Peripatidae
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As peripatidae refers to a family of Stummelfüßern (Onychophora). The animals, which look superficially like worms with legs , like all velvet worms , live exclusively in tropical areas and feed on smaller invertebrates. All Peripatidae are viviparous, which is a comparatively rare occurrence outside of vertebrates.
The family was named by Richard Evans in 1901 after the type genus Peripatus GUILDING 1826.
construction
Most of the animals are probably colored inconspicuously red to brown for camouflage; their height varies quite a bit between 0.5 and 15 centimeters. The number of stubby pairs of legs can be variable within a species and is between 19 and 43, as a rule, considerably higher than in the other family of stubby legs, the Peripatopsidae . Otherwise, the two families are very similar, so that the anatomy of the Peripatidae largely corresponds to that of all velvet worms. Some special features are listed below.
So at each leg at the height of the projection at the belly side facing a particular organ Coxalorgan , Coxalsack or Coxalvesikel is known and can be turned inside out. Its exact function is unknown; However, it is assumed that it serves to absorb moisture from the environment - a useful adaptation to their sometimes very warm habitats for the water-dependent columbus.
In addition, so-called crural papillae also occur predominantly in the males at the abdominal attachment of the stump legs . These are the openings of special glands, the crural glands , which are located inside the leg and from there usually extend into the body cavity. Since they are very likely to secrete chemical messengers, so-called pheromones , they are probably used for inter-sex communication.
In contrast to the Peripatopsidae, the salivary glands have their own reservoir, so that the saliva does not have to be formed first if necessary. Another difference can be seen in the nerve supply to the heart: While in the Peripatopsidae only a single rear nerve cord occurs, in the Peripatidae species there are two additional nerve cords that run dorsolaterally , i.e. on both sides of the midline of the back of the body.
The genital opening or gonopore is found in both sexes between the penultimate pair of legs. It is characteristic of the females that lay their eggs in the ovaries or ovaries, often a so-called Ovarialtrichter have, endogenously are, that is, they are not in contact with the body cavity of the animals, the pseudo or Hämocoelom . In many viviparous species , a placenta forms in the womb , the uterus, to feed the young , through which nutrients can migrate into the organism of the growing embryo.
The males usually have a relatively long vas deferens; a penis-like structure has not yet been observed within the Peripatidae in contrast to the Peripatopsidae, even if the gonopore protrudes slightly outward in some males.
Genetic abnormalities in animals are a relatively small genome of the mitochondria , the "power plants" of the body cells, and a nuclear genome that is rich in the bases adenine and thymine .
distribution and habitat
The Peripatidae show a circumtropical distribution, even if the climate is sometimes more subtropical due to the altitude .
In detail, they can be found in central Mexico and southern Central America , as well as on the northeast coast, parts of the west coast and occasionally in the interior of South America . In the Caribbean, they can be found on numerous West Indian islands, including Jamaica , Hispaniola , Puerto Rico and the Lesser Antilles , but not in Cuba ; Finds in the Republic of the Congo are known from equatorial West Africa . In India the animals are found in the north near the Himalaya mountains; they are also found on the Malay Peninsula and on some Indonesian islands such as in northern Borneo and in central Sumatra .
Like all velvet worms, the Peripatidae place high demands on the humidity and are therefore mainly found in habitats where the risk of drying out is low, e.g. under fallen trees, in leaf litter, under stones or the like. In the Caribbean, they were also found in cocoa or banana plantations . A species from Jamaica, Speleoperipatus spelaeus , lives in caves.
A maximum population density of around two individuals per square meter of soil is known from Central American Costa Rica , which shows how comparatively rare the animals are.
Reproduction
Asexual reproduction is known only in one species, Epiperipatus inthurni ; the females reproduce here parthenogenetically , i.e. without a fertilization process, so that no males are known in this species.
