how does a sponge obtain food how does a clam move

In the protostomes (Greek, “mouth first”), the mouth arises from the blastopore, and the anus forms later.The point to remember here is that the overall pattern of gastrulation immediately after the blastopore stage divides the triploblastic animals into two major groups: Gastrulation will be covered in detail in Chapter 38. Increasingly, studies of higher-level relationships have come to depend on genomic sequence comparisons, as genomes are ultimately the source of all inherited trait information. Evidence about the evolutionary relationships among animal groups can be found in fossils, in patterns of embryonic development, in the morphology and physiology of living animals, in the structure of animal proteins, and in gene sequences. Nearly 80 percent of the 1.8 million named species of living organisms are animals, and millions of additional animal species await discovery. Such coordinated groups of cells eventually evolved into the larger and more complex organisms that we call animals. Coordination among groups of cells could have improved by means of specific regulatory and signaling molecules that guided differentiation and migration of cells in developing embryos. Once this functional specialization had begun, cells could continue to differentiate. Once multicellular colonies were formed in the ancestral animal lineage, it is likely that certain cells in the colony began to be specialized-some for movement, others for nutrition, others for reproduction, and so on. Go to LaunchPad for discussion and relevant links for all INVESTIGATION figures.ĪR. Experiments with living species of choanoflagellate show that they spontaneously form multicellular colonies in response to signaling compounds that are found on certain species of planktonic bacteria they eat ( FIGURE 23.3). Why did these early animal ancestors begin to form multicellular colonies? One hypothesis is that multicellular colonies are more efficient than are single cells at capturing their prey. The common ancestor of animals was probably a colonial flagellated protist similar to existing colonial choanoflagellates ( FIGURE 23.2A), which have similarities to the multicellular sponges ( FIGURE 23.2B). The Hox genes specify body pattern and axis formation, leading to developmental similarities across animals (see Chapter 14). Similarities in the organization and function of Hox and other developmental genes provide additional evidence of developmental mechanisms shared by a common animal ancestor. Animal cell junctions and extracellular matrix molecules are described in Concept 4.5

How does a sponge obtain food how does a clam move