L4 Phyla: Porifera, Cnidaria and Cnetophora

Question 1

Lower Metozoans

Answer 1

Earliest multicellular organisms thought to have a common ancestral group likely as the choanoflagellates (zooflagellates).

The sponges!

Question 2

Hypothesis of arising multicellularity

Answer 2

The syntactical hypothesis that a plasma membrane formed within the cytoplasm of a large protist with multiple nuclei.

The colonial hypothesis is that a dividing protist produced daughter cells that stuck together and formed a colonial protist which then invaginated on itself creating a second cell layer.

Question 3

All animals arose from this animal-like protist

Answer 3

Zooflagellate - ancestral choanoflagellate

Question 4

Characteristics of Phylum Porifera

Answer 4

1) Asymmetry or superficial radial symmetry
2) no tissues = aceolomate
3) 3 cell types aka division of labour: pinacocytes, mesenchyme cells, choanocytes
4) central cavity for water circulation and filter feeding
5) sessile

Question 5

Pinacocytes

Answer 5

Flat, thin cells that line the outer surface. They can contract and can change the shape of the sponge. Can be porocytes ( little holes that are shaped like tubes through the cavity that allow water through the body wall).

Question 6

Mesenchyme cells

Answer 6

Found in the mesophyl (Jelly like midlayer). Ameboid cells that are specialized for:

• reproduction
• secreting skeletal elements
• transport & storage of food

Question 7

Choanocytes

Answer 7

Collar cells. Flagellated cells that

• create water current through the sponge
• acts as filters to sift through food particles
• recognizes and passes the sperm to the mesenchyme cells in reproduction

Link sponges evolutionarily to the Protists.

Question 8

Spicules

Answer 8

Calcareous (calcium carbonate or silica) skeleton secreted by the amoeboid cells (mesenchyme cells) to provide structural support to the sponge but also used to deter predators.

Question 9

Classes of Phylum Porifera

Answer 9

Class Calcarea
Class Hexactinellida
Class Demospongiae

Question 10

Class Calcarea

Answer 10

Calcium carbonate spicules 
Spicules with 3-4 rays 
Marine only 
Any of the 3 body forms 
(Ascon, sycon, leucon)

Question 11

Class Hexactinellida

Answer 11

Silica spicules
Spicules with 6 rays
Sycon or leucon body forms
Marine

Question 12

Class Demospongiae

Answer 12

Spongin or silica spicules
Needle shaped spicules 
Leucon body form 
Much bigger in size and colours 
Incurrent and excurrent canals (leading to and away from chambers lined with choanocytes)

Question 13

Ostia

Answer 13

The outer openings of porocytes where water enters the sponge

Question 14

Osculum

Answer 14

The opening at the top where the water exits

Question 15

Spongocoel

Answer 15

Chamber located in the middle of the sponge lined with choanocytes

Question 16

Grantia

Answer 16

A sponge belonging to the Class Calcarea and is a sycon sponge

Question 17

Eumetazoa

Answer 17

Phyla that have clearly recognizable tissues and organs

Question 18

Phylum Cnidaria & characteristics

Answer 18

The simplest form of eumetazoa

1) diploblastic organization > only mesoglea between the endo and ecto derms
2) gastrovascular cavity
3) radial or biradial symmetry
4) cnidocytes
5) nerve cells organized into a nerve net

Question 19

Classes of phyla Cnidaria

Answer 19

Class Hydrozoa
Class Anthozoa
Class Scyphozoa

Question 20

Cnidocytes

Answer 20

Produced by epidermal or gastrodermal cells

Used for attachment defence & feeding

Question 21

Cnidocil

Answer 21

A small cilium like part of the cnidocyte that when stimulated forces the operculum open

Question 22

Nematocysts

Answer 22

The nematocysts launches forwards into prey or substrate. Can be toxic, barbed, sticky etc. 6 different types on 1 animal.

Question 23

Polyp

Answer 23

Tube shape (body called the column) with tentacles surrounding the mouth for food gathering. Sessile at the aboral end. Mostly asexual.

Question 24

Medusa

Answer 24

Tentacles pointing downwards (jellyfish) with an inverted bowl like body mouth pointing downwards. Dioecious and free swimming.

Question 25

Alterations of generations

Answer 25

When asexual polyp stage AND medusa stage are in the life cycle

Question 26

Class Hydrozoa

Answer 26

1) Cnidocytes located only in the epidermis
2) alteration of generations
3) gametes are epidermal and released to the outside rather than in the gastrovascular cavity
4) lack of subdivisions aka no cells in the gastrovascular/ digestive cavity.

Hydra

Question 27

Class Scyphozoa

Answer 27

1) nematocysts in the gastrodermis and epidermis
2) medusa stage is prominent
3) medusa lacks a velum

Aurelia

Question 28

Class Hydrozoa

Answer 28

1) nematocysts located only in the epidermis
2) alteration of generations
3) gametes are epidermal and released to the outside rather than in the gastrovascular cavity
4) lack of subdivisions aka no cells in the mesoglea

Question 29

Class Anthozoa

Answer 29

Sessile always

Sea anemones and corals

Question 30

Life cycle of Aurelia

Answer 30

Planula > Scyphistoma (polyp) > strobila with ephyrae (polyp) > young medusa > adult medusa

Question 31

Anthozoa

Answer 31

Sessile always
Sea anemones and corals
2 types of corals