cardisoma guanhumi is a large, fast-moving
species that inhabits burrows near the shoreline. Males have asymmetrical
claws, the smaller one being used for food-scavenging and the larger one
for biting defense and perhaps also to hold the female during copulation.

  Other semiterrestrial crabs in the Caribbean that employ their claws for defensive purposes are:
 
photograph of semiterrestrial ghost crab Ocypode sp. photograph of soldier crab Coenobita sp.
Ghost crabs Ocypode sp. These extremely fast-moving crabs inhabit burrows in sand
at the top of the shore. They scavenge the beach area for food and, when frightened, rush for their burrow or a neighbour's burrow, and then the fighting ensues
Soldier hermit-crabs Coenobita sp. These large crabs occuply the biggest shells available on the shore. The largest claw is used for fighting and also, when the crab is withdrawn into the shell, as a stopper for the opening 1X
photograph of semiterrestrial crab Gecarcinus lateralis photograph of sally-lightfoot crab Grapsus grapsus
Semiterrestrial crabs Gecarcinus lateralis inhabit burrows deep enough to contact seawater. During reproductive season females of this species undertake migrations to the sea to release their larvae, and the migrations may number in the tens of thousands Another fast-moving, hard-biting crab is the intertidal surf-inhabiting sally-lightfoot Grapsus grapsus. It is a scavenger, eating seaweeds as well as animal matter. The species has good eyesight, lightning quick reaction times, and is exceedingly hard to catch
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of Caribbean fiddler crab Uca sp. taken from a video

"Once again, we're a little out of our depth here, but fiddler crabs have interesting defensive behaviour. They wave their big claws not only to scare off rivals, and to clout them on their heads, but also to attract females, who seem enamoured with large-clawed males." - Margarita Island, Venezuela 2006

NOTE genus Uca

 
 

photograph of ocellate swimming crab Portunus sebae courtesy Florent Charpin
If fast swimming doesn't do the job, the ocellate swimming crab has quick use of its claws, which are very sharp. Photo courtesy Florent Charpin Florent's Guide to the Tropical Reefs.

 

 

 

Note the paddle-like limbs
on Portunus sebae and the
sharply pointed claws 0.75X

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a mantid shrimp taken from a video

"Well, lookee here, this busy little fellow is a mantid shrimp. It's known as a "thumb-crusher" because the lever system in its claw creates a fast and strong reverse strike for catching prey and defending itself. I know you wouldn't, but don't even think about touching it!" - Turneffe Island, Belize 2000. Video courtesy Andy Stockbridge, Belize.

NOTE possibly the dark mantid Gonodactylus curacaoensis

 
 

photo/drawings showing types of pedicellariae in a sea urchin
In addition to spines, sea urchins and some sea stars have small biting jaws called pedicellariae scattered over their skin surface. Some types of pedicellariae act independently of the animal beariing them, while other types, notably the toxic ones, are under at least partial nervous control. Of all echinoderm, sea urchins possess the most diverse array. There are 3 kinds of smaller ones that nip or crush, and one kind of larger one that is toxic. As shown in the drawing, the larger type has 3 sharp jaws for piercing a predator, and it is through the wounds created by the jaw tips that the toxin is injected.

NOTE lit. "foot units"

 

photograph of toxic pedicellariae of sea urchin Tripneustes ventricosusThe nippiing/crushing types of pedicellariae function to kill small larvae and algal spores or at least discourage them from settling, while the toxic type acts against larger predators. Regardless of how deadly they may look, however, the toxin of most sea-urchin pedicellariae seems to be no more than just an irritant to potential predators such as sea photograph of sea star biten by toxic pedicellariae of a purple sea urchin Strongylocentrotus purpuratusstars, and no Caribbean species with pedicellariae seems to be toxic to humans.

Toxic-type pedicellariae of
Caribbean Tripneustes
ventricosus
raised, open,
and ready to bite 3X



Example from the Pacific west coast: a sunflower star Pycnopodia
helianthoides
responds to the toxin of a pedicellaria-bite from a
purple sea urchin Strongylocentrotus purpuratus 0.6X

 
 

Invertebrate defenses: behaviour: autotomy

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of crab being held in water by one leg "We can support this little crab by its claw, but not for long because it might cast it off if it thinks it's in the grasp of a predator." - Grand Cayman 2006
 
 

Crabs and other arthropods are the most likely reef-dwelling invertebrates to autotomise a limb, and the most likely crabs to do so are fast-moving terrestrial or semiterrestrial species. The limb is cast off through contraction of special muscles acting on a suture line near the base of photograph of marsh crab Armases cenereum showing autotomy membrane a limb. These muscles forcefully disarticulate the segments involved, and the distal part falls away. A membrane forms almost instantly at the breakage site to miminise loss of hemolymph ("blood"). The autotomised part is thought to distract a predator, either visually or, as shown in the photograph below, physically, allowing the intended prey to depart the scene.

NOTE suture lines in arthropods indicate where adjoining segments, such as found in limbs, meet. For articulating segments, as in a limb, these joints are separated by flexible membranes that allow the parts to move independently of photograph showing autotomised claw of marsh crab Armases cinereum biting a human thumbone another. Other narrower suture lines are found throughout the exoskeleton and indicate joining points

The sealing membrane is
visible on the wound site
in this subtropical marsh
crab Armases cinereum

 


An autotomised claw can bite for several moments after its release, giving
time for strategic withdrawal of its owner. Note in the photograph, which shows
the claw doubled back on itself, that a similar membrane also seals off this
part of the breakage site. This prevents the hemolymph from leaking out
and thus ensures maximal energy materials to allow the biting to continue

 
 

photograph showiing an autotomised arm from a sunflower star Pycnopodia helianthoides crawling along the sea bottom
Some sea stars and brittle stars can voluntarily release one or more arms, or parts of arms, in defensive response to a predatory attack. As in crabs, the function is to distract a predator while the owner crawls away. If not consumed immediately by the predator, the arm may live and even crawl around for a few days before dying and being eaten by scavengers. The process is enabled by a temporary liquefaction of the connective tissues binding the calcareous ossicles of the skeleton together.

NOTE in species of the tropical Linckia sea star, arm autotomy is a reproductive strategy to clone new individuals. For more on this topic go to ASEXUAL REPRODUCTION: SEA STARS

Shown here is the autotomised arm of a temperate sea-star species, the sunflower star
Pycnopodia helianthoides.
But for a portion of the digestive gland hanging out on the right
side, the arm appears in good health . However, as the arm has no mouth, it cannot eat and will soon die

 

photograph of nudibranch Discodoris evelinae courtesy Anne Dupont, FloridaA few Caribbean nudibranch species can autotomise parts of the mantle edge of its body when irritated. The nudibranch then crawls away or, in the case of the one featured here, crawls or swims to safety. Photograph courtesy Anne Dupont, FL.

 

 

Nudibranch Discodoris evelinae 1X

 
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