Lab Practical 2: Survey of the Animal Kingdom Phyla Porifera and Cnidaria

Phyla Porifera and Cnidaria

sponges and cnidarians are eukaryotic, multicellular, and ingestive feeding heterotrophs

Phylum Porifera (2)

sessile filter feeding heterotrophs, asymmetrical bodies without distinct tissues or organs (sponges)
-choanocytes/collar cells
-amoebocytes

Phylum Cnidaria (Coelenterata, 3)

radially symmetrical and diploblastic, digestive space lined by gastrovascular cavity with single opening (jellyfish, corals, sea anemones)
-cnidocytes
-two body forms
-four classes in two major clades

Phylum Cnidaria: cnidocytes

defensive/prey capture cells on tentacles surrounding mouth, contain stinging organelle called nematocysts

Do any features of Grantia clearly distinguish this organism as an animal? If so, which ones?

These sponges are motile, multicellular, eukaryotic, and lack rigid cell walls

structure of sponges (5)

-epithelial layer lines wall
-spongocoel inside sponge, central cavity
-choanocytes/collar cells lines spongocoel
-ostium cells are pores where moving flagella draw water through and into spongocoel
-osculum is a large hole at the end of sponge where filtered water exits through

Are choanocytes significant to a fundamental process for sponges? What is the process and how are choanocytes significant?

choanocytes are significant for eating because the moving flagella draw water through pores into the spongocoel and across the collars of the choanocytes to trap food particles

Grantia (4)

-has a folded wall that forms incurrent canals opening to the outside and flagellated canals opening to the central spongocoel
-canals are lined with choanocytes
-specialized collar of microvilli surrounding flagellum of a choanocyte traps food particles that are engulfed by the cell body
-digestion is intracellular (occurs inside cells)

Wall of a sponge (1)

contains amoebocytes, crystalline skeletal structures called spicules, and a gelatinous matrix called mesenchyme
-amoebocytes: move through body to consume and transport nutrients, produce spongin and spicules, and become other cell types

How do spicules help sponges survive in their environment?

spicules provide the sponge with a rigid structure and make it unpalatable to predators

Do sponges appear to have any organs or organ systems?

no

What is the advantage of a folded or convoluted wall in sponges?

it creates incurrent canals opening to the outside and flagellated canals opening to the central spongocoel, thus enhancing efficiency for the sponge's ability to gather food and oxygen, and to rid itself of waste

What function other than support might spicules serve?

deter predators

How many prongs do spicules of Grantia have?

3 prongs

What characteristics of Spongia make them useful as a household sponge?

they are pourous, so they're able to absorb materials, thus enabling them to be useful in cleaning

Are spicules significant to a fundamental process for sponges? In what way?

allows sponges to facilitate water exchange, support cells of sponges, enhance reproductive success, and catch prey

sponge reproduction (3)

-asexual reproduction includes budding and the release of stress resistant aggregates of amoebocytes called gemmules (can grow into a mature organism in favorable conditions)
-in sexual reproduction choanocytes and amoebocytes differentiate into gametes, eggs remain in mesenchyme but sperm are released into water and captured by other sponges, captured sperm are transported to eggs and fertilization occurs, embryo is then expelled from sponge
-most sponges are hermaphroditic (produce male and female gametes, but usually at different times)

Phylum Cnidaria: body wall (3)

-two cellular layers: ectoderm and endoderm
-gelatinous mesoglea separates the two body layers
-cells are organized into true tissues (nervous, muscular, and reproductive) but organs are loosely organized

Phylum Cnidaria: polyp body form (1)

generally sessile, oral side directed up
-cylindrical animals with a mouth surrounded by tentacles atop the cylinder

Phylum Cnidaria: medusa body form (1)

free swimming, oral side directed down
-umbrella shaped animals, mouths are surrounded by hanging tentacles

Cnidarian life cycle (6)

-characterized by alternation between polyp and medusa (polymorphism)
-use meiosis to produce and release eggs and sperm into water for fertilization (some retain their eggs, gametes are only haploid stage)
-zygote develops into a swimming mass of ciliated cells called a planula larva
-settles to substrate and develops into a polyp
-reproduces asexually by budding other polyps or may continue sexual cycle by budding immature medusae called ephyrae
-ephyra develops into a mature medusa

Are cnidocytes significant to fundamental processes for cnidarians? In what ways?

these stinging cells are used to catch prey and defend from enemies

How could polymorphism contribute to the evolutionary success of cnidarians in their environment?

