Benjamin Kennedy1, Steven A. Trim2, Damien Laudier3, Elise E.B. LaDouceur4, and John E. Cooper5 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 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: 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. In scorpions, two types of embryonic development occur: apoikogenic (eggs containing yolk) and katoikogenic (yolkless – the embryos are nourished orally via diverticula in the female’s oviuterus) (Cloudsley‐Thompson 1993). Scientific investigation of the morphology of arachnids began with the naturalist and physician Martin Lister (1639–1712), who published his Tractatus de Araneis, in Latin, in 1678. The father of microscopy, Antonie van Leeuwenhoek (1632–1723), described the dissection of spiders in one of his letters in 1673. There have been many important contributions to our knowledge of arachnids, including their histology in the latter part of the twentieth century. Legendre, writing in French, detailed the structure of the gastrointestinal tract and nervous system of spiders (Legendre 1958, 1953). Kerkut, Freeman, and Bracegirdle and Leake described the microscopic anatomy during presentations at the Arachnology International Conference, which included seminal studies in English, French, and German (Freeman and Bracegirdle 1971; Kerkut 1959; Leake 1975; Merrett 1978). Various texts during the same period discussed the responses of arachnids and other arthropods to various insults – for example, alcohols, heavy metals, and pesticides (Sparks 1972). Descriptions of pathologic examination of invertebrates have included histologic methods for examining insects; much of this is relevant to arachnids (Barbosa et al. 2015; Cooper and Cunningham 1991; Newton and Smolowitz 2018). In this chapter, the emphasis is on Araneae with some discussion of other orders, predominantly Scorpiones, Ricinulei, and Solifugae. The bias is based on species frequently encountered and therefore studied, so although Opiliones, Pseudoscorpiones, and Acari are discussed, there are few data of other orders. The life expectancy of arachnids ranges from a few weeks (some species of mites) to several decades, with one mygalomorph spider reported to have lived to 43 years (Mason et al. 2018). Females often outlive males. Arachnids typically lay eggs except for Scorpiones, which develop eggs that hatch internally. In oviparous species, sometimes eggs are merely dropped into the environment, but in many arachnids, there is parental care, in the form of protective webs (some spiders). Mothers may transport egg‐cases or young (some spiders and scorpions). Arachnids undergo an “incomplete metamorphosis”; a juvenile that resembles the adult emerges from the egg and then, through a series of skin changes (ecdysis), grows to maturity. Arachnids vary greatly in their methods of feeding. Some mites feed on plant juices, others on organic debris. Most ticks ingest blood or hemolymph. The majority of spiders and scorpions are “carnivorous”; the former ingest prey through external digestion of internal organs and hemolymph. Some arachnids are threatened species, either at an international level (through Convention on Trade in Endangered Species [CITES] and the IUCN) or nationally (species and/or habitat protection). A substantial number of arachnids, notably ticks and mites, are a threat to agriculture (livestock/crops). Of the venomous arachnids (the majority of spiders, all scorpions, some pseudoscorpions), a few are hazardous to humans and other vertebrate animals, some are even lethal. Some species, such as harvestmen, are harmless. Trade in arachnids is restricted to species that are kept in zoos or by private arachnologists, and those that are used in biomedical research. The list of traded species is constantly growing with new species turning up in the pet trade before scientific description, as evidenced by taxonomic papers citing captive material as their source, such as for some Tapinauchenius (Hüsser 2018). Traded species are predominantly theraphosid spiders, but many scorpions and true spiders are also frequently traded in the international pet trade, although few are protected. As of January 2019, only 26 species are listed under the CITES all Appendix II, EU Annex B. These are species in the genus Brachypelma (family Theraphosidae), Aphonopelma albiceps, and Aphonopelma pallidum (family Theraphosidae, previously in genus Brachypelma), and