Indian River Lagoon Species Inventory
Sponge Structure and Function
Sponges are sessile (i.e., permanently attached or unable to move), mostly marine animals lacking a tissue level of organization. They exhibit a wide variety of sizes and shapes from encrusting sheets to elaborate upright forms. Their morphology or shape often is determined by environmental conditions (i.e., substratum or water currents).
Leuconoid –complex invagination of body pockets that increases the efficiency of water movement. The largest species of sponge have this body type.
Incoming water provides nutrients and oxygen to the sponge as it is circulated, and water eliminated through the osculum carries away wastes. An animated illustration of water circulation in sponges can be found at www.biology.ualberta.ca/courses.hp/zool250/animations/Porifera.swf.
The major components of a sponge and its water canal system are:
Ostium (Ostia plural) – tiny pores (holes) covering the sponge body where water enters.
Osculum (Oscula plural) – large opening where water exits the sponge.
Mesohyl (mesenchyme) – a proteinaceous matrix containing spicules, spongin, and some cells that is located between the exterior layer of pinocytes and the interior choanocytes.
Spiicules – can be siliceous or calcareous and of various morphologies or shapes, including simple rods (monaxons) to more complex forms with three (triaxons), four (tetraxons), or more (polyaxons) axes. Spicules, along with spongin, provide structural support, and are considered to be an anti-predator mechanism. They are also a helpful diagnostic tool for sponge identification.
Spongin – a collagenous, fibrous protein that, along with the spicules, forms the “skeleton” of most sponges.
Pinocyte – forms the exterior layer of the sponge body.
Choanocyte (collar cell) – lines the spongocoel and other chambers where its single flagellum beats in coordination with other choanocytes to circulate water and its collar of hairlike projections filters food from the passing water.
Archaeocyte (amoeboid cell) –found in the mesohyl where it moves throughout the sponge’s body and is capable of becoming other types of specialized cells as needed (that is archaeocytes are totipotent). Archaeocytes serve a variety of functions from engulfing large food particles to transporting nutrients, and in some sponges, they play a pivotal role in reproduction.
Most of the food utilized by a sponge is trapped by the choanocytes (collar cells). Water pumped by the choanocytes through the sponge body contains suspended material such as microplankotn and bacteria as well as dissolved organic matter. As this food-laden water passes through the sponge, food particles are filtered from the water by the choanocytes and ultimately transferred into the sponge mesohyl. Very small food particles are trapped by the projections in the collar cells. In the mesohyl, larger food particles are phagocytized by specialized amoebocytes, digested and the nutritional material is transferred to other areas of the sponge.
Reproduction in Sponges
Sponges reproduce both asexually and sexually. Asexual reproduction is accomplished either through fragmentation or, more rarely, through a process called budding. Fragmentation occurs when a piece of sponge is mechanically broken from the adult and regenerates into a new individual. Budding occurs when a group of cells forms on the exterior of the sponge, attains a certain size, and then drops off. The new sponge may settle near the “parent” sponge or be carried away in the current and settle elsewhere if/when suitable substratum is found. A few marine sponges, when dying, are capable of producing gemmules that can become dormant and survive adverse environmental conditions. In sexual reproduction, male gametes, i.e., sperm, are released into the water column (http://www.ucmp.berkeley.edu/porifera/poriferalh.html) to be captured by specialized choanocytes of another individual. These choanocytes become motile, metamorphose into amoeboid cells, and transport sperm through the mesohyl where they can be engulfed by eggs. Most fertilized eggs remain within the adult until they hatch into planktonic larvae that are released into the water column through the osculum. Most sponges are hermaphroditic, producing both male and female gametes, but some are dioecious and only produce either male or female gametes.
Microbial and Chemical Ecology of Sponges
Sponges have been found to contain a vast array of microbial organisms including bacteria, cyanobacteria, archaea and unicellular protists, such as diatoms and dinoflagellates. These microorganisms often are abundant in the mesohyl, and can form mutualistic relationships with the sponge. They utilize the sponge for habitat but, in return, provide the host with a variety of benefits, including a source of nutrition and benefits derived from their metabolic functions, such a nitrification, photosynthesis, anaerobic metabolism and secondary metabolite production. Some of these microbes, however, can be pathogenic or parasitic. Teasing apart the extent and exact nature of these sponge-microbial associations is often difficult. For example, some secondary metabolites, initially thought to be isolated from sponges, were later shown to be products of associated microflora.
