The ecological habitat and cell structure of chytrids have much in common with protists. Chytrids usually live in aquatic environments, although some species live on land. Some species thrive as parasites on plants, insects, or amphibians Figure 1 , while others are saprobes. The chytrid species Allomyces is well characterized as an experimental organism. Its reproductive cycle includes both asexual and sexual phases. Allomyces produces diploid or haploid flagellated zoospores in a sporangium.
Figure 1. The chytrid Batrachochytrium dendrobatidis is seen in these light micrographs as transparent spheres growing on a a freshwater arthropod and b algae.
This chytrid causes skin diseases in many species of amphibians, resulting in species decline and extinction. The zygomycetes are a relatively small group of fungi belonging to the Phylum Zygomycota. They include the familiar bread mold, Rhizopus stolonifer , which rapidly propagates on the surfaces of breads, fruits, and vegetables. Most species are saprobes, living off decaying organic material; a few are parasites, particularly of insects. Zygomycetes play a considerable commercial role.
The metabolic products of other species of Rhizopus are intermediates in the synthesis of semi-synthetic steroid hormones. Zygomycetes have a thallus of coenocytic hyphae in which the nuclei are haploid when the organism is in the vegetative stage. The fungi usually reproduce asexually by producing sporangiospores Figure 2.
Figure 2. Zygomycetes have asexual and asexual life cycles. In the sexual life cycle, plus and minus mating types conjugate to form a zygosporangium. The black tips of bread mold are the swollen sporangia packed with black spores Figure 3. When spores land on a suitable substrate, they germinate and produce a new mycelium.
Sexual reproduction starts when conditions become unfavorable. The developing diploid zygospores have thick coats that protect them from desiccation and other hazards. They may remain dormant until environmental conditions are favorable. When the zygospore germinates, it undergoes meiosis and produces haploid spores, which will, in turn, grow into a new organism.
Figure 3. Sporangia grow at the end of stalks, which appear as a white fuzz seen on this bread mold, Rhizopus stolonifer. The b tips of bread mold are the spore-containing sporangia.
The majority of known fungi belong to the Phylum Ascomycota , which is characterized by the formation of an ascus plural, asci , a sac-like structure that contains haploid ascospores. Many ascomycetes are of commercial importance. Some play a beneficial role, such as the yeasts used in baking, brewing, and wine fermentation, plus truffles and morels, which are held as gourmet delicacies.
Magnification x. M4V file. Mesozoic rock from Arizona showing numerous brachiopods, evidence of a shallow sea along a continental shelf. An articulate hinged brachiopod. Gastropods shells cowries and cone shells from the south Pacific island of Moorea and Tetiaroa Atoll in French Polynesia.
The lower right shell is from a land snail. The common garden snail Helix aspersa. This snail was introduced into California in the s by European immigrants for use as food.
It turned out to be a poor substitute for the edible snail escargot served in French restaurants Helix pomatia. It has since become well-established and a major nuisance in California gardens. Homeowners spend more money on eradicating this creature than all other invetebrate pests combined. The head has two pairs of retractile tentacles. The longer, upper tentacles each have an eye at the tip.
The shorter, lower tentacles bear chemosensory organs equivalent to taste and smell. The ventral side contains a mouth with a rasping tongue radula for feeding. This snail is hermaphroditic bisexual with both male and female sex organs. Although capable of self fertilization, the normal method is cross fertilization between two mating partners. The snail moves by the gliding action of its large muscular foot. Mucus secreted from slime glands on the foot provides a lubricant to facilitate movement, and leaves a silvery slime trail.
Snail mucus is used in "snail cream" cosmetics. The cream is used to treat damaged skin and as a skin moisturizer. The formidable bloodworm Glycera , a predaceous intertidal worm phylum Annelida with four fanglike jaws at the anterior end red arrow.
The hollow fangs inject poison from venom glands into its prey. The elongate body is composed of many segments, each segment with fine bristlelike setae for locomotion. This interesting worm lives in tubular gallaries constructed in muddy bottoms. Lying in wait within its tube, the worm can detect the surface movements of prey by changes in the water pressure. It slowly moves to the opening of its burrow and then seizes the prey, such as small crustaceans and other invertebrates, with its proboscis.
The proboscis can be extended to about one fifth the length of its body. When retracted, the proboscis occupies approximately the first 20 body segments. During the capture of prey, the proboscis is everted with explosive force, and the four venom fangs emerge at the tip.
Peanut worms phylum Sipunculoidea are named after their shape when when fully contracted, such as when they are handled. These interesting worms live in burrows under rocks of the intertidal zone. They are sometimes very abundant in tunnels they bore in coralline rocks, reportedly up to per square meter in some Hawaiian reefs. The slender anterior end has a mouth surrounded by hollow tentacles. Phylum Arthropoda Arthropods. These microscopic objects are not eggs.
They are the dead, chitinous, bivalve carapaces of minute crustaceans called mussel or seed shrimps. When they were alive, a tiny shrimplike animal occupied each white case. They belong to the order Ostracoda which is considered a class in some textbooks.
Another order of minute crustaceans Conchostraca are called clam shrimp; however, the bivalve carapace of an ostracod is more strikingly similar to a clam shell. Photo was taken along the shore of a desiccated vernal pool in the Santa Rosa Plateau of Riverside County, California. A thriving population of brine shrimp Artemia monica in Mono Lake, California. These minute crustaceans belong to the order Anostraca, along with the endangered fairy shrimp Branchinecta.
During the summer months, the shoreline of Mono Lake is colored pinkish-red by massive colonies of brine shrimp. The Phalarope right is swimming in circles as it feeds on the brine shrimp. A common southern California centipede Scolopendra polymorpha. The name centipede is derived from the Latin words "centi" and "pede" foot.
Centipedes belong to the class Chilopoda in the phylum Arthropoda. Adult centipedes in North America may have fewer or more than legs, one pair per body segment. The mastigomycetes Hypochytridiomycota Sparrow, ; Oomycota Winter, ; incert. Chytridiomycota Sparrow, Glaucophyta Bohlin, Zhang, Z.
Animal biodiversity: An introduction to higher-level classification and taxonomic richness. Zootaxa 7— Pages 1 2 Last ». Segmented Worms. Includes earthworms, leaches and marine segmented worms. Echiura, Pogonophora, and Sipuncula, which used to be independent phyla, are now part of Annelida. Life … Eukaryota Opisthokonta Metazoa. Comb Jellies. Gelatinous marine animals. Predators feeding on zooplankton such as fish eggs, copepods, amphipods, and larvae.
Includes terrestrial groups like insects, spiders, millipedes, centipedes as well as predominantly marine groups like crustaceans and sea spiders. Many species have yet to be discovered. Life … Eukaryota Opisthokonta Metazoa … Deuterostomia. Includes the well-known vertebrates fishes, amphibians, reptiles, birds, mammals as well as tunicates Urochordata and lancelets Cephalochordata.
0コメント