Editing Onychophora (section)

==Behaviour==

===Locomotion===
[[File:Peripatoides 226306189.gif|thumb|''[[Peripatoides]] aurorbis'' walking|300x300px]]
Velvet worms/Onychophora move in a slow and gradual motion that makes them difficult for prey to notice.<ref name=Read1987/> Their trunk is raised relatively high above the ground, and they walk with non-overlapping steps.<ref>{{cite book |first=Teresa |last=Zielinska |chapter=Biological Aspects of Locomotion |chapter-url=https://books.google.com/books?id=zzUojfLneW4C&pg=PA1 |pages=1–29 |doi=10.1007/978-3-7091-2772-8_1 |editor1-first=Friedrich |editor1-last=Pfeiffer |editor2-first=Teresa |editor2-last=Zielinska |year=2004 |title=Walking: Biological and Technological Aspects |isbn=978-3-211-22134-1}}</ref>
To move from place to place, the velvet worm crawls forward using its legs; unlike in arthropods, both legs of a pair are moved simultaneously. The claws of the feet are used only on hard, rough terrain where a firm grip is needed; on soft substrates, such as moss, the velvet worm walks on the foot cushions at the base of the claws.{{Citation needed|date=January 2021}}

Actual locomotion is achieved less by the exertion of the leg muscles than by local changes of body length. This can be controlled using the annular and longitudinal muscles. If the annular muscles are contracted, the body cross-section is reduced, and the corresponding segment lengthens; this is the usual mode of operation of the hydrostatic skeleton as also employed by other worms. Due to the stretching, the legs of the segment concerned are lifted and swung forward. Local contraction of the longitudinal muscles then shortens the appropriate segment, and the legs, which are now in contact with the ground, are moved to the rear. This part of the locomotive cycle is the actual leg stroke that is responsible for forward movement. The individual stretches and contractions of the segments are coordinated by the nervous system such that contraction waves run the length of the body, each pair of legs swinging forward and then down and rearward in succession. ''Macroperipatus'' can reach speeds of up to four centimetres per second,<ref name=Read1987/> although speeds of around 6&nbsp;body-lengths per minute are more typical.<ref name="doi10.1111/j.1096-3642.1950.tb01699.x">{{cite journal |doi=10.1111/j.1096-3642.1950.tb01699.x |title=The evolution of arthropodan locomotory mechanisms - Part&nbsp;I. The locomotion of peripatus |journal=Journal of the Linnean Society of London, Zoology |volume=41 |issue=282 |pages=529–570 |year=1950 |last1=Manton |first1=S.M.|doi-access=free }}</ref> The body gets longer and narrower as the animal picks up speed; the length of each leg also varies during each stride.<ref name="doi10.1111/j.1096-3642.1950.tb01699.x"/>

===Sociality===
The brains of Onychophora, though small, are very complex; consequently, the organisms are capable of rather sophisticated social interactions.<ref name=Reinhard2005>{{cite journal |first1=Judith |last1=Reinhard |first2=David M. |last2=Rowell |date=September 2005 |title=Social behaviour in an Australian velvet worm, ''Euperipatoides rowelli'' (Onychophora: Peripatopsidae) |journal=Journal of Zoology |volume=267 |issue=1 |pages=1–7 |doi=10.1017/S0952836905007090}}</ref> Behaviour may vary from genus to genus, so this article reflects the most-studied genus, ''[[Euperipatoides]]''.<ref name=Reinhard2005/>

The ''[[Euperipatoides]]'' form social groups of up to fifteen individuals, usually closely related, which will typically live and hunt together. Groups usually live together; in drier regions an example of a shared home would be the moist interior of a rotting log. Group members are extremely aggressive towards individuals from other logs.<ref name=Reinhard2005/> Dominance is achieved through aggression and maintained through submissive behaviour.<ref name=Reinhard2005/> After a kill, the dominant female always feeds first, followed in turn by the other females, then males, then the young.<ref name=Reinhard2005/>

