Nematodes and Aschelminthes Overview

Nematodes

• Roundworms, threadworms
• Unsegmented, triploblastic, pseudocoelomic
• Body wall with cuticle and epidermis
• Mostly parasitic, some free-living
• Cylindrical, elongated, tapering at both ends
• Bilaterally symmetrical
• Organ system level of organization
• Body cavity not lined by mesoderm
• Complete digestive system, mouth and anus
• Respiration through body surface
• Excretory system with intracellular canals or lateral ducts
• Nervous system of circum-pharyngeal nerve ring and longitudinal nerve cords
• Sense organs like papillae, amphids, and phasmids
• Separate sexes, sexual dimorphism
• Internal fertilization, direct or indirect development
• Larval forms: rhabditiform, filariform, and microfilaria
• Various lateral lines and pores on body surface

Aschelminthes

• Superphylum encompassing various phyla (Rotifera, Gastrotricha, Kinorhynca, Nematomorph, Nematoda)
• Nematoda is a large group

General Characteristics

• Mostly parasitic
• Cylindrical and elongated
• Triploblastic
• Bilaterally symmetrical
• Organ system level
• Body unsegmented
• Body cavity filled with muscle tissue
• Pseudocoelomate

Phylum Echinodermata

• Mostly marine animals
• Radial symmetry in adults
• Example: Starfish, Sea urchins, Sea cucumbers, Brittle stars, Sea lilies
• Multicellular organisms with well-developed organ systems, aquatic
• Water vascular system for exchange of gases, nutrients, and wastes
• Star-like appearance, sometimes spherical or elongated
• Spiny-skinned, predominantly marine
• Organ system level of organization

Phylum Chordata

• Animals with a notochord
• Bilateral symmetry, triploblastic
• Segmented body design
• Well-developed organ systems
• Example: Tunicates (sea squirts), lancelets, vertebrates

Classification of Subphylum Vertebrata

• Vertebrates with cranium encasing the brain
• Notochord replaced by vertebral column in adults
• Multi-layered epidermis
• Three types of muscles (striped, unstriped, cardiac)
• Well-developed coelom, complete digestive system, respiratory and excretory systems

Arthropoda

• Jointed appendages, segmented bodies
• Mostly terrestrial, some aquatic
• Exoskeleton made of chitin
• Three body regions: head, thorax, and abdomen
• Respiratory systems: tracheae, gills, book lungs
• Excretion by Malpighian tubules or coxal glands
• Includes insects, crustaceans, arachnids, and myriapods

Mollusca

• Soft body, often with a shell
• Bilateral symmetry
• Organ system level of organization
• Examples: Clams, snails, oysters, octopus
• Mantle: glandular skin surrounding the body organs
• Radula: tongue-like organ with rows of teeth
• Various body shapes (e.g., conical, flattened)
• Mostly marine and freshwater, some terrestrial

Annelida

• Segmented body, bilateral symmetry, exhibit organ system level of organization
• Body divided into segments containing repeating body parts and organs
• Hermaphroditic (having both male and female reproductive organs in one organism)
• Exhibit organ system characteristics, examples: earthworms, leeches
• Complete digestive system
• Respiration through body surface or gills
• Excretory organs often in pairs, such as nephridia

Other Phyla (Examples)

• Class Hirudinea (Leeches): Mostly freshwater, some terrestrial or parasitic; body segmented with suckers; hermaphroditic; internal fertilization; no larval stage.
• Class Arachnida (Spiders, scorpions): Mostly terrestrial; two body sections (cephalothorax and abdomen); four pairs of legs; respiration via book lungs; excretion by Malpighian tubules.