Porifera, Cnidarians, and Ctenophores

Phylum Porifera-

The Porifera phylum consists of pore-bearing sponges that are multicellular, aquatic, asymmetrical, lacking true tissues and organs and composed of spongin and spicules. These are sessile suspension feeders that use a unique aquiferous system to eat, breathe, and reproduce. There are three classes of Porifera- Calcarea, Demospongiae, and Hexactinellida.

The Water Path

Water enters through the Ostia which are incurrent pores found throughout the sponge. Water then passes through the central cavity or sponogocoel before exiting through the osculum. Sponges contain choanocytes which are flagellated collar cells that line the spongocoel and create water currents necessary to obtain food and oxygen.

The Three Body Types of Porifera:

• Asconoid: The simplest body type.

• Syconoid: The spongocoel is folded into canals that increase the choanocyte-lined surface area of the sponge.

• Leuconoid: The most complex and efficient body type, contain grape-like clusters of choanocytes at the ends of small canals.

Strutural Components of Porifera

As said previously, sponges are made of spicules and spongin.

Spicules are spikes made of calcium carbonate or silica that aid in structure and defense. Spongin is a collagen protein that the spicules are embedded in and forms fibrous skeleton that is soft and flexible.

Porifera Reproduction

Porifera can reproduce both sexually and asexually. In sexual reproduction, the sponge uses broadcast spawning where the sperm and egg is released and brooding where the sperm is released and the egg is retained. Asexual reproduction occurs by fragmentation, budding, and gemmules. Included below is a link to a video of a barrel sponge spawning in the Florida Keys.

https://youtu.be/5zWrSmpkV_I

Class Calcarea

• Marine

• Contains calcium carbonate spicules

• Skeletons with a mesh or honeycomb-like structure

• Smaller sponges

• All three body forms can be present on calcarea

Class Demospongiae

• Freshwater and Marine

• Most sponge species

• Dense

• Sparse spicules, but made of silicon dioxide if present

• Only posses the leuconoid body type

• Expansion/Contraction abilities

Class Hexactinellida

• Deep water marine

• Also known as Glass Sponges

• Contains 6-pointed silicon dioxide spicules that form to create a net-like structure

• Posses syconoid/leuconoid body types

Phylum Cnidaria

The Cnidarian phylum consists of nettle-like jellyfish, corals, sea anemones and hydras. Cnidarians have radial symmetry and are diploblastic meaning they have an endoderm and ectoderm. They also contain mesoglea which is the jelly-like matrix between body layers. These animals have no organs for circulation, respiration or excretion. It consists of four classes- Hydrozoa, Scyphozoa, Cubozoa and Anthozoa.

Distinguishing Characteristics

• Hydrostatic Skeleton

• Primitive Nervous System

• Ocelli

• Statocysts

• One digestive tract opening (both mouth and anus) with surrounding tentacles

• 2 body forms- Polyp (sessile) and Medusa (free-floating)

• Cnidocytes: Stinging cells that function in defense and prey capture that contain barbed nematocysts

• Medusa (free-floating) and Polyp (sessile) stages

Reproduction

Cnidaria, like Porifera use broadcast spawning and brooding in sexual reproduction. Asexual reproduction is done by budding, fission or pedal laceration.

Class Anthozoa

• E.g: Corals, Sea Anemones and Sea Fans

• Freshwater or Marine

• Solitary or Colonial

• Polyp form only (sessile)

• Reproduce by spawning or fragmentation

• Algae symbiont zooxanthellae

• Calcium carbonate skeleton

Fun Fact: I am currently working on a research project with Professor Jacob Warner at University of North Carolina at Wilmington focusing on the microbiology behind the regeneration capabilities of the sea anemone Nematostella vectensis. For more information about the lab and research being conducted visit https://warnerlab.org

Class Scyphozoa

• E.g: True Jellyfish- Cannonballs and Moon-jellys

• Medusa form dominant

• Gastric cirri in gut

Class Cubozoa

• E.g: Box jellys

• "Box" formed by four groups of tentacles

• Medusa dominant

• Well developed ocelli and image forming eyes

• Strong swimmers

Class Hydrozoa

• Eg: Man-of-War, hydra, lobelia

• Solitary or colonial

• Polyp or Medusa life stages

• Hydra is found only in the polyp form

• Hydra

• Obelia

Phylum Ctenophora

Also known as comb jellies, Ctenophores differ from Cnidarians, as they have both a mouth and an anal opening, possess comb plates, and colloblasts.

Comb Plates: Mode of locomotion- long fused cilia, row beat in unison,

Colloblasts: Specialized glue cells, found on tentacles