The pharmacological potential of natural products isolated from sponges and other organisms is one of the most actively pursued areas of marine chemical ecology. It is estimated that 70% of small molecule drugs produced between 1981 and 2006 have a link to natural products. These natural products, generally thought of as secondary metabolites, are chemicals produced by an organism with no apparent role in primary metabolic functions, i.e., compounds not essential to growth and development. Yet many of these compounds have been shown to be biologically active, with anti-bacterial, anti-viral, anti-cancer, and anti-inflammatory properties. These compounds often are produced in response to environmental stress. Why are sponges such a rich source of these compounds? The answer most likely can be attributed to the sessile lifestyle of the sponge (www.carsten-thoms.net/sponges/ecology/1_frames.html). Keep in mind that these soft-bodied invertebrates cannot flee from predators, are unlikely to fully camouflage themselves, need to compete aggressively for space to attach and grow, and must keep themselves free of biofouling organisms that block water flow. It is not surprising that the highest incidence of secondary metabolites is found in those sponge species occurring in coral reef environments, where competition for space and feeding by carnivorous fish are intense. Hence, these sponges have developed an arsenal of chemical weaponry, with extremely potent secondary metabolites that enable the sponge to survive and compete in such an environment.
Cnidarians (Phylum Cnidaria) are a diverse group of animals ranging from feathery, inconspicuous hydroids growing on pier pilings to large, majestic tropical reef-forming corals. Cnidarians are considered to be more “advanced” than the Porifera (sponges) because they have developed a tissue level of organization (although they lack organs) and they possess two distinct embryonic germ layers: the external ectoderm and the internal endoderm lining the gut. The gelatinous mesoglea occurs between these layers.
The cnidocyte or stinging cell and radial symmetry are two characteristics common to cnidarians. Many cnidarians also display two distinct body forms during their life cycle: the benthic, cylindrical polyp and the free-floating, medusoid stage. Cnidocytes (stinging cells) enable cnidarians to capture prey, and they also are used for defense. Housed within each cnidocyte is an organelle called the nematocyst or cnidocyst. The nematocyst is a fluid filled capsule containing a coiled, thread-like structure (tubule) that can be sticky, spiny, and/or elongated. This tubule can be ejected quickly, i.e., within fractions of a second, when the external triggering mechanism, the cnidocil, is stimulated tactilely or chemically. Perhaps the most venomous of nematocysts occur in box jellyfish (Class: Cubozoa) common to Australian waters, e.g., the “sea wasp” Chironex fleckeri, is considered to be the most toxic marine animal known. More familiar to Floridians is another infamous cnidarian with potent nematocysts – the Portuguese man o’ war, Physalia physalis (Class: Hydrozoa, Order: Siphonophora). In contrast, some cnidarians, such as Aurelia, rely more heavily on mucus covering their bells to capture prey items, and consequently, their nematocysts are much less potent.
The bodies of Cnidarians exhibit radial symmetry, which means similar parts of the animal’s body are arranged and repeated around a central axis, i.e., the animal looks the same from all sides. Radial symmetry often is seen in slow-moving or sessile animals, with one advantage being the ability to reach out and respond to external stimuli (positive or negative) coming from all directions.
During the life cycle of most cnidarians, their body form alternates between polyp and medusa, with one form often being dominant and more conspicuous than the other. In some cnidarians, however, either the polyp or medusoid stage is absent altogether. The cylindrical polyp is sessile and sac-like, with the aboral end attached by a holdfast organ. The free-floating, planktonic medusa can be thought of as a bell-like, upside down polyp with tentacles located around the perimeter of the bell.
The mesoglea layer of the medusa is often thick and jelly-like. Both stages have a centrally located orifice, i.e., mouth, surrounded by tentacles containing nematocysts that are used to capture prey. The mouth opens into a gastrovascular cavity that is essentially a blind gut where food is digested. Polyps extend their tentacles, particularly at night, and with the aid of the nematocysts, capture prey items passing by in the current.
Cnidarians were formerly placed in the phylum Coelenterata along with the ctenophores (comb jellies). Discoveries of structural differences led taxonomists to create separate phyla, the Cnidaria and the Ctenophora respectively. The phylum Cnidaria consists of four classes: 1) the Hydozoa (diverse group including mostly hydrozoans but also fire coral and the colonial Portuguese man o’ war); 2) the Scyphozoa (true jellyfish); 3) the Cubozoa (box jellies); and 4) the Anthozoa (sea anemones and corals, among others).
