BY WELFREDO L./BSEd-BIO.SCI.3 A.Y.2016-2017/COLLEGE OF TEACHER EDUCATION SDSSU-MAIN

1. Phylum
Arthropoda-
Trilobita
Prepared by Welfredo Yu

2. • "Three Lobes"
• Earliest known group of Arthropods
• Crab like animals, not bugs!
• They are a very diverse Class of animal.
WHAT IS TRILOBITES?

3. • First evolved in the Lower Cambrian
and became extinct by the end of the
Permian.
• They are most common during the
Cambrian, Ordovician and Silurian.
• Therefore they have no modern
equivalents and an understanding of
their soft parts has to be based on
modern day arthropods that show
some similarity i.e. crustaceans.
• They are marine animals.

4. • Some were filter feeders,particle feeding
some were scavangers, others were predators.
They probably ate anything smaller than
themselves, including other trilobites.
• Trilobites had a thick exoskeleton for
protection.
• Some have beautiful spines, some have no
eyes, some have long tails.
• Some Could Enroll:Some trilobites could enroll them selves
into a ball for protection, similar to what little pill bugs do.

5.  Protection
ENROLLED TRILOBITES

6. • Trilobites, a common fossil, were known to
people throughout history.
The first "scientifically" described trilobite comes
from Wan Shizen of China. In 1689 he described
trilobite pygidia (tails) as batstones.
• The first scientific drawing of a trilobite comes
from Rev. Edward Lhwyd. He has a sketch of a
trilobite in the 1698 volume of "The
Philosophical Transactions of the Royal Society".
The trilobite, which we know as Ogygiocarella
debuchii, is called a "flatfish".
DISCOVERY

7. •
TRILOBITE pygidia (tails) as batstones

8. •
Ogygiocarella debuchii, "flatfish".

9. • They are segmented animals and have a
chitinous exoskeleton.
• They have a bilateral symmetry i.e.
either side is symmetrical.
• They have jointed limbs with an
identical pair on the either side of the
body.

12. • The body can be divided into segments:
Laterally:
• A central or axial segment.
• Bounded by two lateral segments.
Transversely into three regions:
• Cephalon - “head” area.
• Thorax - “body” with hinged segments.
• Pygidium - “tail” with fused segments.

14. DORSAL VENTRAL
TOP SIDE OF CEPHALON BOTTOM OF CEPHALON

15. DORSAL VENTRAL

16. • Body Size: 1 mm to 72 cm in size!
The smallest trilobite is
currently Acanthopleurella stipulae at
around 1 mm, that's the size of a
fleck of pepper.
• The largest trilobite is
currently Isotelus rex which has been
found to reach 72 cm. That's over 2
feet!
BODY SIZE

17. • Trilobites tend to be fairly small being 5 - 8 cm long on
average although extremes do occur from 5 mm to 70 cm.
• Because they had a rigid exoskeleton growth caused
problems.
•  How did they grow?
• They malted i.e. they shed their exoskeletons for a larger by
a process called “ecdysis”.

18. •ECDYCIS
• the facial sutures (red) split, opening the cephalon.
• This provides an exit for the molting trilobite (purple) from
its old exoskeleton (orange).

19. • Trilobites Molted:
Like crabs and lobsters, trilobites had to molt when
growing. Just after molting, or shedding their
exoskeleton, they were soft and vunerable. Most
trilbite fossils are actually molted exoskeletons.

21. • This is the head shield, which
consists of a central region
GLABELLA, or axial region.
• The glabella is usually convex
but does vary in size and
shape in different species.
• The FACIAL SUTURE is the
line along which the skeleton
is cracked to allow ecdysis, it
divides the cheeks into 2
areas:
• FIXED CHEEK: That part which
stays attached to the glabella.
• FREE CHEEK: That part which
becomes separated during
ecdysis.
CEPHALON

23. Here are some examples of the three
suture types:
Eodiscina
(proparian)
Phacopina
(proparian)
Calymenina
(gonatoparian)
Ptychopariina
(opisthoparian)
Asaphida
(opisthoparian)

25. Glabella end
ANTERIOR
Pygidium
end
POSTERIOR

26. • Trilobites can be divided into
three from side to side.
• Trilobites can be divided
into three from side to
side.
• It has a central axis
separated from the 2
lateral regions by the
AXIAL FURROW.
• Each segment of the lateral
area has PLEURA.
• The thorax contains
segments, which are
jointed and able to move
independently.

