Animals: Invertebrates Flashcards
Animals
monophyletic group descended from a common ancestral protist
- fossil evidence suggests that multicellular animals first emerged in the Proterozoic Eon
- it was not until the Cambrian Explosion at the start of the Phanerozoic Eon that animals life began to greatly diversify
- animals are monophyletic, but land-based animals are NOT monophyletic
Common Adaptations of Animals
Animals are also called METAZOANS, and a subset of metazoans are categorized as EUMETAZOANS
ALL METAZOA:
- Multicellular Body Plans
- Cells that lack cell walls
- Heterotrophy
- Movement at some point in their life cycle
Eumetazoans
include all animals except sponges (Porifera) and a group of amoebae-like “flat animals” (Placozoa)
ALL EUMETAZOA:
- possess true differentiated tissues
- nervous system
- muscle cells
the Phylum Cnidaria (modern day sea anemones, corals, jellyfish) likely includes the first eumetazoan
Invertebrate
animals that are without a cranium (skull) or defined vertebral column (spine)
- most also lack an endoskeleton and instead possess either a hydrostatic skeleton or exoskeleton
- The first animals were invertebrates and aquatic
Adaptations of Invertebrates:
- Multicellularity + Cell Specialization
- True Tissues
- Tissue Layers
- Symmetry
- Digestive Systems
- Coelom + Pseudocoelom
- Nervous Systems
- Respiratory + Circulatory Systems
- Segmentation
- Limbs
- Wings
Multicellularity + Cell Specialization
all animals are multicellular with specialized cell types, including Poriferans + Placozoans
- these two animal types do have specialized cells for digestion + reproduction but lack true tissues
True Tissues
a group of similarly-structured cells that move together to carry out a specific function; all Eumetazoans have true tissues
- the evolution of TT allowed for the evolution of complex organs and organ systems
Organ
a structure comprised of 2+ specialized tissues that together carry out a specific function
Tissue Layers
Eumetazoans can be categorized by the # of embryonic tissue layers present during early development:
- Diploblasts
- Triploblasts + Mesodermal Tissue
Diploblasts
Eumetazoan where its tissues develop from 2 embryonic tissue layers called the ECTODERM (outer layer) and ENDODERM (inner layer)
- these layers limit the # of tissue types that can be formed within an organism
- Lack complex organ systems and are typically very thin/flat such that every cell in the body can exchange O2/Co2 directly with the environment
- EX: Cnidarians
Triploblasts + Mesodermal Tissue
animals with 3 embryonic tissue layers: the ectoderm, mesoderm, and endoderm
- MESODERM (middle layer) allowed for the evolution of new tissues such as muscle, complete digestive systems, and vascular systems
- allowed for more complex body structures and organ systems
- all animals classified as Bilateria are triploblastic
Symmetry
evolved early in animal evolution; Eumetazoans can be categorized by:
- Radial Symmetry
- Bilateral Symmetry
Radial Symmetry
first Eumetazoans; the body has a repeating pattern around a central axis
- sufficient for slow-moving or sessile (non-moving) organisms but is less efficient at allowing movement compared to bilateral symmetry
- EX: Jellyfish, Starfish
Bilateral Symmetry + Cephalization
- Evolutionary advantage allowing for more controlled left/right or front/back movement
- bilateral symmetry is a consequence of cephalization (symmetry with clear left/right or top/bottom
- EX: worms, flies
Cephalization
the concentration of nerve tissue at one end of the body, forming a “head” region
- bilateral symmetry is a consequence of this
Digestive Systems
animals are heterotrophic - they must obtain carbon from an organic source
- carbon is obtained by eating another organism; an animal must digest/break down the tissues of another organism into biologically-available molecules
- Eumetazoan’s have 2 types of digestive systems: Incomplete + Complete
Incomplete Digestive System
early Eumetazoans; there is a digestive cavity (AKA gastrovascular cavity) with a single opening that serves as both mouth and anus
- typically found in diploblastic organisms with radial symmetry like modern day Cnidarians
Complete Digestive System
there are separate opening as the mouth + anus for both unidirectional movement of food and specialization of regions along the digestive tract
- more efficient, allowing animals to eat while digesting food + eliminating waste
- all Bilateria except flatworms
- roundworms were some of the first to evolve a CDS
Coelom/Pseudocoelom
ancestors of nematodes (roundworms) evolved a pseudocoelom, or a partial body cavity filled with fluid. ancestors of annelids (earthworm) later developed a true coelom lined by mesodermal tissue
- most Bilateria classified animals have a CDT except flatforms
- cavity allows room for internal organs to develop (often from mesodermal tissue) and remain attracted to the mesodermal lining, anchoring them in place within the body
- the fluid cushions + protects internal organs from physical damage
- pressure exerted by fluid gives internal support in a form of a HYDROSTATIC SKELETON
Hydrostatic Skeleton
the skeleton allows for efficient + coordinated movement driven by muscles
Nervous Systems
evolution of neurons + nervous systems allowed for integration of sensory inputs + coordinated responses, like movement away/to a stimulus
- all animals have one except porifera + placozoa
- radically symmetric animals typically have a NERVE NET
- radially symmetric Echinodermata which evolved from bilateral ancestors have a central nerve ring around the mouth, a set of radial nerves that extend out to the body
- a central nervous system is present in most animals demonstrating cephalization
Nerve Net
a set of interconnected neurons without a brain or any sort of cephalization
Central Nervous System
consisting of a brain structure in the head region and at least a nerve cord that extends through the body
- Platyhelminthes: 2 nerve cords
- Arthropoda: ventral nerve cord
- Chordates: dorsal nerve cord
Respiratory + Circulatory System
evolution of a respiratory system with a dedicated structure for O2 + CO2 exchange, combined with a circulatory system as a means to move gas + nutrients throughout the bodies
- allowed the evolution of larger + more complex bodies
- freed animals from “flat” body shape required for gas exchange in the absence of a respiratory system
Segmentation
the division of the body into multiple segments; evolved multiple times in animal lineages
- increases flexibility + a wider range of motion by providing pivot points within the body
- Annelida, Arthropoda, Chordata
Limbs
evolved multiple times in animal evolution including Arthropoda + vertebrata
- occurred in aquatic species, allowing them to move onto land
Wings
Evolved multiple times in animal evolution, including insects, birds, bats