Hydrozoans are a complex and diverse group of mostly marine animals, with about 3,500 species occurring worldwide. The Indian River Lagoon Species Inventory lists ten documented species that occur in the IRL. Hydrozoans occur in a variety of shapes and sizes from inconspicuous, feathery or bushy, benthic colonies of tiny, polyps (Obelia bidentata – double toothed hydroid) to massive colonies resembling stony corals (Millepora spp.) Other hydrozoans, the siphonophores, have developed a pelagic stage that is often confused with true jellyfish (Order: Scyphozoa). Physalia physalis – Portuguese man o’ war and Velella velella – by-the-wind sailor are examples of these pelagic, tightly integrated, colonial hydrozoans. Because of morphological variation and often complex life histories, hydrozoans are a difficult group to categorize. In fact, there is much discrepancy concerning hydrozoan taxonomy – see http://www.ville-ge.ch/mhng/hydrozoa/ for a current, authoritative, taxonomic source.
Although hydrozoans show similarities to scyphozoans, they differ in several fundamental respects. For example, most hydrozoans show an alternation between the polyp and medusoid stage during their life cycle similar to that seen in the Scyphozoa. However, in the Hydrozoa, the polyp stage usually predominates. Hydrozoan medusae have a velum, i.e., a thin, muscular ring of tissue along the inner margin of the bell that enhances swimming ability. This structure is lacking in the Scyphozoa. The mesoglea of hydrozoans is acellular, whereas the mesoglea in scyphozoans contains amoeboid-like cells.
In colonial hydrozoans, reproductive polyps asexually produce minute transparent medusae that release gametes. The fertilized egg develops into a free-swimming planula larva that settles on the bottom and metamorphoses into a polyp that matures into the colony. Polyps of colonial hydrozoans called zooids are specialized for various functions: feeding is accomplished by gastrozooids; dactylozoids provide defense; and gonozooids are used in reproduction.
Members of the class Scyphozoa are the true jellyfish. They are strictly marine animals and some can consist of up to 98% water. The dominant life history stage of scyphozoans is the relatively large medusoid stage, comprising a gelatinous umbrella-shaped bell that can be contracted for locomotion. The bell is equipped with tentacles used to capture prey.
In contrast to the tiny hydrozoan medusae, bells of scyphozoans are typically several inches in diameter, and in some species, e.g., Cyanea capillata, bell diameters can reach up to 6 to 7 feet with tentacles extending hundreds of feet from the bell.
Although scyphozoans are capable of weakly swimming by rhythmic contraction of the bell (facilitated by a ring of muscle fibers located in the mesoglea of the bell’s rim), they still are considered to be planktonic because their swimming is not strong enough to overcome the vagaries of ocean currents. However, many jellyfish are capable of detecting bright light via photoreceptors, and they remain low in the water column during bright daylight hours and come to the surface at dusk and on cloudy days.
Using their tentacles embedded with stinging cells, most scyphozoans actively prey upon small crustaceans and fish. In contrast, some jellyfish are considered to be filter feeders that use their tentacles to strain plankton from the water column.
The mesoglea, complete with amoeboid cells, gives some structural integrity to jellyfish, but it contains no specialized excretory or respiratory structures. The mouth of a scyphozoan medusa opens into a central stomach often elaborated into compartments (i.e., diverticula and radiating canals) to increase surface area for digestion. The lining of the digestive system contains additional cnidocytes, along with cells that secrete digestive enzymes.
Most jellyfish are gonochoristic (having separate sexes). Although a few scyphozoans brood their young, most release gametes into the water where fertilization takes place. The planula larva is usually a short-lived planktonic stage. After attaching to suitable substratum, the planula metamorphoses into an inconspicuous sessile polyp, the scyphistoma, which then develops into a colony of hydroid polyps, the strobila. The strobila asexually produces ephyra, or young, tiny medusae, that are released into the water column where they mature into adult jellyfish to complete the life cycle.
Members of this class include some of the most dangerous marine animals known. They are cube-shaped medusae that appear square when viewed from above (hence the name “box jellies”). They possess four tentacles (or four bunches of tentacles) armed with stinging cells containing notoriously potent venom that can inflict painful, sometimes fatal injuries to humans. They are essentially transparent making them difficult to see in the water.
In Australia, the most infamous of the Cubozoa is the largest species in the class, Chironex fleckeri. It has been implicated in numerous fatal encounters with humans. Although the most venomous species of cubozoans are located in the tropical Indo-Pacific, other species can be found in the tropical and subtropical eastern Pacific and Atlantic. One species of cubozoan, Chiropsalmus quadrumanus, has been documented in the Indian River Lagoon, FL.
