The biosphere

Kent C. Condie , in World as an Evolving Planetary Organization (Quaternary Edition), 2022

Origin of metazoans

Metazoans (multicellular animals) appear to accept evolved from single-celled ancestors that developed a colonial habit. The adaptive value of a multicellular style of life relates chiefly to increases in size and the specialization of cells for different functions. For instance, more than suspended food settles on a big organism than on a smaller one. Since all cells do not receive the same input of food, nutrient must exist shared among cells and a "segmentation of labor" develops among cells. Some concentrate on food gathering, others on reproduction, while still others specialize in protection. At some point in time when intercellular communication was well developed, cells no longer functioned equally a colony of individuals but as an integrated organism.

The trace fossil record suggests that metazoans were well established by m   Ma (Fig. 9.x), and the great diversity of metazoans of this age suggests that more than 1 evolutionary line led to multicellular development. Leaf-shaped fossils in North Cathay suggest that some grade of multicellular life had evolved by 1.7   Ga (Shixing and Huineng, 1995). On the ground of their size (five–xxx   mm long), probable development of organs, and possible multicellular structures, these forms are probable benthic multicellular algae (Fig. 9.11). Recently discovered centimeter-sized structures from two.1-Ga black shales from West Africa are interpreted equally colonial organisms, also probably metazoans (El Abani et al., 2010). Although metazoans appeared past about 2   Ga, because of an inadequate fossil record we cannot nevertheless trace these organisms back to their unicellular ancestors.

Fig. 9.10

Fig. nine.10. Time distribution of diverse Proterozoic fossil groups.

Fig. 9.11

Fig. 9.11. A carbonaceous multicellular fossil (Antiqufolium clavatum) from the ane.7-Ga Tuanshanzi Formation, Northward China. Scale bar 2   mm.

 Courtesy of Zhu Shixing.

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Living Systems

Kent C. Condie , in Earth as an Evolving Planetary System, 2005

Origin of Metazoans

Metazoans (multicellular animals) appear to have evolved from single-celled ancestors that developed a colonial addiction. The adaptive value of a multicellular way of life relates importantly to increases in size and the specialization of cells for dissimilar functions. For instance, more suspended food settles on a large organism than on a smaller 1. Because all cells practise not receive the same food input, food must be shared amongst cells and a "division of labor" develops among cells. Some concentrate on food gathering, others on reproduction, and others on protection. At some point, when intercellular communication was well developed, cells no longer functioned equally a colony of individuals but every bit an integrated organism.

The trace fossil record suggests that metazoans were well established by g Ma (Fig. 7.ten), and the great variety of metazoans of this age suggests that more than than one evolutionary line led to multicellular development. Findings of leaf-shaped fossils in northward Communist china suggest that some form of multicellular life had evolved by i.7 Ga (Shixing and Huineng, 1995). On the ground of their size (5–xxx mm long), probable development of organs, and possible multicellular structures, these forms are likely benthic multicellular algae (Fig. seven.11). Although metazoans appeared by 1.7 Ga, they did not become widespread until less than 1 Ga. Because of an inadequate fossil record, investigators cannot trace these groups of multicellular organisms back to their unicellular ancestors.

Figure 7.10. Fourth dimension distribution of various Proterozoic fossil groups.

Figure 7.11. A carbonaceous multicellular fossil (Antiqufolium clavatum) from the 1.7-Ga Tuanshanzi Formation, n Cathay. Scale bar = 2 mm.

 Courtesy of Zhu Shixing.