four species of Scorpionidae of the genus Pandinus (Pandinus dictator, Pandinus gambiensis, Pandinus imperator, and Pandinus roeseli) (UNEP 2019). In total, 286 species have been evaluated by the IUCN redlist (www.IUCNredlist.org) with 52 species found to be critically endangered, thus conservation evaluation in the arachnid taxa to date has only evaluated a small percentage of the global species and these are heavily biased to the large spiders. In biomedical research, peptides found in the venom of arachnids are becoming increasingly important in studying drug targets such as ion channels and others (Escoubas and Rash 2004). Although pain and neuroscience are the predominant indications (Trim and Trim 2013), other indications are also pursued including pesticides (Hardy et al. 2013). Alpha‐latrotoxin (Tzeng and Siekevitz 1978) from the black widow spider (Latrodectus mactans) and imperatoxin from the emperor scorpion (Pandinus imperator) have been used to understand the biology of neurons. Zoonosis is, strictly, an infection that can be acquired by humans from a vertebrate animal but it should be noted that certain arachnids can be a source of nematodes of the family Panagrolaimidae (Pizzi 2009; Pizzi et al. 2003), which can be of medical concern to humans. Although all arthropods have abundant segmentation embryonically, arachnids have reduced outward segmentation in adults. This is most pronounced in animals from the subclass Acari, which have no external segmentation. Most other arachnids are segmented into an anterior prosoma and a posterior opisthosoma with a narrow waist called a pedicel (the seventh embryonic segment) joining the two. The opisthosoma is segmented in eurypterids and scorpions; most other arachnids do not have opisthosomal segmentation. Some species also have a telson, or tail. In scorpions, the telson contains a venom gland and is connected to the aculeus (stinger), and in palpigrades, uropygids, and schizomids it acts as a sensory flagellum. Arachnids have six paired appendages. The first are the chelicerae, the second are the pedipalps, and the last four are the walking legs. Each chelicera is attached to the cranial aspect of the prosoma via a fixed basal segment that is articulated with a movable fang. The fangs typically rest in a groove in the basal segment, from which they pivot outward to strike prey. Venom is delivered through a slit in the subterminal portion of the fang. The chelicerae are not only used for capturing prey, but also for defense and for grasping various objects. These are most well developed in the Solifugidae (Klann 2009). The second appendages, the pedipalps, have segmentation similar to the legs except they lack one segment, the metatarsus. Pedipalps are not used for locomotion (except in Aranae), but for capturing and manipulating prey. The first segment of the pedipalps, the coxa, forms the preoral cavity and is frequently modified to macerate prey. In all but the Aranae, Solifugidae and Ricinulei, the pedipalps form grasping claws with a single mobile finger opposing a fixed finger. Additionally, male spiders produce a bulbous distension of the terminal aspect of the pedipalps, called the palpal bulb, upon sexual maturity, for copulation. Four pairs of walking legs attach to the prosoma caudal to the pedipalps. Walking legs have seven segments, including (from proximal to distal) the coxa, trochanter, femur, patella, tibia, metatarsus, and tarsus. The tip of the tarsus bears claws. The number of leg segments and number of claws may vary between species (Ruppert et al. 2004). Paired eyes are on the craniodorsal aspect of the prosoma; in Araneidae, there are four pairs on an ocular tubercle. The cranioventral aspect of the opisthosoma has a number of book lung slits (in pulmonate species) that are adjacent to the epigastric furrow. The cloaca and spinnerets are located on the caudoventral aspect of the opisthosoma. The opisthosoma is typically covered by setae in Theraphosidae. Setae are detachable and urticating in most new‐world theraphosids. There is a great deal of variation of the gross anatomy within Arachnida. Gross external anatomic features are provided for Theraphosidae in Figure 8.1, Scorpiones in Figures 8.2 and 8.3, and Acaridia in Figure 8.4. There are multiple dissection techniques that can be applied to arachnids. The method described here is the authors’ preferred technique with