At one time, cubozoans were placed in the Class Scyphozoa along with the true jelly fish. However, it was discovered that cubozoans differ in several fundamental respects, most notably because of the presence of the velarium*. This structure is located on the underside of the umbrella and concentrates and increases water flow leaving the bell, which enables cubozoans to swim with relative agility and at faster speeds. Hence, cubozoans are able to swim against currents, are not considered planktonic, and are rarely found washed up on beaches. Cubozoans also are considered to have a more well developed nervous system than most scyphozoans, and they have true eyes, complete with retinas, corneas and lenses.
Cubozoans are ecologically important members of nearshore ecosystems. Their strong swimming ability, along with their relatively well-developed eyesight enables cubozoans to pursue prey actively, and they feed voraciously on fish, worms and crustaceans.
Cubozoan planula larvae can develop inside females or be released into the water column, depending on the species. After settlement, they develop into polyps, mature for several months and eventually metamorphose directly into small medusae.
*The cubozoan velarium differs structurally from the hydrozoan velum, and it is thought to be derived from the scyphozoan-like marginal lobes.
Many of us have had the privilege to dive or snorkel on a coral reef and have wondered in astonishment at the biodiversity and topographic complexity of these amazing ecosystems. Many of the magnificent reef-dwelling organisms making up the coral reef ecosystem are cnidarians belonging to the class Anthozoa.
Although there is debate over classification, most agree that the Anthozoa comprise three subclasses (one of which is extinct). The two extant subclasses of anthozoans are the Octocorallia and the Zoantharia. Octocorallia, as the name implies, are characterized by having eight tentacles and are mostly colonial. The subclass includes, among others, soft corals (Order: Alcyonacea) and sea fans (Order: Gorgonacea). Members of the subclass Zoantharia have six tentacles (or multiples thereof), and can be either solitary or colonial. Zoantharians include stony corals (Order: Scleractinia) as well as sea anemones (Order: Actiniaria) and black corals (Order: Antipatharia).
Anthozoans take on a variety of forms, occupy various habitats and play multiple ecological roles. Soft corals (Alcyonacea) lack the calcium carbonate skeleton of stony corals, and although they may be abundant on a reef, they do not contribute to its calcium carbonate structure. Sea fans (Gorgonacea) use a small space for attachment, but their elaborate, branching, rod-like colonies, with hard, protein skeletons extend out into surrounding waters. They are well adapted for exploiting the water column for food. In contrast, stony corals (Scleractinia) secrete hard, sometimes massive, calcium carbonate skeletons that along with calcareous algae build reef structure. Reef building corals are colonial animals made up of many polyps connected by a thin layer of tissue. Another colonial form, black corals (Antipatharia) are found in deep water, often in large tree-like formations. Their black or dark brown, hard protein skeletons of are covered with tiny spines. Unlike many other Anthozoans, sea anemones (Actiniaria) are solitary, with large muscular polyps that rely on complex mesenteries to digest large prey
Although corals can be found throughout the world’s oceans, even in polar waters, reef-building (hermatypic) corals are confined to subtropical and tropical waters in the Western Atlantic and Indo-Pacific oceans. They require warm (23–25 °C), sunlit waters (rarely found below 200 feet) for optimal growth. They often do best in areas subject to wave action where nutrients and oxygen are constantly replenished and wastes are carried away. Florida is the only state in the continental U.S. to have established coral reefs occurring near its shoreline. These reefs provide extensive habitat, shelter and breeding ground for many species of fish and invertebrates that are commercially and recreationally significant.
Coral reefs are one of the most productive, biodiverse ecosystems on earth, but they occur in nutrient poor, tropical waters. They are able to thrive in these areas because of a symbiotic relationship between the coral animal and microscopic dinoflagellates known as zooxanthellae found within the coral polyp’s tissue. More than 90% of the coral’s nutrition is provided by this mutualistic relationship. The coral animal provides suitable habitat, nutrients such as nitrogen and phosphorus, and carbon dioxide to the micro-algae while the zooxanthellae, in turn, provide the coral with oxygen and nutritious compounds derived from photosynthesis, such as glucose and amino acids. This mutualistic relationship enhances coral growth and deposition of the coral’s calcium carbonate skeleton.
