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AATHROPODA
SUBPHYLUM
CHELICERATA
Defining Characteristics
• chelicerates have segmented bodies with
jointed limbs, all covered in a cuticle made of
chitin and proteins
• chelicerate bauplan consists of two tagmata,
the cephalothorax and the abdomen, except
that mites have lost a visible division
between these sections
• Chelicerate are the only appendages that
appear before the mouth
Defining Characteristics
•has the open circulatory system typical of the
arthropods, in which a tube-like heart pumps blood
through the hemocoel, which is the major bod cavity
•Marine chelicerates have gills, while the air-breathing
s
forms generally have
both book lungs and trachea
•Absence of antennae
•Marine species are horseshoe crabs, sea spiders , &
mites
SUBPHYLUM CHELICERATA
Class Merostomata
Class Pycnogonida
Class Arachnida
Class Merostomata
Defining characteristics:
-Appendages on the abdomen are
flatted and modified for gas
exchange as “book gills”.
-Terminal portion of body drawn
out into an elongated site.
•Only four living species: the
horseshoe crabs
•The cephalothorax & abdomen
are covered by a hard non-jointed
carapace.
Class Merostomata
REPRODUCTION
Unusual in arthropods, it has gonochoric and
have true external fertization
 In male gonadal network is formed.
- duct
- testes being attached as small alveoli.
 In female
- ovary forms all the branches.
CLASS PYCNOGONIDA
Class PYCNOGONIDA
Defining characteristics:
- Body is not divided into distinct
regions.
- Unique proboscis at anterior end,
with an
opening at its tip.
- Includes the sea spiders, several of
which
are common in our area.
- Feed on soft bodied invertebrates,
hydroids, bryozoans colonies &
sponges.
Sea Spiders
Have a long proboscis for feeding & a digestive
tract with gonads extending into walking legs.
Difficult to discern the cephalothorax &
abdomen
Anterior appendages may bear cheliceras that
group pieces food.
Ovigers-structures used by makes to carry eggs
on body
When eggs are mature they are deposited in a
hydroid colony
CLASS ARACHNIDA
•They have paired, jointed appendages
(parts that are attached to the main body)
• Present of hardened exoskeleton
( exo means "outer")
• Segmented (divided into parts) body, and
a well-developed head.
• Their body consists of two main parts: a
fused head and thorax, and an abdomen
CLASS ARACHNIDA
CLASS ARACHNIDA
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They have paired, jointed appendages
(parts that are attached to the main body)
Present of hardened exoskeleton
( exo means "outer")
Segmented (divided into parts) body, and
a well-developed head.
Their body consists of two main parts: a
fused head and thorax, and an abdomen
Most arachnids live on land
 They breathe by means of
book lungs (so called because their
thin membranes are arranged like
the pages of a book)
by tracheae (small tubes that
distribute air from the outside
throughout the body)
or both.