Lab 4: Dissection Flashcards
Why study worms/invertebrates?
Worms were the first group an animals to acquire a complete digestive tract and display sexual dimorphism
Define bilateral symmetry
body in which internal and external features are divided by a central longitudinal plane that are mirror images of each other
Describe characteristics of bilaterally symmetric animals
motile (move in direction of their heads)
bodies are streamlined
The back of an animal is referred to as the
dorsal surface
The belly of the animal is defined as the
ventral surface
Structures close to the midline are said to be ___
medial
Structures close the midline are known as
medial
Structures closer to the body are
proximity
Structures close to the sides are termed
lateral
Structures farther from the center of the body are
distal
A cut made through an organism is called a
section
Define sagittal and a mid-sagittal section
a longitudinal plane that divides the body of a bilaterally symmetric organism in to right and left sections
mid-sagittal section is cut down the midline and divides the animal into right and left halves
Define a frontal section
plane parallel to the long axis of the body. Perpendicular to sagittal plane and separates body into dorsal and ventral portions
Define transverse section
plan perpendicular to the long axis of the body. A cut through the body along this plane is commonly referred to as “cross section”
divides organism into posterior and anterior
Define radial symmetry
body that lacks a discernable sideness, often shaped like a pie or barrel. It is divided into two equal halves by any plane through its central axis
Describe some characteristics of radially symmetric animals
Their sensory organs are not concentrated in one particular region.
Tend to be either immobile or slow moving. Motile individuals move equally well in all directions
Where is the mouth of a radially symmetric animal located?
Located at or near the center of one surface, can be at the top or bottom
True or False: The terms dorsal and ventral are used for both radially and bilaterally symmetric animals
False, only for bilateral
The surface of a radially symmetric organism that contains the mouth is called the ___ while the opposite surface is called ___
oral
aboral
The axis of symmetry in radially symmetric organisms is the
imaginary line that connects the center of the oral and aboral surfaces
A plane that runs parallel and through the axis of symmetry in radially symmetric organisms is considered the plane of symmetry if___
it divides the body into two equal mirror image halves
Structures located close to the oral/aboral axis are said to be ___ while those farthest away are termed ___
central
peripheral
TorF: radially symmetric organisms have only one plane of symmetry
false, can have multiple that are often displayed in fives
Free swimming larval sea star demonstrate ____ symmetry. Adult sea star demonstrate ___ symmetry.
bilateral
radial
The direction of caudal is___ and opposite ___
toward or regarding the tail
cephalic
The direction of deep is ___ and opposite ___
toward the center
superficial (toward exterior)
Pectoral is in the direction __ and opposite ___
regarding the shoulders
pelvic regarding the hips
A tissue is
an integrated collection of cells that functions as a unit with a common purpose
A zygote divides mitotically in a process known as
cleavage
True or False: during cleavage, each mitotic division doubles the number of cells without an appreciable increase in the volume of the sphere due to lack of cell growth between division
true
A blastula is
a hollow ball of cells made after cleavage
Gastrulation can best be defined as
cells in the blastula move inward, a hollow tube is formed within the blastoceol with a single opening in the exterior
During gastrulation, the gastrula contains a single layer of kin tissue on the exterior ____ and a single layer if interior dermal tissue __. This will ultimately give rise to the __
ectoderm
endoderm
the digestive tract
Dipoblastic animals can be defined as
animals that have two germ (ectoderm and endoderm) layers
mouth/anus
Triploblastic animals can best be defined as
bilaterally symmetric animals that contain a third germ layer, the mesoderm (between ecto and endo)
In protostomes, the blastophere develops into the ___. In deuterostomes, the blastopore develops into the __
mouth of the organism protostomes
Blastopores develops into the anus and second opening into the mouth
True or False: Cnidaria are dipoblastic, bilaterally symmetric animals
False: They are dipoblastic, but they are radially symmetric
All Cnidaria possess _____, specialized cells which they use to immobilize their prey for protection
cnidocytes
The gastrovascular cavity in Hydra is __ cell layers thick and was developed by ___
two
the migration of cells into the blastocoel during gastrulation
The cells in the epidermis contain contractile ___ fibers, which enable the animal to contract into a ____. These cells are enidocytes that contain _____
contractile muscle fibers contract into a ball
contain nematocysts
Nematocytes are
enidocytes on epidermal layer of hydra that discharge stinging barbed projectiles
Nematocysts can be distinguished from cell nuclei with
their-dark staining nucleoli and appear as translucent vacuole-like spheres
The epidermis of the Hydra’s basal disc is composed of ___ which anchors the animal to the substrate
a single layer of columnar epithelial cells
The inner layer of Hydra cells is called _____. They are thicker than epidermal cells of the main column. They also contain ____ which secrete digestive enzymes into the body cavity
gastrodermis
epitheliomuscular cells
How are hydra able to move?
