Peripatopsidae
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Peripatoides sp. |
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| Peripatopsidae | ||||||||||||
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As peripatopsidae refers to a family of Stummelfüßern (Onychophora). The animals, whose appearance is reminiscent of worms with legs, live exclusively in the temperate zone of the southern hemisphere. In contrast to the other group of poles, the Peripatidae , there are a number of genera that do not give birth to living young, but lay eggs, i.e. are oviparous .
The family was first described in 1907 and named after the type genus Peripatopsis .
construction
Peripatopsidae species come in numerous colors, but the most common is an iridescent blue-green. With a length between 0.5 and 8 centimeters, they are usually shorter than the Peripatidae species and also have fewer legs; the number of these stubby body appendages is always constant within a species and varies between 13 and 29 pairs. The last pair of legs is sometimes stunted, and occasionally apparently not even there.
The general anatomy corresponds largely to that of all velvet worms and is dealt with in detail in the corresponding article; In the following, therefore, there are primarily special characteristics of the Peripatopsidae. These include, for example, the nerve supply to the heart, which, unlike the Peripatidae, takes place exclusively through a rear nerve cord, but also the simple structure of the salivary glands, which have no reservoir in which the saliva could be temporarily stored.
Crural glands , special organs that lie within the stump bones , often extend into the body cavity and are primarily used for communication between the sexes, occur in principle in both sexes. As is the case with the Peripatidae, in which they are only found in the males, but through openings at the base of the abdomen, the crural papillae , chemical messengers, so-called pheromones . Coxal sacs , structures that are presumably used to absorb water in other velvet worms, are not found in the Peripatopsidae.
The genital opening, which in the Peripatidae always lies between the penultimate pair of legs, is found in the Peripatopsidae behind or between the last remaining pair of legs, which supports the already mentioned thesis that another pair of legs was lost in the course of the tribal history of the Peripatopsidae.
The reproductive organs also show some peculiarities: The eggs in the ovaries of the females are exogenous , which means that the follicles are in contact with the body cavity, the hemocoeloma , and can absorb nutrients from it, for example to build yolks. In contrast, a placenta , as found in many Peripatidae species, does not occur in principle.
There are also some special adaptations in the males. For example, species of the genus Paraperipatus have a real penis; its use in copulation has not yet been observed. Even more unusual are some of the moveable structures that can be found on the heads of the males of numerous Australian species. These are probably modifications of the sensory papillae that occur on the skin of all velvet worms, which are formed into thorns, claws or stilettos and presumably serve to transmit sperm packages. In the species Florelliceps stutchburyae , for example, there is a single long thorn that can be stretched out from a fold of skin that runs forward from about eye level.
distribution and habitat
The Peripatopsidae live in the temperate zones of the southern hemisphere and thus have a so-called circumaustral distribution: They are found in the east and southwest, locally also in the central south of Australia , in Tasmania , New Guinea and New Zealand , as well as in Chile and in two narrow coastal strips of South Africa , on the one hand south of the Cape Fold Mountains , on the other hand beyond the eastern Great Ridge on the rainy sea side.
The geographical distribution of the species testifies to the origin of the group on the former southern supercontinent of Gondwana ; they were transported from there together with their current habitat in the course of the continental drift to their present areas of distribution.
Like all velvet worms, the Peripatopsidae also depend on high humidity. They therefore only live in a damp environment, especially in forests, for example under stones, in or under dead wood such as fallen tree trunks or in the leafy layer of the ground. In Southwest and South Australia they are also found in dry forests, in South Africa even on otherwise bare grassland. A South African species, Peripatopsis alba , lives in caves.
The largest known population density within the family was also found in South Africa to date; there are occasionally up to 10 individuals per square meter of soil.
It is known from Australia, whose stubby fauna has been best studied so far, that genetically distinct species often share one and the same habitat, which could indicate a sympatric speciation , i.e. the development of two or more species without geographical isolation.
Reproduction
All Peripatopsidae species reproduce sexually. The genetic diversity within a population is often not very great, at least in the particularly well-studied Australian species, which suggests frequent matings between siblings or other closely related animals and, in individual cases, strong stabilizing selection .
Females are fertilized vaginally almost everywhere. In viviparous species, this creates the problem that the growing embryos in the uterus of the pregnant female obstruct the path of the sperm to the ovaries. Presumably for this reason, fertilization takes place in most species before sexual maturity. Inside the female, the sperm can remain viable for more than nine months in special sacs and in this way fertilize the eggs at a later point in time. However, the sachets are not always used for long-term storage of the semen - sometimes there are only a few days between insemination and fertilization, so that they have more of the function of a short-term storage.
