Category: Invertebrates

That is, some embryos with spiral cleavage appear indeterminate, and some with radial cleavage appear determinate. Like many spiders, some insects can walk on water, and they do so in much the same way—by balancing the pull of gravity on their featherweight bodies with the physical principles of buoyancy and surface tension. Each pouch eventually pinches off from the gut as a complete coelomic compartment. Most of the muscle bands in tardigrades consist of only a single muscle cell or a few large muscle cells each.

Some species are annuals (especially small-bod- ied calcareous sponges of colder waters); hence they grow from larvae or gemmules to reproductive adult- hood in a matter of months. About 160 species have been described in two families. Gastrulation is by invagination of micromeres, bringing the flagellated cells again inside the body, lining a cavity which later becomes spongocoel. The evidence to date suggests that echinoderms are osmoconformers. The activities of receptor units represent the initial step in the usual functioning of the nervous system; they are a critical link between the organism and its sur- roundings.

Further infor- mation on the giant Gippsland earthworm Megascolides australis (McCoy 1878). Some zoologists, however, view these similarities as convergent features resulting from adaptations to pelagic lifestyles. The two main groups of animals are vertebrates and invertebrates. These vessels end abruptly where their contents move into the coelom or other large space where gas, nutrient, and waste exchange take place directly between the cells (tissues) and hemolymph (or lymph—at this point the fluid could be described as extracellular fluid).

Inside the oocyst, the zygote under- goes a meiotic reduction division followed by schizo- gony to form sporozoites that are released from the oocyst into the gut, to migrate to the salivary gland where they remain until the next time the insect feeds. The fluid-filled blastocoelom is not spacious. Medusae are tetramerously symmetrical as are scyphomedusae and four radial canals and four tentacles are usually present. Zoology Oct 22 Pt 2 Notes.docx - Chapter 28 Introduction to...

Mammal species of the world: a taxonomic and geographic reference. In some kinds of leeches, the posterior midgut is struc- turally differentiated from the anterior portion. In worm beds, look for land planarians attached to earthworms by mucus membranes. The exploitation of similar habitats by animals with different phylogenetic histories is frequently ac- companied by the appearance of convergent similarities. Please leave a comment, I love hearing from you! This circulation pattern is used by the slit shells, abalones, and volcano limpets.

Attachment is accomplished by mucous secretions from the basal disc. Nervous System and Sense Organs Turbellarians. Another nonfiltering suspension feeding method is called “scan-and-trap” (LaBarbera 1984). In addition to the other signs of stress that I mention in my previous articles, the most drastic response a stressed cucumber can make is to expel its Cuvierian tubules. About 1,000 genes code for the surface glycoproteins, although only one gene is expressed at a time. Current advances in the phylogenetic reconstruction of metazoan evolution.

Many sponges, for example, have an irregular growth form and lack any clear plane of symmetry. In addition, they are usually highly touch-sensitive. Little is known about the functioning of aesthetes, but they apparently medi- ate light-regulated behavior. Have each child cut out pictures from science and nature magazines to make his own vertebrate and invertebrate collages. Conjugation is perhaps most easily understood by first describing it in Paramecium.

Haeckel be- lieved that these ancestral creatures (the blastea and gas- trea) were recapitulated in the ontogeny of modern ani- mals, and the gastrea was viewed as the metazoan precursor to the cnidarians. Subphylum Crustacea Body composed of a 5-segmented cephalon, or head, and multisegmented postcephalic trunk; trunk divided into thorax and abdomen (except in remipedes and os- tracods); segments of cephalon bear first antennae (an- tennules), second antennae, mandibles, maxillules, and maxillae; one or more anterior thoracomeres may fuse with the head (in some Remipedia, Maxillopoda, and Malacostraca), their appendages forming maxillipeds; cephalic shield or carapace present (secondarily lost in some groups); with antennal glands or maxillary glands (excretory nephridia); both simple ocelli and compound eyes in most groups, at least at some stage of the life cycle; compound eyes stalked in many groups; with nauplius larval stage (suppressed in some groups), and often a series of additional larval stages.* An estimated 67,829 (living) species.

Whereas most of the free-living species are micro- scopic, many of the parasitic forms are much larger; and members of one species attain lengths of 8 m. But this shared characteristic provides little useful insights into invertebrate biology. The cyst develops a re- sistant outer wall and remains dormant for an indefinite period of time. For this reason a few recurring funda- mental themes become apparent.

Copyright 2010 United Press International, Inc. (UPI). Apparently these loose cells reattach to the gut wall after they have “fed.” It has been suggested that upon re- attachment these errant cells first pass their digested food contents to the fixed cells of the gut wall, then assume an excretory function by picking up metabolic wastes, de- taching again and being eliminated via the anus. Hutchinson University Library, London. [A lovely review of slug biology.] Salvini-Plawen, L. von and G.