POLYPLACOPHORA

Chitons belong to Class Polyplacophora and they are found in varying sizes. The term used for these marine molluscs was previously Amphineura. These species are also termed as loricates, polyplacophorans.

Polyplacophora is also commonly termed as Sea cradles or Coat of mail shells due to their appearance. The shells of these marine animals are composed of eight different shell plates.

Chitons belong to the kingdom Animalia. The sub-kingdom of this marine species is specified as Mollusca. The shells of this species are composed of separate eight valves or shell plates. These plates help the chiton in protection against enemies.

POLYPLACOPHORA
Source://en.wikipedia.org

Chitons are flexible enough to curl up into a ball when they are dislodged from rocks. A skirt surrounds the shell plate of these marine animals which is known as a girdle.

Nomenclature

TypeDetails
Common NameGumboot Chiton
Scientific NamePolyplacophora
Synonymsmollusk, limpet, snail

Vernacular Names

The common names of sea cradles are mentioned below:

Dutch: Keverslakken

Finnish: Nivelkotilot

German: Käferschnecken

Japanese: 多板綱

Portuguese: chíton, poliplacoforo, quÌton, quíton

Russian: Панцирные

Swedish: Ledsnäckor

History of Polyplacophora

The origin and history of this marine species are specified with the help of fossil records. The details are mentioned below:

Origin

The name Chiton is originated from a Latin word chiton. The meaning of this term is mollusc and this has been derived from a Greek work Khiton. It also means tunic in general terms.

The scientific name of Chiton has also been derived from Greek words such as poly, plako, and phoros. This is because of the fact that Polyplacophora has a total of eight shell plates.

Fossil Record

According to extensive researches, chitons are quite diverse creatures. During the period of Late Cambrian which was after 500 million years ago. They were also found to be important grazers. The fossil records of chitons were previously considered to be of Problematica or other phyla including Annelida or Brachiopoda.

Ecology and Habitat

The habitat as well as other details regarding the locality of this species is explained below:

Geo-Distribution

According to research, it has been found that 23 species of these marine animals exist in the Mexican Tropical Pacific Coast. Chitons are also found at the boulder slopes of West Island in South Australia. Also in these slopes, 16 species of chitons were observed.

Most of the species of these Polyplacophora exist at a depth of 4-5 m where buried boulders are present.

Habitat

Chitons exist all around the globe whether it is cold waters or tropical regions. They reside on surfaces which are hard such as rock crevices or under the rocks. Some species of these marine species can live quite high and get exposed to light and air for a longer interval of time. Most of the chiton species live in the subtidal and intertidal zones. However, some species can also reside as deep as 6000m(20,000 feet).

These small animals are fully marine in their habitat. Certainly, they prefer residing on a solid substrate which consists of rocks and stones. These zones are commonly included in the areas where sweeping if waves occur at a relatively low depth.

These molluscs are very slow moving. They are found in rocky shores and water levels which are shallow. Also, A few among them which are categorized under the family name Lepidopleuridae are found in deep zones.

During the day, they keep themselves concealed under the ricks. They can also roll up their bodies which makes them look like Diplopods. They are herbivorous in nature.

Homing Ability

A number of species of Chitons show homing abilities. This means that they can for food search and come back at exactly the same spot. The method of their return to the same spot is not known so far.

A theory about this behavior is that Polyplacophora remembers the topographic profile of a region. As a result, it enables them to return back to the same spot.

The teeth of these marine species are made up of magnetite. Also, the iron crystal present inside them takes part in magnetoception. This means that they can sense the inclination or polarity of the magnetic field of the earth. It has been observed during research that chitons respond to magnetism.

Poluplacophora
Source://www.alaskasealife.org

Feeding Habits

Among the chitons six species are herbivorous in behavior, three are carnivorous and seven are observed to be omnivorous. These feeding habits are further categorized into general and specific feeding types.

The chiton species falling under the specific category normally eat drift seagrass, crustose coralline algae, petroderma custs, sponge and amphipods. The distribution of algae does not affect the depth in which these marine species reside.

The food supply also does not limit the number of chitons located in a certain geographical region. The algae and seagrass ate by these animals normally exist at a depth of 4-5 m. As a result of which we can locate them at this depth easily in abundant quantities.

