Biology: Phylum Porifera (Sponges)

Phylum Porifera (Sponges)

• Basal taxon, meaning they diverged earlier from other animal lineages
• No tissues, just cell layers
• Two types of pores: ostia (smaller openings) and osculum (larger opening)
• No organs, just different types of cells (e.g., choanocytes, amoebocytes, pinacocytes)
• Choanocytes have flagella that trap food particles, which are then engulfed by the cell through phagocytosis
• Amoebocytes (also known as archaeocytes) have pseudopodia, help with digestion and nutrient distribution, and can become other cell types
• Pinacocytes form the outer covering of the sponge
• Endoskeleton made of spicules (sharp, spiny objects) secreted by amoebocytes
• Classification of sponges is based on the material of the endoskeleton (e.g., calcium carbonate, silicon dioxide, protein)
• Three main classes of sponges: Calcarea (calcareous sponges), Demospongia (includes bath sponges), and Hexactinellida (glass sponges)

Phylum Cnidaria (Simple Animals)

• Eu-metazoan, meaning they have true tissues
• Radial symmetry
• Gelatinous body with three main layers: ectodermis (outer), mesoglia (middle), and gastrodermis (inner)
• Gastrovascular cavity is used for digestion and circulation
• Incomplete or closed digestive system (one opening for mouth and anus)
• Stinging cells called cnidoblasts contain nematocysts, used for capturing prey and defense
• Hydrostatic skeleton helps with movement and support
• Nerve net is a simple type of nerve arrangement, useful for regulating the hydrostatic skeleton
• Two main body types: polyp (cylindrical) and medusa (bell-shaped)
• Three main classes of cnidarians: Hydrozoa, Cubozoa, and Anthozoa
• Other characteristics: diploblastic (two embryonic layers), radial symmetry, and simple nervous system

Other Phyla

• Phylum Ctenophora (Comb Jellies) has bioradial symmetry and eight rows of cilia (comb-like structure)

Phylum Porifera (Sponges)

• Basal taxon, meaning they diverged earlier from other animal lineages
• Characterized by the absence of tissues, with only cell layers present
• Two types of pores: ostia (smaller openings) and osculum (larger opening)
• Lack of organs, with different types of cells performing specific functions
• Choanocytes have flagella that trap food particles, which are then engulfed by the cell through phagocytosis
• Amoebocytes (also known as archaeocytes) have pseudopodia, help with digestion and nutrient distribution, and can become other cell types
• Pinacocytes form the outer covering of the sponge
• Endoskeleton made of spicules (sharp, spiny objects) secreted by amoebocytes
• Classification of sponges is based on the material of the endoskeleton (e.g., calcium carbonate, silicon dioxide, protein)
• Three main classes of sponges: Calcarea (calcareous sponges), Demospongia (includes bath sponges), and Hexactinellida (glass sponges)

Phylum Cnidaria (Simple Animals)

• Eu-metazoan, meaning they have true tissues
• Characterized by radial symmetry
• Gelatinous body with three main layers: ectodermis (outer), mesoglia (middle), and gastrodermis (inner)
• Gastrovascular cavity is used for digestion and circulation
• Incomplete or closed digestive system (one opening for mouth and anus)
• Stinging cells called cnidoblasts contain nematocysts, used for capturing prey and defense
• Hydrostatic skeleton helps with movement and support
• Nerve net is a simple type of nerve arrangement, useful for regulating the hydrostatic skeleton
• Two main body types: polyp (cylindrical) and medusa (bell-shaped)
• Three main classes of cnidarians: Hydrozoa, Cubozoa, and Anthozoa
• Other characteristics: diploblastic (two embryonic layers), radial symmetry, and simple nervous system

Phylum Ctenophora (Comb Jellies)

• Characterized by bioradial symmetry
• Eight rows of cilia (comb-like structure) are present

Bilateria Clade

• Characterized by bilateral symmetry and cephalization
• Concentration of sensory organs in the head region

Phylum Platyhelminthes

• Flattened body shape with dorsoventral compression
• Free-living and parasitic species, including planarians and liver flukes
• Three germ layers: ectoderm, mesoderm, and endoderm
• Hydrostatic skeleton reliant on muscle cells, water pressure, and a tough cuticle
• Negative phototaxis: move away from light

Classes within Phylum Platyhelminthes

• Class Turbellaria: free-living flatworms
• Class Monogenea: monogenean parasites
• Class Trematoda: flukes, including liver flukes
• Class Cestoda: tapeworms

Phylum Rotifera

• Pseudocoelomates with a mesoderm-lined cavity
• Complete digestive system with mouth and anus
• Corona: ciliated, band-like structure surrounding the mouth
• Most species exhibit parthenogenesis (asexual reproduction)

