Arachnids
Arachnids are a class of joint-legged invertebrate animals, including spiders, scorpions, ticks, and mites. They are characterized by having two body segments, eight legs, and no antennae. Arachnids play important roles in ecosystems as predators and scavengers, and some species are venomous. Their diverse adaptations have allowed them to thrive in various habitats worldwide.
7 Key excerpts on "Arachnids"
eBook - ePubGood Garden Bugs
Everything You Need to Know About Beneficial Insects
- Mary Gardiner(Author)
- 2014(Publication Date)
- Quarry Books(Publisher)
...11 Other Arachnids (Arachnida) Beyond spiders, there are a few additional predatory Arachnids that are simply too remarkable to leave out of this book. Many of these odd creatures are legendary and have been the focus of strange and incorrect urban legends. Here you will learn their real story, which is fascinating in its own right. In addition to spiders, the class Arachnida also includes mites, scorpions, and many others. Like spiders, the arthropods in this class have two body segments (cephalothorax and abdomen), four pairs of legs, pedipalps, and mouthparts called chelicerae. They also lack antennae and wings. These arthropods are generalists that feed on a vast array of prey, with both pests and beneficial species comprising part of their diet. These Arachnids develop via gradual metamorphosis, meaning they hatch from an egg (or in some cases, females give live birth) as immature nymphs and undergo several molts to reach adulthood with no pupal stage. Some of these Arachnids, such as mites (Acari) and harvestmen (Opiliones), are very common in home gardens. Others, such as whip spiders (Amblypygi) and wind scorpions (Solifugae), are rare but might be found by those willing to spend time in their garden after dark, particularly in the southwestern United States. Predatory Mites (Acari) T he Acari includes mites and ticks. This mega-diverse order includes species that feed on plants and others that consume fungi, decomposing organic matter, and algae. Many species are parasites that attack invertebrates, while others parasitize vertebrates (such as ticks, chiggers, and scabies mites), and still others live as nonthreatening species with other animals, including the mites that live in the pores on all of our faces (Demodex)! Here, we focus on families that include species of beneficial predators of common garden pests, including spider mites (Tetranychidae), thrips (Thripidae), whiteflies (Aleyrodidae), and other tiny plant feeders...
eBook - ePub- Elise E. B. LaDouceur, Elise E. B. LaDouceur(Authors)
- 2021(Publication Date)
- Wiley-Blackwell(Publisher)
...8 Arthropoda : Arachnida Benjamin Kennedy 1, Steven A. Trim 2, Damien Laudier 3, Elise E.B. LaDouceur 4, and John E. Cooper 5 1 Veterinary Invertebrate Society, Venomtech Ltd, Discovery Park, Sandwich, Kent, UK 2 Venomtech Ltd, Discovery Park, Sandwich, Kent, UK 3 Laudier Histology, New York, NY, USA 4 Joint Pathology Center, Silver Spring, MD, USA 5 Wildlife Health Services, UK 8.1 Introduction 8.1.1 Taxonomy Arachnids (class Arachnida) are arthropods that are largely terrestrial but a few, such as Argyroneta aquatica (the diving bell spider), are secondarily aquatic (Ruppert et al. 2004). The largest order of Arachnids is the Araneae, the spiders, with over 40 000 described species (Ruppert et al. 2004). The taxonomy of the Arachnids has been somewhat contentious (Harvey 2002 ; Sharma et al. 2014). It is generally accepted that Arachnida is one of the three classes of Chelicerates, along with Merostomata (horseshoe crabs) and Pycnogonida (sea spiders) (Ruppert et al. 2004 ; www.itis.gov). There are numerous orders of Arachnids, including: Amblypygi – tailless whip scorpions Araneae – spiders Opiliones – harvestmen Palpigradi – micro whip scorpions Pseudoscorpiones – pseudoscorpions Ricinulei – hooded tick spiders Schizomida – short‐tailed whip scorpions Scorpiones – scorpions Solifugae – sun spiders or camel spiders Uropygi – whip scorpions In addition, there is a huge diversity of organisms within the subclass Acari (mites and ticks). Several schemes have been suggested in attempts to classify the Acari, many with complex layers of taxonomic ranks. In excess of 50 000 species have been described and by some estimates, more than a million species may exist. The salient reproductive features of Arachnids include cleidoic eggs or ovoviparity...
