REEF CRUSTACEA
The Crustacea vary considerably in the complexity of their larval development. In most cases, crustaceans are gonochoric, with the exceptions of barnacles. As a rule, if eggs are broadcast the larval type is less complex. The most basic and most broadly applicable larval stage is called the nauplius. This is a non-feeding stage characterized by a simple median eye in the head, sometimes called a nauplius eye, plus three sets of appendages. The first two are the first and second antennae; the third is a pair of mandibles, or more accurately, appendages that will eventually become mandibles. Further growth and molting produces more appendages typical of the adult. Copepods, barnacles and de
capod shrimp hatch as nauplii.
Copepod nauplius larva (10x)
Modified from http://www.permaflate.com/photqual.htm
Brachyuran zoea has a typical, Anomuran zoea above lacks one
long rostral spine on the head
note well developed eyes and appendages typical of zoea larvae
www.microscopy-uk.org.uk/ mag/artjun98/wimren2.htm
192.171.163.165/ pil/Anomura_Galathea%20_zoea.htm
users.tpg.com.au/.../biology/ lifecycle.html
www.science-in-salamanca.tas.csiro.au/ themes/...
With 42,000 species, crustaceans are the second most diverse group of organisms after the gastropods. The reef-dwelling representatives account for a substantial proportion of this number, including such diverse forms as the familiar decapods (true crabs, shrimp and lobsters), as well as barnacles, stomatopods and important planktonic groups including copepods and mysid shrimp. You are referred to the appended arthropod review.pdf to become familiar with the general features these groups. The following will serve to highlight some examples of reef dwellers. Copepods are without question the most important group of animal plankton in most oceanic systems, reefs included. There are ~12,000 species that have been described, including some benthic and bizarre parasitic ones in addition to the planktonic variety. As in other crustaceans the body is segmented, and there are two sets of antennae, one larger than the other. The second set is under the larger pair in this photograph. The thoracic appendages are typically highly branched as are the accessory feeding appendages (maxillae, maxillipeds) that are used to capture phytoplankton. Planktonic copepods spend their entire lives in the plankton and are food sources for many filter feeding and suspension-feeding organisms, from cnidarians to fish. Copepods are the most important group of reef zooplankton from a numerical perspective, constituting 70-80% of the zooplankton present. There are are groups (orders) of copepods that are pelagic, but form daytime swarms in the waters near or on the reef, as well as those that swarm closely associated with the reef itself. In either case, the copepod swarming behavior ceases at night and copepods spread out over the reef. The abundance of zooplankton at night is several fold more than during the day, accounting for nocturnal feeding behavior of many reef organisms including reef corals. It appears that most of the reef zooplankton is not imported from the surrounding pelagic environment, but are reef residents or residents of adjacent communities.
A copepod of the
genus Candacia www.amonline.net.au/.../ zooplankton03.htm
Mysid shrimp
Mysids (order Mysidacea)
belong to a group (superorder)of crustaceans called the Pericarida, which includes the
isopods, amphipods and several other groups known only to those who have had
a course in invertebrate zoology. Mysids are small
shrimp-like organisms (sometimes called opossum shrimp)distinguished as pericarids
by their ventral marsupium under the thorax. Fertilized eggs are
brooded in the marsupium and are released as juveniles.
The first few segments of the thorax are often fused with the head to form
a carapace. The compound eyes are stalked
as in decapod shrimp. Mysids
are filter feeders like copepods. Two statocysts that appear as bull’s eyes (see figure below) are
found in the tail fan and this (plus the marsupium)
are the two easiest means of distinguishing mysids
from small decapod shrimp. Mysids
are common inhabitants of caves and overhangs on reefs during the day and
serve as planktonic food when they emerge at night.
They are not unique to reefs as a group and they are not all ma
rine,
but they are several species are important coelobites
(cave dwellers) on the reef. They can also be seen congregating around the
spines of long-spinned the sea urchins during the day, and retreat among them
when approached. These crustaceans, along with copepods, spread out over the
reef at night constitute some fo the most abundant plankton after the copepods.
