Marine Bio: Major Characteristics of Poriferans and Cnidarians

Radial symmetry

Involves similar form with respect to a center point in all directions (jellyfish and corals)

Bilateral symmetry

Involves a plane of symmetry, with similar form on either side of the plane; also involves an anterior and a posterior (worms, lobsters)

Cleavage in deuterostome

Symmetric radial cleavage (echinoderms, chordates)

Cleavage in protostomes

Asymmetric spiral cleavage (flatworms, annelids, molluscks, and arthropods)

What are the 3 cell layers?

Ectoderm, mesoderm, and endoderm

Which phyla has 2 cell layers instead of 3?

Cnidaria

Coelom

Cavity that develops in embryo with mesoderm which is found in several phyla (arthropods and molluscs)

Gut

May be absent in porifera, blind (corals) or complete with a mouth and anus

Symmetry in Poriferans

Asymmetrical or radial symmetry

Cells in Poriferans

Has loosely organized cells with no distinct tissues or organs

Do Poriferans have a gut or body cavity?

No

What are the 3 types of cells in Poriferans?

Pinacocytes, Mesenchyme cells (amoebocytes), and choanocytes

Pinacocytes

“Skin cells” of sponges which line the exterior of the sponge body wall. Some specialize into porocytes which regulate water circulation

Mesenchyme (amoebocytes/archeocyte) cells

Found in the jelly-like mesenchyme layer underneath the pinacocytes. Move around in mesohyl

What are mesenchyme cells specialized for?

Specialized for reproduction, transporting and storing food, secreting skeletal elements (spicules)

Choanocytes (collar cells)

Found beneath the mesenchyme cells, and line the inner chambers of sponges. Flagellated cells with a ring of microvilli surrounding the flagella. Drive water through pores and cavities for filter feeding.

Skeleton of Poriferans

Consists of spicules formed by a type of mesenchyme cell made of CaCO3, silica or spongin

Sclerocytes

A type of mesenchyme cell found in poriferans which make up the skeleton of sponge

What are water currents generated by in Poriferans?

Choanocytes

What does water movement do for sponges?

Water movement brings food and oxygen while removing waste

3 major porifera body forms

Ascon, sycon, and leucon

Ascon Porifera body form

The simplest and least common body form. Vaselike where the porocytes lead directly to spongocoel lined with choanocytes.

Where does the water exist in ascon sponges?

Water exists through the osculum (single large opening at the top)

Sycon Porifera body form

Body form has a folded wall where pores open into radial canals, which ultimately lead into spongocoel. Choanocytes line the radial canals moving water from radial canals to spongocoel.

Where does water enter and exit in Sycon Porifera

Water enters through dermal pores at opening of incurrent canals and exits out through osculum

Leucon Porifera Body form

Body form that has an extensively branched canal system. Absent of a spongocoel and has excurrent canals as they lead away from chambers

How does water move in Leucon Porifera?

Water enters through pores and moves through branched incurrent canals which lead to choanocyte lined chambers. There are multiple exit points for water leaving the sponge

Porifera Diet

Includes bacteria, phytoplankton, protists, and suspended organic matter

Which cells filters particles from water?

Choanocytes

How do sponges absorb nutrients?

Absorb nutrients by active transport

How do sponges remove waste?

Removes waste via diffusion

Do Poriferans reproduce sexually and asexually?

Yes and most are monoecious

Porifera reproduction

Are monoecious (both sexes on 1 sponge), they do not self fertilize so the eggs and sperm are ready at different times. Reproduce asexually by producing buds that form new sponges

Phylum Cnidaria characteristics

-Epidermis and gastrodermin

-Jelly like mesoglea between 2 layers

-Radial symmetry

-Blind gut

-Well formed digestive system

-Generally dioecious (separate sexes)

-Network of nerve cells

-Excrete through diffusion

What are the 2 basic stages of Cnidarians?

Sessile polyp and swimming medusa where they both use stinging cells to capture prey

Cnidocytes

Specialized stinging cells in Cnidarians which contain organelles called nematocysts

Where are cnidocytes found?

Present around mouth and tentacles

Nematocysts

Organelles on cnidocytes which contain coiled threads which may have barbs when fired can penetrate or ensnare organisms

Cnidocils

Hairlike projections on nematocysts that are on the outside of cells and are touch triggered

Class Hydrozoa (Cnidarians)

Simplest Cnidarians which alternate between benthic colony and planktonic medusa stage

Benthic stage of Hydrozoa

Polymorphic stage where both feeding and reproductive polyps are attached to one another

Class Cubozoa (Cnidarians) characteristics

-Carnivorous

-Square shaped

-4 evenly spaced out tentacles

-Well developed eyes

-Strong swimmers

-Benthic polyp stage

Chironex fleckeri

-Sea wasp

-Size of human head

-Extremely venomous

-Only polyps observed on undersides of stones

Class Scyphozoa (Cnidarians) characteristics

-True jellyfish

-Carnivorous

-Covered in sensory structures

-Longer planktonic stage and shorter polymorphic stage

-Shed gametes into water which develop into planula larvae and develop benthic stage

-Move via muscle ring contraction forcing water out of bell

Class Anthozoa (Cnidarians) characteristics

-Anemones, sea fans

-Carnivorous

-Supplement diet via symbionts (zooxanthellae)

-Polyp stages dominant part of life cycle; no medusa stage

-After gametes are produced, embryos develop into swimming planula larvae

-Planula settle and then polyp stage