Classification of Invertebrates
Phylogenetic classification of invertebrates can be based on a variety of morphological and biological traits. A synopsis of some of the main invertebrate phyla is provided below:
1. Porifera (Sponges):
- Functioning tissues and organs are absent.
- A body with radial symmetry or asymmetry.
- Use specialized cells known as choanocytes to filter feeders.
- Have a porous body with a canalized water circulation system.
2. Cnidaria (Jellyfish, Corals, and Anemones):
- Radial symmetry is present.
- Polyps (sessile) and medusas (free-swimming) are the two basic body shapes.
- Tentacles equipped with nematocysts, which are cnidocytes with stinging features.
- A basic neural net for synchronization.
3. Flatworms, or platyhelminthes:
- A flattened, bilaterally symmetric body.
- Do not have an acoelomate, or bodily cavity.
- Display cephalization by having a recognizable head region.
- While some are free-living, others are parasitic.
4. Nematoda (Roundworms):
- A cylindrical, unsegmented body.
- Two-way symmetry.
- The pseudoelomate external cavity.
- Occurs in a variety of settings, such as water, soil, and parasites.
5. Mollusca:
- Mollusca, which includes snails, clams, and squids, are soft-bodied animals with muscular feet, visceral masses, and mantles.
- They also frequently have hard outer shells.
- For feeding, Radula (rasping tongue) is used.
- Many species have an open circulatory system.
6. Annelida (Segmented Worms):
- Repeated units (segments) in a segmented body.
- Coelomate, or true coelom.
- An advanced nervous system.
- In certain classes, the circulatory system is closed.
7. Arthropoda (Crustaceans, Arachnids, and Insects):
- Segmented body with a chitin-based hard exoskeleton.
- Arthropoda means Jointed limbs.
- Extremely niche body areas (head, thorax, abdomen).
- An open cardiovascular system.
8. Echinodermata (Starfish, Sea Urchins):
- As adults, they frequently have pentaradial symmetry and radial symmetry.
- The circulatory system of water for feeding and mobility.
- The endoskeleton is made up of calcium-rich plates.
- Tube feet for movement and catching prey.
9. Chordata (Cephalochordates, Vertebrates, and Urochordates):
- Notochord at some developmental stage.
- The nerve cord is dorsal hollow.
- Slits in the paranasal gills.
- The post-anal tail, in certain cases.
Every phylum in this taxonomy offers a wide overview, and its constituent classes, orders, and species are diverse in their traits and adaptations.
Characteristics of Phylum Arthropoda
Unique Characteristics of Invertebrates
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