Tropical Marine Invertebrates CAS BI 569 Phylum ARTHROPODA by John R. Finnerty 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.
Whither the Coelom? 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. A Generalized Arthropod
Exoskeleton composition Arthropods Epicuticle Procuticle Lipoprotein Lipids Chitin (a polysaccharide) + associated proteins 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 subphylum Trilobitomorpha 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.
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 arrangement 19 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