Protostomes, Platyhelminthes & Nematoda

Introduction to Protostomes

• Brachiopods are coelomates, possessing a cavity completely lined with mesoderm.
• A lophophore's primary function is suspension feeding, using tentacles in bryozoans and cilia/mucus in brachiopods; it also aids in respiration for brachiopods.

Platyhelminthes

• Flame cells in Platyhelminthes, also known as protonephridia, function in excretion and osmoregulation to maintain fluid balance.
• Platyhelminthes possessing both male and female sex organs are termed monoecious or hermaphroditic.
• Cestoda and Trematoda within Platyhelminthes utilize hooks and suckers.

Nematoda

• Nematodes are not segmented.
• Nematodes possess a complete digestive tract.
• Nematodes are mostly dioecious.
• Nematodes have simple excretory and digestive systems, but lack circulatory or respiratory systems.
• The order of reproductive structures from smallest to largest in male Ascaris is testes, vas deferens, seminal vesicles.
• Nematodes possess only longitudinal muscles.
• Modern nematodes exhibit two distinct evolutionary milestones: the formation of a gut cavity via pseudocoelomate structure, which subsequently allowed for the inclusion of organs for digestive and reproductive systems.

Molluscs and Annelids

• Molluscs are not segmented.
• Bivalvia (clams, oysters, scallops) use suspension feeding.
• Molluscs possess an exoskeleton.
• Gastropoda contains snails and slugs.
• Cephalopoda contains octopuses and squids.
• Bivalvia contains oysters, clams, and scallops.
• Polyplacophora (Chitons) and Scaphopoda (Tusk shells) are two other clades of molluscs.
• Torsion, the twisting of the visceral mass causing the mantle cavity to be over the head, occurs in Gastropoda.
• Labial palps in Bivalvia secrete mucus onto the gills to aid in feeding.
• Metamerism is segmentation, which allows for specialization of body segments and finer motor control in Annelida.
• Annelids possess a coelomate body cavity completely lined with mesoderm.
• Annelida are predominantly monoecious (hermaphroditic).
• Annelida have both longitudinal and circular muscles.
• Annelida respires through skin, gills, or parapodia.
• Polychaeta (clamworms) use parapodia.
• Hirudinea includes leeches.
• Oligochaeta includes earthworms and is not a clade.
• Two earthworms align in a 69 position, with their clitellum secreting mucus, sperm travels from seminal vesicles to seminal receptacles.
• The clitellum secretes a mucus cocoon which collects sperm/eggs, and detaches with the fertilized eggs, from which baby worms hatch.
• Nephridia are excretory structures in oligochaeta.
• Seminal vesicles are larger than seminal receptacles because they produce gametes.
• Clitellum is the main reproductive structure in earthworms.

Arthropods

• Arthropods possess striated muscles.
• Arthropods have an open circulatory system containing hemolymph.
• Hemocoel is the primary body cavity containing hemolymph.
• Major arthropod clades and their respiratory structures:
  • Merostomata (horseshoe crabs): Book gills
  • Crustacea (crayfish, crabs): Gills
  • Arachnida (spiders): Book lungs
  • Insecta and Myriapoda (Butterfly, Millipedes): Tracheae and spiracles
• Chelicerata lacks antennae and uses modified first appendages (chelicerae) for feeding.
• The second appendage in Chelicerata is called pedipalps.
• The "tail" in Clade Merostomata is the telson, used for attachment and flipping.
• Tracheal spiracles are external openings in the abdomen for gas exchange.
• Spinnerets are used in spinning silk.
• Myriapoda includes Dilpopoda (two pairs of legs per segment) and Chilopoda (one pair of legs per segment).
• Malacostraca and Decapoda are clades within Crustacea containing crayfish, crabs, and lobsters.
• Male crayfish have copulatory swimmerets, while females have a seminal receptacle.
• The modified first appendage in Crustacea is called chelipeds.
• Uropods are the lateral sections of the fins on crayfish.
• Telson is the medial section of the tail fin on crayfish.
• The cardiac stomach contains the gastric mill for grinding food.
• The pyloric stomach is posterior to the cardiac stomach.
• Green glands function in excretion and osmoregulation.
• Gastric ceca, which look like "sausage fingers", aid with chemical digestion.
• Malpighian tubules function in excretion.
• The tympanum receives sound waves and creates vibrations.
• Female grasshoppers possess an ovipositor, while males do not.
• Clade Hemiptera contains true bugs.
• Clade Hymenoptera contains bees and ants.
• Clade Lepidoptera contains butterflies.
• Clade Orthoptera contains grasshoppers and crickets.
• Clade Coleoptera contains beetles.
• Clade Diptera contains flies and mosquitoes.