Chapter 32 Deuterostome

32.1 what is a deuterostome

In deuterostome the mouth forms second in embryonic development
Deuterostomes include some of the largest-bodied and most morphologically complex of all organisms.
There are two major groups of bilaterally symmetrical, triploblastic animals: protostomes and deuterostomes. Of the two, many deuterostomes are morphologically larger than any protostomes and morphologically more complex.

32.2 what is an echinoderm

Echinoderms all have an exoskeleton, symmetry, and a vascular water system with tube feet that grow from underneath the body used for movement
Echinoderm larvae are bilateral symmetric, while the adult echinoderms are radically symmetric
Crinoidea (Feather stars, sea lilies) Have 5-200 flexible arms held upward in the water
Asteroidea (Sea stars) have 5 to 40 arms radiate out from a central region; most spines occur as small knobs
Ophiuroidea (Brittle stars, basket stars) have 5 to 7 snake-like arms radiate out from a small central disk
Echinoidea (Sea urchins, sand dollars) sea urchins have globe shaped bodies and long spines; sand dollars are flats
Holothuroidea (Sea cucumbers) have soft-bodies and elongated, with a mouth at one end and an anus at the other

32.3 what is a chordate

All chordates are defined by the presence of four morphological features at some stage in their life cycles

pharyngeal slits or pouches, which are openings into the throat or pouches in the throat;
a dorsal hollow nerve chord, which runs the length of the body;
a notochord, a stiff and supportive but flexible rod that runs the length of the body; and
a muscular, post-anal tail, meaning a tail that contains muscle and extends past the anus.
The Chordata include the vertebrates, or animals with backbones. The vertebrates, in turn, comprise the hagfish, lampreys, sharks and rays, bony fishes, amphibians, mammals, and reptiles (including birds).

32.4 what is a vertebrate

The Chordata include the vertebrates, or animals with backbones. The vertebrates, in turn, comprise the hagfish, lampreys, sharks and rays, bony fishes, amphibians, mammals, and reptiles (including birds).
The bone in early vertebrates formed a protective “head shield.”

DYNAMIC STUDY MODULE

The hypothesis that tetrapod limbs evolved from fish fins has been supported by molecular genetic evidence.
Amniotic eggs have four membranes with four distinct functions.
The amnion contains the embryo.
The yolk sac contains nutrients.
The allantois contains waste from the embryo.
The chorion allows gas exchange.
More than 95 percent of the known animal species are invertebrates, but the vertebrates dominate within the deuterostomes.
Following the appearance of vertebrates, the fossil record documents a series of key innovations that occurred as this lineage diversified, one of them being the amniotic egg. The amniotes are named for a signature synapomorphy and adaptation: an amniotic egg, which is an egg that has membranes surrounding a food supply, a water supply, and a waste repository. These membranes provided support and extra surface area for gas exchange, allowing amniotes to produce larger, better-developed young.
Unlike most other parts of the vertebrate skeleton, both jaws and gill supports are derived from the same type of specialized embryonic cells. These are called neural crest cells.
An ectotherm that has a swim bladder and protrusible jaws and carries out external fertilization is most likely to be found in nature.
All chordates are defined by the presence of four morphological features at some stage in their life cycles
1. pharyngealslits or pouches, which are openings into the throat or pouches in the throat;
2. a dorsal hollow nerve chord, which runs the length of the body;
3. a notochord, a stiff and supportive but flexible rod that runs the length of the body; and
4. a muscular, post-anal tail, meaning a tail that contains muscle and extends past the anus.
A second noteworthy feature of the echinoderm body, in addition to the pentaradial symmetry, is its endoskeleton, which is a hard structure located just inside a thin layer of epidermal tissue that provides protection and support.
Sea stars are carnivores. The sea star clamps onto each half of a mussel’s shell with its tube feet. Once a gap exists, a sea star can evert its stomach to digest its prey through the narrow opening. Upon contact with the visceral mass of the bivalve, the stomach of the sea star secretes digestive enzymes, turning the mussel to a nutritious soup that the sea star stomach can then absorb. Sea urchins are herbivores. A sea urchin has five calcium carbonate teeth operated by muscles for grazing in its mouth called Aristotle’s lantern. The entire apparatus can be extended and retracted during feeding, increasing the animal’s reach. The teeth scrape up material from the substrate or cut pieces from algae such as giant kelp.
Today, most biologists recognize three deuterostome phyla: the Echinodermata, Hemichordata, and Chordata. The Chordata include the vertebrates, or animals with backbones. The vertebrates, in turn, comprise the hagfish, lampreys, sharks and rays, bony fishes, amphibians, mammals, and reptiles (including birds).
The bone in early vertebrates formed a protective “head shield.”
Reptile skin is made watertight by a layer of scales made of keratin.
Many deuterostomes share key features of embryonic development. When a deuterostome embryo is just beginning to grow, the gut starts developing from posterior to anterior—the anus forms first and the mouth second. The coelom develops from outpockets of mesoderm (rather than the splitting of blocks of mesoderm).
However, because the placenta's blood vessels provide nutrients to the embryo and remove nitrogenous wastes from the embryo, the egg's yolk sac and allantois are significantly reduced in importance.
A remarkable event occurred early in the evolution of echinoderms: the origin of five-sided radial symmetry, or pentaradial symmetry, in adults. Radially symmetrical animals do not have heads, and as a result, they tend to interact with the environment in all directions at once instead of facing the environment in one direction. Adult echinoderms that are capable of movement tend to move equally well in all directions.
Marsupial young spend more time developing outside the mother's body than inside.
Current research indicates that the lines between deuterostome and protostome are somewhat blurred. However, phylogenies based on molecular evidence confirm the monophyly of the deuterostomes.