Tropical Marine Invertebrates - Boston...
Transcript of Tropical Marine Invertebrates - Boston...
Phylum ARTHROPODAby John R. Finnerty
CAS BI 569
TropicalMarine
Invertebrates
Phylum Arthropoda
Well over 1 million described extant species
Four critical bodyplan features. Chitinous exoskeleton Segmented body plan Tagmatization Jointed paired appendages
Profound changes in “axial complexity” occur during Arthropod evolution.
The rigidity of the body wall (the sclerotized chitinous exoskeleton) was accompanied by other major changes to the body plan with important biomechanical ramifications.
peristaltic locomotion using the coelom as a hydrostratic skeleton is no longer possible
loss of circular body wall muscles extreme reduction of coelom—remnants found in the
reproductive system and excretory system new large spacious body cavity, the hemocoel.
Whither the Coelom?
A Generalized Arthropod
Exoskeleton composition — Arthropods
Lipids
Chitin (a polysaccharide)+ associated proteins
Epicuticle
Procuticle
Lipoprotein
Functional Specialization of Segments
Functional Redundancy
Functional Specialization
Fusion of Segments (Tagmatization)
“head” “thorax” “abdomen”
Tagmatization
Phylum Tardigrada“water bears”
Onychophora
Phylum Arthropoda subphylum TRILOBITOMORPHA subphylum CHELICERIFORMES
class CHELICERATA subclass ARACHNIDA (ticks, mites, scorpions, spiders, etc.) subclass MEROSTOMATA
order Eurypterida (extinct sea scorpions) order Xiphosura (5 extant species of horseshoe crabs)
class PYCNOGONIDA subphylum CRUSTACEA subphylum HEXAPODA
class INSECTA class ENTOGNATHA (e.g., springtails)
subphylum MYRIAPODA
Originated in the Cambrian and went extinct in the end-Permian extinction, 250 million years ago.
Anterior-posterior furrows divide body into 3 lobes. Dorso-ventrally flattened. The anterior section is covered by a head shield. This head section bears eyes. Each segment posterior to the mouth has a pair of
biramous appendages. The outer ramus bears setae, and is specialized for
swimming, breathing, or feeding. The inner ramus lacks setae, and is specialized for
walking. In the earliest trilobites, all the appendages were
nearly identical. In later forms, some appendages differentiated and even lost one ramus.
subphylum Trilobitomorpha
Trilobite Anatomy
subphylum Cheliceriformes two tagmata
the anterior PROSOMA (cephalothorax) the posterior OPISTHOSOMA (abdomen)s
CHELICERAE— the most anterior appendages on the prosoma are modified into claws (e.g., horseshoe crabs) or fangs (e.g., spiders)
PEDIPALPS — second pair of appendages on prosoma used for prey manipulation
WALKING LEGS — fours pairs follow the pedipalps on the prosoma.
Appendages on the opisthosoma are typically modified for respiration (e.g., the gills of horseshoe crabs of the book lungs of spiders).
subclass Merostomata, order Eurypterida
“sea scorpions”originated in the Cambrian (~510 MYA) perished in the end-Permian extinction
(248 MYA) possible the largest arthropods that
ever lived, up to 2 meters in length.
Limulus Anatomy
subclass Arachnida spiders, scorpions, ticks,
mites, whip scorpions ~73,000 species almost all terrestrial opisthoma appendages
modified into spinnerets in spiders or pectenes in scorpions (a sensory appendage)
respiration by tracheae or “book lungs”
Spider Anatomy
subphylum Crustacea head, thorax, and abdomen head comprises five
segments 2 pair of antennae 1 pair of mandibles 2 pair of maxillae
thoracic appendages maxillipeds (food manip.) pereopods (walking legs)
abdominal appendage pleopods
Malacostrocan Anatomy
subphylum Hexapoda, class Insecta very conserved segmental
arrangement19 segments
five head segments with five head appendages
antenna clypeus mandibles maxillae labrum
3 thoracic segments 11 abdominal segments “for every human alive, there
are an estimated 200 million insects” —Brusca & Brusca