Extend their bodies by contracting circular muscle fibers or retract their bodies by contracting longitudinal fibers
As predators, Hydras hunt by
bending sideways and grabbing onto an adjacent structure with their tentacles
Hydra capture ___ by using their outstretched tentacles.
plankton/Daphnia
How do hydra acquire plankton?
prey cause the nematocyst to fire. A finger-like barbed projection penetrates and anchors the prey, a hollow thread delivers venomous chemicals.
Once the prey is immobilized, it is pulled to the mouth
The mouth then seals off the gastrovascular cavity. dissolved nutrients are circulated through the digestive cavity by water currents generated by cilia
Nutritive cells absorb the nutrients to meet the metabolic needs of the organism
TorF: Hydras lack a true excretory system
True
The main waste of Hydra’s excretory system is
ammonia
Note the difference between excretion and defection in hydra
excretion: dissolved waste diffuse from the cell layers into the surrounding water and are carried away by the water current
defecation: feces are expelled through the same aperture as they were acquired (the mouth)
How is oxygen and CO2 exchanged between layers in Hydra?
Diffusion
Describe the Hydra nervous system
neurons innervate both tissue layers, neurons are interlaced through mesoglea
Describe asexual reproduction in Hydra
Grow and regenerate through mitotic differentiation of interstitial/stem cells
Describe sexual reproduction in hydra
Hydra are hermaphroditic
The sperm are released into a pore in a mound into the surrounding water
Earthworms are part of the phylum..
annelida
Annelida are phylum who
all possess a cylindrical body divided into segments
why are annelida evolutionarily significant
a. one of the simplest groups to possess a true coelomic cavity with related organs grouped into definite regions (digestive, circulatory)
b. lays the groundwork for a more highly organized type of animal
Septa in annelida are composed of
connective tissue sandwiched between esothelium
The worm is divided into distinct anterior and posterior regions by the
clitellum
The U shaped region in the earthworm gut is the___ the interior is referred to as
typhlosole
the intestinal lumen
Earthworm move by
alternating serial contractions of the circular and longitudinal muscles in their body wall
Earthworms are detritovores, which are…
heterotrophs that feed by consuming decomposing organic matter found in the soil
The earthworm gizzard is
a chamber whose thick, muscular walls mechanically grind up the contents into small particles, increasing the surface area of the mixture
Earthworms possess a __ circulatory system, where blood travels exclusively through well-defined vessels
closed
There are two major earthworm longitudinal blood vessels, the
dorsal and ventral
Surrounding the esophagus of the earthworm are the five pairs of ____
pseudo-hearts
Describe the process of respiration for earthworms
blood vessels supplying the epidermis brings carbon dioxide where it diffuses across the moist layer. This requires a moist layer. Earthworms have no specialized tissue for gas exchange
When the soil becomes too dry to maintain normal activity, worms can enter a dormant state known as
estivation
Unlike a hydra whose nerve net is generalized, worms are among the first animals to
demonstrate cephalization, a concentration of sensory and neural structures toward the head of the organism
The earthworm is a hermaphroditic, however it still requires
two individuals to create offspring since self fertilization is an anatomical impossibility
The members of the echinodermata phylum are divided into six classes
asteroida, echinoidea, holothuroidea, crinodes, crinoided, ophiureda, and concentricycloidea
The most striking feature of echinoderms is their
radial symmetry shown in the adult form of the organism, but bilateral symmetry in the larva
The six characteristics of echinoderms include
- cylindrical, round, unsegmented, or star shaped bod with five or more radial divisions
- an endoskeleton of calcareous plates
- a unique water-vascular system
- a lack of cephalization
- an absence of excretory organs
- respiration through dermal branchiae
Describe sea star locomotion
Internal skeletons serve as framework to anchor bundles of muscle and connective fibers
fluid filled compartments act as a hydrostatic skeleton, allowing muscle contractions
Do sea stars have excretory structures?