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Groundwater Metazoans⁎

Florian Malard , in Reference Module in World Systems and Environmental Sciences, 2022

Food webs

Metazoans direct contribute to energy flow through groundwater ecosystems via trophic linkages. Until the 2000s, groundwater food webs were predicted to be relatively simple, having no autotrophs and strict predators, and containing up to two trophic levels predominantly occupied by generalist consumers and omnivores ( Gibert and Deharveng, 2002). Nevertheless, the quantitative investigation of trophic linkages using stable isotope assay, compound specific isotope analysis on amino acids and Dna metabarcoding of bacteria in the gut of metazoans is offering a new perspective of groundwater food webs (Saccò et al., 2019, 2021). Starting time, groundwater food webs are primarily fueled by microbial biomass but the importance of biomass produced by chemolithoautotrophic bacteria relative to that of heterotrophic bacteria might take been under-estimated (Hutchins et al., 2016; Venarsky et al., 2018). The written report by Herrmann et al. (2020) suggested that biomass produced by chemolithoautotrophy represented a rather stable resources that supported complex food webs with several trophic levels in oligotrophic groundwater. Second, François et al. (2016) recently challenged the assumption of generalist feeding by demonstrating that some cavern isopod species showed a stiff trophic specialization on sedimentary biofilm, a resource that is both arable and stable in caves. Third, feeding sources appear to vary both among and within species with the abundance of resources in the environment. Francois et al. (2020) showed that asellid isopods, among which there are a number of obligate groundwater species, fed more selectively when the availability of resource in the environment was high. Saccò et al. (2021) showed that high rainfall periods triggered a trophic pour effect: increased input of organic matter led to proliferation of microbial biofilm that was grazed past primary and secondary consumers (copepods and amphipods), which constituted the casualty of tiptop predators (larvae and adults of beetles). Fourth, groundwater food chains are longer than previously idea because they comprise four or fifty-fifty v trophic levels and include strict predators in the most species-rich aquifers (Hutchins et al., 2016; Premate et al., 2021).

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Volume ii

Connie Lovejoy , in Encyclopedia of the World's Biomes, 2020

Metazoan Zooplankton

Metazoan zooplankton are truthful animals and, in the Arctic Bounding main, as elsewhere, include an array of invertebrates, including some invertebrate larval stages too equally larval stages of fish (ichthyoplankton). However, hither nosotros focus on zooplankton that are planktonic for their entire life bike. The majority of zooplankton actively swim and accept some control over their vertical position in the water column. Copepods in particular comport out daily and seasonal vertical migrations ( Darnis et al., 2017). Newly hatched invertebrate zooplankton live for months to years and virtually have well defined life cycles, with feeding and egg product closely tied to water ice algal and phytoplankton productivity (Leu et al., 2011; Dvoretsky and Dvoretsky, 2015), with predictable seasonal cycles. Most deep h2o species are also found within specific depth ranges across the Arctic'south central basins (Kosobokova and Hopcroft, 2010).

Arctic zooplankton are taxonomically and trophically various, ranging from species that consume bacteria and single celled microbial eukaryotes to those that prey on other zooplankton. Around i-quarter of the zooplankton species plant in the Arctic are restricted to the Arctic, with most other species shared with the plankton fauna of the N Atlantic or North Pacific (Lovejoy et al., 2017). By far the all-time-studied zooplankton in the Chill are copepods. These are estimated to account for 80–90% of the zooplankton biomass in the Arctic, with over 150 copepod species amidst the c. 350 zooplankton species reported for Arctic (Bluhm et al., 2011).

Copepods are straight consumed by many fish, some seabirds, and baleen whales (Darnis et al., 2012). Three species of Calanus, with somewhat similar life cycles, dominate Arctic zooplankton; C. glacialis, C. hyperboreus, C. finmarchicus. All three species feed in surface waters during bound and summertime with daily migrations in and out of the photic zone. They drift to deeper waters over winter, triggered by 24-hour interval-length or in response to "adequate" lipid stores (Hafker et al., 2018; Schmid et al., 2018). Once in the deep waters they maintain depression metabolic rates referred to every bit diapause until spring, when they return to the surface in response to physiological or environmental signals.

Larger crustaceans such as hyperiid amphipods and euphausiids (krill) feed on smaller zooplankton and in turn serve as prey for marine vertebrates. Arctic euphausiids are mostly reported at the inflows to the Chill and in more productive regions, but are almost absent from the key basins (Lovejoy et al., 2017). The nearly widespread complimentary-living hyperiid amphipods are species of Themisto.