It allows organisms of the same species to evolve during 2 different life cycles, independently of each other. Basically, having different life cycles within the same species allows a species to become more diverse, thus increasing its chances of survival

Phylum Cnidaria: Class Hydrozoa (6)

-polyp stage dominates but medusa occurs too
-ectoderm and endoderm surround gastrovascular cavity and these layers are separated by the gelatinous acellular mesoglea
-amoeboid cells circulate in the mesoglea
-ectodermal cells include cnidocytes and muscular contractile cells
-endodermal and glandular cells secrete enzymes into the gastrovascular cavity for extracellular digestion
-gastrodermis lacks cnidocytes

Class Hydrozoa: Hydra (6)

-small, usually less than 1 cm tall
-live in shallow freshwater ponds
-prey on smaller invertebrates among the filaments and leaves of freshwater algae and plants
-have no medusa stage
-cells are organized into specialized tissues
-interior gut cavity is specialized for extracellular digestion

Class Hydrozoa: Obelia life cycle (3)

-polyps reproduce by asexual budding forming colonies
-reproductive polyps may also give rise to medusae which reproduce sexually via gametes
-gametes fuse producing zygotes that develop into planulae which in turn produce polyps

Class Hydrozoa: Obelia (2)

typifies most hydrozoans because it has colonial polyps and free swimming medusae
-appear plantlike and branch from a tube
-polyps are polymorphic because some are specialized feeding polyps gastrozooids and others are reproductive polyps called gonozoids

How do hydra respond to a tap on their substrate? What tissues must exist for this response?

They move their tentacles. Nervous and muscle tissues.

Hydra are predators. How actively do Hydra stalk their food?

their bodies don't move much when they're feeding because they're sessile, but they do wave their tentacles around and they are attracted to chemical cues from food

What specialized cells of tentacles aid in capturing prey?

cnidocytes

What structures determine whether a polyp of Obelia is a gastrozooid (feeding polyp) rather than a gonozoid?

gastrozooids have upward extended tentacles, whereas gonozoids do not have tentacles (although the medusae that bud from them have down-ward pointing tentacles)

How do gonozoids obtain their food in this colonial organism?

when gastrozoids capture prey, they push the prey inside into a tubular gastrovascular cavity that is shared by all of the colony including the gonozoids

Gonozoids continue the reproductive cycle by budding medusae. About how many maturing medusae are visible in a typical gonozoid?

typically only one recognizable medusa, plus another 10 or so medusa buds

Class Hydrozoa: Gonionemus (5)

has an atypically large medusae
-medusae are more gelatinous than polyps because the mesoglea is more extensive
-velum on the inner periphery of the medusae and the mouth at the end of the manubrium
-gastrovascular cavity radiates from center as ring canals connected by a circular canal
-gonads (tissue that produces gametes) attach to the radial canals and appear similar in males and females
-tentacles have a rough surface

Which cells give tentacles of Gonionemus their rough surface?