Another pericarid group, the isopods, are
also fairly common on reefs, but are most often noticed as ectoparasites
on fish as shown on the left. Isopods are dorso-ventrally
flattened and are sometimes called “sea roaches”, but are not insects.
Parasitic isopod on cardinalfish
www.lawrence.edu/.../biol_81a/ invert/invert.html
Mycidacea:
Neomysis kadiakensis www.calacademy.org/.../SFBay2K/
mysid_shrimp.htm
The common name of the sedentary crustacean animals constituting
the crustacean subclass Cirripedia. Barnacles are
exclusively marine and are quite unlike any other
crustacean because of the permanently attached, or sessile, mode of existence
for which they are highly modified. Typical barnacles attach to the substrate
by means of an exceedingly strong adhesive cement,
produced by a cement gland, and secrete a shell, or carapace, of calcareous
(limestone) plates, around themselves. Colonies of such barnacles form
conspicuous encrustations on wharves, boats, pilings, and rocky shores. They
range in length from under 1 in. (2.5 cm) to 30 in. (75 cm). Their shells are
commonly yellow, orange, red, pink, or purple, sometimes with striped patterns.
Because of their sedentary life and enclosing shells, barnacles were thought to
be mollusks until 1830, when their larval stages were discovered. Much of what
is known about barnacles is the result of research by Charles Darwin, who
published a monumental work on the subject in the 1840s.
Shelled and Shell-less Barnacles
Barnacles with a
calcareous shell (order Thoracica) include the
gooseneck barnacles, which are attached to the substrate by means of a stalk,
or peduncle, and the acorn, or rock, barnacles, which are attached directly to
the substrate. The stalk of gooseneck barnacles is simply an elongation of the
attached end of the animal’s body. In some gooseneck barnacles the stalk as
well as the body is covered by calcareous plates; in others it is a naked
leathery or horny structure. A gooseneck barnacle found in large numbers on
ships and pilings is Lepas, which has a leathery
stalk and flattened shell and looks like a small clam attached by its siphon.
Balanus is an acorn barnacle commonly found on rocks; it has a thick
conical shell attached at its wide base, with an opening at the top. As in many
of the acorn barnacles, the plates of the surrounding carapace form an
impenetrable wall, and the opening is equipped with two movable plates that can
be pulled down to close off the body completely.
In both gooseneck and
acorn barnacles the feathery legs of the animal may sometimes be seen
protruding through the carapace opening. When the animal feeds, these jointed
legs, called cirri, sweep organic particles and minute planktonic
organisms toward the mouth, which is located deeper inside the shell. The attached
end of the animal is its anterior, or head region: the barnacle has been
described as a shrimplike animal standing on its head
in a limestone house and kicking food into its mouth with its feet. Barnacles
lack gills; gas exchange occurs through the cirri and the body wall. Some
shelled barnacles are commensal, attaching themselves
to living animals such as whales, porpoises, turtles, crustaceans, and
echinoderms. The gooseneck barnacle Conchoderma may be found growing on the acorn barnacle Coronula, which grows on the skin of whales.
Besides the shelled
barnacles, there are naked barnacles (orders Ascothoracica
and Rhizocephala), which live on, and in some cases parasitize, other invertebrate animals. There are also
shell-less boring barnacles (order Acrothoracica),
which live inside holes that they drill in shells and corals.
barnacle Lithotrya sp.
boring into beachrock
from www.wooster.edu/geology
Because they burrow into hard
substrates, they only have to build their own calcareous plates to cover the
opening of their burrow. Acorn
barnacles on the other hand, secrete calcareous plates to completely cover
their bodies. These plates protect the animal from many predators and
from drying out when they are exposed to the air during low tides. Acorn
barnacles (Thoracica) are the rough white barnacles
seen on rocks in the intertidal all over the
world. Members of the Thoracica are found many
other places besides intertidal rocks. A giant acorn barnacle the size of
a softball is found in the depths of the Southern Ocean off of
Reproduction
Although nearly all other
crustaceans have separate sexes, most barnacles are hermaphrodites, with cross-fertilization between adjacent individuals being
the rule. Some species, however, have dwarf males, which are parasitic on
female or hermaphroditic individuals. The fertilized egg develops into a
free-swimming larva, called a nauplius larva (see appended reference), of the basic crustacean type, with
paired antennae. This form then molts to become a cypris
larva, which eventually attaches itself to a suitable substrate by its first
pair of antennae and undergoes metamorphosis into an adult.