Another ubiquitous zooplankton grouping in the Arctic Ocean and surrounding seas are the appendicularian tunicates Oikopleura vanhoeffeni and Fritillaria borealis, which are widespread in productive open up water regions of the Arctic (Deibel et al., 2017). Appendicularia are intermission feeders, making a mucilaginous "house" that collects bacteria and pocket-sized phytoplankton. The "house" and trapped prey are after consumed by the animals, creating a primal linkage betwixt the smallest microbial plankton and college trophic levels.

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Cambrian explosion

Nelson R. Cabej , in Epigenetic Mechanisms of the Cambrian Explosion, 2020

Development of bilateral symmetry

All metazoans, except Cnidaria and Ctenophora, and collected Porifera and Placozoa, belong to the supergroup Bilateria. The origin and nature of the Urbilateria is not resolved and continues to be subject to controversy. What tin be stated with a high degree of probability is what can be inferred from the appearance of the outset generally accepted Precambrian fossils of the bilaterian organism, Kimberella, virtually 558 meg years ago. The identification of Kimberella as a protostome organism suggests that the partition protostome–deuterostome in bilaterians (nephrozoans) occurred earlier the Cambrian, whereas the cnidarian–bilaterian carve up may have occurred about 570–580 Mya (Erwin and Davidson, 2002).

While nerveless sponges and placozoans have no strictly adamant body symmetry, cnidarians evolved radial symmetry. The transition from the cnidarian radial symmetry to bilaterality (animals with right and left sides) is ane of the major transitions in eumetazoan history (Fig. four.6). Trace fossils show that some bilaterian organisms appear past the cease of the Ediacaran eon. Bilaterality was of disquisitional importance for the Cambrian explosion. It not only enabled easier streamlined intentional locomotion that increased metazoans' ability to faster approach sources of nutrition, hunt the casualty, and escape predators but also facilitated the evolution of more complex and diversified animals by multiplying the amount of positional information (Genikhovich and Technau, 2017). The advent of bilaterality in animals coincided with (and probably is related to) the emergence of the centralization of the nervous system, besides as with the appearance of triploblasty (the evolution of mesoderm, the third embryonic layer), which implies the evolution of the ability of the directed move of particular groups of cells (Meinhardt, 2006).

Figure 4.6. Schematic of hypothesized nonbilaterian (total group Porifera, Cnidaria, and Ctenophora) and Bilaterian diversification during the Ediacaran–Cambrian metazoan radiation, showing the fossil record of probable earliest metazoans (shown by a rangeomorph reconstruction), the Kotlin crunch, followed by two phases of Cambrian Explosion, separated by the Sinsk effect extinction (with a possible expanded interval of anoxia during Stage 1) and extending to the Ordovician Radiation through the SPICE extinction. Nonbilaterian stalk group case is a stalk group archaeocyath sponge; crown group is a crown group demosponge. Bilaterian stem group is shown by a tommotiid; crown group by a trilobite.

 From Zhuravlev, A.Y., Wood, R.A., 2018. The two phases of the Cambrian Explosion. Sci. Rep. 8, 16656.

Nix certain can be said near the mechanism(s) that made possible the major transition from the radial to bilateral symmetry. All the same, a conspicuous fact related to this transition is the coincidence of the evolution of the centralized bilobed encephalon, on the one hand, and the advent of bilateral symmetry, the advent of the ventrolateral axis, specialized sense organs and organ systems (digestive, circulatory, and excretory), on the other. The development of the CNS facilitated the intentional locomotion of bilaterians toward the sources of nutrition to hunt the casualty, escape predators, etc. From an evolutionary viewpoint, it is likewise worth mentioning that planula larvae of a radially symmetric organism, such every bit the cnidarian sea anemone, Nematostella vectensis, develops a concentration of neurons in the anterior (oral) function of the torso (Watanabe et al., 2014) and bilateral torso, in stark contrast with the mature grade of the cnidarian that has a diffuse nervous arrangement and radial symmetry.

