The detritus are heterotrophic animals that feed on material organic decomposed, thus obtaining the energy they need to fulfill their vital functions. Debris forms on the ground or at the bottom of bodies of water, as a product of the decomposition of plants and animals.
These organisms feed on elements from carnivorous and herbivorous animals and from primary producers. For this reason they are present in all trophic levels of the ecosystem .
In the food chain, detritivores are at the highest level, since they contribute to the degradation and recycling of organic matter.
With some frequency, the terms detritivores and decomposers are used interchangeably. However, there are some differences between these. One of these is related to the behavior of both groups to obtain their nutrients.
Decomposers, including bacteria and fungi, obtain the food substances dissolved in the substrate by osmotic absorption. Detritivore animals do so by fagotrophy, ingesting small masses of detritus.
Some representative examples of this group of animals include slugs, the fiddler crab, fishes in the Loricariidae family, and earthworms.
These animals are heterotrophs, because they do not produce the food they consume. They have to take it from decomposing organic matter, coming from animals and plants, and transform it into nutrients and energy.
In this way they are recycling the debris, making it a fundamental part of the energy flow in the different ecosystems and trophic chains.
In addition to this, fungi and other microorganisms convert the feces of this group of animals into substances such as inorganic carbon. In this way they are helping to close the cycle of this component, returning it to the earth.
Detritivores can be found in almost all environments, although the vast majority live on land. However, they can be found in aquatic environments, as is the case with some crustaceans and fish.
Its digestive system is varied. In some the oral apparatus sucks the detritus, as in fish, and in others the pieces of the mouth allow them to chew the decomposed mass, which may still have some remains of insects without decomposing.
Also, some have a structure known as a gizzard, which contains sand particles from the soil. In this structure, the decomposed material is crushed, favoring its digestion.
Its nutrition is mainly based on debris, which is an important source of energy. Within this organic mass are numerous bacteria, which add immense nutritional value to the substrate.
Debris can appear in the terrestrial environment as litter or as humus. In the water, this decomposed material is suspended like “snow”, which then falls to the bottom in a layer.
During the first stages of disintegration of the material, the detritivores take the largest particles, helping to break the material into smaller pieces. In this way, the surface area where bacteria act increases, thus accelerating the decomposition process.
During digestion, some lipids, carbohydrates and proteins are also separated into simpler substances. All the water-soluble nutrients, which are produced through leaching, enrich the mineral composition of the soil.
The material that is excreted, as part of the digestive process, is rich in potassium, nitrogenous waste and phosphorous, which make the soil a highly nutritious substrate.
There is a group of fish that feed on detritus. Among them are the species belonging to the Steindachnerina and Cyphocharax genera, and those that make up the Loricariidae family.
Detritivore fish have a small subminal mouth, which allows them to take puffs of the sedimented material, through suction from the soft bottoms. The stomach in these species is small, their intestines are long and they lack teeth.
They have a gizzard with muscularized walls, which allows the debris to be crushed by the grains of sand it contains.
The group of detritivore animals is wide. Within these are beetles, mollusks, some species of snails and slugs.
There are also earthworms and millipedes, which inhabit the soil and decayed wood. There are aquatic animals , which include certain varieties of fish, echinoderms, such as sea cucumbers, and some crustaceans.
Due to this great variety of species, their reproduction has peculiarities of each group. In general, it can be divided into two main types:
It is characterized because an individual can originate, through the process of cell division, one or more individuals with the same external characteristics and the same genetic information.
In this type of reproduction, there are no sex cells. Among detritivores, some millipedes could reproduce asexually.
Where the genetic information of the offspring contains the genetic contribution of both parents, therefore they will be genetically different from them.
In this type of reproduction, males and females have sex cells or gametes, which fuse during the reproductive process.
Examples of reproduction in detritivore animals
This annelid is hermaphroditic, however they cannot self-fertilize. To reproduce, two earthworms are placed very close, with their heads in opposite directions.
At that moment, the clitellus secretes a kind of mucus that holds them together. The sperm are then transferred by each animal to the seminal receptacle of the other, where they are stored.
After this the worms separate. When the egg-laying time arrives, the clitellus secretes a snotty tube. On the way out to the outside, when it passes through the female sexual orifices, the ovules come out. These are fertilized when the tubule reaches the seminal receptacle.
Once outside, the tube closes forming a cocoon, where the eggs continue to develop. After two or three weeks the worms hatch.
Fiddler Crab ( Uca pugnax)
These crustaceans have their own courtship behaviors, in which the males wave their claws with the intention of attracting females. They carry their fertilized eggs in a kind of mass, located in the lower part of their body.
The female remains in the burrow during gestation. After two weeks it comes out to release the eggs. The larvae inhabit the plankton for approximately 2 weeks.
In this animal, as in all diplopods, fertilization is internal. Secondary sexual organs may not be visible, as is generally the case in females, or in some cases they may be lacking.
Fertilization in species of the order Polyxenida occurs when the female takes spermatophores directly from the ground. For this it is guided by a chemical signal left by the male.
In the rest of the millipedes, the males have 1 or 2 pairs of legs known as gonopods. These are used to transfer sperm to the female during copulation. Some species could reproduce asexually, through parthenogenesis.
Moisture bugs ( Armadillidium vulgare)
The moisture scale is a terrestrial crustacean that needs humid environments to live. In the males of this species there is no copulatory organ, but appendages that have undergone modifications to fulfill this function.
Sperm transfer is carried out through a spermatophore, which is a structure secreted by the accessory sex glands.
The female places her eggs inside the marsupium, where they fully develop. Because there is no metamorphosis in the moisture mealybug, when the eggs hatch, the young have characteristics very similar to their parents.
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