The mode of sperm transfer is different in the different genera: As already mentioned, a penis-like structure occurs within the genus Paraperipatus , which, however, has not yet been observed in function, while in many Australian species in the males there are special structures on the head that also exist seem to be used for sperm transfer. More precise observations are only available of the species Florelliceps stutchburyae from New South Wales: Here a special spike apparently serves to position a sperm packet (spermatophore) in the female's vagina; possibly it is already opened by this and the contained sperm are released. During copulation, the male presses his head firmly against the genital opening ( gonopore ) of the female, who supports her partner by gripping the skin papillae of the male at the head end with the claws of the last pair of legs. In this mating position, both animals are so firmly connected that even the handling by the investigating scientists did not lead to the mating position being abandoned. However, the animals perform slow, but coordinated movements, in which the female in front is obviously leading. How the spermatophore gets from the sexual opening of the male to the head is still unclear. This unusual mating variant may have developed as an adaptation to narrow habitats, such as those found in dead tree trunks - there it is a very effective transmission path for the sperm.
Two South African species, Peripatopsis capensis and Peripatopsis sedgwicki , have taken a completely different route . In both cases, fertilization does not take place through the vagina; accordingly, there are no bags to store the sperm. Instead, the male lays a sperm packet about one millimeter in diameter on the flanks or on the back of the female. Special cells called amebocytes , which are contained in the blood of the female, then secrete enzymes that specifically dissolve the skin underneath the sperm packet and at the same time its shell. As a result, sperm pass through this self-made "wound" into the body cavity of the female and penetrate from there to the ovaries, the walls of which they penetrate. In this way they get to the egg cells, which can now be fertilized. This fertilization, called cuticular after the scientific term for the outer, inanimate skin layer , is unusual in that normal skin injuries in columbles usually lead to death very quickly due to bacterial infections - there must therefore be a mechanism that can prevent such infections in the case of a "mating wound" effectively prevented.
Although mating in the females often begins before sexual maturity, further copulations are possible in the further course of life. Females of the Australian species Euperipatoides rowelli are apparently fertilized by several partners in the course of their lives, so it can happen that offspring from different fathers grow in the female at the same time.
Most Peripatopsidae - like all animals of their sister group, the Peripatidae - are viviparous; however, there are some egg-laying ( oviparous ) species. The eggs, which are 1.3 to 2.0 millimeters in size and are surrounded by a shell containing chitin, contain a correspondingly large amount of yolk on which the growing embryos feed. The remaining species are divided into egg-bearing ( ovoviviparous ) and genuinely live-bearing ( viviparous ) forms, although only a few species have a viviparous way of life. In contrast to many Peripatidae species, there is basically no placenta in them.
It is believed that the original mode of reproduction of the Peripatopsidae was ovoviviparous; both oviparity and viviparity are therefore presumably secondary.
The development time of the embryos is between six and seventeen months. In the viviparous species, one or two young are born, which are usually a little lighter in color than their parents, but already have the correct number of legs for their respective species.
In males, the first mating takes place after about nine to eleven months; it is known that they have a higher mortality rate than the females. These mate for the first time between 9 and 24 months of age, depending on the species. The first birth or oviposition takes place accordingly after about two to three years; the average number of offspring varies between 6 and 23 young animals per year, depending on the species.
Danger
Since many species of the Peripatopsidae family were not discovered until the 1990s and, in addition, many regions such as New Guinea could hardly be scientifically investigated, only little reliable information is available about the actual endangerment of most species.
With the 2009 edition, seven species are included on the Red List of the International Union for Conservation of Nature :
- Peripatopsis leonina from New Zealand may already be extinct, but is still listed as critically endangered together with the South African species Opisthopatus roseus .
- Tasmanipatus anophthalmus from Tasmania is classified as endangered ("Endangered").
- Four other species are classified as endangered (Vulnerable):
- Peripatopsis clavigera and Peripatopsis alba from South Africa as well
- Peripatoides indigo and Peripatoides suteri from New Zealand.
The protection status differs depending on the state. While in South Africa all velvet worms are legally protected and special permits are required for both the collection and the export of the animals, no special regulations are known from Chile. There are no collection restrictions in Australia, but there are export restrictions. A regional project specifically aimed at two Tasmanian species, Tasmanipatus anophtalmus and Tasmanipatus baretti , the so-called velvet worm conservation plan , which pays attention to these two groups, which is rarely found in invertebrates, is considered exceptional .
Tribal and Discovery History
The Peripatopsidae have not been passed down in fossil form , so that their tribal history must be inferred from knowledge of modern species and their geographical distribution.
They probably separated from their presumed sister group, the Peripatidae, before the breakup of the southern supercontinent Gondwana about 130 million years ago. The splitting of the velvet worms probably already took place in the geological epochs of the Triassic or Jurassic . This is also supported by a 100 million year old Cretaceous velvet fossil, Cretoperipatus burmiticus , which already belongs to the Peripatidae family.