The coincidence of the evolution with the bilaterality, the evolution of the brain, emergence of sense organs and organ systems may be a contingent occurrence, but there is no visible reason to dominion out a causal relationship in their simultaneous emergence.

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Body of water Urchins: Biology and Ecology

Nicholas D. Holland , in Developments in Aquaculture and Fisheries Science, 2013

3.7.3 Symbiotic metazoans

The metazoans almost likely to exist encountered in the lumen of the sea urchin digestive systems (especially the intestine) are several dozen rhabdocoel turbellarian species, exclusively within the family Umagillidae – all in the genera Syndesmis and Syndisyrinx (Jangoux, 1987; Doignon and Artois, 2006). Many of these worms are host-specific, although a few occur in more than one ocean urchin species. Although before workers assumed that symbiotic umagillids fed exclusively on ciliates, Shinn (1981) found prove that the worms were semiparasites, supplementing their protistan diet past browsing on the inner epithelium of the digestive arrangement of the host. In improver, Leydig (1854) described a nematode, Oncholaimus echini, plant in the digestive system of Echinus esculentus, and Gooding and Lützen (1973) described a eulimid gastropod, Robillardia cernica, from the rectum of Echinometra sp.

Some crabs are known to have up residence in the rectums of regular echinoids. Ane species of pinnotherid carb, Pinaxodes chilensis, is institute in nigh all specimens of Caenocentrotus gibbosus (Jackson, 1912), enlarging the rectum and sometimes fifty-fifty distorting the aboral part of the sea urchin's body. Inside the pilumnid crabs, all three species in the genus Echnioecus inhabit the rectums of body of water urchins (Chia et al., 1999). In Echinoecus pentagonus, only the larger females live permanently confined to the rectum, where they scan on fecal pellets and coelomocytes; the smaller females and males can be found crawling on the host's surface (Castro, 1969). Another arthropod associate in an echinoid digestive organisation was reported by Veits (1939), who found adults and nymphs of a halacarid mite living in the intestine of an aspidodiadematid ocean urchin dredged from 430 k.

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Body of water Urchins: Biology and Ecology

Nicholas D. Holland , in Developments in Aquaculture and Fisheries Science, 2020

3.vii.3 Symbiotic metazoans

The metazoans virtually likely to be encountered in the lumen of the regular ocean urchin digestive systems (especially the intestine) are several dozen rhabdocoel turbellarian species, exclusively within the family Umagillidae—all in the genera Syndesmis and Syndisyrinx (Jangoux, 1987; Doignon and Artois, 2006). Many of these worms are host specific, although a few occur in more than one regular body of water urchin species. Although earlier workers assumed that symbiotic umagillids fed exclusively on ciliates, Shinn (1981) plant evidence that the worms were semiparasites, supplementing their protistan diet by browsing on the inner epithelium of the digestive system of the host. Cavaliero et al. (2018) review the morphology of the umagillid endosymbionts and provide a molecular phylogeny of species within the group. In addition, Leydig (1854) described a nematode, Oncholaimus echini, found in the digestive system of Echinus esculentus, and Gooding and Lützen (1973) described a eulimid gastropod, Robillardia cernica, from the rectum of Echinometra sp.

Some crabs are known to have upwardly residence in the rectums of regular echinoids. One species of pinnotherid carb, Pinaxodes chilensis, is found in almost all specimens of Caenocentrotus gibbosus (Jackson, 1912), enlarging the rectum and sometimes even distorting the aboral office of the host's body. Within the pilumnid venereal, all three species in the genus Echnioecus inhabit the rectums of regular sea urchins (Chia et al., 1999). In Echinoecus pentagonus, only the larger females live permanently confined to the rectum, where they browse on fecal pellets and coelomocytes; the smaller females and males can exist found crawling on the host's surface (Castro, 1969). Another arthropod associate in an echinoid digestive system was reported by Viets (1939), who institute adults and nymphs of a halacarid mite living in the intestine of an aspidodiadematid dredged from 430   thousand.