Economic Significance
Barnacles are
economically significant because they settle on ship hulls and harbor
installations; the resulting encrustation of the ships greatly increases
friction, diminishing speed and increasing fuel consumption. Ships are treated
with plastic coating or with antifouling paints containing copper or tin to
prevent or diminish encrustation.
Classification
Barnacles are classified in the phylum Arthropoda, subphylum Crustacea, class Cirripedia. If you are not familiar with these groups, read the appended review of arthropods.
The
order Stomatopoda
is constituted by 300 mostly tropical species of organisms called “mantis
shrimp”. Stomatopods are highly specialized ambush predators of fish,
mollusks and other crustaceans. Their dorso-ventally
flattened body and oval compound eyes on stalks are two ways to recognize
them, but the primary identifying key is the second pair of claws that are
distinctively subchelate,
meaning that they are jointed more like a jacknife
than the typical pincer claw called a cheliped. The inner side or end of the claw is armed with sharp
teeth, like those of a praying mantis (hence the common name), and it uses
this “raptorial claw” to slice
or stab through its prey. The largest of them is over a foot long, but most
reef-dwelling species are much smaller (fortunately). Gills are attached to
the pleopods (swimmerets) and are thus abdominal. Although
this is an unusual place for gills in crustaceans, abdominal gills are also
found in isopods. They are highly colored, living in coral crevices or burrows.
The female broods up to 50,000 eggs held together by an adhesive material,
but the brood is in the burrow, not in a marsupium. Stomatopods are not pericarid crustaceans. The eyes are extraordinary.The
compound eyes of some stomatopod species represent
the most complicated visual systems yet found in any animal. Each compound
eye is functionally divided into three general regions: two hemispheric regions
are bisected by a narrow midband which is clearly
seen as a curved region in the equatorial plane of the eyes. The ommatidia of the upper and lower
hemispheres are structurally and functionally similar to those in other crustaceans,
but the midband shows features that are unique to
stomatopods. Functionally, the two hemispheres in
a SINGLE eye allows stereoscopic vision. The midband
region is responsible for color vision. They have >10
visual pigments (not just red, blue and green like humans), and can see into
the near UV and the infra-red.
Stomatopod morphology (top left) compared with photo of whole organism (bottom) and complex eyes (upper right).
www.nhm.org/guana/bvi-invt/bvi-surv/stom-inf.htm
http://www.blueboard.com/mantis/pics/eyes.htm
www.mov.vic.gov.au/crust/stombiol.html
References
Cronin TW, and
Cronin, T.W., N. J. Marshall, C. A. Quinn
and C. A. King.
1994. Ultraviolet photoreception in mantis shrimp. Vision Research
34:1443-1452.
Crustaceans with the first three thoracic
appendages that are chelate and and five pairs of thoracic appendages
are in the order Decapoda, and include the most
familiar crustaceans. The true decapod shrimp (suborder Natantia)include
the commercial, edible variety, but there are other shrimp that are important
on reefs. One example is the snapping shrimp (Family Alpheidae).
Anyone who has taken the time to listen
while on a reef will have heard snapping shrimp. Hundreds of species live in
shallow seawater habitats all over the world. And they are so loud that they
can actually interfere with acoustic devices — including naval sonar. The
shrimp use the snapping sound to deter predators, to stun prey, and even to
communicate with other shrimp. Even a large sponge can have thousands of
snapping shrimp living within its galleries, and within the crevices of the reef
itself, snapping shrimp are abundant. It can get pretty noisy down there.
