BIOL 1202 : TEST 4
TEST 4
Chapter 33: Invertebrates
• most recent hypothesis about animal phylogeny (figure 32.11)
• invertebrates- animals that lack a backbone
o account for 95% of known animal species
o occupy almost every habitat on earth- adaptations produce large diversity of forms
Concept 33.1: Sponges are basal animals that lack true tissues
o phyla Calcarea and Silicea- known informally as “sponges”
o sponges used to be classified in the single phylum- Porifera
o live in both fresh and marine waters, lack true tissues and organs, and asymmetrical body, vary in
size, inactive (mistaken for plants by Greeks), simplest animal, basal animals (represent lineage
originating near the root of the phylogenetic tree of animals)
• sponges
o suspension feeders- filter food particles suspended in water passing though their bodies
o spongocoel- central cavity water is drawn through pores
o osculum- larger opening where water flows out of a sponge
o most sponges and snails are hermaphrodites- each one functions as both male and female in
sexual reproduction (sperm and egg), functioning first as one sex then the other
o sponge gametes arise from choanocytes or amoebocytes.
▪ eggs reside in mesohyl (where fertilization occurs) and sperm are carried out of sponge
through water current
▪ cross-fertilization results from sperm being drawn into neighboring individuals
▪ in fertilization in mesohyl, zygote develops into flagellated/swimming larvae dispersing
from parent sponge. larvae develop into sessile adult after settling on suitable substrate
• anatomy of a sponge (figure 33.4)
o choanocytes- flagellated cells lining the interior of the spongocoel, they beat flagella creating a
current drawing water in through pores and out of osculum
▪ movement of flagellum draws water through the collar of fingerlike projections, food
particles become trapped in mucus coating the projections, are engulfed by
phagocytosis, and either digested or transferred to amoebocytes.
▪ similarities between choanocytes and choanoflagellates shows molecular evidence that
animals evolved from choanoflagellate-like ancestors.
o mesohyl- “middle matter”, gelatinous region separating two layers of cells covering the wall of
the sponge
o amoebocytes- named for their use of pseudopodia, wander through the mesohyl and have the
functions:
▪ take up food from water/choanocytes, digest, and transport nutrients to other cells of
spongy body
▪ produce skeletal fibers (spicules- made from calcium carbonate/silica) from mesohyl
▪ become any type of sponge as needed, produce flexible fibers consisting of the protein
spongin
o epidermis- outer layer of sponge consisting of tightly packed epidermal cells
o pores/porocyte- formed by doughnut-shaped cells that span the body wall through which water
enters the epidermis
o spongocoel- cavity which water passing through pores enters into
CLICKER: water movement through a sponge would follow what path? -pore > spongocoel >osculum
Concept 33.2: Cnidarians are an ancient phylum of eumetazoans
• cnidarians- one of the oldest lineages in the clade Eumetazoans
o a wide range of sessile and floating forms including jellyfish, corals, and hydras
o most still exhibit simple diploblastic, radial body plan
▪ basic body plan is a sac with a central digestive cavity- gastrovscular cavity- single
opening of this cavity serves as both mouth and anus
▪ two variation to this body plan: sessile polyp and motile medusa
• sessile polyp- cylindrical forms that adhere to substrate by aboral (opposite of
mouth) end of body and extend tenticles waiting for prey ex. hydras and sea
anemones
• motile medusa- flat/mouth-down version of polyp, moves freely in water by
combination of passive drifting and contractions of bell-shaped body ex. free-
swimming jellies
▪ mesoglea layer between epidermis and endodermis (gastrodermis)
o some exist only as polyps or only as medusa, but others have both in their life cycles
o carnivores that often use tentacles arranged in a ring around their mouth to capture prey and
push the food into gastrovascular cavity where digestion begins
o specialized cells found in cnidarians:
▪ cnidocytes- cells that arm the tentacles and are unique to cnidarians that function in
defense and prey capture
• contain cnidae- capsule-like organelles capable of exploding outward and give