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Principles of Salmonid Civilisation

David Eastward. Bruno , Anthony Eastward. Ellis , in Developments in Aquaculture and Fisheries Science, 1996

Biological science and Classification of the Main Groups Pregnant to Salmonid Civilization

The metazoan parasites are multicellular organisms expressing both ecto- and endoparasitic life styles causing significant pathology and mortalities. These parasites are represented in several groups including monogenetic and digenetic trematodes, cestodes, nematodes, acanthocephalans, leeches, molluscan larvae and crustaceans. The of import metazoan parasites of salmonids are summarized in Table five.

Table 5. Important metazoan parasites of salmonids.

Genera Class or group Location in fish
Acanthobella Hirudinea Skin
Acanthocephalus Acanthocephala Intestine
Anisakis Nematoda Musulature
Argulus Crustacea Skin, fins, gills
Bulbodacnitis Nematoda Intestine
Contracaevum Nematoda Intestine
Cotylurus Digenea Center
Crepidostomum Digenea Gall bladder, liver
Cystidicoloa Nematoda Swim bladder
Dactylogyrus Monogenea Gills
Diphyllobithrium Cestoda Intestine
Diplostomum Trematoda Eyes
Echinorhynchus Acanthocephala Intestine
Ergasilus Crustacea Skin, fins
Eubothrium Cestoda Intestine
Glochidia larvae Mollusca Gills
Gyrodactylus Monogenea Gills, Pare, fins
Illinobdella Hirudinea Gills
Lepeophtheirus Crustacea Peel
Lernaea Crustacea Skin, fins
Pisciola Hirudinea Skin, fins
Pseudoterranova Nematoda Muscle
Salmincola Crustacea Gills
Sanguinicola Digenea Heart, gills

Monogenea. Monogenean (trematodes) are more often than not small-scale, ranging upwards to a few millimetres in length. They have a direct life cycle and many are host specific. Ciliated free-swimming larvae chosen oncomiricidia hatch from relatively large eggs and must and so infect a suitable host inside a curt catamenia in social club to mature. All the same, gyrodactylid trematodes produce viviparous immature. Based on the morphology of the posterior zipper organ (haptor or opisthaptor), two major groups are distinguished: Monopisthocotyle (east.g., Gyrodactylus and Gyrodactyloides) and Polyopisthocotyle (eastward.g., Discocotyle). In general, further classification will include reference to morphological characters including the number of marginal hooks, haptor, hamuli and the morphology of the testis and ovaries (Beverley-Burton 1984). Malmberg and Malmberg (1993) have underlined the importance of complementary morphometric, experimental infection investigations and DNA assay in order to help distinguish natural and "cultured populations of similar Gyrodactylus species on salmon.

Digenea. The life wheel of digeneans is often circuitous. The free-swimming miracidium hatch from the eggs to infect the first intermediate host which is a species of snail (family unit Lymnaeidae), within which they undergo a phase of asexual reproduction in the liver tissue. Somewhen the gratis-swimming cercariae are released which may either infect fish as final hosts where they mature into adult trematodes, or infect fish every bit intermediate hosts, ofttimes through the gill region, to form the metacercarial phase. In the latter case, completion of the life cycle occurs when the infected fish is eaten by a suitable concluding host, e.grand., birds. Although the metacercariae may display many of the taxonomic features of the adult, they usually lack adult reproductive organs. Hence classification is often carried out on the adult past examining the ventral holdfast organ, location of the genital pore, and the presence of cephalic structures effectually the oral crenel (Schell 1985). Genera important in salmonids include Sanguinicola, Cardicola and Diplostomum.

Cestoda. In full general, cestodes or tapeworms affecting fish accept a life cycle involving more than one host. Fish may deed as final or intermediate hosts. Eggs are released in the faeces, and either the eggs or the hatched larvae (coracidium) are eaten past an invertebrate host where they penetrate the gut wall to undergo further development. For maturation to occur in fish, the procercoid must be eaten past some other suitable host to continue its development. In some cases the plerocercoid (larval) stage develops in the fish (eastward.g., Diphyllobothrium) and evolution just continues when eaten past the definitive host, e.g., bird, carnivorous fish.