When
a snapping shrimp snaps, it opens wide its enlarged “claw,” then slams it
quickly shut. Up until very recently, researchers thought the loud noise
generated by snapping shrimp came from the lightening-quick slam of the
shrimp's claw. But it turns out that for one species of snapper,
at least, the noise comes from a very different source. In fact, a collapsing
bubble causes the shrimp's loud “SNAP.”
But that's just what a group of
researchers from the
Reference Brown,
K. (
Cleaning shrimp and Anemone shrimp
Without
going into the excruciating details of shrimp taxonomy, there
are three families of reef shrimp including the Stenopodidae, the
Palaemonidae and the Hippolytidae. Examples of each are given below.
Stenopodids have a spiny carapace and abdominal region, as well as a distinctively
large 3rd set of chelate thoracic appendages. Example: red and white banded
shrimp shown below. Hippolytid cleaner shrimp lack the distinctively large
spines and claws of stenopodids and the most common genus (Lysmata- see below)
has one or more bright longitudinal stripes along the body. Both of these
are brightly colored reef inhabitants that pick ectoparasites and other undesirable material from the gills,
oral surfaces, fins and the body of relatively large reef fish, usually from
established cleaner stations (described later) on the reef to advertise themselves.
Fish indicate their willingness to be cleaned by approaching the station,
opening their mouths, flaring their gills and even changing color.The family
Palaemonidae is a large group, only some of which are associated with reefs.
These are often small, cryptically colored and are usually
associated with an invertebrate host. Anemone shrimp (shown below) are nearly
transparent except for blue spots. These reef palaemonids live within the
tentacle of sea anemones and clip the tentacles for
food. It is not clear if the anemone benefits from the relationship as much
as the shrimp.
Banded cleaner shrimp (family Stenopodidae- note large chelate appendages) on moray eel.
www.blueiceberg.com/prints/ gal7/gal7a/773.htm
Anemone
shrimp
(genus Periclimenes) on host Dental
shrimp?
Don’t
ask
www.billsbest.com/plshrimp.html
www.bonairetalk.com/newsgroup/messages/
116771/156953.html
Lobsters are in the decapod
suborder Reptantia, which includes all of the bottom- dwelling,
benthic and heavily calcified groups including everything that is not a shrimp.
Thus the Reptantia is often subdivided into lobsters, crabs and hermit crabs
that are each considered sections of the suborder. A section
sits between a superfamiliy and a suborder. There are some taxonomies that
consider the decapods as a subclass or a suborder rather than an order. This
would elevate the "sections" to an order, infraorder or suborder.
In the following taxonomy we will eliminate the Reptantia and elevate the
sections to suborders to keep things simple. The suborder Macrura (large
tails) the lobsters. They are dorso-ventrally flattened
decapods with elongated, muscular abdomens. Pleopods (swimmerets)
are adapted for holding eggs rather than swimming. There are about 700 species,
but there are several families of lobsters, three of which are considered
here. The reef-associated forms include the clawed lobsters (Family
Nephropidae) some of which are occasionally found on reefs, the shovel-nosed
lobsters (Family Scyllidae), and the spiny lobsters (Family
Panuliridae). Lobsters without chelipeds (large
claws) represent the largest group of lobsters and while many of them
are not reef associated, some are. The genus Panulirus has a circumtropical distribution. In the
Modified
from www.mov.vic.gov.au/crust/lobbiol.html
lobster is P. argus. Like most other reef lobsters
it is primarily an omnivorous night feeder, and will eat algae, mollusks or
sessile organisms. This species is gregarious and undergoes a mass migration
into deeper water, especially late in the year with colder weather. Its close
relative, the
(P. guttatus) is smaller, and does not
migrate or live in social groups. Little is known about its food and feeding or
habits. Even less is known of the biology of the uncommon clawed lobster Enoplometopus.