eBook - ePub- Helmut F. van Emden(Author)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
...13 Class Arachnida 13.1 Introduction OK, this is supposed to be a book about entomology. So what is another Class of the Phylum Arthropoda other than the Class Insecta doing here? The answer is that, for applied entomologists rather than purists, some of the Arachnida (particularly the spiders and mites) are ‘honorary insects’ because they co-occur with insects in crop ecosystems as beneficial and pest organisms, which have to be recognised as such when making pest management decisions. However, the Class is much broader than those members that occur in crops. Ticks live on animals and are thus also relevant for this book as pests of livestock in agriculture. But the Class has some Subclasses which will not be mentioned again after this brief introduction. These Subclasses include the Scorpionidea (scorpions, though agricultural workers in the tropics need to look out for them!), the Pseudoscorpionidea (common tiny predators that have scorpion-like pedipalps and live under bark and in leaf litter) and the Opiolones (harvestmen). In this Chapter, we shall concern ourselves with only two Subclasses, the Araneida (spiders) and the Acarina (mites and ticks). The basic life history in these groups is rather simple. There is no major metamorphosis, and the ‘nymphs’ hatching from the eggs are not much different from miniature adults, and usually share the same habitat. Like insects there are a number of instars with moulting until the adult stage is reached. 13.2 Subclass Araneida (Spiders) Spiders (Fig. 13.1 a) are immediately different from insects in having only two divisions to the body. The anterior division is the prosoma (= front body) and the posterior one is the opisthosoma (= back body). In relation to the insect division into head, thorax and abdomen, the division between the prosoma and the opisthosoma is part way down the abdomen. The prosoma bears a battery of single-lens eyes and the mouthparts...
eBook - ePubInsects and Wildlife
Arthropods and their Relationships with Wild Vertebrate Animals
- John Capinera(Author)
- 2011(Publication Date)
- Wiley-Blackwell(Publisher)
...1.2). They tend to be carnivorous, and often the digestion occurs largely outside the body (predigestion) because enzymes are secreted into the prey, with the resulting fluid taken up. Four pairs of legs are normal, although the occurrence of enlarged pedipalps in some may give the appearance of five pairs of legs. The most important Arachnids are: Order Scorpiones, the scorpions Order Pseudoscorpiones, the false scorpions Order Solifugae, the sun spiders or wind scorpions Order Uropygi, the whip scorpions Order Aranaea, the spiders Order Opiliones, the harvestmen or daddy longlegs Order Acarina, the mites and ticks The scorpions (order Scorpiones) seem to be the oldest terrestrial arthropods, and may have been the first to conquer land. They are nocturnal (night-active) and secretive, hiding by day in burrows and beneath stones and logs. They are found widely in both arid and moist environment. Scorpions are well known for their long abdomen that terminates in a sting apparatus. The venom of scorpions is sufficient to kill many invertebrates, but not usually dangerous to humans, producing pain equivalent to a yellow jacket. A few species, however, are quite dangerous, and can kill a human. In the southwestern USA, species of Centruroides fall into this ‘quite dangerous’ category. The front appendages, which appear to be legs, are really enlarged mouth structures (pedipalps) bearing claws for capturing prey. They feed mostly on arthropods, but occasionally on small vertebrates. Scorpions can be up to 18 cm in length. There are about 2000 species of scorpions. Fig. 1.2. Representative Arachnids (phylum Arthropoda, class Arachnida): (a) a spider (order Aranaea); (b) a tick (order Acarina); (c) a pseudoscorpion (order Pseudoscorpiones); (d) a sun spider (order Solifugae); (e) a scorpion (order Scorpiones); (f) a mite (order Acarina). The pseudoscorpions (order Pseudoscorpiones) are smaller than scorpions, barely exceeding 8 mm in length. About 3400 species are known...
