Dichotomous Key for Animals
Zoological Dichotomous Key
1. Acellular animal.....................................................Protozoa
1. Acellular animal................................................................Protozoa
1. Cellular animal...................................................................2
1. Cellular animal................................................................................2
2. Has no notochord..............................................................3
2. Without notochord.......................................................................3
2. Has notochord...................................................................5
2. With notochord.............................................................................4
3. Body segmented and differentiated into head and trunk
3. Bilaterally symmetrical body dorso-ventrally flattened
bearing parapodia, with well-developed coelom, complete
and unsegmented, with incomplete or absent digestive
digestive
system, photonephridial excretory system, and ladder-like
tract,
nephridial
excretory
system, closed
nervous
nervous system................Phylum Platyhelminthes (Tapeworm)
system.....................................................Phylum Annelida...4
4. Bilaterally symmetrical body segmented either only in
4. Setae present................Classes Oligochaeta or Polychatea
larval stage or until adult stage with an endoskeleton of
4. Setae absent..................................Class Hirudinea (Leech)
notochord, tubular dorsal nerve cord and pharyngeal pouches
5. Body segmented and well-differentiated (head, thorax,
or slits................................................................Phylum Chordata...5
abdomen),
chitinous
5. Sac-like with siphons.........................Subphylum Urochordata
exoskeleton, with complete digestive tract, hemocoele body
5. Body differentiated into head, trunk and tail.......................6
cavity, ganglionic nervous system, varied excretory and
6. Without vertebrae.....................Subphylum Cephalochordata
respiratory
6. With vertebrae................................Subphylum Vertebrata...7
circulatory
system,
covered
organs,
and
with
and
ganglionic
calcareous
jointed
or
or
stumped
appendages.........................................Phylum Arthropoda...6
6. With jaws, antennae....................Subphylum Mandibulata
6. Without jaws, antenna..............Subphylum Chelicerata...7
7. With compound eyes............................Class Merostomata
7. Without compound eyes...................................................8
8. Abdomen vestigial/degenerate................Class Pantopoda
8. Abdomen present........................Class Arachnida (spider)
7. Appendages in the form of fins............................Class Pisces
7. Appendages in the form of limbs..............................................8
8. Body naked............................................................Class Amphibia
8. Body covered with hair.....................................Class Mammalia
8. Body covered with feathers.....................................Class Aves
8. Body covered with scales....................Class Reptilia (turtle)
Animal Dichotomous Key
Dichotomous Key for Zoology
1. Acellular animal.....................................................Protozoa
1. Acellular animal........................................................Protozoa
1. Cellular animal...................................................................2
1. Cellular animal......................................................................2
2. Lacks true tissues.......................................Phylum Porifera
2. Without true tissues....................................Phylum Porifera
2. Has true tissues...................................Clade Eumetazoa...3
2. With true tissues...................................Clade Eumetazoa...3
3. Radially symmetrical.........Phyla Cnidaria and Ctenophora
3. Radially symmetrical..Phyla Cnidaria and Ctenophora
4. Bilaterally symmetrical...........................Clade Bilateria...5
4. Bilaterally symmetrical...........................Clade Bilateria...5
5. Development begins with spiral, determinate cleavage,
5. Devt begins with radial, indeterminate cleavage, with
with coelom forming from splits in the mesoderm and the
coelom forming from outpocketings of the mesoderm and the
mouth forming from the blastophore..........Clade Protostomia
anus
5. Development begins with radial, indeterminate cleavage,
.....................................................................Clade Deuterostomia
with coelom forming from outpocketings of the mesoderm
5. Devt begins with spiral, determinate cleavage, with coelom
and
the
anus
forming
from
the
blastophore
...........................................................Clade Deuterostomia...6
6. Has no notochord............................Phylum Echinodermata
6. Has notochord.....................................Phylum Chordata...7
5. Sac-like with siphons....................Subphylum Urochordata
5. Well-differentiated body (head, trunk, tail).......................6
6. Has no vertebrae....................Subphylum Cephalochordata
6. Has vertebrae..............................Subphylum Vertebrata...7
7. Fin appendages........................................Class Pisces (eel)
7. Limb appendages...............................................................8
8. Covered body.........Classes Amphibia, Aves or Mammalia
8. Naked body....................................Class Amphibia (frog)
forming
from
the
blastophore
forming from splits in the mesoderm and the mouth forming
from the blastophore..................................Clade Protostomia...6
6. Bilaterally symmetrical body dorso-ventrally flattened
and unsegmented, with incomplete or absent digestive
system, photonephridial excretory system, and ladder-like
nervous system......Phylum Platyhelminthes (Conical Fluke)
6. Unsegmented body cylindrical and tapering at both ends,
with complete digestive tract, ganglionic nervous system,
lateral excretory canals, tubular and thread-like gonads
(paired in females), and integument consisting of an outer,
elastic cuticle...............................Phylum Nematoda (Ascaris)
