Spicules

The larva of a hexactinellid sponge. (Illustration by Emily Damstra) laminar proteinaceous structure. While it undoubtedly serves as a partial barrier to the free exchange of materials, electric currents can flow through it and transport vesicles are able to move through pores in its structure. Between cellular and syn-cytial components of the sponge there is a very thin collagen layer, the mesohyl. This layer is believed to be too thin for cells to migrate within, as is the case with other...

Physical factors Light

Sunlight has an important role in both terrestrial and marine environments, powering the process of photosynthesis that provides energy either directly or indirectly to nearly all forms of life on earth. The diel, or 24-hour cyclical migra tions of epipelagic species, are at least in part active responses to changing light levels. Epipelagic refers to the upper levels of the ocean that are penetrated by enough sunlight for photosynthesis to occur. Aurelia aurita approaches the surface during...

Significance to humans

Some echinoids are commercially valuable. In the United States, for example, red sea urchin, Strongylocentrotus francis-canus, purple sea urchin, S. purpuratus, and green urchin, S. droebachiensis, are harvested for their roe. In Japan, urchin eggs and their reproductive organs are eaten as a delicacy. In European waters, overexploitation of Paracentrotus lividus has resulted in habitat destruction and decline in population numbers. In areas where predators of urchins have been over-fished,...

Species accounts

Haliclona oculata Pallas, 1766, British Isles. OTHER COMMON NAMES Dutch Geweispons. Clusters of thin, commonly somewhat flattened branches, up to 12 in (30 cm) high, arising from a common stalk and attached to the substrate with a small pedicel or foot. In places with strong water currents, branches may fuse to the point of becoming flabellate, or fan-shaped. Oscules (small mouthlike openings) are small and circular, regularly distributed along the narrower sides of the branches. Sponges have a...

Sea lilies and feather stars

Phylum Echinodermata Class Crinoidea Number of families 25 Stalked or stalkless organisms with a crown composed of a calyx, five or multiple arms, an anal cone, and a mouth pointing upward Photo Feather star arms trapping plankton near Sipadan Island, Borneo, in the South China Sea. (Photo by Jeff Rotman Photo Researchers, Inc. Reproduced by permission.) Crinoids are a living lineage of echinoderms more than 500 million years old. The first crinoids were stalked forms (the sea lilies), whose...

Demosponges

Phylum Porifera Class Demospongiae Number of families 80 Soft, elastic, but also tough, friable, or hard, frequently brightly colored sponges varying in shape from encrusting, massive, tubes, or branches to cups or vases the body reinforced by spongin, siliceous (containing silica) spicules, or a combination of both Photo A row pore rope sponge (Aplysina cauli-formis) seen near the Cayman Islands. (Photo by Andrew J. Martinez Photo Researchers, Inc. Reproduced by permission.) The demosponges...

Physical characteristics

Most species in the class Scyphozoa, excluding the order Stauromedusae, have two life stages, the predominant medusa stage (up to 80 in, or 2 m, in diameter) and the small, inconspicuous polyp stage (less than 0.13 in, or 4 mm, long). The medusa, or jellyfish, stage has a saucer- to umbrella-shaped body with two epithelial layers (epidermis and gastrodermis) separated by a thick layer of mesenchyme, a gelatinous connective tissue containing cells. Near the edge of the bell in the orders...

Need for biodiversity

When a species is commercially important and goes extinct, its loss can be assigned a dollar value. Atlantic cod, American mahogany, and great auks are listed by the IUCN Red List as Vulnerable, Endangered and Extinct species respectively. All are or were harvested commercially, and all could be ascribed some worth by the industries that made use of them. Such large organisms as whales, tigers, bison, and manatees are mammalian megafauna that, while not commercially important, hold symbolic or...

Placozoans

Phylum Placozoa includes only one species, Trichoplax adhaerens. Because this phylum is so small, it has no classes or orders assigned to it. There is one family, the Trichoplacidae. Little is known about this organism because it has never been observed in the wild it has been studied from samples cultured in laboratory aquaria around the world. Trichoplax ad-haerens was first discovered in the aquarium of the Graz Zoological Institute in Austria in 1883. A second species, Trichoplax reptans,...

Oriental liver fluke

Some scientists now use the genus designation Opisthorchis for this fluke. English Chinese liver fluke French Douve du foie chinoise, douve du foie orientale German Chinesischer Leberegel. The adults are flattened cigar-shaped flatworms 0.4-1.0 in (10-25 mm) long and 0.1-0.2 in (3-5 mm) wide. The pointed front end has an oral sucker at its tip. Much of the anterior half of the animal is filled with a looping uterus. A small, slightly lobed ovary follows with...

Evolution and systematics

As for most soft-bodied animals, the fossil history of holothuroids, or sea cucumbers, is threadbare. Only 19 species have been described from body fossils, although one form, an Achistrum species from the Middle Pennsylvanian Mazon Creek Formation in North America, is known from study of several thousand, often quite well-preserved, specimens. Most ancient species are known from study of isolated fossils of their ossicles. These microscopic skeletal elements, found in the body walls and...