Some corals occurring in deep water, where sunlight does not penetrate, lack symbiotic zooxanthellae, and yet, they can form substantial, productive ecosystems. Oculina reefs found at depths of 250 to 300 feet along Florida’s east coast, and nowhere else in the world, are an example. They are built from the delicate ivory tree coral, Oculina varicosa, which can form impressive mounds and pinnacles reaching 100 feet high. Fortunately, these reefs, stretching roughly from Ft. Pierce to Cape Canaveral, are protected from bottom fishing in what is called the Oculina Bank Habitat Area of Particular Concern.
Corals can reproduce either asexually through budding or fragmentation or sexually through internal or external fertilization. Most corals are hermaphroditic so they release both eggs and sperm into the water column. Some species are brooders that release sperm into the surrounding water but retain fertilized eggs in their gastrovascular cavities until they develop into larvae. Each planula larva remains in the water column for a few hours to days before settling out on suitable substratum and subsequently metamorphosing into a “founder” polyp that eventually develops into an adult colonial coral.
Echinoderms (Phylum: Echinodermata)
Echinoderms are probably some of the most familiar, marine invertebrate organisms, and they capture the imagination and fascination of young and old alike. They occur at all depths in the ocean from the intertidal to the abyss. The name echinoderm or “spiny skinned” refers to the spiny projections on many species. Most adults display pentamerous radial symmetry (radial symmetry based on five parts), although all echinoderm larvae exhibit bilateral symmetry (body divided into similar right and left halves along a central axis). The water vascular system of echinoderms is unique to this phylum, and it consists of a network of water-filled canals that function in feeding, gas exchange and excretion. Many of these canals lead to structures called tube feet that can end with suckers. Groups of tube feet allow echinoderms to either attach to the substratum or move about, and in some species, they are used for feeding. In many echinoderms, the water vascular system connects to the outside through a madreporite, a porous plate on the aboral surface. Echinoderms possess an internal skeleton (endoskeleton) that is made of calcium carbonate plates and covered by a thin layer of ciliated tissue. Spines and tubercles project outward from these plates giving the animal a “spiny” appearance.
Echinoderms are represented by four classes: 1) the Asteroidea (sea stars); 2) the Ophiuroidea (brittle stars and basket stars, among others); 3) the Echinoidea (sea urchins and sand dollars, among others); and 4) the Holothuroidea (sea cucumbers).
Sea stars typically consist of a central disk with five radiating arms (rays). Each arm of a sea star contains an ambulacral groove located on the oral surface with tube feet used for locomotion. When water is pumped through the water vascular system into the tube feet, the feet project from the ambulacral groove. The tube feet attach and then shorten via muscular contraction that forces water back into the groove to pull the animal in a specific direction.
Sea stars are both scavengers and carnivores that can actively pursue prey. The sea star’s arms are flexible, and they can wrap around prey items such as a bivalve, and pry it open. The sea star will then evert a portion of its stomach into the bivalve and consume it by secreting digestive enzymes. Other sea stars are capable of swallowing their prey whole to digest it inside their stomachs.
Sea stars reproduce both sexually and asexually. Sexes are usually separate (dioecious), and eggs and sperm are released into the water column where fertilization takes place resulting in planktonic larvae. The free-swimming ciliated larval stage (bipinnaria) can be either lecithotrophic (yolk feeding) or planktotrophic (plankton feeding). A few species of sea stars will brood their eggs. Asexual reproduction is accomplished when a sea star divides itself into parts along its central disk, i.e., fission, or by autotomy of its arms. Remarkably, the separated parts will then regenerate missing portions of the disk and missing arms. Sea stars can regenerate new arms, and some species can even regenerate an entire individual from one autotomized arm if a portion of the central disk is present.
A notable exception to the pentamerous (five part) radial symmetry displayed by most echinoderms is the nine-armed sea star, Luidia senegalensis, which occurs in the Indian River Lagoon, FL.
Brittle stars (also known as serpent stars) and basket stars belong to the class Ophiuroidea. Although brittle stars superficially resemble sea stars because of their pentamerous radial symmetry, the central disk in brittle stars is distinctly delineated from the radiating arms. Brittle star arms are slender, heavily spined, and easily detached from the central disk, hence the name “brittle” star. When detached, their delicate, whip-like arms can undulate wildly for some time. This behavior is thought to be an avoidance mechanism that distracts potential predators while the somewhat compromised brittle star escapes. Most ophiuroids can autotomize either part or all of an arm and regenerate it. Brittle stars are often cryptic, avoiding light by hiding under rocks and in crevices. Basket stars are usually found in the deep ocean.