Predators

The predators of Chitons include humans as well as seagulls, crabs, lobsters, sea stars and various fish.

Distinctive Features

The distinct features of these marine animals are explained in detail below :

Reproduction

Chitons are dioecious in nature. It means that Polyplacophora can be both male and female. The sperm is released by the male chiton into the water. The females take it and then the egg is fertilized. These eggs are then shed into the water as single as well as gelatinous strings. Then the egg develops itself into a trochophore larva. After that metamorphose occurs and an adult chiton is formed.

Morphology

The morphology of chitons is summarized below :

Shell

The shape of a chiton is oval and the body is dorso-ventrally flattened. In contrast, the dorsal side of these marine species appears convex. However, the ventral side is flat. The middle section of the dorsal side is comprised of overlapping calcareous shells. These shells are arranged in an anteroposterior pattern. The shells are also termed as plates or valves.

This arrangement of shells allows the animal to roll into a ball when danger is around. They take the form of a ball when they dislodge from a rock or any other surface. The colors of the valves on shell can vary in different species. The pattern can also differ and it can be smooth or sculptured as well.

The shape of the anterior plate is crescent-like. It is termed as cephalic plate and is also referred to as the head plate. The plate at the most posterior is known as the anal plate as well as the tail plate. Chitons do not have a tail.

The layers present inside the shell is termed as articulamentum. Also, this layer can be produced in the form of notched plates. Some of the plates could be attached to the anterior border as well.

The valve’s sculpture is considered as a taxonomic characteristic in addition to spinulation or granulation of the marine species girdle.

When the chiton dies, the girdle is no longer present. As a result,t the shells are torn apart. The plates sometimes wash up on beaches in a beach drift. Due to the shape of these shells, they are also termed as butterfly shells.

Girdle Ornament

The girdle of these animals might be ornamented with a layer of scales or spicules. These layers are mineralized by aragonite. However, The material present at the spinules in shells and teeth is different from this one.

The minerals deposited in the girdle resemble the crystals formed inorganically. The proportion of protein matrix is higher in these as compared to mollusc shells.

The likely functions of the girdles have been found out to be defense as well as camouflage. The cells secreting the spicules are surrounded by engrailed expressing cells. As a result, larger spines are secreted in some of the taxa. The organic pellicule is certainly found in the Hanleya chitons.

Life Span

The lifespan of Gumboot chitons is up to 20 years approximately.

Largest Species

The largest species of chitons are up to 33 cm long and it is specified ad the brick-red gumboot chiton. Also, This type is commonly found in the Pacific Northwest.

Behavior and Sensory Organs

The muscular foot of a chiton helps it to crawl slowly. The adhesion power of these species is quite high and they can cling to rocks just like a limpet.

The mouth is linked to a radula(tongue-like structure) and another subradular organ. Chitons do not have a head. This factor makes them fit to belong to subgroup molluscs.

The chiton does not have tentacles or brain but it can still adapt to surroundings. When a Polyplacophora is touched it responds rapidly. In response, it clamps down using powerful foot and muscles to a rock with high tenacity.

A chiton can also choose when it needs to cling tightly and does not waste energy on clinging tight all the time. However, They often move from one point to another in search of food or shelter.

The shell in which chitons live is different from other molluscs and they have small shell organs known as esthetes.

They also have photosensory organs larger in size. As a result, when a predator creates a shadow over them they clamp tightly and let loose when the shadow is not there.

Taxonomy

Fun Facts about Polyplacophora

A few interesting facts about these marine species are mentioned below :

References

  1. www.bioone.org
  2. www.biologydiscussion.com
  3. biology.fullerton.edu
  4. www.wikipedia.org

Azka Hassan

A software engineering graduate from UET Taxila, I started my carrier as an SQA engineer in the year 2013 and have worked as a Quality Assurance Engineer and Content Creator at various organizations. Currently working as a Content Manager at Tapedaily. Writing research-based content related to Plants, Animals, and various kingdoms are my key interest.

1 comment

  • Thank you so much for this very interesting contribution enlightning my restraint knowledge about this tiny
    marine animal.

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