Two sub-classes are distinguished, the more primitive Cestodaria and the Euscestoda. In the Cestodaria no scolex is present. Nomenclature of mature cestodes is based on the characteristics of the scolex and the organs within the mature proglottid, whereas immature cestodes are classified on a general morphological basis (Overstreet 1978).

Acanthocephala. The Acanthocephala (spiny-headed worms, e.g., Echinorhynchus spp.), are worms occurring in both fresh and marine environments. Hooks on a retractable armed proboscis become embedded in the intestinal tract of their host. Each member of this grouping requires an invertebrate host, usually an arthropod, to complete their life cycle. The egg contains an acanthor larvae, which is released when ingested. Following its development into a cystacanth the parasite volition develop to a mature worm if consumed by the last host. Paratenic hosts, where the immature acystacanth encysts within the mesentery without farther development, contribute to the completion of the life cycle past providing a link betwixt an intermediate and final host. The characteristics of the proboscis, presoma and other internal structures are used to place the adult worms (Yamaguti 1963a).

Nematoda. Near nematodes are cylindrical, elongate worms of the abdominal tract occurring in freshwater and marine fishes. The eggs are passed with the faeces of the host and hatch into free-swimming larvae generally to be eaten by an intermediate host, e.g., arthropods. Other groups produce viviparous larvae. Many develop to adult forms in a suitable fish host, although some species only employ the fish as an intermediate host and will mature in the abdominal tract of a suitable final host, including mammals, other fish or birds. Genera important to salmonids include Anisakis, Pilonema, Contracaecum, Bulbodacnitis and Cystidicola. The classification of nematodes relies upon identifying external and internal anatomical features (Anderson and Bain 1982).

Mollusca. Mature freshwater bivalve molluscs, in detail members of the family Unionidae, release large numbers of larvae known as glochidia, which are obligate larval parasites on the gill lamellae of fish (Bruno et al. 1988).

Crustacea. There are two subclasses of Crustacea that incorporate parasites for salmonids, Branchiura (e.g.,Argulus) and Copepoda (e.g., Lepeophtheirus). Some of these are economically important in freshwater and marine aquaculture throughout the world. The classification of parasitic crustaceans is based on the body segmentation, the course of the attachment organ, morphology of the egg sac, and number and structure of the limbs (Yamaguti 1963b ).

The Branchiura are dorso-ventrally flattened, obligate ectoparasites of the skin and fins. Most belong to the genus Argulus. The juveniles are morphologically like to the adults, possessing a proboscis-like mouth for feeding, and curved hooks and suckers that serve as organs of attachment.

The Copepoda are considered the most important ectoparasitic group on fish, specially every bit they may act equally intermediate hosts for other diseases (Mulcahy et al. 1990). Four families, Ergasilidae, Lernaepoidae, Lernaeidae and the Caligidae, contain well-nigh of the marine and freshwater copepods important to salmonid aquaculture. The Ergasilidae are parasitic on the gills or buccal cavity of freshwater fish where they are found attached by specialized prehensile hooks. Ergasilus caeruleus has been reported from rainbow trout and three other species take been reported from sockeye salmon.

Most of the parasitic members of the Lernaepoidae belong to the genus Salmincola (gill maggots), which are parasitic on salmonids including Atlantic salmon, brook trout and Arctic grayling (Thymallus arcticus) in fresh h2o. S. salmoneus is host-specific to Atlantic salmon and is well adapted to the anadramous life bike of salmon (McGladdery and Johnston 1988). Gratis-swimming larvae locating a host attach to the gill tissue by means of a filament and second maxillae forming a permanent structure termed the bulla.

The Lernaeidae are best represented by the genus Lernaea, the "anchor worms", which mainly bear on freshwater fish worldwide including salmonids. The head of the female parasite is modified into a branched anchor-shaped construction with cephalic horns and becomes embedded in the body wall of the host.

