The document provides an overview of invertebrate animal classification, describing key characteristics of major phyla. It discusses porifera, cnidarians, flatworms, nematodes, annelids, molluscs, arthropods, and echinoderms. For each group, it describes anatomy, examples of types of animals in the group, and sometimes life cycles or additional details.

1. Pablo León Cruz www.biogeosfera.es
KINGDOM ANIMALIA: INVERTEBRATES

2. The classification of animals

3. The classification of animals
Invertebrate Animals
Invertebrate animals have no spine, nor do they have an internal
skeleton, but some do have an external skeleton (exoskeleton).
 Porifera
 Cnidarians
 Worm-Shaped Animals
 Flatworms (Platyhelminthes)
 Nematodes
 Annelids
 Molluscs
 Arthropods
 Echinoderms

4. Porifera
Porifera, also called sponges, are very simple animals that
inhabit aquatic environments.
Characteristics of the Porifera
 Irregular body shaped like a sack.
 Lack any form of symmetry.
 Internal skeleton made of spicules.
 Almost all live in marine environments.
 Sessile organisms, that is, they do not move.
 Feed by filtration.
 They lack organs and biological systems.
 Reproduce asexually and sexually.

5. Porifera
The spicules are calcareous or silica skeletal units, which are part of the skeleton
of porifera and soft corals.

6. Porifera
Anatomy of porifera

7. Porifera

8. Cnidarians
Cnidarians are very simple marine animals that have stinging
cells. Among them are jellyfish and corals.
Characteristics of cnidarians
 They have a soft, sack-shaped body.
 They have tentacles with which they attack prey.
 They have radial symmetry.
 They have a gastrovascular cavity used for the digestion of
food and for communication with the outside through an
opening that functions as a mouth and an anus.
 Lack a circulatory system, breathing apparatus or excretory
system.
 Possess a very simple nervous system.
 Reproduce asexually and sexually.
 They have two forms of organization: polyp and jellyfish.

9. Cnidarians
Body organization of cnidarians
Polyp phase Medusa phase
They are sac-shaped, with tentacles
and mouth/anus at the top of their
body (looking up). They are sessile, so
they live fixed at the bottom of the sea.
They are shaped like an umbrella, with
the tentacles and the mouth/anus at
the bottom of its body (looking down).
They are not sessile, so they can move
actively.

10. Cnidarians
Anatomy of a cnidarian

11. Cnidarians
The life cycle of a jellyfish

12. Cnidarians
The life cycle of a jellyfish

13. Cnidarians

14. Cnidarians

15. Worm-shaped animals
Flatworms, nematodes and annelids are three groups of worm-
shaped animals that have several characteristics in common.
Characteristics of the worm-shaped animals
 Their body is soft and elongated.
 They have bilateral symmetry.
 They lack legs and move by crawling.
 Divided into the flatworms, nematodes (roundworms) and
annelids (segmented worms).

16. Worm-shaped animals
Flatworms Nematodes Annelids
They are flattened-bodied
animals, which is why they
are also called flatworms.
They can be parasites like
tapeworms, which live in the
intestines of some animals, or
be free-living, like planarians.
They are slim, cylindrical-
bodied animals, with pointed
ends. They are free-living
animals, although some are
parasites, such as trichina or
roundworms.
Son animales de cuerpo
cilíndrico que está dividido
en pequeños anillos. Pueden
ser parásitos o de vida libre y
se clasifican en sanguijuelas,
lombrices de tierra y gusanos
marinos.

17. Worm-shaped animals
Anatomy of a flatworm
Planarian Tapeworm

18. Worm-shaped animals

19. Worm-shaped animals
Anatomy of a nematode

20. Worm-shaped animals

21. Worm-shaped animals
Anatomy of an annelid
Earthworm
Leech

22. Worm-shaped animals

23. Molluscs
Molluscs form the largest group of invertebrates behind
arthropods, including species such as octopuses, slugs, squid,
mussels and clams.
Characteristics of molluscs
 Their body is soft and not segmented.
 They have bilateral symmetry.
 Body divided into three regions: head, visceral mass and foot.
 Almost all have a shell that protects the visceral mass.
 The foot is a muscle organ with a different function in each
group.
 They have an organ called a radula, made up of tiny teeth.
 They are aquatic or terrestrial animals that live in humid places.
 They are classified into gastropods, bivalves and cephalopods.

