Chelicerata

(redirected from Chelicerates)
Also found in: Dictionary, Thesaurus.

Chelicerata

(kəlĭs'ərät`ə), subphylum of ArthropodaArthropoda
[Gr.,=jointed feet], largest and most diverse animal phylum. The arthropods include crustaceans, insects, centipedes, millipedes, spiders, scorpions, and the extinct trilobites.
..... Click the link for more information.
, including the horseshoe crabs (order Xiphosura), the arachnids (class Arachnida), and the sea spiders (class Pycnogonida). The extinct giant water scorpions (order Eurypterida, not true scorpions) also are chelicerates. The chelicerates are characterized by the absence of antennae and jaws and the presence of feeding structures (chelicera), which are modified pincerlike appendages used mainly for grasping and fragmenting food.

Nearly all the xiphosurans are extinct, the only living representative being Limulus, the horseshoe crabhorseshoe crab,
large, primitive marine arthropod of the family Limulidae, related to the spider and scorpion and sometimes called a king crab (a name also used for the largest of the edible true crabs).
..... Click the link for more information.
 and its relatives, which inhabits the soft bottom mud of shallow, coastal seas. Members of class Pycnogonida are commonly known as sea spiderssea spider,
common name for members of the class Pycnogonida, long-legged, rather spiderlike organisms of the subphylum Chelicerata, widely distributed in marine waters. Most are tiny, from 1 to 9 mm (0.04–0.36 in.
..... Click the link for more information.
. These exclusively marine invertebrates are spiderlike in appearance, mostly carnivorous, and range in body length from 4-100 in. (1 mm) to 4 in. (5 cm); the leg spread is sometimes over 2 ft (61 cm). Most sea spiders have four pairs of legs. They feed with a sucking proboscis on other invertebrates and are found in oceans all over the world.

The largest class of chelicerates, class Arachnida, includes the subclass Acari (or Acarina, ticks and mites) and the orders Araneae (spiders), Opiliones (daddy longlegs or harvestmen), and Scorpiones (scorpions), among the most important. Arachnidsarachnid
, mainly terrestrial arthropod of the class Arachnida, including the spider, scorpion, mite, tick, harvestman (daddy longlegs), and a few minor groups. The body is divided into a cephalothorax with six pairs of appendages, and an abdomen.
..... Click the link for more information.
 are predominantly terrestrial, and most are carnivorous, with the digestion of prey starting outside the body. The body is composed of an unsegmented anterior region (prosoma), with a pair of chelicera, a pair of leglike appendages (pedipalps), four pairs of walking legs, and a posterior region (opisthosoma); it is equipped with book lungs or tracheae, for respiration. Arachnids are an ancient group, their fossil records dating back to the Carboniferous period.

Chelicerata

A subphylum of the phylum Arthropoda. The Chelicerata can be defined as those arthropods with the anteriormost appendages as a pair of small pincers (chelicerae) followed usually by pedipalps and four pairs of walking legs, and with the body divided into two parts: the prosoma (corresponding approximately to the cephalothorax of many crustaceans) and the opisthosoma (or abdomen). There are never antennae or mandibles (lateral jaws). The Chelicerata comprise three classes: the enormous group Arachnida (spiders, ticks, mites, scorpions, and related forms); the Pycnogonida (sea spiders or nobody-crabs); and the Merostomata (including the Xiphosurida or horseshoe crabs).

Both Merostomata and Pycnogonida are marine, but the enormous numbers and varied forms of the Arachnida are almost entirely terrestrial. The respiratory structures of chelicerates include gills, book-lungs, and tracheae. Sexes are normally separate, with genital openings at the anterior end of the opisthosoma. Some mites and other small chelicerates are omnivorous scavengers, but the majority of species of larger chelicerates are predaceous carnivores at relatively high trophic levels in their particular ecotopes. See Arthropoda

Chelicerata

 

a subphylum of invertebrates of the phylum Arthropoda. The body consists of a cephalothorax (prosoma) with six pairs of appendages (chelicerae, pedipalps, and four pairs of legs) and an abdomen (opisthosoma), on which there are appendages only in Xiphosura. Antennae are absent. In many mites and ticks the number of legs is reduced.

Fossil aquatic Chelicerata are known from the Cambrian, and terrestrial species are known from the Devonian. The subphylum includes two classes: Merostomata, which live only in seas, and Arachnoidea, which are mainly terrestrial.

Chelicerata

[kə‚lis·ə′räd·ə]
(invertebrate zoology)
A subphylum of the phylum Arthropoda; chelicerae are characteristically modified as pincers.
References in periodicals archive ?
Habelia now shows in great detail the body architecture from which chelicerates emerged, which allows us to solve some long-standing questions," CAaAaAeA@dric Aria, a post-doctoral researcher at the Nanji Institute of Geology and Palaeontology in China, who led the research, said.
The same pattern of paralogous opsin pairs has not been observed so far in other chelicerates, and other chelicerates have fewer opsins--six in the transcriptome of the spider Cupiennius salei (Eriksson et al.
Thus, chelicerates join crustaceans and insects in the list of arthropod groups in which visible light-sensitive opsins expressed in MEs are unique to that eye (Henze and Oakley, 2015).
Habelia now shows in great detail the body architecture from which chelicerates emerged, which allows us to solve some long-standing questions.
Taken together, there are several instances in chelicerates where eye development may not depend on Pax-6 ortholog expression.
Our new find is exciting because it shows that mandibulates (to which crustaceans belong) and chelicerates were already present as two distinct evolutionary trajectories 520 million years ago, which means their common ancestor must have existed much deeper in time.
The extinct eurypterids, or sea scorpions, are the most diverse Paleozoic chelicerates.
Phylogeny and systematic position of Opiliones: a combined analysis of chelicerate relationships using morphological and molecular data.
In certain other crustaceans and in chelicerates, phenoloxidase activity in the hemolymph appears to be due only to the hemocyanin, since no o-diphenolase activity has been observed in hemocytes (Decker et al.
The horseshoe crab is one of the oldest living chelicerates, showing many ancestral characters during embryogenesis (9).
The relatively large size of scorpions, compared with most other chelicerates, implies that low depth of field issues are not likely to be experienced unless imaging the smallest of scorpions, or very small structures such as chelicerae and tarsi.
Intertidal spawning may have preadapted the early chelicerates for the initial animal invasion of land (Stormer, 1977; Little, 1983).