Sponges, Cnidarians, and Platyhelminthes

Question 1

What does Phylum Placazoa mean?

Answer 1

“Flat Animals”

Question 2

What is the simplest of all non-parasitic multicellular animals?

Answer 2

Phylum Placazoa

Question 3

What species is included in Phylum Placazoa?

Answer 3

Trichoplax adhaerens, composed of a bilayer of a few thousand cells

Question 4

How do Phylum Placazoa reproduce?

Answer 4

Asexually by dividing into two or budding off many multicellular individuals

Question 5

What’s special about Phylum Placazoa?

Answer 5

There’s no fossil record, and they possess no tissues or organs, no digestive, circulatory, or nervous systems

Question 6

General characteristics of Phylum Porifera (Sponges)

Answer 6

About 5500 species, sessile, filter feeders, lack true tissues

Question 7

What environment do sponges live in?

Answer 7

Marine (few freshwater)

Question 8

What is the morphology of a sponge like?

Answer 8

Asymmetrical, diploblastic (2 tissue layers), skeleton made of collagen and spicules, no tissues and organs, “body” is a system of pores and canals through which water passes

Question 9

Spicules

Answer 9

Rodlike structures found in sponges that are made of silica, calcium carbonate, and spongin (protein)

Question 10

Mesoglea

Answer 10

Gelatinous matrix in sponges where skeletal elements, choanocytes, and other cells are embedded

Question 11

Choanocytes

Answer 11

Specialized cells found in sponges that are flagellated and aid in the movement of water through the sponge

Question 12

How do sponges feed?

Answer 12

They are filter feeders, so they capture food that is brought close by water currents created by choanocytes. Food particles taken in by individual cells through phagocytosis, then digestion occurs in the individual cells

Question 13

Are sponges asexual or sexual?

Answer 13

-They are hermaphroditic (produce both male and female gametes)
-Reproduce both sexually and asexually
-Asexual via buds
Sexual reproduction occurs in mesoglea

Question 14

How does sexual reproduction work in sponges?

Answer 14

Sperm released in water captured by choanocytes, choanocytes lose their “collars” and transform into amoeba-like cells, which carry the sperm to the eggs. Fertilized egg develops into a blastula that is released into the water. Blastula develops into a larva which can either immediately settle and transform into an adult or may swim before settling down. Adults are sessile.

Question 15

What is included in Phylum Cnidaria?

Answer 15

Jellies, Corals, and Hydras

Question 16

What type of body symmetry do Cnidarians have?

Answer 16

Radial

Question 17

General characteristics of Phylum Cnidaria

Answer 17

Diploblastic, tissue level of organization (no organs), hydrostatic skeletons, gastrovascular cavity, no respiratory system, simple nervous systems

Question 18

What is the nervous system of cnidarians like?

Answer 18

Simple; they have ganglia to coordinate nerve messages along the body and nerve nets (diffuse network of neurons which conducts impulses in all directions from a point of stimulus)

Question 19

Gastrovascular Cavity in Cnidarians

Answer 19

One way digestive system; food goes in oral cavity, digested with enzymes, then waste eliminated out of oral cavity

Question 20

Cnidoblast

Answer 20

Specialized cell found in Cnidarians; it’s a venomous cell used to capture prey and defend against predators

Question 21

Nematocyst

Answer 21

Found in cnidocytes; have unique organelles and function to help capture prey and defend the animal–works like a jack in the box

Question 22

How do cnidarians reproduce asexually vs sexually?

Answer 22

Asexually through polyps that reproduce by budding
Sexually through medusae that reproduce via gametes

Question 23

Sexual reproduction Cnidarians

Answer 23

Medusae produced on specialized polyps, release gametes that fuse, forming a zygote, which develops into a bilateral ciliate larva. Larvae swim for a little while then settle and develop into polyps, growing asexually as new polyps grow and branch from older ones

Question 24

Describe coral’s general characteristics

Answer 24

-colonies of polyps
-enclosed in a skeleton of calcium carbonate
-sometimes form symbiotic relationship with photosynthetic dinoflagellates
-Dinoflagellates live inside polyps, receiving shelter and CO2 from the coral, and the coral gets sugars and O2 from the dinoflagellate
-if a coral reef loses its partner it will die (coral bleaching)

Question 25

What organism is Phylum Platyleminthes?

Answer 25

Flatworms, over 20,000 species

Question 26

Flatworm general characteristics

Answer 26

-bilaterally symmetrical
-protostomes
-triploblastic
-hydrostatic skeleton
-acoelomate
-dorsoventrally flattened =flat worms
-no segmentation
-tissues
-organs
-distinct brain
-have a highly branched gastrovascular cavity (GVC)
-no circular system
-cephalized nervous system

Question 27

What is an acoelomate?

Answer 27

An animal that lacks a formal body cavity or coelom

Question 28

How do flatworms reproduce?

Answer 28

-Sexually: they’re hermaphroditic and possess male and female organs, but individuals cannot fertilize their own eggs and have to mate with another flatworm
-Asexually: body splits in two near the middle, and each piece regrows the missing part. Regrowth also occurs if the flatworm is cut in two

Question 29

Phylum Platyhelminthes Class Turbellaria

Answer 29

-Free living flatworms (some aquatic, some terrestrial)
-Bilateral symmetry
-Dorsoventrally flattened
-Unsegmented
-Cephalization (very primitive brain and system of sheathed nerve fibers)
-Blind ending gut

Question 30

Platyhelminthes Class Trematoda (Flukes)

Answer 30

-bilaterally symmetrical
-dorsoventrally flattened
-2 external suckers
-no respiratory system
-excretory system (flame cells)
-nervous system consists of a brain comprised of a pair of ganglia in head region
-hermaphrodites (flukes can only reproduce inside mammal)

Question 31

What happens with flukes in humans?

Answer 31

They can only reproduce in a mammal, humans become infected when they wash or walk in water where infected snails live, blood fluke crosses their skin and reproduces in their body, causes schistosomiases