24. Molluscs
Gastropods
 Head: Highly developed with two pairs of tentacles, one
housing the eyes and the other used for touch.
 Visceral Mass: Covered by a spirally coiled protective shell,
except in slugs.
 Foot: Large, housing the stomach and used for movement.
Mouth
Mantle cavity
Anus
Gills
Heart
Visceral mass
Shell
Mantle

25. Molluscs
Examples of gastropods: snails, slugs, sea snails…

26. Molluscs
Gastropod Shells

27. Molluscs
Bivalves
 Head: Underdeveloped.
 Visceral Mass: Covered by a protective shell formed by two
pieces or articulated valves that join.
 Foot: Small and axe-shaped and is used to dig or bury itself in
the sand or move.
Shell
Mantle Visceral mass Heart
Anus
Mantle cavity
Gills
Mouth

28. Molluscs
Examples of bivalves: mussels, oysters, cockles, scallops…

29. Molluscs
Bivalve shells

30. Molluscs
Cephalopods
 Head: Very developed and having a large pair of eyes with
excellent vision.
 Visceral Mass: Hydrodynamic form and in most species,
there is an internal shell.
 Foot: Found as tentacles with suction cups that the animal
uses to catch prey.
Internal shell
Mantle
Heart
Gills
Mantle cavityAnus
Siphon
Mouth
Tentacles

31. Molluscs
Examples of cephalopods: squid, cuttlefish, octopus, nautilus…

32. Molluscs
Internal shell of a cephalopod

33. Arthropods
Arthropods form the largest group of living beings of all, with
more than 1,200,000 species discovered, representing at least
80% of all animal species.
Characteristics of arthropods
 Bilateral symmetry.
 They are metameric: body is divided into segments.
 Three parts: head, thorax and abdomen.
 They have articulated appendages: legs, wings, antennae…
 They have a hard and resistant chitinous exoskeleton.
 As they grow, they molt out of their old exoskeleton.
 Depending on their habitat they can be terrestrial or aquatic.
 Can be carnivores, herbivores or parasites.
 Divided into myriapods, arachnids, crustaceans and insects.

34. Arthropods
Insects
 Beetles, cockroaches, grasshoppers, bees, dragonflies…
 They live in all kinds of environments except the open sea.
 They are carnivores or herbivores.
 Have 6 legs.
 Have a body divided into:
 Head: With a pair of antennae, a mouth adapted to their type
of feeding, two compound eyes and several simple eyes.
 Thorax: It has legs and sometimes one or two pairs of wings.
 Abdomen: Segmented and has no appendages.

35. Arthropods
Insect anatomy

36. Arthropods

37. Arthropods
Arachnids
 Spiders, Scorpions, ticks, mites and harvestmen.
 Live in warm, dry environments.
 Carnivorous.
 Have 8 legs.
 Have a body divided into:
 Cephalothorax: Formed by the fusion of the head and chest,
where they have the chelicerae (jaws) which are protected by
the pedipalps (second pair of appendages that have a
defensive function).
 Abdomen: Commonly in the shape of a balloon.

38. Arthropods
Anatomy of an arachnid

39. Arthropods

40. Arthropods
Crustaceans
 Crabs, lobsters, prawns, barnacles and isopods.
 They live in aquatic environments, but some are terrestrial.
 Some are carnivorous and other filter-feeders.
 They have 10 legs, some of which are claws.
 They have a body divided into:
 Cephalothorax: Formed by the fusion of the head and chest
and protected by a carapace. On the head there is a pair of
antennae, a pair of eyes and chewing jaws.
 Abdomen: Divided into segments for easy swimming. The last
segment is called the telson and has a pair of swimming fins.

41. Arthropods
Anatomy of a crustacean

42. Arthropods

43. Arthropods
Myriapoda
 Centipedes and millipedes.
 Live in damp places such as leaf litter, between logs or under
stones.
 Can be carnivores or herbivores.
 They have a lot of legs.
 They have a body divided into:
 Head: With two antennae, simple eyes and a mouth.
 Trunk: Formed by the fusion of the chest and abdomen and is
formed by a variable number of individual segments.
 Depending on the number of legs per segment, they can be:
 Diplopods: A flat body and a pair of legs.
 Chilopods: A cylindrical body and two pairs of legs.

44. Arthropods
Anatomy of a myriapod

45. Arthropods

46. Echinoderms
Echinoderms are marine animals that include starfish, sea
urchins, sea cucumbers, brittle stars and sea lilies.
Characteristics of the echinoderms
 They have radial symmetry in the adult state.
 They don’t have a segmented body.
 The head is no different than the rest of the body.
 They have an internal skeleton made of calcium carbonate
plates called ossicles.
 Contain a system of ducts and vesicles that fill with water
to communicate and end in the ambulacral (water-vascular
system) feet.
 Ambulacral feet are used to move and attach to the
substrate.

47. Echinoderms
Asteroidea
They have a flattened body and a star shape. They have five or
more limbs that they use to move around and can regenerate
fragments of their body. Commonly known as starfish or sea
stars.

48. Echinoderms
Echinoid
They have a globe-shaped body and lack limbs. Their shell is
coated with spines that have a defensive function. They are
commonly known as sea urchins.

49. Echinoderms
Crinoids
They have the body formed by a stem that ends up in the chalice,
a branched structure containing the organs of the animal. They
live fixed to the substrate and look like plants. Commonly called
the sea lilies.

50. Echinoderms
Ophiuroidea
They have the body formed by a flattened disc from which five
very thin arms come out and can also regenerate fragments of
their body. Commonly known as brittle stars.

51. Echinoderms
Holothuroidea
They have an elongated cylinder-shaped body and lack limbs. At
one end they have a mouth opening surrounded by tentacles.
Commonly known as the sea cucumbers. In some countries they
are eaten as a meal!

52. Echinoderms
Anatomy of an echinoderm