Enoplometopus antillensis, a clawed reef lobster (Family Nephropidae)
The spotted spiny lobster
P. guttatus (Family Panuliridae)
www.wgn.net/~fabio/gallery/belize-spotted-spiny-lobste.htm
http://biomar.free.fr/enoplometopus/images/enoplometopus_antillensis_gonzales_p132_74.jpg
Social spiny lobster, Panulirus argus http://claycoleman.tripod.com/id51.htm
Shovelnose lobsters (Family Scyllidae) inhabit reefs and adjacent sediments;
they forage in the open at night. Bivalves are among their favorite food items.
www.islanddivers.com/images/MVC-021S.JPG
Decapod crabs (the suborder Brachyura- short tail) are the largest single group of crustaceans
(> 4500 species in 16 families), and vary considerably in form. Their principle characteristic is the severe reduction of the tail that usually resides in a special ventral groove in the thorax. The sexes are separate and it is a simple matter to distinguish them. The females have a wide flap-like abdomen suitable for carrying eggs, while the males have a long and narrow abdomen
with two gonopods, specialized appendages for copulation.There are no other appendages on the male abdomen. The first pair of thoracic appendages in both males and females are chelate as chelipeds although in some species the there is a distinction in the size of the claws that differentiates males and females. There are too many crab groups to review here, but some examples below will suffice.
Carpilius corallinus is a member of the stone crab family Xanthidae. It uses its powerful claws to tear open mollusks and sea urchins. They are typically small and have no commercial value. http://www.cs.brown.edu/people/twd/fish/Los%20Roques/doeppne-066.jpg
www.divegallery.com/decocrab4.htm
Decorator crabs are members of the Family Majidae, the spider crabs. Majids are typically pointed at the front end of the carapace and have long spider-like legs, especially the ones with chelipeds. Not all of them have curved setae that allow the attachment of organisms to the shell. Those that do, use sponges (see below) and other invertebrates to camouflage themselves. This specimen is an inch across. Perhaps after staring at this for a while you see where the crab is. Another majid that is common on reefs is the arrow crab shown below.
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| Majid decorated with sponges | The arrow crab is a majid that does not camouflage itself |
This one is not a decorator, nor is the largest crab in the world. The latter is Japanese spider crab that is two meters long when the chelipeds are extended. This majid crab, also not a decorator, has been introduced to
Another family, the Dromiidae, include those called sponge crabs that have a specialized 5th pair of thoracic appendages (periopods) that are on top of the posterior thorax. These are used to carry sponges and encourage their growth over the dorsal surface of the crab. These legs cannot be seen unless the sponge is removed. Dromiids are typically hirsute with fine setae that give them a fuzzy feel. Most dromiids are NOT sponge crabs.
The swimming crabs are in the family Portunidae. They are easy to distinguish by their pointed carapace and the 5th pair of thoracic appendages that are flattened as paddles and are adapted for swimming. These are not characteristic of reefs, but are common enough to include here. The example shown below is the commercially valuable blue crab, Callinectes sapidus.
Callinectes sapidus, the common blue crab is a portunid. Note 5th pair of legs and pointed carapace.
The Calappidae are the box crabs, specialized predators of mollusks that are capable of opening a shell with its specialized, notched “can-opener”-like chelipeds. Another common name for calappids is the “shame-faced” crabs, because their wide claws must be carried in front of their body as if to hide their “face” in shame.
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Calappa flamea, with can-opener claws |
The last group of crabs to be considered here are land crabs in the family Gecarcinidae. The species that is common in |
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The carapace can get up to 13 cm wide (5”) and the claw spread can be up to 60 cm (~2 feet). The claws are asymmetrical with one (usually the right) being larger than the other. They are also sexually dimorphic with males larger than females. They are getting difficult to find in many parts of south
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mass migration of red gecarcinid crabs
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Christmas Island is a possession of Australia and most of it is incorporated into a national park. The island is known for its endemic wildlife. http://www.deh.gov.au/parks/christmas/fauna/redcrabs.html
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Hermit Crabs (suborder Anomura) have considerable variability in the development of the abdomen. It may be normally developed but tucked under the thorax, as it is in the porcelain crabs (Family Porcellanidae), which are well-represented on reefs. Porcellanids often have relatively large claws, but are delicately calcified, hence the common name. They also have a reduced 5th pair of legs carried on the end of the body. The one shown here is often associated with anemones and is referred to as an “anemone crab” but there are many of these that are not porcellanids. Unfortunately, the abdomen is not shown, but it has three segments with a tail fan including telson and uropods under the thorax.