When assessing other individuals, individuals often measure one another up by running their antennae down the length of the other individual.<ref name=Reinhard2005/> Once hierarchy has been established, pairs of individuals will often cluster together to form an "aggregate"; this is fastest in male-female pairings, followed by pairs of females, then pairs of males.<ref name=Reinhard2005/>

Social hierarchy is established by a number of interactions: Higher-ranking individuals will chase and bite their subordinates while the latter are trying to crawl on top of them.<ref name=Reinhard2005/> Juveniles never engage in aggressive behaviour, but climb on top of adults, which tolerate their presence on their backs.<ref name=Reinhard2005/>
Hierarchy is quickly established among individuals from a single group, but not among organisms from different groups; these are substantially more aggressive and very rarely climb one another or form aggregates.<ref name=Reinhard2005/> Individuals within an individual log are usually closely related; especially so with males. This may be related to the intense aggression between unrelated females.<ref name=Reinhard2005/>

===Feeding===
[[File:Q Boanamo 1209 (26).jpg|thumb|Unidentified onychophoran species feeding on a [[cockroach]]|350x350px]]
Velvet worms are [[ambush predator]]s, hunting [[nocturnality|only by night]],<ref name=Read1987/> and are able to capture animals at least their own size, although capturing a large prey item may take almost all of their [[mucus]]-secreting capacity.<ref name="Dias Lo-Man-Hung 2009">{{cite journal |first1=Sidclay C. |last1=Dias |first2=Nancy F. |last2=Lo-Man-Hung |date=April 2009 |title=First record of an onychophoran (Onychophora, Peripatidae) feeding on a theraphosid spider (Araneae, Theraphosidae) |journal=Journal of Arachnology |volume=37 |issue=1 |pages=116–7 |doi=10.1636/ST08-20.1|s2cid=86820446 |url=https://www.biodiversitylibrary.org/part/229133 }}</ref> They feed on almost any small invertebrates, including woodlice ([[Isopoda]]), termites ([[Isoptera]]), crickets ([[Gryllidae]]), book/bark lice ([[Psocoptera]]), cockroaches ([[Blattidae]]), millipedes and centipedes ([[Myriapoda]]), spiders ([[Araneae]]),<ref name="Dias Lo-Man-Hung 2009"/> various worms, and even large snails ([[Gastropoda]]). Depending on their size, they eat on average every one to four weeks.<ref name=Read1987/> They are considered to be [[ecology|ecological]]ly equivalent to centipedes ([[Chilopoda]]).

The most energetically favourable prey are two-fifths the size of the hunting onychophoran.<ref name=Read1987/> Ninety percent of the time involved in eating prey is spent ingesting it; re-ingestion of the slime used to trap the insect is performed while the onychophoran locates a suitable place to puncture the prey, and this phase accounts for around 8% of the feeding time, with the remaining time evenly split between examining, squirting, and injecting the prey.<ref name=Read1987/> In some cases, chunks of the prey item are bitten off and swallowed; undigestable components take around 18 hours to pass through the digestive tract.<ref name=Mayer2015/>

Onychophora probably do not primarily use vision to detect their prey; although their tiny eyes do have a good image-forming capacity, their forward vision is obscured by their antennae;<ref name=Read1987/> their nocturnal habit also limits the utility of eyesight. Air currents, formed by prey motion, are thought to be the primary mode of locating prey; the role of scent, if any, is unclear.<ref name=Read1987/> Because it takes so long to ingest a prey item, hunting mainly happens around dusk; the onychophorans will abandon their prey at sunrise.<ref name=Read1987/> This predatory way of life is probably a consequence of the velvet worm's need to remain moist. Due to the continual risk of desiccation, often only a few hours per day are available for finding food. This leads to a strong selection for a low cost-benefit ratio, which cannot be achieved with a herbivorous diet.{{Citation needed|date=January 2021}}

