Ref: Lesson 18
Introduction to
Marine
Invertebrates
Kingdom
Animalia

97% of animals
on Earth are
invertebrates

Except for
insects, most are
marine

Exception is
Phylum
Chordata which
contains both.
97% of animal species on Earth are
invertebrates. On Earth today,
insects are the most numerous
invertebrates. Many vertebrates
are described as "fish",
encompassing a large group of
disparate classes or subphyla.
Structure and Function of
Feeding in Invertebrates

Found nearly
everywhere in
the ocean

Majority speak
their juvenile
stages in the
plankton
community
Structure and Function of
Feeding in Invertebrates

As adults – attach to substrates
 Seafloor
 Inside
self-created shells/skeletons
 Floating
among plankton
 Crawling
on seafloor
 Swimming
within water column
Adult: much larger
than juveniles
Niches

Multiple body forms allow for invertebrates
to take on many “jobs” in their ecosystem

Each species occupies a different niche

Ex: 2 species of fish might eat the same
smaller fish species, but one hunts at night
while the other hunts during the day
Ex: Barnacles
Morphology

Important characteristic of how the organism
carries out its niche is its structure

In animals, it is termed anatomy

Study of processes within its anatomy is called
physiology
Body Plans

Asymmetry – animal lacks symmetry
 Simplest

Radial - arranged around a central axis so
that each part extends from the center
 Tend

animals
to be sessile (immobile)
Bilateral – has identical halves
 Best
for mobile creatures
Evolution of Body Plans
Anatomy
Physiology of Starfish
Feeding Techniques

1) Filter feeding
 Great
deal of food suspended in water
column
 Plankton
or remains of larger organisms
Feeding Techniques

Many bivalves pump water through
their bodies
 Known
as active filter feeders

Bivalves have a characteristic muscular foot on bottom
and siphon on top

Bivalves pump water through incurrent siphon

Feather-like gills are enlarged to gather oxygen and food

Covered in cilia which beat to maintain constant water flow

Cilia trap food and push towards digestive system

Mouth, stomach, intestine, and anus
Active filter feeder - Clams

Wastes (CO2 & food) released through excurrent siphon

Active pumping allows animal to counteract buoyancy of
plankton
Geoduck Clam – “Gooey duck”
Suspension Feeding

Type of filter feeding in which organisms do not
create their own water currents

Rely on movement of water to bring them food

Ex: Crinoids
Suspension Feeders

Members of Phylum Echinodermata are
suspension feeders

Lined with tube feet connected to animal’s
water vascular system

Sticky tube feet capture food particles

Transfer food to mouth an digestive system
https://www.youtube.com/watch?v=H
PhAGyDceLo
3) Deposit Feeders

Feed on detritus – remains of decomposing plants
and animals on seafloor

Sift through sediment for food particles

Ex: Sea Cucumber
3) Deposit Feeders

Uses modified feet around its mouth to scoop sand in

Important to marine ecosystem to recycle nutrients
3) Deposit Feeders

Unique strategy for evading predators

When threatened, permanently eject all internal
organs through mouth or anus

This is called evisceration

Distracts predator so sea cucumber can escape

Eventually organs grow back and its good as new
https://www.youtube.com/watch?v=a
CxKFc3XtJs
4) Herbivory

Eat plants and algae (including
seaweed, some of which are protists)
 Ex:
Sea Urchin
Sea Urchins

Coordinate tube feet and spines to move
slowly along seafloor and rocks

Specialized organ called Aristotle’s Lantern
– resembles ancient Greek lantern
 Urchin
pushes 5 teeth through its mouth
 Scrapes
pieces of kelp or algae
Aristotle’s Lantern
Urchins are major part of Sea
Otter’s diet. Keeps the population
in check
5) Predation

Many invertebrates feed on
other animals

Predators that subsist almost
solely on other animals are
carnivores
- Ex: Sandworm from
Phylum Annelida
- classic segmentation,
crosswire rings
5) Predation

Polychaetes that
have fleshy
extensions called
parapodia
 bristles
used for
swimming or
crawling

powerful hook-like
jaws to grab their
prey