The typical hermit crab (Family Paguridae) lives in mollusk shells to protect its abdomen, which is carried under the thorax, but is asymmetrically curved and exhibits a reduction of appendages. The abdomen is usually soft and not covered with a chitinous and calcified exoskeleton. However the appendages and the thorax are well-developed and chelipeds are prominent. Most species select from abandoned shells, changing shells to accommodate growth, but at least one Hawaiian species is impatient and extracts the mollusk occupant before claiming the shell for itself.
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A pagurid crab removed from its shell shows
a twisted, asymmetrical abdomen (arrow).
A hermit crab (Dardanus sp.) in a gastropod shell that is common in the
These are also hermit crabs, but they live in galls, possibly created by serpulid polychaetes.
They feed on passing plankton, caught with their long, feathered antennae.
These specimens are each only about 1/2 inch long, and are often referred to as
“coral hermit crabs”.www.divegallery.com/coralcrabs.htm
Other hermit crabs (family Coenobitidae) have become adapted to living on land. The most spectacular of these is the Coconut crab, aka robber crab (Birgus latro). These animals are totally adapted to life on land and some live 6 km from the sea. In fact, they will drown if submerged in water for more than a few minutes. But they still respire through gills. The gills are surrounded by spongy tissues and the crab keeps the gills moist by dipping its back legs into water and stroking them over the gills. They drink by dipping their front claws into water and dripping water droplets into their mouths! They can survive dry spells by absorbing moisture from damp earth, or by if it has been very dry, by sealing up their burrows.
Size: they can be up to a meter from claw to claw and weighing up to 5kg, but usually about 3kg
Lifespan: more 10-30 years.
Distribution: islands and coastal areas of the western Pacific, including the
Habitat: Coastal forests.
Classification: Robber Crabs are anomuran crustaceans, but unlike pagurid hermit crabs, coconut crabs have a hardened shell over the abdomen which they keep tucked under their thorax. This protects them from predators and from water loss. This also means they don't depend on having to find abandoned shells to protect their abdomen, and all things other being equal, can grow for a number of years and thus get quite large.
Food:They dig burrows in the sand to hide in during the day and come out at night when its cool to look for anything food. It is very fond of coconuts, which gives it its common name. Coconuts that are split or sprouted a bit, can be cracked open through the eye of the coconut using its powerful claws, but contrary to popular belief, the coconut crab probably cannot open fully developed coconuts from the tree. They also eat fruits, rotting vegetation and even dead animals. On the 
Coconut crab from
Reproduction: Coconut crabs mate on land and the female deposits the fertilized eggs in the sea. The larvae are a zoea (then a megalops) and spend the first month or so in the plankton. Within a month, they look more and more like the adults with every molt. They are eventually washed up on the beach to start their lives on dry land. Because their abdomens are still soft, juveniles use abandoned shells like other hermit crabs do. As they get bigger and run out of suitable shells some may use discarded coconut shells. Some experts believe the crab could not have achieved its present widespread inter-island distribution with only a 30-day aquatic larval stage unless they rafted to distant islands, possibly by husks of moist, floating coconuts.
Status and threats: They are threatened by deforestation, overharvesting for human food, and by introduced animals that attack them. They are slow growing and require 4-8 years to mature. According to the IUCN Red List criteria, there is not enough information on this species to make an assessment of its risk of extinction based on its distribution and/or population status. It is therefore classified as Data Deficient (DD). Nonetheless, the coconut crab has been hunted to near extinction or to very small numbers on several relatively heavily populated island groups where they were once abundant.