27. • This flexibility allows some trilobites to roll up to give
protection to the softer under part.
• The number of these segments varies e.g. 2 - 40.
• However, in any Genera the number is constant e.g. 13 in
Calymene.
• These are in pairs one on each side of the body.
THORAX

28. PYGIDIUM
• This is a semicircular or triangular shield.
• These have a number of fused segments, which varies
from 2 - 30 but cannot move independently.
• the pygidium (tail piece) can range from extremely small
(much smaller than the cephalon) to larger than the
cephalon. There are four general categories of pygidium
relative size, shown below:
micropygous
pygidium much smaller
than cephalon
subisopygous
pygidium subequal
to cephalon
isopygous
pygidium equal
to cephalon
macropygous
pygidium larger
than cephalon

29. eye ridges: These are consistently present in
primitive trilobites, connecting the front of the
palpebral lobe with the axial furrow (a feature
lost in many post-Cambrian trilobites)
pygidium: The posterior tagma of greater
than one segment is a conspicuous feature
of all trilobites (but not restricted to Trilobita).
Pygidia are typically very small in primitive
forms (e.g., Olenellina)
Together with the organization of the
body into three anterior-posterior
divisions (cephalon, thorax, and
pygidium), and the three longitudinal
lobes (axial lobe and two flanking pleural
lobes), the body features on this page
serve to readily distinguish
trilobites from all other known arthropod
groups.
calcitic compound eyes: While other
compound eyes are found in Cambrian
arthropods, only those of trilobites have corneal
surfaces composed of prismatic calcite lenses
(with the crystallographic axis normal to the
lens surface).circumocular sutures: In
Cambrian holochroal
trilobite eyes, a suture around the edge of the
shared
corneal surface assisted in molting of holaspid
trilobites.
In post-Cambrian trilobites this feature is
secondarily
lost, leaving the corneal surface attached to the
librigena.
rostral plate: a ventral anterior plate separated
from the rest of the cephalic doublure by
sutures
is very well developed in primitive trilobites
(e.g.,
Redlichiida), narrower in other trilobite orders,
and
secondarily lost in some advanced forms (e.g.,
Asaphida and Phacopida)
•
•

30. Compound eye

31. 3 STAGES OF LIFE CYCLE

32. • TRILOBITES GROW AND MOLTED
1.PROTASPIS-planktonic and consisted of
little more than a small cephalon.
2.MERASPIS-the animal is seen to have
both cephalon and pyrigium but without
thorax.
3.HOLASPIS-three body sections but it
still has considerable growing to do before it
becomes an adult.
3 STAGES OF LIFE CYCLE

33. Agnos
tida
Redlic
hiida
Coryn
exochi
da
Odont
opleuri
da
Lichid
a
Phaco
pida
Proeti
da
Asaphi
da
Harpeti
da
Ptycho
pariida
10 orders in the class
AGNOSTIDA - Among the early
trilobites, with a basic, clamshell-like
appearance.
Suborders Agnostina and Eodiscina.
Representative species pictured
here: Ptychagnostus
akanthodes (Agnostina)
REDLICHIIDA- Including the most
primitive trilobites from the lower
Cambrian.
Suborders Olenellina and Redlichiina.
Representative species pictured
here: Redlichia sp. (Redlichiina)

34. 10 orders in the class

35. 10 orders in the class

36. 10 orders in the class

37. 10 orders in the class

38. 10 orders in the class

39. 10 orders in the class

40. 10 orders in the class

41. 10 orders in the class

42. 10 orders in the class