eBook - ePubThorp and Covich's Freshwater Invertebrates
Ecology and General Biology
- James H. Thorp, D. Christopher Rogers, James H. Thorp, D. Christopher Rogers(Authors)
- 2014(Publication Date)
- Academic Press(Publisher)
...Arachnids are nested within the arthropod subphylum Chelicerata, and share with other chelicerates the morphological features of chelate mouthparts (at least ancestrally) and complete lack of antennae. Features of extant Arachnids include having eight pairs of jointed legs as adults and simple single-lensed eyes; however, eurypterids and some extinct scorpions had compound eyes. The various groups of Arachnids differ in tagmatization, but most orders have a cephalothorax in which mouthparts, sensory organs, and walking legs are unified as one tagma, and an abdomen (=opisthosoma) that houses digestive and reproductive organs and may or may not show segmentation. There are 15 extant orders of Arachnids: Scorpiones (true scorpions), Palpigradi (palpigrades), Solifugida (sun spiders), Uropygi (whipscorpions), Amblypygi (whipspiders), Schizomida (micro-whipscorpions), Araneae (true spiders), Pseudoscorpiones (pseudoscorpions), Ricinulei (ricinuleids), Opiliones (harvestmen), and two superorders of mites in the subclass Acari. The latter include the Parasitiformes (the “tick-like” mites, with three orders), and the Acariformes (the “mite-like” mites, with two orders) (mite classification from Krantz and Walter (2009)). Although the vast majority of arachnid species are terrestrial, the Chelicerata originated in marine habitats, and the most basal extant chelicerates, the horseshoe crabs (Class Merostomata, Order Xiphosura), are still restricted to the ocean. The sea spiders (Pycnogonida) also have chelate mouthparts and lack antennae, but their phylogenetic affinities are murky. They may or may not share a common ancestor with the Chelicerata, and are often treated as a separate subphylum. Relatives of the horseshoe crabs, the completely extinct order Eurypterida, or sea scorpions, included the most massive arthropods in earth’s history. How or when the ancestors of the Arachnida transitioned to land is unclear (Walter and Proctor, 2013)...
eBook - ePub- David B. Rivers, Gregory A. Dahlem(Authors)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
...The name Arthropoda literally means joint (arthro) foot (poda) and an easy way to picture an arthropod is as an armor-plated relatively small animal with jointed legs (Figure 4.4). Phyla are subdivided into distinctive groups called classes. The class Insecta includes arthropods that share a common ancestor and exhibit distinctive characteristics, including six legs, three body parts, external mouthparts, one pair of antennae, compound eyes, and (usually) four wings as adults. Other classes in the Arthropoda that you are probably familiar with are the Arachnids (Arachnida) such as spiders and scorpions, centipedes (Chilopoda), millipedes (Diplopoda), and crabs and their relatives (Malacostraca). In addition to these familiar animals, there are many other distinctive groups that you have probably never seen or heard of, like pauropods and sea spiders (Pycnogonida). While most arthropods that are important in a forensic context will be insects, there are other groups that may be of importance in specific case studies (e.g. Merritt et al., 2007). Going back to a discussion of external morphology, we need to have an understanding of general terms of orientation in order to find our way around the insect body. Insects are bilaterally symmetrical and their body can be described along three axes: ventral refers to the lower surface; dorsal refers to the upper surface; lateral refers to the side; medial refers to the center (usually the longitudinal midline); anterior indicates toward the head end; posterior indicates toward the hind end; distal or apical refers towards the tip; proximal or basal refers towards the body or base (Figure 4.5). These terms are used repeatedly in just about any identification key that you may use...
- Charles M. Hendrix, Ed Robinson(Authors)
- 2016(Publication Date)
- Mosby(Publisher)
...With more than 900,000 species, insects are by far the largest class within the phylum Arthropoda. Technician's Note The insects are the largest class in the phylum Arthropoda, with more than 900,000 species. Key Morphologic Features The name arthropod means “jointed foot” (arthro means “joint,” and pod means “foot”). All adult arthropods have jointed appendages. All arthropods are covered with a chitinous exoskeleton that is composed of segments. Chitin is a hard (yet elastic) body covering that envelops the entire body of all arthropods. Whenever you step on a cockroach, the chitin makes the “crunch” sound. Arthropods have a hemocoel, a body cavity filled with hemolymph. Hemolymph is a bloodlike fluid that bathes the internal organs of an arthropod. When a flying insect hits the windshield of a speeding car and “splats,” hemolymph is the fluid that creates the splat. Arthropods have a very simple circulatory system composed of a heartlike dorsal tube. This dorsal tube is actually a primitive heart that pumps the hemolymph to the arthropod's head. The digestive system of arthropods begins with a ventral mouth and ends with a terminal anus. Arthropods possess a variety of respiratory systems; they may use gills, book lungs, or tracheal tubes as respiratory organs. Arthropods have complex nervous and excretory systems. However, the most important organ system of the arthropods is the reproductive system. Arthropods have separate sexes; they are dioecious. Reproduction is by means of eggs. Arthropods have a tremendous reproductive capacity. Technician's Note Arthropods are dioecious and use eggs for reproduction...