respect to Araneae. The dissection method may need to be modified for other orders of Arachnida. Successful microdissection is greatly aided by stereo microscopy with 2×–5× magnification and through the use of size 5 microforceps and bow scissors. The prosoma and opisthosoma are dissected separately starting with the prosoma. The prosomal carapace is cut at its periphery with shears and then gently lifted to expose the underlying muscle and nerves (Figure 8.5a,b). Muscular attachments from the carapace to the underlying structures will need to be cut for the carapace to be easily removed. The eyes and the optic stalk can be visualized and these can be followed down to the cranial part of the supraesophageal ganglion (sometimes referred to as the central ganglion, protocerebrum or “brain”) (Figure 8.6). Gentle dissection of dorsal musculature will expose a hard cartilaginous structure, the endosternite. In Araneae, the endosternite is centrally located and proximal to the pedicle originating from the dorsal opisthosoma. Dorsal to the endosternite is the esophagus and stomach which leads to the opisthosoma. Beneath the endosternite is the central ganglion. The central ganglion can also be easily identified by removing a leg and following the nerve branch to the central ganglion. Figure 8.1 Gross anatomy. Dorsal (left) and ventral (right) view of theraphosid spider. Figure 8.2 Gross anatomy. Dorsal (left) and ventral (right) view of scorpion. Figure 8.3 Mesolense image of unidentified Pseudoscorpion from Peru. Source: Reproduced with permission from G. McConnell (University of Strathclyde, and R. Piper and D. Wilcockson (University of Aberystwyth). Figure 8.4 Gross anatomy. Dorsal (left) and ventral (right) view of ascarid mite. Roman numerals correspond to numbering of coxae. Figure 8.5 Dissection of a theraphosid spider (Therophosa stirmi). The prosomal carapace has been cut away (a). On higher magnification using a dissecting microscope (b), the edge of the prosomal carapace is at the margin of the image (arrowheads). Most of the exposed tissue is dorsal carapacial muscle (asterisk). The pedicel is also visible (dashed circle). It is advisable to detach a leg for individual dissection; this is best achieved by applying firm traction upwards while holding the femur of the leg. Cutting the cuticle around the leg is often necessary to fully expose the nerve and muscles within the leg. Muscles surround the nerve and artery, which runs parallel to the nerve. For the opisthosoma, careful removal of the exoskeleton in a similar way to the prosoma is recommended. Organs within the opisthostoma are tightly adhered together with connective tissue, so dissection of the internal organs is best done with an appreciation of the different textures of the organs, along with their gross locations. Silk glands (Araneae) are usually simple to identify as they have a distinctive spheroid appearance similar to a “bunch of grapes” and exist ventrocaudally. Silk glands in males are often smaller than in females. Ovaries and testes are cranial to the silk glands but can be difficult to differentiate from them. Some arachnid species have paired and unpaired reproductive tracts. The luminal alimentary tract can be dissected by navigating from the cloaca and stercoral sac and working through the tract cranially. Very gentle dissection is required. Malpighian glands are interspersed with the midgut diverticula and appear as spherical distinct organs. They terminate in a series of ducts into the luminal alimentary tract though this is often very difficult to see on gross dissection. Cardiac tissue can be challenging to identify, but when the opisthosomal cuticle is carefully dissected, it is possible, in some species, to see the indentation of the pericardial sac on the ventral cuticle and this can aid in dissection and identification (Figure 8.7). Figure 8.6 Dissection of a theraphosid spider (Therophosa stirmi) using a dissecting microscope, continued from Figure 8.5. The prosomal carapace has been removed, leaving only the edge of the prosomal carapace is at the margin of the image (arrowheads). The endosternite (ES) has also been cut away to expose the underlying tissues. Dorsal carapacial muscle (asterisk) and the pedicel (dashed circle) are visible at the periphery. The subesophageal ganglion (G) is at the center of the image, off of which branch the optic nerve (ON), and multiple small