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Questions and Answers
What characteristic is not found in adult and larval arthropods?
What characteristic is not found in adult and larval arthropods?
What is the primary material that forms the cuticle in arthropods?
What is the primary material that forms the cuticle in arthropods?
Which statement correctly describes the process of ecdysis in arthropods?
Which statement correctly describes the process of ecdysis in arthropods?
What type of circulatory system do arthropods possess?
What type of circulatory system do arthropods possess?
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Which feature of arthropod vision is responsible for creating images?
Which feature of arthropod vision is responsible for creating images?
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What is a defining characteristic of the Mandibulata subphylum?
What is a defining characteristic of the Mandibulata subphylum?
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What role do ovigers serve in arachnids?
What role do ovigers serve in arachnids?
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Which statement about the Myriapoda class is correct?
Which statement about the Myriapoda class is correct?
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What is unique about the larval form of Crustacea?
What is unique about the larval form of Crustacea?
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What distinguishes Hexapods as a subgroup of Pancrustacea?
What distinguishes Hexapods as a subgroup of Pancrustacea?
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Which of the following statements is true regarding Chilopoda?
Which of the following statements is true regarding Chilopoda?
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What is a shared trait between Hexapods and Myriapods?
What is a shared trait between Hexapods and Myriapods?
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Which characteristic is NOT associated with Branchiopoda?
Which characteristic is NOT associated with Branchiopoda?
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Which of the following is a defining characteristic of the Subphylum Chelicerata?
Which of the following is a defining characteristic of the Subphylum Chelicerata?
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What is the primary function of the chelicerae in Chelicerata?
What is the primary function of the chelicerae in Chelicerata?
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Which of the following classes does NOT belong to the Subphylum Chelicerata?
Which of the following classes does NOT belong to the Subphylum Chelicerata?
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In which class would you find horseshoe crabs?
In which class would you find horseshoe crabs?
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Which of the following classes is characterized by a body without tagmata?
Which of the following classes is characterized by a body without tagmata?
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What is a notable feature of the merostomata's opisthosoma?
What is a notable feature of the merostomata's opisthosoma?
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Which order within Class Malacostraca includes pillbugs and woodlice?
Which order within Class Malacostraca includes pillbugs and woodlice?
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Which characteristic is NOT associated with the Subphylum Trilobitomorpha?
Which characteristic is NOT associated with the Subphylum Trilobitomorpha?
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Study Notes
Arthropods
- 85% of all metazoans are Arthropods.
- Defining characteristics:
- Segmented, jointed, and sclerotized chitinous exoskeleton with musculature between individual joints of appendages
- Loss of cilia in adults & larvae
- Metameric (segmented) development, new segments arising from a zone at the rear of the animal
- Tagmatization: regions of the body modified from fused segments
- Cuticle made of chitin, secreted over the whole body by epidermal cells, water-impermeable, highly resistant to dehydration, thin and flexible in some regions
- Exoskeleton shedding (ecdysis): process of shedding and regrowing, under hormonal and neural control, increasing animal size
- Striated muscles, contracting faster than smooth muscles due to the rate nerve impulses are delivered to fibers
- Open circulatory system with a heart and ostia
- Vision through ocelli (light-sensitive, non-image forming), and compound eyes (image-forming, ommatidia, wide visual range)
Major Arthropod Groups
-
Subphylum Trilobitomorpha:
- Class Trilobita (trilobites), extinct, 2 anterior furrows dividing the body (2 lateral, 1 central), flattened dorsoventrally, covered by a carapace, biramous appendages, compound eyes with ommatidia
-
Subphylum Chelicerata:
- Lack antennae
- Body divided (prosoma and opisthosoma), no distinct head,
- First pair of appendages are chelicerae (feeding),
- Includes classes: merostomata (horseshoe crabs), arachnida (spiders, mites, ticks, scorpions) and pycnogonida (sea spiders),
- Chelicerae for biting and shredding
- Lack mandibles
-
Class Merostomata (Horseshoe Crabs):
- Flattened appendages on opisthosoma modified into book gills
- Telson with elongated spike
- Prosoma (cephalothorax) covered with a carapace, composed of chelicerae, 5 pairs of walking legs, first pair=pedipalps, last pair=chiliaria,
- Opisthosoma with 6 pairs of appendages & book gills
-
Class Pycnogonida (Sea Spiders):
- Body without tagmata
- Proboscis with an opening
- Varied number of walking legs
- Ovigers for grooming and carrying eggs
- Parasitic larvae
-
Class Arachnida (spiders, mites, ticks, scorpions):
- Prosoma & opisthosoma are the tagmata
- Appendages: chelicerae, pedipalps, maxilla, walking legs
- Book lungs with spiracles and tracheae
- Spinnerets in spiders
Mandibulata vs. Pancrustacea
-
Mandibulata:
- Mandibles on third head segment for chewing/grinding food
- Retinula of compound eyes: 8 cells
- Includes subphyla myriapoda, insecta, and crustacea
-
Pancrustacea:
- Recent molecular data showing close relationship to myriapoda and chelicerates
- Morphological characteristics
New Organization
- Hexapods are a subgroup of Pancrustacea.
- Old Crustacea are paraphyletic
- Many traits in hexapods and myriapods are convergent
- Single pair of antennae
- Tracheal system
- Mandibulates are a group distinguished by mandibles vs. chelicerate mouthparts
Myriapoda
- Includes chilopoda (centipedes) & diplopoda (millipedes)
- Unwaxed cuticle
- Lack compound eyes, have ocelli
- Chilopoda (centipedes): carnivorous, tracheae with open spiracles, nocturnal for water conservation, repugnatorial glands
- Diplopoda (millipedes): detritivores, pairs of segments fuse, 2 pairs of legs per diplosegment, calcium salts to discourage predation
Crustacea
- Defining characteristics:
- Head bearing 5 pairs of appendages (including 2 pairs of antennae),
- Larval form (nauplius) bearing 3 pairs of appendages & medial eye
- Includes classes: malacostraca, branchiopoda, ostracoda, copepoda, pentastomida, cirripeda
Branchiopoda
- Coxa of leg modified to make flattened paddle for gas exchange & locomotion
- Filter feeders
- Some lack a carapace
Cirripeda (Barnacles)
- Highly modified to attach to hard substrate or other organisms,
- Thoracic limbs (cirri) modified as filtering structures
- Lack abdomen, shell (carina, rostrum, scutum, terga), cirri for feeding, lack abdominal segments, and heart, reduced head
- Non-motile
Malacostraca
- Thorax with 8 segments, abdomen with 6–7 segments plus a telson
- Appendages on 6th abdominal segment flattened to form uropods
- Includes orders: decapods, euphausiids, stomatopods, isopods, and amphipods
- Rostrum (beaklike projection on head), compound eyes.
- Antennae, mandibles, maxillae, maxillipeds, walking legs, uropods, and chromatophores
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