Onychophora in the context of "Central nervous system"

A spiracle or stigma is the opening in the exoskeletons of insects, myriapods, velvet worms and many arachnids to allow air to enter the trachea. Insect respiratory system differs from vertebrates'. The circulatory system plays a relatively minor role in circulating oxygen and removing carbon dioxide; instead, trachea and air sacs in the insect body allow direct gas exchange, and these tracheal tubes eventually connect to the external environment via spiracles.

In most species, the spiracles are controlled by motor neurons in the central nervous system. It can be opened and closed in an efficient manner to admit air while minimizing associated physiological costs, such as water loss during respiration. Many sensory stimuli can affect the control of spiracles in insects, e.g. chemosensory (carbon dioxide, oxygen, etc.) or mechanosensory (sound, touch, etc.). It has been shown that during metabolically intensive behaviors, such as flight, insects can dynamically modulate the spiracle opening size just so to meet the metabolic demand of flight, while not losing too much water.

Apposition eyes are the most common form of eye, and are presumably the ancestral form of compound eye. They are found in all arthropod groups, although they may have evolved more than once within this phylum.Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus, the horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point. Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion.

The arthropods ancestrally possessed compound eyes, but the type and origin of this eye varies between groups, and some taxa have secondarily developed simple eyes. The organ's development through the lineage can be estimated by comparing groups that branched early, such as the velvet worm and horseshoe crab to the advanced eye condition found in insects and other derived arthropods.

Panarthropoda is a clade comprising the greatest diversity of animal groups. It contains the extant phyla Arthropoda (Euarthropoda), Tardigrada (water bears) and Onychophora (velvet worms), although the relationships among these remained uncertain according to studies published in 2023 and 2024. Panarthropods also include extinct marine legged worms known as lobopodians ("Lobopodia"), a paraphyletic group where the last common ancestor and basal members (stem-group) of each extant panarthropod phylum are thought to have risen. However the term "Lobopodia" is sometimes expanded to include tardigrades and onychophorans as well.

Common characteristics of the Panarthropoda include a segmented body, paired ladder-like ventral nervous system, and the presence of paired appendages correlated with body segments.

Peripatus /pəˈrɪpətəs/ is a genus of velvet worms in the Peripatidae family. The name "peripatus" (unitalicised and uncapitalised) is also used to refer to the Onychophora as a whole, although this group comprises many other genera besides Peripatus. The genus Peripatus is found in Central America, the Caribbean and northern South America. This genus is viviparous, with mothers supplying nourishment to their embryos through a placenta.

Peripatidae is a family of velvet worms. This family includes more than 90 described species distributed among 13 genera, but some authorities deem only 80 of these species to be valid. The oldest putative representatives of the family herald from Burmese amber dated to the mid-Cretaceous, around 100 million years ago, with representatives from Dominican and Baltic amber attesting to a broader distribution in the Palaeogene / Neogene; molecular variability suggests that the family's crown group may have arisen in the early Mesozoic.

Peripatopsidae or the Southern Velvet Worms are one of two extant families of velvet worm. This family includes more than 140 described species distributed among 41 genera, but some authorities deem only 131 of these species to be valid. The French zoologist Eugène Louis Bouvier proposed this family in 1905 with Peripatopsis as the type genus.

Antennipatus montceauensis is an extinct species of onychophoran, a group colloquially known as velvet worms, from the Montceau-les-Mines lagerstätte of what is now France. The animal is the sole member of its genus and notably the oldest confirmed onychophoran fossil. While known of since the 1980s, Antennipatus was described almost 4 decades later in 2016. Currently, the animal has three described specimens with varying levels of preservation. All of are 305 million years old and date to the Stephanian stage of the Late Carboniferous.

Anatomically, Antennipatus resembles modern velvet worms. The animal had rings of dermal papillae along most of its body, with those on the antennae alternating between wide and narrow bands. On its underside, Antennipatus had a putative ventral mouth that preserved what were likely lip papillae. The animal had stubby legs, and on one specimen, definite slime papillae.