Basic information

• Arthropods- largest and the most diverse phylum in the animal kingdom
• They are generally bilateral with visible segmentation forming into fusions called tagmas – namely, the head, thorax and abdomen
• Possess a cuticle and/or chitinous exoskeleton composed of overlapping plates, and a procuticle endoskeleton with appendages being externally jointed.
• Muscle bundles are of the striated type and are also attached to the procuticle.
• Molting or ecdysis is the mechanism by which arthropods are able to discard their undersized “shells” and replaced with a larger one
• The arthropods are schizocoelomate (the coelom is involved with the circulatory system).
• Blood flows in the sinuses of the coelom to the heart and out via the ostia.
• Amoebocytes with hemocyanin (rarely hemoglobin) can be found in the blood.
• The nervous system exhibits cephalization with a large brain and well-developed senses such as eyes and antennae.
• Respiration is accomplished either by tracheal systems, book gills or book lungs.
• The digestive system is complete with variable mouth apparatus.
• Excretion is accomplished through the release of uric acid or ammonia via the coxal glands or green glands to the malphigian 4tubules leading to the gut.
• Reproduction is basically through the fusion of gametes produced by dioecious organisms.
• Fertilization is commonly external for aquatic arthropods and internal among terrestrial ones.
• Some male members are equipped with a piercing apparatus used to deposit sperm in the coelom because some female arthropods have no organ for reception.
• Subphylum Trilobitomorpha


  trilobites, it became extinct during the Paleozoic era

  
• Trilobitomorpha- characterized by a generally flattened oval body that can be divided into the cephalon, thorax and pygidium
• Trilobitomorpha- three visible lobes along the longitudinal axis of the organism.
• Trilobitomorpha- Fossil study of the organism indicate a diversity in form adapted for burrowing, epibenthic, crawling, planktonic or swimming environ have been found.
• Ventral view of Trilobite

  
• Subphylum Chelicerata


  modification of the first pair of appendages into the chelicerae and the 2nd pair into the pedipalps.
• Chelicerata- Fusion of body segments into the cephalothorax or ophistosoma is a typical characteristic. They have no antennae with 4 pairs of walking appendages.
• Classes under Chelicerate- MAC

  Merostomata, Arachnida, Crustacea
• Class Merostomata- aquatic sand burrowing horseshoe crabs with a body divided into the cephalothorax and abdomen
• Class Merostomata- The dorsal side would show the prosoma as covered by a carapace, two lateral eyes, and a caudal tail or telson.
• Class Merostomata- Ventrally the mouth apparatus labrum would contain the chelicerae and attached to the cephalothorax are 4 pairs of appendages. The abdomen would have two genital pores and six gill pairs.
• Dorsal view of Horseshoe crab

  A) Telson

  B) Opisthosoma

  C) Prosoma

  D) Hinge

  E) Eyes

  F) Compound Eyes

  G) Flange

  
• Ventral view

  A) Pedipalp

  B) Mouth

  C) Flange

  D) Anus

  E) Telson

  F) Book gills

  
• Class Arachnida. Composed of the spiders, scorpions, ticks, mites and allies, and are largely terrestrial.
• Arachnida- Their body is divided into the cephalothorax and the abdomen. The "head” portion has sensory hairs and eyes (compound and simple).
• Arachnida- Attached to the cephalothorax are 4 pairs of appendages; the two anterior pairs adapted for feeding and the rest for movement.
• Arachnida- The abdomen has minute pore openings called spiracles that eventually lead to the several internal lamellae called book lungs.
• Anatomy of a scorpion

  A) Pedipalp

  B) Femur

  C) patella

  D) Chelicerae

  E) Lateral eyes

  F) Median eyes

  G) Prosoma

  H) Mesosoma

  I) Metasoma

  J) Telson

  K) Aculeus

  L) Chela

  M) Leg
• Class Crustacea. Crustaceans can be found in marine, freshwater or terrestrial environ, ranked from the most common to the least. Their body can be divided into two regions: the head and trunk (thorax and abdomen with biramous legs).
• Crustacea- The head is covered by a carapace with 10 pairs of appendages, namely the antennules, antennae, mandibles and the rest are maxillae.
• Crustacea- The thorax is also covered with a carapace, is externally segmented with several peraeopods (walking legs). The abdomen has pleiopods (swimmerets) and terminates with a telson.
• Class crustacea has 4 subclasses- BC TM (BUSY TOO MUCH)

  Branchiopoda, Copepoda, Thecostraca, Malacostraca
• Branchiopoda


  Found as planktons in aquatic environs, it is characterized by a flattened leaf-like trunk and appendage. The coxa has a flattened epipodite that serve as a gill and terminal processes called cercopods.
• Subclass Copepoda


  zooplankton in both freshwater and marine ecosystems. It is characterized by the presence of a median nauplius eye. The body is divided into an anterior metstome and a posterioir urosome.
• Copepoda

  There are three types of copepods – namely, cycolopoid, calanoid or harpacticoid. The females are commonly parthenogenetic.