Invertebrate Zoology Quiz on Mollusks & Arthropods

Invertebrates

• Invertebrates are animals that lack a cranium and a defined vertebral column or spine.
• These animals make up nearly 97% of the animal kingdom.
• Examples, include sponges, flatworms, jellyfish, nematodes, arthropods, mollusks, and annelids.
• Skeletons can be made of many things, like bones, or exoskeletons or hydrostatic skeletons.

Animal Phylogenetic Tree

• The phylogenetic tree of animals is based on morphological, fossil, and genetic evidence.
• All animals share a common ancestor.
• Animals are a monophyletic clade.
• Metazoa (animals) includes organisms with tissues.
• Eumetazoa (animals with specialized tissues) includes organisms with tissues.

Phylum Porifera (Sponges)

• Sponges are among the simplest animals.
• Sponges are generally considered to be at the base of the animal phylogenetic tree.
• They are aquatic, living mostly in marine environments.
• Approximately 5,000 named species of sponges are known and likely thousands more to be classified.
• Sponges lack true tissues and have an asymmetrical body plan.
• Sponges have choanocytes, which are flagellated feeding cells similar to choanoflagellates.

Phylum Cnidaria (Jellyfish, Corals, Anemones)

• Cnidarians are mostly marine.
• There are over 11,000 species.
• These animals have a diploblastic body plan with two tissue layers.
• They have radial symmetry.
• Cnidarians have cnidocytes which have nematocysts that are used for prey capture.

Phylum Platyhelminthes (Flatworms)

• Most flatworms are acoelomates.
• Flatworms lack a true coelom; the mesoderm forms a solid mass between the outer epidermal surface and the digestive system.
• Flatworms lack a complete gut, having only a single opening that serves as both mouth and anus or they lack a gut entirely.
• There are over 20,000 different flatworm species catalogued.
• Most are free-living in moist environments, but some species are parasitic.

Phylum Mollusca (Snails, Clams, Squids)

• Mollusks are a diverse group with a wide range of morphologies.
• They are predominantly marine but some live in freshwater or moist terrestrial habitats.
• Some species have shells, others do not.
• They have a muscular foot used for movement.
• Most mollusks are dioecious.
• A radula is used by most for scraping food.
• Mollusks are coelomates.

Phylum Annelida (Segmented Worms)

• Annelids are segmented worms with a body plan that has repeated internal and external morphological features.
• They have a closed circulatory system and respiration can be across moist skin.
• Most annelids are coelomates with bilateral symmetry.
• Annelids are found in various aquatic and moist terrestrial habitats.
• There are approximately 22,000 described species of annelids.

Phylum Nematoda (Roundworms)

• Nematodes are tiny, slender worms.
• They are found nearly every ecosystem from marine to terrestrial environments.
• They come in free-living and parasitic forms.
• They exhibit bilateral symmetry and are triploblastic.
• They have a complete digestive system.
• They have a nervous system with head ganglia and tail ganglia.
• Most species are dioecious (separate sexes)
• There are between 40,000 and 100,000 species.

Phylum Arthropoda (Insects, Arachnids, Crustaceans)

• Arthropods have a chitinous exoskeleton that they shed periodically during molting.
• They have segmented bodies with jointed appendages.
• There are approximately 1.134 million described species worldwide.
• Arthropods have a variety of body forms, mouthparts, antennae, legs, and tail parts.
• Arthropods have an open circulatory system, with a central body cavity called a hemocoel.

Subphylum Hexapoda (Insects)

• Insects have a head , thorax and abdomen.
• The insects are the most diverse and numerous group of arthropods.

Subphylum Myriapoda (Millipedes, Centipedes)

• Myriapods are bilaterally symmetrical and have many legs.
• They are primarily terrestrial and have a variety of functional groups.

Subphylum Crustacea (Crabs, Lobsters, Shrimp)

• Crustaceans are aquatic, and have a variety of forms due to different morphologies and appendages
• They have a complex segmented body.

Subphylum Chelicerata (Scorpions, Spiders)

• Chelicerates have a body plan with a head/thorax and an abdomen tagma.
• They do not have antennae.
• They have appendages called chelicerae that have a claw like or fanglike structure.
• These animals are mostly terrestrial.

Phylum Echinodermata (Sea Stars, Sea Cucumbers)

• Echinoderms evolved from bilateral animals, but have a radial symmetry as adults.
• Echinoderms have an endoskeleton made up of small bony plates covered by epidermis.
• There are about 7,000 described living species.
• Many are exclusively marine.
• They have a water vascular system that is used for movement, feeding, gas exchange, and sensory reception.

Phylum Chordata (Vertebrates and Invertebrates)

• Chordates have a dorsal hollow nerve cord, a notochord, pharyngeal gill slits, and a post-anal tail at some stage in their life.
• There are three subphyla: Urochordata, Cephalochordata, and Vertebrata.
• Vertebrates include all animals with a backbone.