Ophiuroids differ from asteroids in several ways. Although ophiuroids are equipped with tube feet, they assist mostly in feeding and, to a limited extent, mobility. Their tube feet lack suckers unlike sea stars. Locomotion in brittle stars is accomplished primarily by swift, wave-like movements of the arms. Also unlike asteroids, the central disk in ophiuroids contains all the internal organs. The digestive and reproductive systems never enter the arms.
Depending on the species, ophiuroids can be scavengers, deposit feeders, filter feeders or carnivores. They tend to burrow in the sediment with their arms exposed on the surface to trap food. Small organic particles can be moved into the mouth by the tube feet. Ophiuroids filter feed, i.e., capture small food particles from the water, by extending their arms into the water and forming a mucous net between spines on adjacent arms.
Most ophiuroids are dioecious (separate sexes) although a few are hermaphroditic. Some ophiuroids brood their developing larvae and give birth to “live young.” Other species release gametes into the water column, and after fertilization, a free-swimming larval stage called an ophiopluteus hatches. The ophiopluteus metamorphoses into an adult while in the water column before settling to the substratum.
The more familiar sea urchins and sand dollars, as well as heart urchins belong to the class Echinoidea – meaning “like a hedgehog.” These echinoderms are benthic dwelling organisms that occur at every depth in the ocean. Sea urchins are referred to as regular or radial echinoids. The rounded endoskeleton or test of the sea urchin is covered with articulated, elongated spines and pedicillaria. The spines are used for protection, and for sea urchins living in rocky intertidal areas, they also serve to dissipate wave energy.
Spines of some species, e.g., Diadema antillarum, the long-spined sea urchin, contain venom that is injected into the victim when the tip of a spine is broken off. The role of the pedicillariae is less well understood, but they may function to keep the test free of debris, such as algae and encrusting organisms. Urchins move about with the aid of their spines and tube feet that end in suckers.
Most sea urchins are herbivores that tend to be found on hard substrata. They feed by scraping off algae, as well as bryozoans, sponges, other encrusting organisms, and dead organic matter, with their five teeth that form a structure known as Aristotle’s lantern. Other urchins, e.g., Lytechinus sp., are found in seagrass beds where they consume substantial amounts of seagrass on a daily basis. Diadema antillarum, mentioned above, is one of the most important algal grazers on Atlantic and Caribbean reefs. Their critical grazing role came to light when a widespread loss of these urchins in the early 1980s was followed by dramatic overgrowth of reefs by algae.
Sexes are usually separate in echinoids, and fertilization is external. After eggs and sperm are released into the water column, the fertilized eggs release planktonic larvae that can remain in the water column for several days to months before settling out.
The “irregular” echinoids tend to be circular and flattened, and include heart urchins and sand dollars. These species are well adapted for living on soft, sandy bottoms. Their tests are covered with many minute spines that facilitate burrowing and locomotion. Most irregular urchins are selective deposit feeders that ingest organic matter after separating it from inorganic sediment.
Sea cucumbers are members of the class Holothuroidea, and have elongated, leathery, warty bodies containing a single gonad. They also are equipped with five rows of tube feet extending from the oral to anal end. They do not have a test, and they lack spines. Their endoskeleton comprises isolated microscopic ossicles, i.e., minute spicules of calcium carbonate joined by connective tissue. Many are found in soft bottom areas, but some cling to rocky substratum in high-energy environments. They usually lie on one side and move along slowly using their tube feet and muscular body contractions. Sea cucumbers have specialized tube feet that are elaborated into branched tentacles surrounding the mouth. Many species use these tentacles to feed directly on sediment as non-selective deposit feeders,
whereas other sea cucumbers are suspension feeders that burrow in the sand and extend their tentacles to feed from the water column. Locally, sea cucumbers can be responsible for recycling nutrients by breaking down detritus and organic matter to make it more available for bacteria and fungi to decompose.
Sexes are usually separate in sea cucumbers. Some sea cucumbers brood their eggs, and others will incubate them externally on the body surface. In either case, planktonic larvae are released into the water column when the eggs hatch.
Lacking a hard test for defense, many sea cucumbers have evolved unique ways of deterring predators. Not only will they secrete toxic substances, some sea cucumbers, when disturbed, will exude spaghetti-like filaments (cuvierian tubules) from their anal region. These sticky tubules can discourage potential predators because they feel the need to clean themselves, which gives the sea cucumber time to escape. Other sea cucumbers will eviscerate their stomachs and other internal organs through their mouth or anus. This sudden, explosive response deters predators, and the sea cucumber eventually regenerates its lost body parts.
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