phylum Cnidaria its name
• nematocysts- specialized cnidae containing a stinging thread that can
penetrate the body wall of the cnidarian’s prey
• defining feature of cnidarians (figure 33.6)
o cnidarians
▪ unique cells that function in defense and the capture of prey
o stimulus causes the cell to evert releasing thread
o some cnidocytes sting, others just entangle prey
• cnidarian diversity into four major classes (figure 33.7)
o hydrozoans-
▪ mostly marine but few freshwater
▪ alternate between polyp (more noticeable colony of interconnected polyps) and
medusa forms
▪ hydras (found in fresh water) are unusual hydrozoans because they exist only in polyp
form
• reproduces asexually in favorable environ. conditions by budding- forming
outgrowths that pinch off from parent and live independently
▪ when conditions deteriorate, reproduce sexually forming resistant zygotes that remain
dormant until conditions improve
o scyphozoans-
▪ all marine, free swimming, up to 2m in diameter
▪ medusa is generally the predominant stage in life cycle
▪ medusa live among the plankton as jellies
▪ coastal- go through small stages as small polyps but those living in open ocean lack
polyp stage completely
▪ ex. jellies
o cubozoans-
▪ all marine, box-shaped medusa stage
▪ complex eyes in the fringe of the medusa
▪ strong swimmers resulting in them less likely to be stranded on shore
▪ live in tropical oceans and equipped with highly toxic/poisonous cnidocytes
▪ ex. sea wasp- sting leads to severe harm and death except for sea turtles
o anthozoans- “flower animals”
▪ all marine, most are sessile (non-moving), many colonial (foreign)
▪ occur only as polyps
▪ ex. sea anemones and corals
▪ corals
• coral reefs are to tropical seas as rain forests are to tropical land areas
• lonely or foreign forms, secrete hard external skeleton of calcium carbonate
with each polyp generation building on skeletal remains of earlier ones
constructing “rocks” (we think of these as coral)
• provide habitat for wealth of other species, but are now being destroyed due
to pollution, overfishing, and global warming
CLICKER: how many planes through the central axis will divide an organism with radial symmetry into roughly
equal halves -many
CLICKER: which of the following animals is responsible for more lethal attacks on humans each year? -
cubozoans
Concept 33.3: Lophotrochozoans, a clade of bilateral identified by molecular data, have the widest range of animal
body forms, and include 18 animal phyla (twice the number in any other clade of animals)
• 1. flatworms -phylum Platyhelminthes
o live in marine(mostly), freshwater, and damp terrestrial habitats
o free-living forms and many parasitic species- flukes and tapeworms
o triploblastic development, but acoelomates (lack body cavity have thin bodies) flattened
dorsoventrally (between dorsal and ventral surfaces)
▪ flat shape places cells close to water in surrounding environment or gut allowing
gas exchange/elimination of nitrogenous waste (ammonia) to occur by diffusion
across body surface
o simple excretory apparatus functioning to maintain osmotic balance with surroundings
▪ consists of protonephridia – network of tubules with flame bulbs (ciliated cells that
pull fluid through branched ducts opening to outside)
Document Summary
Chapter 33: invertebrates: most recent hypothesis about animal phylogeny (figure 32. 11) invertebrates- animals that lack a backbone, account for 95% of known animal species, occupy almost every habitat on earth- adaptations produce large diversity of forms. Clicker: how many planes through the central axis will divide an organism with radial symmetry into roughly equal halves -many. Clicker: which of the following animals is responsible for more lethal attacks on humans each year? cubozoans. Clicker: cnidarians use _____ to immobilize or trap prey. Clicker: three of the four animals listed below possess some type of coelom. select the exception - platyhelminths. 5 rows of tube-feet- around the mouth modified as feeding tentacles: 6. concentricycloidea- sea daisies live on submerged wood, armless, disk-shaped. 5-sided organization measuring less than a centimeter ridged with small spines, absorb nutrients through membrane surrounding them. Chapter 34: vertebrates chordate phylogeny (figure 34. 2: each lower has extra features added to original.