Cnidocytes because they contain nematocycsts

What functions might radial and ring canals serve?

radial canal carries water out of arms from ring canal

Phylum Cnidaria: Class Scyphozoa (4)

sea jellies, gelatinous medusa dominates life cycle
-polyp is reduced to small larval stage (scyphistoma)
-mesoglea has amoeboid cells
-gastrovascular cavity is divided into 4 radiating pouches and the gastrodermis has cnidocytes
-includes largest invertebrate in the world, Cyanea capillota, can exceed 2m in diameter

Class Scyphozoa: Aurelia life history (3)

-male and female medusae produce gametes (only haploid stage) from meiosis for fertilization in water
-zygote develops into a planula larva that settles to the substrate and forms a scyphistoma (polyp) that produces ephyrae (immature medusae) by budding
-medusae separate from polyp and swim away

How do medusae of Aurelia and Gonionemus differ in size, arrangement of tentacles, and shape of manubrium?

-Aurelia (Scyphozoan):
large; short, thin, and fringe-like tentacles (evenly spaced); manubrium divided into four oral lobes
-Gonionemus (Hydrozoan): much smaller; longer, thicker, and fewer tentacles; tubular manubrium

Phylum Cnidaria: Class Anthozoa (4)

anemones and corals
-largest class of cnidarians
-polyps are solitary or colonial, no medusa
-mouth leads to a tubular pharynx and to a gastrovascular cavity with septet compartments
-gonads are gastrodermal

Class Anthozoa: Metridium (3)

fragmentation asexual reproduction, sessile but attachment isn't permanent so new individuals form when pieces or basal disk tear away
-gastrovascular cavity is partitioned by thin septa which distinguishes anthozoan polyps
-gonadal tissue and threads of tissue (acontia) along edges of septa
-acontia have cnidocytes that protrude through pores in body wall

Locate the radial ridges within each depression on a piece of coral. What structures within the polyp did they support?

tentacles above and mesenteries (attaches organs to posterior wall of abdomen) of partitioned gastrovascular cavity

What is the advantage of a partitioned gastrovascular cavity?

increased surface area for nutrient absorption

How does fragmentation contribute to the evolutionary success of anthozoans in their environment?

Fragmentation is a quick, relatively low-cost method of reproduction. It's asexual, so it doesn't increase the genetic variation of offspring, but it allows the anthozoans to spread quickly in ocean environments to which their genotypes are suited.

What is the difference between a polymorphic life cycle and the typical life cycle of other animals?

alternates between medusa and polyp forms

How does the feeding method of a sponge compare with that of a coral?

sponges filter feed while coral catch their food using tentacles

Phylum Cnidaria: Class Cubozoa (3)

box-shaped medusae
-tentacle is found at each corner of box
-strong swimmers and voracious predators of fish in tropical and subtropical waters
-stings can be fatal to humans

How does the shape of a box jelly compare to that of scyphozoans?

look similar to true jellyfish but cubozoans have a square shape when viewed from above, have four evenly spaced out tentacles or bunches of tentacles, and have well-developed eyes

Which group within kingdom Protista probably gave rise to sponges? On what evidence to you base your answer?

the protist ancestor was probably a choanoflagellate because they resemble the choanocytes of sponges both in their morphology and in DNA sequences, plus both are used for feeding

Why are spicules used as a primary characteristic to classify sponges?

essentially only variable to differentiate

Sponges and cnidarians have no lungs or gills. How do they exchange gases with the environment? Are humans better off having lungs? If so, how?

diffusion from the water column is the source of gas exchange, it's sufficient in sponges because they are so small, but humans are better off with lungs because they are so large and many cells are too far away from the natural environment to rely on diffusion

Why are sponges considered to be an evolutionary dead end?

they are so specialized in pumping water through their bodies that it is considered impossible to be modified into anything else

Explain how cnidocytes with their nematocysts function in food capture and defense.

Cnidocytes in cells of tentacles shoot out nematocysts which deliver toxins to their prey or predator that stings them

Discuss how polymorphism in the cnidarians might have influenced adaptive radiation of the group.

alternation of their forms between medusae and polyps allows the ability to find the best fit in any environment

How does digestion in cnidarians differ from digestion in sponges?

Cnidarians possess a well-formed digestive system and carry out extracellular digestion while sponges lack a true digestive system and depend on intracellular digestion