Marine Invertebrates
Marine Acoelomates and Pseudocoelomates
Traits
Three tissue layers
Bilateral Body Symmetry
click to edit
click to edit
click to edit
Lacking internal cavity or a poorly developed one that separates the body wall from the digestive tract
Phylum Nematoda
Phylum Platyhelminthes
Marine Coelomates
Traits
Characterized by internal body cavity. The development of this cavity allowed for the evolution of more complex body systems, especially ones that allow for more effective circulation
Larger gonads to increase reproduction rates by creating more gametes
Body wall muscles function independently and have a number of specialized functions. The structure of these kinds of organism do not use a rigid internal skeleton system. Rather variations of hydrostatic skeleton or a exoskeleton.
click to edit
Examples
Phylum Arthopoda
Phylum Mollusca
click to edit
click to edit
Ctenophora
Porifera
Cnidaria
Two tissue layers: Inner and Outer body walls, separated by gelatinous mesoglea.
Traits
Centrally-located mouth, opening to bag-like gastrovascular structure, which is an incomplete digestive system.
Components:
Tentacles surrounding mouth used to snare prey. Armed with stinging structures called nematocysts
Can be adhesive, paralyzing, or tangling
Porifera stems from "pores" meaning there are holes and perforations within the bodies of sponges that filter water and collect nutrients
Osculum: Excurrent pore where water exits
Nematocysts produced and housed in cnidocytes: a. characteristic of this phylum. ⭐
Variants
Choanocytes: Flagellated current-producing cells which line the spongocoel
Spongocoel: Internal cavity where food and oxygen are extracted
click to edit
Free-swimming Medusa
Attached, benthic Polyp
Tentacled directed upward
Example: anenomes
Tentacled directed downward
Example: jellyfish
Most members of this phylum are planktonic and not exceeding a few centimeters in size
Spicules: some spongin are supported by hard and sharp spicules which are either calcareous and siliceous
Morphologically similar to Cnidaria: Radial symmetry, tentacles
Complete digestive tract
8 external bands of cilia called comb rows⭐, led to ctenophores common name: "comb jellies"
Date back to the Cambrian period
Spongin: some spongin are supported by internal networks of flexible spongin fiber
Structure I: multicellular organisms that lack tissues and organs such as muscles and nerves
Structure II: May appear radially symmetrical but usually conform to the surface shape to which they are attached or are shaped by the water currents around them
Location II: typically non-mobile creatures unless attached to other moving creatures
Location: typically exist in marine habitats and will attach to hard surfaces such as rocks;
click to edit
click to edit
click to edit
click to edit
Also know as roundworms. Typically marine nematodes are found in bottom sediments and at almost every water depth. Their movement is poorly developed. 
Also know as flatworm. They are acoelomates meaning they lack the internal cavity their body wall and digestive tract. They tend to be parasitic. They are covered in cilia which aids them in movement. They have an incomplete digestive tract, so one opening is used for food entering and waste leaving.
Lacking a circulatory system or as a somewhat open system.
click to edit
click to edit
Small bodies with high surface to volume ratio
click to edit
click to edit
click to edit
click to edit