no, nitrogeneous wastes diffuse across epidermal layers in the form of ammonia
TorF: sea stars lack a circulatory system with defined vessels and a pumping organ. Fluids move through the coleomic cavities by the actions of ciliated epithelia along defined pathways
true
Describe sea star respiration
dissolved gases are circulated by ciliary actions of the peritoneal linings
Describe sea stars nervous system
lack a brain and no cephalization
with no head or anterior structures, they easily move laterally in any direction
Describe asterias reproduction
separate male and female individuals, they are impossible to tell apart externally
gametes meet in a water column and divide mitotically
The sea star spines are extensions of the ___, which underlies the ____
endoskeleton
epidermis
The madreporite of the sea star is…. it can be found at
the small circular opening of the water vascular system
found at the periphery of the central disc, junction of arms 1 and 2
Asterias pedicellariae are
specialized ossicles that form jaw-like pincers covered by a thin epidermal layer
Describe the sea star digestive tract
short, complete
mouth opens to an indistinguishable esophagus, which connects to cardiac stomach chamber
Cardiac stomach attacks to a smaller pyloric stomach
pyloric connects to short intestine, and then anus
Sea stars are able to evert the cardiac chamber of their stomach, meaning
they can force their stomach out through their mouth, into or around their food
Nitrogeneous wastes generated from asterias digestive process are released into
the coeolomic fluid
Although starfish have little solid waste, it is eliminated by
being carried from the pyloric stomach to the anus by the intestine
When asterias meal is done, the stomach is retracted into the
coelomic cavity
TorF: Asterias have no true excretory structures
true
How does waste leave asterias?
leave water vascular system through the tube feet and coelom via dermal branchiae
Asterias coelomocytes can
capture wastes released in the cavity and accumulate to the tips of the dermal branchiae, then the waste is ejected by exocytosis
Describe sea star circulatory system
lack defined vessels and heart
fluids move through coelomic cavities by ciliated epithelia
Describe sea star respiration
dissolved gases are circulated by ciliary actions of the peritoneal linings.
Gas exchanged between perivisceral coelom and exterior at the dermal branchiae
Describe sea star nervous system
lack cephalization and brain
generalized nerve net that lies within epithelia and extends into the body wall, connects with many different types of sensory cells.
Chemo and mechanoreceptors distributed through epidermis
eyes consist of photoreceptors
Unlike hydra, sea star nerve plexus is
interconnected to circumoral nerve ring from which five radial nerves extend, innervating the arms.
TorF: asrterias is dioecious
true
TorF: it is possible to distinguish male from female asterias post dissection
false, gonads are difficult to locate and absent in juveniles
additionally, they spawn seasonally
Describe sea star reproduction
when ripe, testes or ovaries fill oral portion of each arm on either side of the amulacral bridge
external, release of gametes in one group triggers release of gametes in the other. clouds of sperm randomly fertilize in suspended water column
Asterias zygotes divide via
mitosis
because asterias blastopore gives rise to the anus in the developing gastrula, it is classified as
a deuterostome
