Subphylum Chelicerata
Class Merostomata
Class Pycnogonida
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Subphylum Chelicerata
Subphylum Chelicerata
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Defining characteristics
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Absence of antennae
Contains three classes, most of the animals
are terrestrial and freshwater
Marine species are horseshoe crabs, sea
spiders, and mites
Subphylum Chelicerata
Chelicerate Segmentation
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Cephalothorax –usually
has 6 pairs of
appendages
– First pair – chelicerae
– Second pair –
pedipalps
– Both function as
mouthparts
– The rest are walking
legs
Subphylum Chelicerata
Taxonomic Summary
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Phylum Arthropoda
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Subphylum Chelicerata
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Class Merostomata
Class Pycnogonida
Subphylum Chelicerata
Class Merostomata
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Defining characteristics
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–
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Appendages on the abdomen are flattened and
modified for gas exchange as “book gills”
Terminal portion of body drawn out into an
elongated spike
Only 4 living species; the horseshoe crabs
Subphylum Chelicerata
Horseshoe Crab Habits
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The cephalothorax
and abdomen are
covered by a hard
non-jointed
carapace
Subphylum Chelicerata
Merostomata Appendages
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Possess an anterior chelicerae and 5 pairs of walking
legs
In males the first pair of walking appendages are
modified for grasping the female during reproduction
All the legs (except the last pair) bear pinchers for
manipulating food
Walking legs bear gnathobases on basal part of legs,
which aid in food manipulation
Subphylum Chelicerata
Respiration
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The abdomen
bears the book
gills and is
endowed with
blood
The blood or
components of
it are used in
pharmaceutical
research
Subphylum Chelicerata
Reproduction
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Subphylum Chelicerata
Class Pycnogonida
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Defining characteristics
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Body is not divided into distinct regions
Unique proboscis at the 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,
bryozoan colonies, and sponges
Subphylum Chelicerata
Sea Spiders
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Have a long proboscis for
feeding and a digestive tract
with gonads extending into
the walking legs
Difficult to discern the
cephalothorax, and abdomen
Anterior appendages may
bear cheliceras that grasp
pieces food
Subphylum Chelicerata
Sea Spiders
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Ovigers –
structures used by
males to carry eggs
on the body
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When eggs are
mature they are
deposited in a
hydroid colony
Subphylum Chelicerata