''Dromia personata,'' also known as the sponge crab or sleepy crab, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of crab found in the

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea, epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the ...

, the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ...

, and connecting parts of the northeastern

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

. Like most other epibenthic crustaceans, the biomass of this species is especially dense in the Mediterranean continental shelf. It mainly resides from the lower shore to a depth of 50 meters (164 ft), often in caves. Occasionally, they are found living in depths as low as 110 meters (360 ft). They serve as prey for octopus, starfish, and other

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...

. Their last two pairs of

legs A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element ...

are positioned dorsally, and are used to hold a

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate throug ...

in place as

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

Reproduction and development

''Dromia personata'' is a

gonochoric In biology, gonochorism is a sexual system where there are only two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric. Gonochorism c ...

species. Courtship prior to copulation is commonly practiced through visual, olfactory, or tactile means. Sperm can only be transferred directly from the male's

gonopod Gonopods are specialized appendages of various arthropods used in reproduction or egg-laying. In males, they facilitate the transfer of sperm from male to female during mating, and thus are a type of intromittent organ. In crustaceans and millipe ...

into the ovigerous female after a molting period, when her exoskeleton has not hardened yet. Females store eggs in a pleopod and can also house sperm for up to nine months. During development, the

blastula Blastulation is the stage in early animal embryonic development that produces the blastula. In mammalian development the blastula develops into the blastocyst with a differentiated inner cell mass and an outer trophectoderm. The blastula (f ...

forms three tissue layers: the ectoderm, mesoderm, and endoderm. The mesoderm tissue produces the

coelum The coelom (or celom) is the main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, it ...

, which gives rise to the body cavity and specialized tissues and organs. Fertilized eggs hatch into

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

e. These undergo four

zoea Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The ...

l stages, followed by a megalopal stage, and finally an adult stage. With each molting period between these three phases, the crab gains new appendages while limbs that were formerly established become more specialized.

Morphology

As an

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

, ''D. personata'' is

bilaterally symmetrical Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take the face of a human being which has a pla ...

. The body is composed of a head, which contains the cephalon, and an elongated trunk, which consists of a thorax and abdomen. From the cephalon, there are two pairs of antennae and a

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

placed anteriorly, in addition to two pairs of maxillae positioned laterally. The trunk sprouts five pairs of walking legs, which are segmented medially to laterally: coxa, basis, ischium, merus, carpus, manus, and dactyl. The coxa, basis, ischium are smaller aspects that serve to attach the jointed limb to the crab's body. The exoskeleton is composed of a chitin cuticle. This is periodically molted when the crab undergoes ecdysis. Following this shedding, other organisms or the crab itself will ingest the former shell to gain its nutrients. Most of ''D. personata'''s body is covered in tiny dark brown hairs that result in a smooth or velvet-like appearance. The only exception is its

cheliped A chela ()also called a claw, nipper, or pinceris a pincer-like organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through New Latin '. The plural form is chelae. Legs bearing a chela are called chelipeds. ...

tips, which are typically white or light pink in color and hairless. These two chelipeds are large, equal in size and shape, and placed ventrally. Typically, crabs have eight pereiopods that are utilized for swimming: the second, third, fourth, and fifth pairs of legs. However, ''D. personata'' only uses its second and third pairs for locomotion. These legs are long and stout. Meanwhile, it utilizes its remaining ambulatory legs, the fourth and fifth pairs, to hold sponges against the hairs of its dorsal cephalothorax. These legs are sort, narrow, flat, and placed dorsally.

Digestion

All decapods have an internal tube that transports food through the mouth, stomach, intestine, and anus. It is divided into three sections: the foregut, midgut, and hindgut. The foregut is split into the cardiac foregut and pyloric foregut. They both contain ossicles, which serve the essential role of mastication. The cardiac foregut is defined by its sac-shaped structure, thin walls, prepterocardiac ossicle, and postpterocardiac ossicle. Meanwhile the pyloric foregut is characterized by its plates, lateral mesopyloric ossicle, and posterior uropyloric ossicle. Previous studies and staining methods were unable to differentiate the calcified structures. However, recent research completed with Alizarin Red S staining has allowed them to be described with correct terminology, and for comparative analyses to be completed between decapod crustacean species to determine their phylogenetic relationships.

Relationship with sponges

''Dromia personata'' is known for adhering a sponge to its back. The two organisms have a symbiotic relationship where the crab is able to

while providing the sponge with physical protection from predators, such as fish,

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked t ...

s, and

sea slug Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary time ...

s. The crab prefers ''

Halichondria panicea ''Halichondria panicea'', commonly known as the breadcrumb sponge, is a species of sea sponge belonging to the family Halichondriidae. This is an abundant sponge of coastal areas of the North Atlantic and the Mediterranean Sea ranging from the ...

, Celtodoryx ciocalyptoides'', and sponges of the ''

Suberites ''Suberites'' is a genus of sea sponges in the family Suberitidae. Sponges, known scientifically as ''Porifera'', are the oldest metazoans and are used to elucidate the basics of multicellular evolution. These living fossils are ideal for studyi ...

'' genus. Upon obtaining a sponge, either when molding its first sponge or obtaining a new one following a period of molting, the fourth and fifth pairs of pereiopods tear the sponge from its edges until it is a spherical size and shape. These same legs support the sponge on the crab's back. As it grows, the sponge conforms to mimic the cephalothorax shape. ''D. personata'' has exhibited protective behavior for its sponge. When another organism attempts to eat or steal its sponge, the host crab attacks with its

chelae A chela ()also called a claw, nipper, or pinceris a pincer (biology), pincer-like organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through New Latin '. The plural form is chelae. Legs bearing a chela are ...

. When concealed within a mass of other sponges, the crab is able to identify the sponge it most recently claimed. In addition, it surpasses considerable physical challenges, such as lifting rocks, in order to retrieve its sponge.

References

External links

* {{Taxonbar, from=Q900924 Dromiacea Crustaceans of the Atlantic Ocean Crustaceans described in 1758 Taxa named by Carl Linnaeus