Trichina worm

OTHER COMMON NAMES English Pork worm. Classified as animal (mammal) parasites and the causal organism of the disease trichinosis, they are small roundworms that live mainly in rats and other small mammals such as pigs that pick up the worm while rooting for food. Adults have a length of 0.055-0.158 in (1.4-4.0 mm), with males measuring 0.055-0.063 in (l.4-1.6 mm) in length and females 0.118-0.158 in (3.0-4.0 mm) in length. Males and females have distinct features. Females possess a uterus and...

No common name

Polypodium hydriforme Ussov, 1885, Black Sea. Polypodium lifecycle as a succession of a free-living stage and of a stage parasitizing the eggs of some Acipenseridae and Polyo-dontidae fishes. The earliest known stage is a binucleate cell, parasitizing previtellogenetic fish oocytes. Further development may last several years, leading to a convoluted didermic stolonal structure, with inverted germ layers, forming numerous inverted buds. Before fish spawning, eversion takes place and the germ...

Habitat conservation

Organisms have evolved to live in certain habitats. It stands to reason, then, that the most severe problem in protecting global biodiversity concerns habitat destruction and fragmentation. Habitats are generally defined by myriad physical parameters like temperature, rainfall, elevation, topography, salinity, soil type and many others. For tuna, habitat might be generally defined as the pelagic ocean within a certain temperature range. For tiny tardigrades, or moss bears, habitat may be forest...

Outer mesoglea

Medusa. (Illustration by Patricia Ferrer) Hydroid anatomy. A. Colony B. Medusa. (Illustration by Patricia Ferrer) and are inappropriately called actinulae, like the juvenile polyps of some Anthomedusae. The Trachymedusae have a bell-shaped umbrella, with circular and radial canals. Gametes ripen on the radial canals. The manubrium is often on a peduncle. The Hydroidomedusa class is represented by a succession of three stages during indirect development. The planula...

Feeding mechanisms and behavior

Lower metazoans demonstrate a remarkable variety of feeding mechanisms. Most sponges are suspension feeders that subsist on such fine particles as bacterioplankton and dissolved organic matter. Sponges acquire food and oxygen from water that flows through them this flow is actively generated by sponges beating their flagella (microscopic whiplike structures). This process also acts as a means of waste removal for sponges. The movement of water through sponges is aided by ambient currents...

Reproductive biology

Asexual reproduction is a common method of reproduction in freshwater and terrestrial turbellarians. Many of the triclads divide by transverse fission the body splits transversely behind the pharynx and each part generates the rest of the body. The posterior portion attaches to the substrate and the anterior portion crawls away until it tears in two. In species such as Dugesia, the cells tend to vary in their ability to regenerate. The cells in the middle portion of the body have the strongest...

Behavioral characteristics of invertebrates

This chapter will familiarize you with issues and examples related to the behavior of invertebrates. The large number and sheer diversity of invertebrates requires a restriction in the types of behaviors (and species) that can be discussed. The behaviors selected were based in part on their importance to the survival of an individual organism. Since there is little known about the behavior of many of the lower invertebrate and deuterstome phyla, examples of insects and other protostomes were...

Human whipworm

OTHER COMMON NAMES English Whipworm, threadworm. Exceptionally thin for nematodes. They derive their name from the characteristic whip-like shape. Adults are 1.2-2.0 in (30-50 mm) in length, with a thread-like anterior end that becomes thicker at the posterior end. Both sexes have two distinct body regions. Males are 1.2-1.8 in (30-45 mm) in length, while adult females are 1.4-2.0 in (35-50 mm) in length. Females are very attenuated on the anterior three-fifths of the body, and become greatly...

Human blood fluke

Schistosoma mansoni Sambon, 1907, Africa. OTHER COMMON NAMES French Schistosome intestinal German Parchenegel PHYSICAL CHARACTERISTICS A sexually dimorphic species, the female is thin and cylindrical, reaching between 0.5-1 in (1.2-2.5 cm) in length. The male is elongated but thicker, and reaches 0.39-0.78 in (1-2 cm) in length. He also has small spiny oral and ventral suckers, and a wrinkled dorsal surface dotted with tubercles (small nodules). A female typically exists in the male's...

Calcareous sponges

Phylum Porifera Class Calcarea Number of families 22 Marine sponges with calcareous skeletal elements (spicules) Photo A calcareous sponge in a cryptic reef environment in waters near the Little Cayman Islands, at a depth of 82 ft (25 m). (Photo by Gregory G. Dimijian, M. D. Photo Researchers, Inc. Reproduced by permission.) The fossil record of unambiguously identified Calcarea is relatively poor and fragmented. Most calcareous sponges in the fossil record were classified as either...

Citrus spine nematode

Criconema civellae (Steiner, 1949), Greenhouse, Beltsville, Maryland, United States. Latest name Crossonema civellae, Menta and Raski, 1971. Females are of length 0.0114-0.0339 in (0.29-0.86 mm), with 40-93 annules. Contains spear muscles that are well developed and large compared to other species. The muscles are 0.000591-0.00394 in (15-100 pm) in length. The labial cap is not easily distinguished from the overall body contour, except for a narrowing that leads to the oral disk. The esophagus...

