-Hox-genes. Homeobox-containing in structure (contain common modules of DNA sequences) and homeotic in function (regulatory genes that function in the development of body form).

-Animals probably evolved from a colonial, flagellated protist “choanoflagellate” that lived over 700 MYA in the Precambrian era.

-There are about 35 phyla of animals, most of them marine, totaling over one million species.

Mitotic cell divisions Multicellular stage

-Embryonic development.

mesoderm, diploblastic, triploblastic, enterocoely, schizocoely, fate of the blastopore

Cells relatively unspecialized.Loose coordination of cells.

Specialized and integrated cells.

Parts radiate from center. Top (oral) and bottom (aboral). No head, rear, left, right.Ectoderm and endoderm

Central axis. Top (dorsal), bottom (ventral), anterior, posterior, left, right.Ectoderm, endoderm, and mesoderm

No space between digestive tract and body wall.

Fluid filled space between digestive tract and body wall.

schizocoely

enterocoely

Crown of ciliated tentacles used for feeding.

Phylogenetic tree of animals based on nucleotide sequencing in the small subunit ribosomal RNA

Coelom development happened early and the acoelomate condition represents the loss of the coelom

Combine animals with lophophorewith animals with a trocophore larval stage.

Name: secrete external skeletons, molt.

Most animal phyla originated in a brief span of geological time.

About 40 million years (about 565-525 MYA) during the late Precambrian and early Cambrian.

-Ediacarian diversity (Precambric).First solid evidence. Limited animal diversity. 565-543 MYA.

-Cambrian explosion (Precambric).Rapid diversification of phyla. 543-525 MYA. Hypotheses: Ecology- Emergence of predator-prey relationships. Geology- e.g. atmospheric O2 to support more active metabolism. Genetics- Evolution of the Hox complex of regulatory genes.Hypotheses are not mutually-exclusive.

Not one but three Cambrian explosions? Bilateria: Lophotrochozoa, Ecdysozoa, Deuterostomia.

•Animals are eukaryotes, multicellular, heterotrophs lacking cell walls but possessing unique intercellular junctions, nervous and muscle tissues, and Hox genes.•The diversity of animal phyla has been studied by looking at body plan and embryonic development and at Small Subunit-rRNA.•Both types of phylogenetic trees are similar in deepest branches and deuterostomes.•Trees differ in protostomes.

- Ecdysozoans & Lophotrochozans•Most animal phyla originated in a brief span of geological time (40 million years) in the Cambrian explosion. 543-525 MYA

SUMMARY

Multicellularity, even if loosely coordinated, allows sponges to draw food from their surroundings into their body: choanocytes (unique in the animal kingdom).

-Sessile (permanently attached).-Without true tissues (cells relatively unspecialized).~9,000 spp., most of them marine. Height: <1 cm to 2 m.-Body resembles a sac perforated with holes.-No true tissues, yet cells sense and react to changes.

Phylum Porifera “pore bearer”: sponges

-Central cavity (spongocoel), large opening (osculum).-Outer epidermal cells, internal choanocytes (“collar cells).-Mesohyl (gelatinous region), amoebocytes.-Skeletal fibers: spicules (CaCO3 or silica) or spongin.-Suspension-feeders (collect food particles from water passed through a food-trapping mechanism).

Tissues allow for different cells to take different roles: cnidocytes, unique in the animal kingdom, and extracellular digestion by gastrodermis allow food larger than individual cells.

Phylum Cnidaria “nettle”: cnidarians-Over 10,000 species, most marine. Diameter up to 2 m.-Sac w/ gastrovascular cavity (central digestive compartment with one opening).-Muscles and nerves simple, with little central control.-Hydra, jellies, corals, anemones, sea fans, Portuguese man-of-war.

-Sessile polyp (adhere by aboral end), floating medusa (oral end downward).-Two cell layers: epidermis (outer, protection), gastrodermis (inner, digestion). Gelatinous layer of mesoglea between them.

-Carnivores, tentacles around the mouth capture prey. -Tentacles armed with cnidocytes: defense and capture of prey.-Food partially digested in gastrovascular cavity, but outside cells (extracellular digestion), fragments then ingested by the cells for intracellular digestion.

Radial symmetry: detection and response to stimuli equally from all directions .

Phylum Ctenophora “comb bearer”: comb jellies Eight rows of comblike plates composed of fused cilia, used

for locomotion. Diameter: 1 to 10 cm.

Bilateral symmetry: allows encephalization and high levels of specialization in the form of organs

Phylum Platyhelminthes “flat worm” -Over 20,000 spp., in marine, freshwater, and damp terrestrial habitats.-Length: <1 mm to over 20 m.-A thin body between dorsal and ventral surfaces, NO coelom.-Bilateral symmetry.-Flatworms, trematodes, tapeworms.

