Misplaced Pages

#467532

28-450: Scutigerella is a genus of symphylans with sub-cosmopolitan distribution. It is the second-largest clade in the family Scutigerellidae , comprising 38 species. Scutigerella comprises the following species as of 2023: [REDACTED]  This article incorporates text by Sierwald, P.; Spelda, J. available under the CC BY 4.0 license. This myriapoda -related article

56-637: A defense and to suspend themselves in the air. The symphylan fossil record is poorly known, with only five species recorded, all placed in living genera. The oldest records of both families are found in Burmese amber from the middle Cretaceous , approximately 99 million years ago. As a result, both families are thought to have diverged before the end of the Mesozoic Era. Despite their common name, morphological studies commonly place symphylans as more closely related to millipedes and pauropods than

84-529: Is a stub . You can help Misplaced Pages by expanding it . Symphylan Scutigerellidae Scolopendrellidae Symphylans , also known as garden centipedes or pseudocentipedes , are soil-dwelling arthropods of the class Symphyla in the subphylum Myriapoda . Symphylans resemble centipedes , but are very small, non-venomous, and only distantly related to both centipedes and millipedes . More than 200 species are known worldwide. Symphyla are primarily herbivores and detritus feeders living deep in

112-424: Is associated with an eversible structure, called a "coxal sac", that helps the animal absorb moisture, and a small stylus that may be sensory in function. Similar structures are found in the most primitive insects. Symphylans breathe through a pair of spiracles on the sides of their head, and are the only arthropods with spiracle openings on the head. These are connected to a system of tracheae that branch through

140-426: Is not too thick it may be possible to see new structures, such as setae , from the outside. However, contact between the nerves and the old exoskeleton is maintained until a very late stage in the process. The new, teneral exoskeleton has to accommodate a larger frame than the previous instar , while the spider has had to fit into the previous exoskeleton until it has been shed. This means the spider does not fill out

168-465: Is soft and generally 2 to 10 millimetres (0.08 to 0.4 in) long, divided into two body regions: head and trunk. An exceptional size is reached in Hanseniella magna , which attains lengths of 12-13 mm (0.5 in). The head has long, segmented antennae , a postantennal organ, three pairs of mouthparts : mandibles , the long first maxillae, and the second pair of maxillae which are fused to form

196-512: Is then secreted into the exuvial space between the old cuticle and the epidermis, this contains inactive enzymes which are activated only after the new epicuticle is secreted. This prevents the new procuticle from getting digested as it is laid down. The lower regions of the old cuticle, the endocuticle and mesocuticle , are then digested by the enzymes and subsequently absorbed. The exocuticle and epicuticle resist digestion and are hence shed at ecdysis. Spiders generally change their skin for

224-497: The centipedes , in the clade Progoneata . Molecular studies have shown conflicting results, with some supporting the Progoneata clade, others aligning symphylans with centipedes or other arthropods, although some are weakly supported. The clade is believed to be monophyletic . Ecdysis After moulting, an arthropod is described as teneral , a callow ; it is "fresh", pale and soft-bodied. Within one or two hours,

252-405: The prosoma with sufficient pressure to crack it open along its lines of weakness. The carapace lifts off from the front, like a helmet, as its surrounding skin ruptures, but it remains attached at the back. Now the spider works its limbs free and typically winds up dangling by a new thread of silk attached to its own exuviae, which in turn hang from the original silk attachment. At this point

280-423: The adult instar , which usually has twelve pairs of legs. This mode of development is known as hemianamorphosis . Although most adult symphylans have twelve leg pairs, the first pair is absent or vestigial in some species (e.g., those in the genus Symphylella ), so adults in some species have only eleven leg pairs. The species with 12 pairs are the only myriapods with actual legs on the first body segment, as

308-436: The back allowing the animal to emerge. Often, this initial crack is caused by a combination of movement and increase in pressure of hemolymph within the body, forcing an expansion across its exoskeleton , leading to an eventual crack that allows for certain organisms such as spiders to extricate themselves. While the old cuticle is being digested, the new layer is secreted. All cuticular structures are shed at ecdysis, including

SECTION 10

#1732798603468

336-420: The cuticle and collapse of air sacs to allow growth of internal organs. The process of moulting in insects begins with the separation of the cuticle from the underlying epidermal cells (apolysis) and ends with the shedding of the old cuticle (ecdysis). In many species it is initiated by an increase in the hormone ecdysone . This hormone causes: After apolysis the insect is known as a pharate . Moulting fluid

364-643: The cuticle hardens and darkens following a tanning process analogous to the production of leather . During this short phase the animal expands, since growth is otherwise constrained by the rigidity of the exoskeleton. Growth of the limbs and other parts normally covered by the hard exoskeleton is achieved by transfer of body fluids from soft parts before the new skin hardens. A spider with a small abdomen may be undernourished but more probably has recently undergone ecdysis. Some arthropods, especially large insects with tracheal respiration, expand their new exoskeleton by swallowing or otherwise taking in air. The maturation of

392-461: The females before maturing. Members of the Mygalomorphae are very long-lived, sometimes 20 years or more; they moult annually even after they mature. Spiders stop feeding at some time before moulting, usually for several days. The physiological processes of releasing the old exoskeleton from the tissues beneath typically cause various colour changes, such as darkening. If the old exoskeleton

