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Symphyla

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Symphylans are small, soil-dwelling arthropods belonging to the class Symphyla. They are often called garden centipedes or pseudocentipedes because of their appearance.

Scutigerella 63392733
Scutigerella 63392733

While they look like centipedes, they are non-venomous and very tiny. These creatures play important roles in their ecosystems as they live in moist environments. They are commonly found deep in the soil, under stones, or in decaying wood. There are more than 200 known species living across the entire world.

The body of a symphylan is long, soft, and lacks pigment or eyes. It is divided into two main regions: the head and the trunk. The trunk consists of 14 segments. These segments are covered by microhairs and various dorsal tergal plates. The number of plates can change between species to help with body flexibility. For instance, Scutigerella and Hanseniella have 15 plates, while Ribautiella can have up to 24.

Garden centipede (Scutigerella immaculata) life stages
Garden centipede (Scutigerella immaculata) life stages

The head features long, segmented antennae that act as sense organs. At the base of these antennae, they have disc-like organs of Tömösváry that likely sense vibrations.

Symphylans have a unique way of growing through a process called hemianamorphosis. When they first hatch, immature individuals have only six or seven pairs of legs. As they grow, they undergo a moult, which is when they shed their skin. They add one additional pair of legs during each moult. Most adults eventually reach a stage where they have twelve pairs of legs. However, some species like those in the genus Symphylella are different. In these species, the first pair of legs is absent or vestigial, leaving them with only eleven pairs.

Most symphylans are herbivores or detritus feeders that eat decaying vegetation. However, their feeding habits can sometimes cause problems in agriculture. The garden symphylan, Scutigerella immaculata, can be a pest because it consumes seeds, roots, and root hairs. Other species of Hanseniella have been noted as pests for pineapples and sugar cane in Queensland. While most eat dead matter, some species are saprophagous. Interestingly, a few species of Symphylella are predominantly predatory instead of eating plants.

Reproduction in symphylans does not involve direct copulation between the male and female. Instead, the male produces between 150 and 450 packages of sperm called spermatophores. He places these packages on small stalks made of silk. The female then uses her mouth to pick up the spermatophores. She stores the sperm in special pouches located inside her mouth. When she is ready, she lays eggs in groups of eight to twelve. She attaches these eggs to moss, lichen, or crevices and smears the sperm over them.

Symphylans possess several physical traits that link them to early insects. They have a labium, which is a structure formed by the fusion of the second maxillae. They also share an identical number of head segments with some primitive insects. Each pair of legs is connected to an eversible structure known as a coxal sac. These sacs help the animal absorb moisture from its surroundings. Additionally, they have a small stylus on each leg that may serve a sensory function. They are also the only arthropods that breathe through spiracles located on the head.

The fossil record for symphylans is quite limited, with only five species currently recorded. These fossils are mostly placed within living genera. The oldest records come from Burmese amber dating to the middle Cretaceous period, about 99 million years ago.

Garden centipede (Scutigerella immaculata) life stages
Garden centipede (Scutigerella immaculata) life stages

One specific fossil, Symphylella patrickmuelleri, was found preserved in this amber. This fossil shows the animal releasing long threads of silk. These findings suggest that the different families of symphylans diverged before the end of the Mesozoic Era.

Scientists continue to study how symphylans are related to other animals. Despite their common name, morphological studies often place them in a clade called Progoneata. This means they are likely more closely related to millipedes and pauropods than to centipedes. Molecular studies have provided conflicting results on this topic. Some DNA evidence supports the Progoneata grouping, while other studies align them with centipedes. Regardless of these debates, the clade is believed to be monophyletic, meaning it shares a single common ancestor.

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File:Scutigerella 63392733.jpg
Scutigerella 63392733.jpg
File:Garden centipede (Scutigerella immaculata) life stages.jpg
Garden centipede (Scutigerella...
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