All other species show a sexual mode of reproduction without exception. The females are likely to be inseminated via the vagina, although copulation processes have not yet been observed. Genetic research shows that sibling fertilization is common; this is likely a consequence of the relatively early point in the female life cycle when mating occurs - the proportion of fertilized females in the wild is over 60 percent. Often they are not sexually mature at the time of the sperm transfer; the sperm are then stored in a special structure, the semen store, where they can apparently be kept alive for several years. Females kept in isolation are in any case able to give birth to young for years without any additional fertilization process. An explanation for the unusually early semen transmission can be seen in the special mode of reproduction of the animals: All species are viviparous; In pregnant females, therefore, there are growing embryos in the "womb", the uterus, almost at all times, which severely impair the transfer of sperm to the ovaries. Early mating, through which, if possible, all eggs that will mature within the ovaries during the female's life span can be fertilized, is therefore a sensible strategy to circumvent this problem.
While many females are fertilized only once in their lifetime, most males appear to be polygamous , so mate with multiple partners whenever possible.
All species are either genuinely viviparous ( viviparous ) or eggs viviparous ( ovoviviparous ). The latter affects two genera , Eoperipatus and Typhloperipatus . In species of both taxa , the females give birth to live young, but no longer feed them inside the uterus, so that the embryos rely on nutrients from the egg's moderate yolk reserves for their energy needs. They also remain surrounded by the thin egg membrane until they are born.
In all other species, however, the embryos are either nourished by maternal secretions that are released into the uterus or by a real tissue connection between the embryo and uterus, the placenta. The latter is found mainly in the Neotropical species, i.e. in America and the Caribbean, less often in the other distribution areas. The presumably more original supply of nutrients through secretions occurs exclusively in the "old world", ie in Africa and Southeast Asia.
Viviparity is a rather unusual trait in invertebrates; in particular the formation of a placenta, a feature found exclusively within the Peripatidae family, is considered remarkable. The Peripatopsidae also include some viviparous species; however, their mode of reproduction probably arose independently.
The development time of the embryos is about a year. At birth (in the viviparous species) only a single young animal is born head first. The number of births per year can vary between one and eight, depending on the species; mostly they are evenly distributed over the year, but apparently do not fall into the dry season, if one exists.
The sex ratio is usually shifted in favor of the males at birth; however, because these have a shorter lifespan than the females, this changes over time, so that there is an excess of females in adult animals.
While males can mate for the first time shortly after their birth, in females this usually only takes place after the first five to nine months of life; accordingly, the first birth takes place in their 17th to 23rd month of life.
Danger
The endangerment situation of most Peripatidae species is difficult to assess, as population data are not available and are difficult to collect in Equatorial Africa, for example. With the 2009 edition, four species are listed on the Red List of the International Union for Conservation of Nature ; but this says practically nothing about the endangerment of the other Peripatidae taxa.
- The species Macroperipatus insularis is endangered ("Endangered").
- The equatorial African species Mesoperipatus tholloni was classified as endangered in 1994 and is now listed as a species with insufficient data ("data deficient").
- The Caribbean species Plicatoperipatus jamaicensis appears to be "Near Threatened".
- The species Speleoperipatus spelaeus , which lives exclusively in caves , is classified as critically endangered.
Caves are known as relatively hostile habitats, they usually only accommodate very small populations; local influences therefore have a much stronger impact on the total population than with species with a more extensive range.
To date there are no plans for targeted countermeasures; possible breeding of the animals is being considered. The parthenogenetic species Epiperipatus inthurni can at least be kept in culture today; which requirements must be met for a successful and sustainable preservation of the population in captivity is still largely unknown.