The further tribal history of the family can be inferred, among other things, by a so-called retrovikariance analysis: This is based on the principle that geographically neighboring species are more closely related than those that are native to widely separated areas of distribution. It becomes non-trivial because the movement of the continents to each other over geological time periods must be taken into account. A retrovikariance analysis can only provide a rough estimate and must not be confused with a phylogenetic analysis based on morphological or molecular genetic characteristics . In the specific case, the following picture emerges:
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The separation between the South African species and all others is probably the most original - it probably took place in the late Jurassic or the early Cretaceous when there was still a land connection between Africa, South America and Australia via Antarctica . The splitting off of a first group of egg-laying (oviparous) species probably goes back to this time.
The Chilean velvet fauna is relatively closely related to the New Zealand and Australian fauna. The latter, however, is unlikely to form a monophyletic group itself - some Australian species seem to find their closest relatives in New Zealand. The colonization of Australia was probably carried out from Tasmania and southeast Australia, the latter being flooded in the meantime and then recolonized secondarily.
In the Eocene, probably about 37 million years ago, at a time when Australia was already isolated from all other continents, the second line of development of oviparous species probably arose there. The settlement of New Guinea can only have taken place after the Pliocene , as the area was previously under water. It stands to reason to assume that the animals during the ice ages of the Pleistocene existing land bridge from Australia immigrated - are molecular biological findings, however, currently contradict this assumption.
Systematics
Whether the Peripatopsidae are a natural ( monophyletic ) group that includes all descendants of their common ancestor is not undisputed, but is considered a good working hypothesis, even if there are isolated arguments in favor of classifying the Peripatidae into the Peripatopsidae.
Due to extensive taxonomic work in Australia, most of the 37 genera are known from there , comprising 92 species . However, many of them cannot be distinguished from the outside. This is why as cryptic designated species instead by molecular biology tools such as allozyme - electrophoresis separated.
The following overview lists the known genera including their area of distribution in alphabetical order:
- Acanthokara (New South Wales, Australia)
- Aethrikos (New South Wales, Australia)
- Akthinothele (Queensland, Australia)
- Anoplokaros (New South Wales, Australia)
- Austroperipatus (Queensland, Australia)
- Baeothele (New South Wales, Australia)
- Centrorumis (New South Wales, Australia)
- Cephalofovea (New South Wales, Australia)
- Critolaus (Queensland, Australia)
- Dactylothele (Queensland, Australia)
- Dystactotylos (Queensland, Australia)
- Euperipatoides (New South Wales, Australia)
- Florelliceps (New South Wales, Australia)
- Hylonomoipos (Queensland, Australia)
- Konothele (Queensland, Australia)
- Lathropatus (Southeast Australia)
- Leuropezos (Queensland, Australia)
- Mantonipatus (South Australia)
- Metaperipatus (South America)
- Minyplanetes (Queensland, Australia)
- Nodocapitus (Queensland and New South Wales, Australia)
- Occiperipatoides (Southwest Australia)
- Ooperipatellus (South Australia)
- Ooperipatus (Victoria and Southeast Australia)
- Opisthopatus (South Africa)
- Paraperipatus (New Guinea)
- Paropisthopatus ?
- Peripatoides (New Zealand)
- Peripatopsis (South Africa)
- Phallocephale (New South Wales, Australia)
- Planipallipus (New South Wales and Victoria, Australia)
- Regimitra (New South Wales, Australia)
- Ruhbergia (New South Wales, Australia)
- Sphenoparme (Queensland, Australia)
- Symperipatus ?
- Tasmania (Tasmania, Australia)
- Tasmanipatus (Tasmania, Australia)
- Tetramerad (New South Wales, Australia)
- Vescerro (Queensland, Australia)
- Wambalana (New South Wales, Australia)
The probable phylogenetic relationships between the genera derived from molecular genetic data are shown in the diagram below. The genera Florelliceps and Tasmania are not yet included due to a lack of phylogenetic information; the genus Ooperipatus is para- or even polyphyletic and is therefore only listed here as a non-natural group for the sake of form.
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The molecular genetic and the findings derived from the analysis of retrovic variance only coincide very imprecisely, so there is a need for further research in both areas.
literature
- DA Briscoe, NN Tait, Allozyme evidence for extensive and ancient radiations in Australia Onychophora , Zoological Journal of the Linnean Society, 114 , 1995, p. 91
- DA Briscoe, NN Tait, Genetic differentiation within New Zealand Onychophora and their relationships to the Australian fauna , Zoological Journal of the Linnean Society, 114 , 1995, p. 103
- AL Reid, Review of the Peripatopsidae (Onychophora) in Australia, with Comments on Peripatopsid Relationships , Invertebrate Taxonomy, 10 , 1996, 663
- NN Tait, JM Norman, Novel mating behavior in Florelliceps stutchburyae gen. Nov., Sp. nov. (Onychophora, Peripatopsidae) from Australia , Journal of Zoology, 253 , 2001, p. 301