Phylum Brachiopoda

• Feeding structure (lophophore) with cilia
• Shell secretion: calcium carbonate or chitin
• Marine animals

Phylum Mollusca

• Developmental stage: trochophore larvae
• Soft, unsegmented body often protected by a shell
• Mantle: specialized epidermal tissue secreting the shell
• Foot: muscular, often divided into branches (e.g., octopus arms)
• Classes: Polyplacophora (chitons), Gastropoda (snails and slugs), Bivalvia (clams and mussels), Cephalopoda (squid and octopus)

Annelids

• Body divided into segments (serial homologs)
• Some have setae (bristle-like extensions), while others do not
• Examples: earthworms, fireworms, Christmas tree worms (feather-duster worms)
• True coelom and complete digestive system present
• Cephalization: sensory organs concentrated around the head region

Annelid Classes

• Polychaeta: "many bristles" with setae on their lateral sides
• Oligochaeta: "few bristles" with fewer setae, as seen in earthworms

Earthworms

• Familiar animals often used as bait in fishing
• Species in North America are smaller than those found in Australia
• Some Australian earthworms can grow up to 9 feet (2.7 meters) in length

Leeches

• Class of annelids with parasitic and non-parasitic species
• Some leeches attach to hosts and feed on their blood
• Leeches secrete an anesthetic-like substance in their saliva

Clade Ecdysozoa

• Most invertebrates belong to this clade due to their bilateral symmetry.
• Two subgroups within Ecdysozoa are Nematodes and Arthropods.

Nematodes

• They are roundworms with a thread-like body.
• Most nematodes are microscopic and are the largest number of animals on earth.
• They can be found in soil, with thousands of worms per cubic centimeter.
• Nematodes are parasites of many organisms, including plants and humans.
• Examples of nematodes include Ascaris and species that can affect the hearts of animals.

Characteristics of Nematodes

• They have a non-segmented body.
• They have a pseudocoelom, a cavity lined by the endoderm and mesoderm.
• They have a tube-within-a-tube digestive tract.
• They have a complete digestive system and a hydrostatic skeleton.
• They have a specialized body structure with a muscular layer and a pseudo-coelom.

Arthropods

• They have a tough exoskeleton that serves as a place for muscle attachment.
• Their exoskeleton provides protection and support to the animal.
• They have jointed appendages, allowing for flexibility and locomotion.
• Examples of arthropods include crustaceans, arachnids, and insects.

Characteristics of Arthropods

• They have a true coelom, a fluid-filled cavity within the body.
• They have an abundance of sensory organs.
• They use ecdysis, a process of shedding and replacing their exoskeleton, to grow.
• Examples of arthropod subgroups include trilobites, chelicerates, myriapods, hexapods, and crustaceans.

Key Facts

• Both nematodes and arthropods practice ecdysis, a process of shedding and replacing their outer covering.
• Ecdysis allows them to grow and develop.
• Nematodes have a hydrostatic skeleton, while arthropods have an exoskeleton.

Deuterostomes

• Deuterostomes are a group of animals that develop from an embryo where the blastopore becomes the anus, and the mouth forms second.
• Characteristics of deuterostomes include having an internal skeleton, a water-based circulatory system, and radial symmetry.

Phylum Echinodermata

• Echinodermata includes animals with spiny skin, such as sea stars, sea urchins, and sea cucumbers.
• Characteristics of echinoderms include:
  • Having spines used for protection and locomotion
  • Using two feet for locomotion
  • Having a unique circulatory system where water is pumped through vessels to extend and retract the feet
  • Having a coelom, a fluid-filled cavity, where organs develop and are lined with ciliated cells that move nutrients
  • Practicing external fertilization, releasing gametes into the water
  • Having prezygotic barriers such as gamete isolation

Classes of Echinodermata

• Class Asteroidea: sea stars, characterized by five arms
• Class Ophiuroidea: brittle stars, characterized by fragile and easily broken arms
• Class Holothuroidea: sea cucumbers, characterized by their elongated body and use of water for locomotion
• Class Crinoidea: sea lilies and feather stars, characterized by their long, slender arms and use of water for movement

Phylum Chordata

• Chordata includes animals with bilateral symmetry, a true coelom, and a single dorsal nerve cord
• Characteristics of chordates include:
  • Having a notochord, a stiff, flexible rod that provides support and protection for the dorsal nerve cord
  • Having a post-anal tail, at least during development
  • Having pharyngeal slits or pouches during embryonic development

Invertebrate Chordates

• Phylum Tunicata: tunicates, characterized by their translucent appearance, and the presence of a notochord during embryonic development
• Subphylum Cephalochordata: lancelets, characterized by their streamlined body, and the retention of the notochord throughout their adult life

Learn about the characteristics of phylum Porifera, including their cell structure, types of pores, and unique cellular features. Discover how they differ from other animal lineages.