Tribal history
The tribal history of the Peripatidae must largely be reconstructed from the phylogenetic relationships between the species living today. The only known fossil species that could be classified into the family are Cretoperipatus burmiticus from Myanmar's Cretaceous amber and Tertiapatus dominicanus from the Caribbean island of Hispaniola . The former is in a comparatively good state of preservation and at an age of around 100 million years it can be assigned to the Peripatidae with certainty, whereas this is not certain for the latter. The existence of Cretoperipatus burmiticus confirms the assumption, which was considered probable even before the discovery of the species, that the Peripatidae separated from their sister group, the Peripatopsidae, which includes all other stumpworts, even before the breakup of the former supercontinent Gondwana in the geological epoch of the Triassic or Jurassic , separated.
Since a cladistic analysis of the relationships between the individual species based on morphological or molecular genetic data is not yet available, one currently has to be content with biogeographical considerations. This approach, known as retrovikariance analysis, assumes that geographically neighboring species are more closely related than those that live in geographically widely separated areas. It is made more difficult by the fact that phenomena such as continental drift , i.e. the movement of the earth's land masses to one another, have to be taken into account over geological time periods .
The result can be summarized in the following diagram:
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Accordingly, the Southeast Asian species probably split off from all other Peripatidae in the Jurassic epoch. Their original habitat was Gondwana, a continent that was made up of South America, Africa, Madagascar, India, Australia and Antarctica, as is the case with all other colibuses today. Since the animals are now distributed in northern India and Southeast Asia, but not in West Asia or North Africa, it is assumed that they did not get there through independent distribution, but through vicariance , the geological transport of their habitat. In this specific case, they were probably brought north with the Indian continent, which separated from all other parts of Gondwana at the beginning of the Cretaceous Period . When India collided with the Eurasian land mass in the Miocene , the way was clear for a spread in nearby Southeast Asia. In southern India, which is also not populated, they would have died out later.
The separation of the West African and Neotropical species probably only took place in the Cretaceous period; In any case, Central America and Mexico can hardly have been colonized earlier. For the colonization of the Caribbean, it is crucial whether the animals already inhabited the Proto- Antilles , which were still contiguous at that time , which formed in the Mesozoic era between North and South America and later migrated eastwards through continental drift. An alternative would be colonization from South America, for example today's Amazon region, which could have taken place much later. It is known that water currents in which the animals could have survived on floating deadwood, for example, move north from the Amazon estuary towards the Caribbean and continue from east to west. An indication of this hypothesis is the fact that the largest and at the same time westernmost of all Caribbean islands, Cuba, is still not inhabited by Peripatidae.
Systematics
Although the monophyly of the group, i.e. the question of whether the taxon includes all descendants of the last common ancestor of all contained species, has not been fully clarified, it is considered quite likely that the Peripatidae form a natural group.
The family is divided into ten genera , which include just over 60 species . The genera are listed below with a brief indication of their geographical distribution area:
- Eoperipatus (Malay Peninsula)
- Epiperipatus (Central America and the Caribbean)
- Heteroperipatus
- Macroperipatus (Central America and the Caribbean)
- Mesoperipatus (Equatorial Africa)
- Oroperipatus (South America)
- Peripatus GUILDING 1826 (Neotropic)
- Plicatoperipatus (Caribbean)
- Speleoperipatus (Caribbean)
- Typhloperipatus (East India)
A phylogenetic analysis of the putative sister group, the Peripatopsidae, also included a total of five genera of the Peripatidae; Naturally, these were not the focus of the investigation. The partial result of the study, which roughly agrees with the biogeographical expectations of the aforementioned retrovikariance analysis, can be seen in the following diagram:
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literature
- R. Evans: On two new species of Onychophora from the Siamese Malay States. In: Quarterly Journal of Microscopical Science, 44, 1901, pp. 473-538.
- J. Monge-Najera, Phylogeny, biogeography and reproductive trends in the onychophora , Zoological Journal of the Linnean Society, 114 , 1995, p. 21
- AL Reid, Review of the Peripatopsidae (Onychophora) in Australia, with Comments on Peripatopsid Relationships , Invertebrate Taxonomy, 10 , 1996, 663