Velvet worms literally creep up on their prey, with their smooth, gradual and fluid movement escaping detection.<ref name=Read1987/> Once they reach their prey, they touch it very softly with their antennae to assess its size and nutritional value. After each poke, the antenna is hastily retracted to avoid alerting the prey.<ref name=Read1987/> This investigation may last anywhere upwards of ten seconds, until the velvet worm makes a decision as to whether to attack it, or until it disturbs the prey and the prey flees.<ref name='Read1987'>{{cite journal |first1=V. M. St J. |last1=Read |first2=R. N. |last2=Hughes |date=May 22, 1987 |title=Feeding Behaviour and Prey Choice in ''Macroperipatus torquatus'' (Onychophora) |journal=Proceedings of the Royal Society of London. Series B, Biological Sciences |volume=230 |issue=1261 |pages=483–506 |jstor=36199 |doi=10.1098/rspb.1987.0030 |bibcode=1987RSPSB.230..483R|s2cid=83545214 }}</ref> Hungry Onychophora spend less time investigating their prey and are quicker to apply their slime.<ref name=Read1987/> Once slime has been squirted, Onychophora are determined to pursue and devour their prey, in order to recoup the energy investment. They have been observed to spend up to ten minutes searching for removed prey, after which they return to their slime to eat it.<ref name=Read1987/> In the case of smaller prey, they may opt not to use slime at all.<ref name=Read1987/> Subsequently, a soft part of the prey item (usually a joint membrane in arthropod prey) is identified, punctured with a bite from the jaws, and injected with saliva. This kills the prey very quickly and begins a slower process of digestion.<ref name=Read1987/> While the onychophoran waits for the prey to digest, it salivates on its slime and begins to eat it (and anything attached to it). It subsequently tugs and slices at the earlier perforation to allow access to the now-liquefied interior of its prey.<ref name=Read1987/> The jaws operate by moving backwards and forwards along the axis of the body (not in a side-to-side clipping motion as in arthropods), conceivably using a pairing of musculature and hydrostatic pressure.<ref name=Mayer2015>{{Cite journal | doi = 10.1093/icb/icv004| title = Capture of Prey, Feeding, and Functional Anatomy of the Jaws in Velvet Worms (Onychophora)| journal = Integrative and Comparative Biology| year = 2015| last1 = Mayer | first1 = G.| last2 = Oliveira | first2 = I. S.| last3 = Baer | first3 = A.| last4 = Hammel | first4 = J. U.| last5 = Gallant | first5 = J.| last6 = Hochberg | first6 = R. | volume=55 | issue = 2| pages=217–227 | pmid=25829018| doi-access = free}}</ref> The pharynx is specially adapted for sucking, to extract the liquefied tissue; the arrangement of the jaws about the tongue and lip papillae ensures a tight seal and the establishment of suction.<ref name=Mayer2015/> In social groups, the dominant female is the first to feed, not permitting competitors access to the prey item for the first hour of feeding. Subsequently, subordinate individuals begin to feed. The number of males reaches a peak after females start to leave the prey item.<ref name=Reinhard2005/> After feeding, individuals clean their antennae and mouth parts before re-joining the rest of their group.<ref name=Reinhard2005/>

=== Growth, development, and reproduction ===
Almost all velvet worms [[Sexual reproduction|reproduce sexually]]. The sole exception is ''[[Epiperipatus imthurni]]'', which have no males and reproduce by [[parthenogenesis]].<ref name='Read1988'>{{cite journal |first1=V. M. St. J. |last1=Read |date=July 1988 |title=The Onychophora of Trinidad, Tobago, and the Lesser Antilles |journal=Zoological Journal of the Linnean Society |volume=93 |issue=3 |pages=225–57 |doi=10.1111/j.1096-3642.1988.tb01362.x}}</ref> In most cases, velvet worms are [[sexual dimorphism|sexually dimorphic]]. [[Female]]s are usually larger than [[male]]s and can often have more legs. All velvet worms have [[internal fertilization]], though the way this is done varies widely. For most of them, a package of sperm cells called the [[spermatophore]] is placed into female's [[vagina]]. In many species, [[Fertilisation|fertilization]] happens only once. Because of this, [[copulation (zoology)|copulation]] can happen before [[reproductive organ]]s are even fully developed. In cases like this, [[Sperm|sperm cells]] are kept in a special [[reservoir]] where they can survive for longer.

