Deuterostomes

It is striking that a similar pattern of HI variant expression during early development has been maintained in the whole subkingdom of Deuterostomes, as illustrated by studies in sea urchin and X. laevis. This possibly dates back to an earlier stage before the separation of Deuterostomes and Mollusca (see the... 

Fig. 1.5. Phylogeny of the deuterostomes indicating position of oldest fossil taxa against the geological record. All neodermatans parasitize vertebrates and, if present, host associations represent historical associations the Neodermata must have parasitized the stem group Gnathostomata between the Cambrian and Ordovician. Tree redrawn from Rowe (2004).

The Hemichordata are a phylum of lower deuterostomes and, therefore, are more closely related to echinoderms and chordates than to annelids. They are discussed here because they are separate lineages that have evolved distinctive metabolites and also because of their feeding mechanisms. Very little work has been done on their natural products, however. 

Figure 7.2 The body plan of chordates (deuterostomes) consists of an internal skeleton, ventral heart and dorsal nervous system, while the Bauplan of arthopods (protostomes) is characterised by an external skeleton, dorsal heart and ventral nervous system.

Figure 7.4 A phylogenetic tree of animal phyla based on the stages of embryonic development. The most significant innovations are the appearance of (1) ectoderm, (2) endoderm, (3) mesoderm, (4) pseudocoelom, (5) coelom, (6) protostome-deuterostome dichotomy and (7) dorsal chord.

The appearance of bilateral symmetry (two halves which are mirror images of each other) was an important evolutionary breakthrough. The most primitive bilaterally symmetrical animals are the flatworms (phylum Platyhelminthes). Platyhelminthes gave rise to the coelo-mates, which have a coelom, or internal body cavity. The coelomates split into two evolutionary lines, the proto-stomes (molluscs, annelids, and arthropods) and the deuterostomes (echinoderms and chordates). A few phyla, such as the phylum Bryozoa, are intermediate between the two lines. Of the nearly 20,000 species of bry-ozoans known, only 3,500 are stUl living. 

Further investigation on the activity of 9 revealed that 9 could selectively inhibit the activities of DNA polymerases (pol. a, 3, y, 5 and e) only from species in deuterostome branch in the animal kingdom, like sea urchin, fish and mammals, but not from protostomes including insects (fruit fly. Drosophila melanogaster) and mollusks (octopus and oyster). Fig. (5) [21]. 

In the primitive nervous system, sensory cells evolved from general epithelial cells. Primitive nervous systems of modern echinoderms and lower deuterostomes are still composed of three cell types that include the primary sensory cells, the neurons that connect the sensory cells to distal targets, and a supporting cell that serves the special physiological needs of such a system (Lacalli, 2001). The basic structural plan of the retina is comparable to such a primitive nervous system. In the course of evolution, the photoreceptive system developed specialized photoreceptor cells (rods and cones), intra-retinal second-order neurons (bipolar cells), and tertiary output neurons (ganglion cells). This evolution perhaps took place in photopic conditions therefore early photoreceptor cells were more like cones. 

Keywords Cannabinoid Anandamide 2-Arachidonoylglycerol Deuterostome Protostome... 

FIGURE 23.1 Organisms discussed in this chapter and their positions on the phylogenetic Tree of Life. Mammals are marked by a bar labeled M. Animals are divided into Vertebrates and Invertebrates, and also divided into five physiological groups, D = Deuterostomes, L = lx)photrochozoans, E = Ecdysozoans, C = Cnidarians, and P = Poriferans. The three domains (supraphyla) are Eukaryotes, Archaens (A), and Bacteria (B). 

Knight J, Taylor GW, Wright P, Clare AS, and Rowley AF. (1999) Eicosanoid biosynthesis in an advanced deuterostomate invertebrate, the sea squirt (Ciona intestinalis). Biochim Biophys Acta 1436 467-478... 

Deuterostome animals are a large group of animals more evolved in both their body and biomechanisms. In their bodies, deuterostomes contains... 

Telford Ml. Xenoturbellida The fourth deuterostome phylum and the diet of worms. Genesis 2008 46(ll) 580-6. 

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