-Carnivores, scavengers (eat dead animals), parasites.-Spill digestive juices on food, pharynx (muscular chamber ending in mouth) sucks food pieces into gastrovascular cavity for more digestion. -Clusters of nerve cells (ganglia) near the head and longitudinal nerve cords constitute a simple central nervous system.-Eyespots detect lights.

Color: serves as a hydrostatic skeleton against which the muscles can work, making movement more efficient than in acoelomates.

Phylum Rotifera- “wheel bearer”: rotifers -Crown of cilia that draws a vortex of water into the mouth.-Size: 0.5 to 2 mm. -Pseudocoelom.-Have a complete digestive tract.

Many evolutionary trends that become fully developed in more derived animals make their first appearance in ribbon worms, such as complete digestive tract.

Phylum Nemertea- “Nemertes”: ribbon worms

~900 spp., most marine, few in freshwater and damp soil.-Length: <1 mm to 30 m.-Similar to flatworms, but have a small fluid-filled sac that might be a primitive coelom and is shaped like a thread or a ribbon.-Carnivores, extensible proboscis (a long, muscular tube to capture prey). -Simplest animals with a complete digestive tract.-Several ganglia and small eyes in the head end and two lateral nerve cords and a mid-dorsal nerve cord that run down the body.

Three phyla have a feeding structure called a lophophore.

Phylum Bryozoa- “moss animal”: moss animals ~5,000 spp., most marine. Length: usually <0.5 mm.-Coelom.-Colonial, superficially resemble mosses.-Colony encased in a hard exoskeleton with pores, one lophophore extends out through each pore.-Lophophore is a horseshoe-shaped or circular fold of the body wall bearing ciliated tentacles that surround the mouth.-Suspension-feeders.-U-shaped digestive tract.

Phylum Phoronida-Phylum Phoronida- “Phoronis”: phoronids“Phoronis”: phoronids

-Only about 15 species of these tube-dwelling marine worms. --Only about 15 species of these tube-dwelling marine worms. -Length: 1 mm to 50 cm.Length: 1 mm to 50 cm.-Coelom, lophophore.-Coelom, lophophore.-Suspension-feeders.-Suspension-feeders.-U-shaped digestive tract.-U-shaped digestive tract.

Phylum Brachiopoda- “arm foot”: lamp shells ~330 species, most marine. Length: 1 mm to 9 cm.-Attached by stalk, resemble clams but shell halves dorsal & ventral. -Coelom, lophophore. -Suspension-feeders, U-shaped digestive tract.

A generalized body paln can become highly specialized within a phylum.

Phylum Mollusca “soft”: molluscs-Over 150,000 species in eight classes; most marine, but several in freshwater and some on land. Length: <1 mm to 21 m or so.-Soft body protected in most by a hard shell made of calcium carbonate. -Well-developed muscles to move the animal or anchor the body.-Nervous system developed at various levels.

Bivalvia: clams, oysters, mussels, scallops

Polyplacophora: chitons

Gastropoda: snails, slugs

Cephalopoda: octopus, squid, nautilus

Three main parts: foot (usually used for movement), a visceral mass (contains most of the internal organs), and a mantle (a fold of tissue that drapes over the visceral mass and secretes the shell).

In many the mantle extends to produce a water-filled chamber, the mantle cavity, which houses the anus and gills (portions of the mantle that increase surface area for gas exchange, making it more efficient).

Filter-feeders, grazers that feed on algae or carnivores that capture prey. Most use a strap like rasping organ called a radula to scrape food.

Segmetation allows a high degree of specialization of body regions (groups of segments can be modified for different functions).

Phylum Annelida “little rings”: segemented worms ~15,000 species in three classes; marine, freshwater and damp soil.-Length: <1 mm to over 3 m.-Body & organs segmented (not digestive tract), resemble fused rings.-Internally, segments divided by partitions called septa.-Circular muscles around each segment provide movement.-Front segments contain sense organs and a well-developed brain.

Most groups have setae, bristles of chitin that help anchor the worms during locomotion.

Segmentation: having a body built from repeated units (segments) allows a more precise control of the development and function of individual segments or groups of segments.

-Most marine. -Well-developed head.-Each segment usually has

fleshy, paddlelike flaps (parapodia) bearing many setae. -Filter feeders or carnivores.-Tube-dwelling and free-

living.

Polychaeta

Oligochaeta-Terrestrial and freshwater.-Reduced head.-No parapodia, a few setae

present.-Eat detritus, aerating and

improving soil texture. -Internal fertilization and

development and the use of skin as a respiratory organ have assisted in the exploitation of terrestrial environments.

General characteristics of reviewed phyla. Reproduction from lab notes.

SUMMARY

Important evolutionary trends in body plan: -Multicellularity: Porifera. -True tissues: Cnidaria. -Bilateral symmetry: Platyhelminthes. -Coelom: reduced or absent in some species These trends helped animals adapt to different environments or exploit the same environment in a different manner.