Everything about Invertebrate totally explained
An
invertebrate is an
animal lacking a
vertebral column. The group includes 97% of all animal
species — all animals except those in the
Chordate subphylum Vertebrata (
fish,
reptiles,
amphibians,
birds and
mammals).
Carolus Linnaeus'
Systema Naturae divided these animals into only two groups, the
Insecta and the now-obsolete
vermes (
worms).
Jean-Baptiste Lamarck, who was appointed to the position of "Curator of Insecta and Vermes" at the
Muséum National d'Histoire Naturelle in 1793, both coined the term "invertebrate" to describe such and divided the original two groups into ten, by splitting off
Arachnida and
Crustacea from the Linnean Insecta, and
Mollusca,
Annelida,
Cirripedia,
Radiata,
Coelenterata and
Infusoria from the Linnean Vermes. They are now classified into over 30
phyla, from simple organisms such as
sea sponges and
flatworms to complex animals such as
arthropods and
molluscs.
Invertebrates form a
paraphyletic group. (For a full list of animals considered to be invertebrates, see
animal.) All the listed phyla are invertebrates along with two of the three
subphyla in Phylum
Chordata:
Urochordata and
Cephalochordata. These two, plus all the other known invertebrates, have only one cluster of
Hox genes, while the vertebrates have duplicated their original cluster more than once.
Within
paleozoology and
paleobiology, invertebrates big and small are often studied within the
fossil discipline called
invertebrate paleontology.
Phyla and common examples
- Annelida — segmented worms (earthworms, leeches, polychaetes)
- Arthropoda — insects, arachnids, crustaceans
- Brachiopoda — lampshells
- Bryozoa — moss animals or sea mats
- Chaetognatha — arrow worms
- Cnidaria — jellyfishes, corals, sea anemones, hydras
- Ctenophora — Comb jellies
- Echinodermata — starfish, sea urchins, sea cucumbers
- Hemichordata — acorn worms, graptolites
- Mollusca — squid, snails, bivalves
- Nematoda — roundworms
- Nematomorpha — horsehair worms or gordian worms
- Onychophora — velvet worms
- Platyhelminthes — flatworms
- Porifera — sponges
- Priapulida — worms
Macroinvertebrates
The term
macroinvertebrates is traditionally used to refer to aquatic invertebrates including
insects (for example larval
Ephemeroptera and
Trichoptera),
crustaceans (for example
amphipods),
molluscs (for example aquatic
snails) and
worms (for example
Platyhelminthes), which inhabit a river channel, pond, lake, wetland or ocean. Historically, their abundance and diversity have been used as an indicator of ecosystem health and of local
biodiversity. They are a key component of the
food chain.
Most indices that are used to determine water quality rank the various forms of
benthic macroinvertebrates with respect to pollution sensitivity. The presence of pollution sensitive macroinvertebrates indicates that the body of water is healthy. Alternatively, the excessive presence of pollution tolerant macroinvertebrates indicates poor water quality. Ideally, a healthy body of water will hold an abundant and diverse macroinvertebrate population.
The macroinvertebrates traditionally seen as being pollution sensitive include:
mayflies (Ephemeroptera),
caddisflies (trichoptera), and
stoneflies (Plecoptera). The macroinvertebrates that have been traditionally considered pollution tolerant include: aquatic worms (Oligocheata), leeches (Hirudinea) and non-biting midges or commonly known as "blood worms" (Chironomidae).
Flow,
food,
habitat and
water quality are the primary determinants of macroinvertebrate abundance and diversity. Food sources include
phytoplankton,
biofilms (for example the layers of bacteria or other micro-organisms that cover submerged surfaces) and terrestrial organic material (for example leaves) that enter the water from the riparian vegetation. Major
predation occurs from other macroinvertebrates and fish. Key habitats for macroinvertebrates are the benthic sediments, aquatic vegetation and woody debris.
Salinity,
temperature,
dissolved oxygen, and
turbidity have a significant impact.
There are many different kinds of arthropods. but they mainly have the structure of a segmented body and jointed legs.
Further Information
Get more info on 'Invertebrate'.
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