Parasitic copepods belonging to the family Caligidae are common external crustacean parasites of wild and farmed fish in the marine environment, and include the genera Caligus and Lepeophtheirus. The former is a large non-specific genus of over 200 species affecting salmonids and many other fish groups. In dissimilarity, fewer species of

Lepeophtheirus take been described, with L. salmonis as a significant parasite of sea-farmed Oncorhynchus, Salmo and Salvelinus species and the cause of serious losses to commercial production. The life cycle of caligid copepods, including L. salmonis and C. elongatus, consists of 10 stages: ii free-living, planktonic naupliar stages, ane free-pond copepodid stage, four attached chalimus stages, two pre-adult stages and an developed phase. Fish are infected by the copepodites nowadays in the upper h2o cavalcade or by adults that may move from one host to another (Bruno and Rock 1990).

Hirudinea. The phylum Annelida contains the class Hirudinea (leeches), of which several genera, including Piscicola, Acanthobdella and Illinobdella spp., have been recorded equally ectoparasites from a variety of salmonids. All the same it is likely that in that location is trivial host specificity inside these groups of parasites. Each animal has a distinct sucker at each end of a flattened or tube-like body.

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Zooplankton

Luc Brendonck , ... Tamuka Nhiwatiwa , in Fundamentals of Tropical Freshwater Wetlands, 2022

ix.five.1 Introduction

Rotifers are acoelomate metazoan animals that are microscopic, ranging betwixt 50 and 2000  µm in size, and are widely distributed in freshwater ecosystems (Fernando, 2002; Segers, 2008). Many rotifers take a transparent body, consisting of two specific organs: the rotatory organ (i.eastward., corona) and a mastax, which is the throat (Brain, 2002; Fernando, 2002). The 2 main freshwater Rotifera classes are Bdelloidea and Monogononta, with the latter being widely distributed in tropical ecosystems. In general, many rotifer species are benthic, living on the substratum and among submerged vegetation. Wetland habitats are favored by many of the Bdelloidea, equally in that location they can shift from the active to the anhydrobiotic stage (i.e., cryptobiosis), enabling them to alive in temporary wetland environments (Encephalon, 2002).

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Marine Ecosystems of Andaman and Nicobar Islands – Species Abundance and Distribution

Nambali Valsalan Vinithkumar , ... Nambali Valsalan Sujathkumar , in Biodiversity and Climatic change Accommodation in Tropical Islands, 2008

4.5 Distribution of Sponges

Sponges, the metazoan invertebrates are sedentary, colourful organisms institute in various shapes and size and generally having mobile larval forms found in all kinds of ecosystems effectually the earth. They are primitive organisms grouped under the Phylum: Porifera and do not have organised body parts such as nervous, digestive or circulatory systems. These are filter feeding organisms use their single layer of flagellated cells chosen choyanocytes to circulate the surrounding h2o though the small pores and opening present in the creature ( Fig. eight.ten). The water circulating canal showing wider complication is unidirectional and brings the external waters with organic food particles, normally planktons to the inside cavities through choyanocytes lined pores and the filtered water with waste are sent out through broad opening called osculum. The sponges are of import organisms in the marine environment associated with microbes to larger organisms like corals. Sponges and their associated microorganisms are known to be the source of diverse bioactive compounds like secondary metabolites. These compounds are known to have applications in industrial and pharmacology, namely, biosurfactants, antifouling, antimicrobial, anticancer, anti HIV and several others. The sponges contribute about 37% of biomedical compounds. The sponges are classified into 4 classes, namely Homoscleromorpha, Demospongiae, Calcarea and Heactinellidae with Demospongea consisting of 85% identified species. In Indian waters 476 species of sponges under 24 orders of in a higher place mentioned iv classes were recorded. In Andaman and Nicobar   Islands 126 species are recorded (Anonymous, ZSI).

Figure viii.10. Growth of sponges, gorgonids, ascidians along with other biofouling organism in coral reef environments of Andaman and Nicobar Islands.

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