And humans

Marine organisms from all marine phyla have been a source of food since humans first began to explore marine environments. In stark contrast to terrestrial plants and animals that have been widely used for remedies of human disorders the World Health Organization (WHO) estimates that 60-80 of the world's population relies primarily on plants for their basic health care only a small number of marine species have been used for medicines, mostly due to human's limited access to marine resources....

Anemones and corals

Ceriantheopsis Americanus

Phylum Cnidaria Class Anthozoa Number of families 130 Exclusively polypoid cnidarians. Tubular body with hollow tentacles around the mouth has a pharynx that opens into a digestive cavity subdivided by infoldings of the gut wall. May be solitary or colonial, with or without an internal or external skeleton. Photo Jeweled anenome (Corynactis californica) ( Shedd Aquarium. Photo by Patrice Ceisel. Reproduced by permission.) Anthozoa is the largest class in the phylum Cnidaria, with over 6,000...

Systematics of lower Metazoa

Molecular, morphological, and paleontological evidence suggests the most primitive phyla are found within two para-phyletic groups, Parazoa and Radiata. The Parazoa includes two phyla, Porifera and Placozoa, which display the most primitive grade of organization and are at the base of the evolutionary tree. The Radiata contains the radiate phyla, Cnidaria and Ctenophora, the first true metazoans prior to the evolution of the bilateral body plan in the Precambrian. Some enigmatic groups with...

For further reading

Invertebrate Learning A Laboratory Manual and Source Book. Washington, DC American Psychological Association, 1990. -. A Primer of Invertebrate Learning The Behavioral Perspective. Washington, DC American Psychological Association, 1994. Abramson, C. I., and I. S. Aquino. A Scanning Electron Microscopy Atlas of the Africanized Honey Bee (Apis mellifera) Photographs for the General Public. Campina Grande, PB, Brazil Arte Express, 2002. Abramson, C. I., Z. P. Shuranova, and Y. M....

Orientation behavior

Over the years various classification systems have been developed to describe orientation, and the terminology used within these systems is confusing. Popular systems in which orientation can be described are kinesis and taxis. Orientation behavior represents an example of the type of behavior referred to as maintenance behavior. The simplest response through which invertebrates find a suitable location to live is referred to as kinesis. The response is not directed toward or away from a...

Gamete exchange

Gametes come together in a variety of ways among the animals in the lower metazoan groups. Sperm are generally motile and engage in oocyte-seeking behavior of some sort. The small size and short-term motility of the sperm, however, mean that their efforts are effective for only a very short time thus sperm motility is only effective for meeting the oocyte within very small spaces. Bringing the sperm and oocyte into these small spaces depends on the behavior of the parent animal, which must...

Symbiosis and animal parasitism

Scientists estimate that up to 50 of all animal species are parasitic symbionts. Some phyla such as the Platyhelminthes, Nematoda, and Arthropoda contain large a number of parasitic species. Hosts and parasites have coevolved together and under natural conditions many have become mutually tolerant. Host organisms can live independently, but, in most cases, the parasite's association with its host is obligatory. Animal parasites affect the health of humans and domesticated animals throughout the...

Girdle wearers

Loricifera is traditionally considered a phylum in the group Introverta. The closest relatives of the loriciferans are the Ki-norhyncha (kinorhynchs) and Priapulida (priapulans). Loricifera includes 11 described species as of 2003. All species have been assigned to one order named Nanaloricida that includes two families, the Nanaloricidae and the Pliciloricidae. As of 2003, more than 100 species have been collected that have not yet been described. Adult loriciferans range in size from 0.008 to...

Origin of lower Metazoa

Syncytial Theory Origin Metazoa

The lower Metazoa comprises a diverse assemblage of animal phyla traditionally considered primitive by most biologists in the nineteenth and twentieth centuries. Despite claims about their primitive appearance (e.g., simple anatomy, small size), the lower Metazoa collectively displays some of the greatest morphological and developmental diversity within the Animalia. There is also mounting evidence to suggest that the primitiveness of many lower metazoans is a secondary phenomenon, i.e., the...

Barbers pole worm

Strongylus contours (Rudolphi, 1803), originally Strongylus ovis-aries ( ), Europe. English Barber pole worm, sheep stomach worm, wire worm. PHYSICAL CHARACTERISTICS A stomach parasitic roundworm found inside ruminants such as sheep, goats, cattle, and wild ruminants. Males have a length of 0.7-0.8 in (18-21 mm) females 0.7-1.2 in (18-30 mm). Females possess white uteri and ovaries that spiral around their red blood-filled intestine, which gives a twisted (barber pole) appearance. The small...

Longspined sea urchin

H Abatus coratus H Astropyga magnifica H Anthocidaris crassispina English Blue eye urchin, black long-spined urchin. PHYSICAL CHARACTERISTICS Relatively flattened, but oval test that can reach 3.1 in (8 cm) in diameter. Distinctive long and slender black or while spines, which vary in length from 1.9-3.9 in (5-10 cm). Test and spines are fragile. It has a distinctive iridescent blue ring around anus. Often mistaken for D. steosum, which has an orange ring. Darker animals tend to exist in the...