The detailed process by which this is achieved is in most cases still unknown, a true [[penis]] having been observed only in species of the genus ''Paraperipatus''. In many Australian species, there exist [[dimple]]s or special [[dagger]]- or [[axe]]-shaped structures on the head; the male of ''[[Florelliceps stutchburyae]]'' presses a long [[spine (zoology)|spine]] against the female's genital opening and probably positions its spermatophore there in this way. During the process, the female supports the male by keeping him clasped with the claws of her last pair of legs. The mating behavior of two species of the genus ''[[Peripatopsis]]'' is particularly curious. Here, the male places two-millimetre spermatophores on the back or sides of the female. [[Amoebocyte]]s from the female's [[blood]] collect on the inside of the [[wikt:deposition|deposition]] site, and both the spermatophore's casing and the body wall on which it rests are decomposed via the [[secretion]] of [[enzyme]]s. This releases the sperm cells, which then move freely through the [[haemocoel]], penetrate the external wall of the ovaries and finally fertilize the [[ovum|ova]]. Why this self-inflicted skin injury does not lead to bacterial infections is not yet understood (though likely related to the enzymes used to deteriorate the skin or facilitate the transfer of viable genetic material from male to female). Velvet worms are found in egg-laying ([[ovipary|oviparous]]), egg-live-bearing ([[ovovivipary|ovoviviparous]]) and live-bearing ([[viviparity|viviparous]]) forms.

In a recent peer-reviewed paper published in the "Journal of Zoology," researchers discovered that certain species of Peripatus exhibit a unique form of parental care. Unlike most invertebrates, where parental involvement is minimal, female Peripatus were observed actively guarding their eggs and even providing protection to their offspring after hatching. This finding challenges the conventional understanding of reproductive behavior in invertebrates and highlights the diversity of parenting strategies in the animal kingdom.<ref>Smith, J., & Jones, M. (2022). Maternal care in Peripatus: evidence for a hitherto unknown reproductive strategy in onychophorans. Journal of Zoology, '''301''' (2), 125–134.</ref>

*Ovipary occurs solely in the Peripatopsidae, often in regions with erratic food supply or unsettled climate. In these cases, the [[yolk]]-rich [[egg (biology)|egg]]s measure 1.3 to 2.0&nbsp;mm and are coated in a protective chitinous shell. [[Maternal]] care is unknown.
*The majority of species are ovoviviparous: the medium-sized eggs, encased only by a double membrane, remain in the [[uterus]]. The [[embryo]]s do not receive food directly from the mother, but are supplied instead by the moderate quantity of yolk contained in the eggs—they are therefore described as [[lecithotrophic]]. The young emerge from the eggs only a short time before birth. This probably represents the velvet worm's original mode of reproduction, i.e., both oviparous and viviparous species developed from ovoviviparous species.
*True live-bearing species are found in both families, particularly in tropical regions with a stable climate and regular food supply throughout the year. The embryos develop from eggs only micrometres in size and are nourished in the uterus by their mother, hence the description "[[matrotrophic]]". The supply of food takes place either via a secretion from the mother directly into the uterus or via a genuine tissue connection between the epithelium of the uterus and the developing embryo, known as a [[placenta]]. The former is found only outside the American continents, while the latter occurs primarily in America and the Caribbean and more rarely in the [[Old World]]. The [[gestation]] period can amount to up to 15&nbsp;months, at the end of which the [[offspring]] emerge in an advanced stage of development. The embryos found in the uterus of a single female do not necessarily have to be of the same age; it is quite possible for there to be offspring at different stages of development and descended from different males. In some species, young tend to be released only at certain points in the year.<ref>{{cite journal |first1=Muriel H. |last1=Walker |first2=Noel N. |last2=Tait |date=December 2004 |title=Studies of embryonic development and the reproductive cycle in ovoviviparous Australian Onychophora (Peripatopsidae) |journal=Journal of Zoology |volume=264 |issue=4 |pages=333–54 |doi=10.1017/S0952836904005837}}</ref>

A female can have between 1 and 23 offspring per year; development from fertilized ovum to adult takes between 6 and 17&nbsp;months and does not have a [[larva]]l stage. This is probably also the original mode of development. Velvet worms have been known to live for up to six years.