420-432: The first pair of legs is modified into forcipules in centipedes, and in pauropods the segment is a reduced collum which bears ventrally a pair of small papillae, while in millipedes it's a collum without any appendages at all. Symphylans have several features linking them to early insects, such as a labium (fused second maxillae), an identical number of head segments and certain features of their legs. Each pair of legs

448-410: The first time while still inside the egg sac, and the spiderling that emerges broadly resembles the adult. The number of moults varies, both between species and sexes, but generally will be between five times and nine times before the spider reaches maturity. Not surprisingly, since males are generally smaller than females, the males of many species mature faster and do not undergo ecdysis as many times as

476-522: The flexibility of the body. Legs are found on the first 12 segments. The 13th segment, which is fused with the 12th segment, bears a pair of spinnerets that resembles cerci , and the 14th segment has a pair of long sensory hairs ( trichobothria ). Around the anal opening there is a small telson . Symphylans have been reported as living up to four years, and moult throughout their life. Immature individuals have six or seven pairs of legs on hatching, but they add an additional pair at each moult until

504-489: The garden symphylan, Scutigerella immaculata can be a pest of crops. A species of Hanseniella has been recorded as a pest of sugar cane and pineapples in Queensland . A few species are found in trees and in caves. A species of Symphylella has been shown to be predominantly predatory, and some species are saprophagous . Symphyla are small, cryptic myriapods without eyes and without pigment . The body

532-459: The head and the first three segments of the body only. The genital openings are located on the fourth body segment, but the animals do not copulate. Instead, the male deposits 150 to 450 packages of sperm, or spermatophores , on small stalks. The female then picks these up in her mouth, which contains special pouches for storing the sperm. She then lays her eggs, and attaches them to the sides of crevices or to moss or lichen with her mouth, smearing

560-563: The inner parts of the exoskeleton, which includes terminal linings of the alimentary tract and of the tracheae if they are present. Each stage of development between moults for insects in the taxon Endopterygota is called an instar , or stadium, and each stage between moults of insects in the Exopterygota is called a nymph: there may be up to 15 nymphal stages. Endopterygota tend to have only four or five instars. Endopterygotes have more alternatives to moulting, such as expansion of

588-426: The limb is a normal, or near normal, size. The term ecdysis comes from Ancient Greek ἐκδύω ( ekduo ) 'to take off, strip off'. In preparation for ecdysis, the arthropod becomes inactive for a period of time, undergoing apolysis or separation of the old exoskeleton from the underlying epidermal cells. For most organisms, the resting period is a stage of preparation during which the secretion of fluid from

SECTION 20

#1732798603468

616-572: The lower lip or labium of the mouth. The antennae serve as sense organs. Disc-like organs of Tömösváry , which probably sense vibrations, are attached to the base of the antennae, as they are in centipedes. The trunk comprises 14 segments, which is covered by microhairs on the lateral and ventral integument, and by a various number of dorsal tergal plates, from 15 in Scutigerella and Hanseniella , and up till 24 in Ribautiella, increasing

644-417: The moulting glands of the epidermal layer and the loosening of the underpart of the cuticle occurs. Once the old cuticle has separated from the epidermis, a digesting fluid is secreted into the space between them. However, this fluid remains inactive until the upper part of the new cuticle has been formed. Then, by crawling movements, the organism pushes forward in the old integumentary shell , which splits down

672-488: The new exoskeleton completely, so it commonly appears somewhat wrinkled. Most species of spiders hang from silk during the entire process, either dangling from a drop line, or fastening their claws into webbed fibres attached to a suitable base. The discarded, dried exoskeleton typically remains hanging where it was abandoned once the spider has left. To open the old exoskeleton, the spider generally contracts its abdomen ( opisthosoma ) to supply enough fluid to pump into

700-419: The soil, under stones, in decaying wood, and in other moist places. They are rapid runners, can move quickly through the pores between soil particles, and are typically found from the surface down to a depth of about 50 centimetres (20 in). They consume decaying vegetation , but can do considerable harm in an agricultural setting by consuming seeds, roots, and root hairs in cultivated soil. For example,

728-500: The sperm over them as she does so. The eggs are laid in groups of eight to twelve. The spinnerets produce secretions that turn into a silk-like thread. One fossil species, Symphylella patrickmuelleri , was found preserved in Burmese Amber releasing long threads of silk. The silk plays a role in reproduction: the male deposits up to 450 spermatophores on stalks of silk. Symphylans have also been reported releasing silk as

756-507: The spider is a callow; it is teneral and vulnerable. As it dangles, its exoskeleton hardens and takes shape. The process may take minutes in small spiders, or some hours in the larger Mygalomorphs. Some spiders, such as some Synema species, members of the Thomisidae (crab spiders), mate while the female is still callow, during which time she is unable to eat the male. Eurypterids are a group of chelicerates that became extinct in

784-403: The structure and colouration of the new exoskeleton might take days or weeks in a long-lived insect; this can make it difficult to identify an individual if it has recently undergone ecdysis. Ecdysis allows damaged tissue and missing limbs to be regenerated or substantially re-formed. Complete regeneration may require a series of moults, the stump becoming a little larger with each moult until

#467532