nerves, each with an accompanying vessel (V and N). Though dissection can be very useful when looking at specific organs and gross pathology, the authors find that histologic sectioning of the whole opisthosoma is more fruitful, especially when trying to determine the presence of pathology, as the overall tissue structure is maintained more successfully. Figure 8.7 Dissection of a scorpion (Parabuthus transvaalicus). The prosomal and opisthosomal carapace has been removed. The inner aspect of the opisthosomal carapace has a groove (arrows) representing the recess in which the heart lies. The dissection reveals the eye (circle), midgut diverticula (MD), heart and neural ganglia (arrowheads), metasomal muscle (asterisks), and telson (T). For dissection of Araneomorph spiders, a similar technique can be followed, but due to the fragile nature of the opisthosoma it needs to be gently peeled back from cranial to caudal, over the dorsal surface. The heart will be found attached to the ventral surface of the cuticle. Acari and Opiliones specimens can be investigated by inserting the microforceps laterally into the anterior portion of the opisthosoma and peeling the cuticle away in sections. The authors’ preferred technique for Opiliones requires removal of legs from one side by breaking off at the trochanter and then the fused prosoma and opisthosoma can be opened by dissecting laterally to remove the dorsal cuticle. The overall body structure can be separated into the prosoma and opisthosoma, all of which is covered by a chitinous exoskeleton. The exoskeleton acts to protect the internal organs from the external environment and as a sensory organ through chitinous hair and slit sensilla. The limbs are required for movement, protection, and sensation. The pedipalps have sensory, feeding and locomotor roles, and the terminal bulb is the location of sperm storage prior to insemination in Araneae. a Alternative names for organs are provided parenthetically, in italics. The cuticle thickness varies across the body of an arachnid, often being thicker over the prosoma and thinner over the opisthosoma. The cuticle presents difficulties in the sectioning stage of processing. Fixation with AZF fixative or Davidson’s fixative for 5–7 days can aid in softening the cuticle and thus make sectioning less disruptive to internal tissues. The cuticle is divided into layers: epicuticle, exocuticle, endocuticle, and epidermis. The epicuticle is thin and acellular; it can often be lost in processing or not take up stain as readily. The exocuticle and endocuticle are much thicker and account for the majority of the cuticle thickness; these layers may be difficult to distinguish from each other or may have a clear bilayer. The endocuticle is eosinophilic and acellular with distinct chitinous layering. With the exception of the oral cuticle, there are frequent cuticular canals and junctions (Kennaugh 1968; Krishnan 1953) (Figures 8.8 and 8.9). The uptake of eosin can vary across the cuticle, with the innermost endocuticle taking on more stain and the outermost exocuticle taking up less. The thickness of and proportion of the different layers of the cuticle vary depending on function, anatomic location, and species. The prosomal cuticle has a thicker endocuticle layer resulting in an overall thicker cuticle whereas articular cuticle is thin and is often predominantly exocuticle and epicuticle (Hadley 1981). Several different structures are within or attached to the cuticle. Hair sensilla and cuticular ducts pass through the cuticle (Schaber and Barth 2015). Striated skeletal muscle and other cartilaginous structures can be directly attached to the basilar aspect of the cuticle as a cuticular junction. Cuticular villi are present in some species. Figure 8.8 Transverse section of wolf spider cuticle showing a simple epidermal layer (Epi) overlain by the endocuticle (En), exocuticle (Ex), and epicuticle (Ep), 400×. Modified trichrome. The dorsal opisthosoma of new‐world Theraphosidae (except Ischnocoline subfamily) contain urticating setae not detected in any other arachnids. These were first described in 1972 as four classes with a further class subsequently discovered on the palps of Ephebopus spp. (Cooke et al. 1972; Foelix et al. 2009). Urticating setae are characterized by a weak attachment breakpoint at their base or sockets (types V and VI) and penetrating tips with barbs on the shaft (Bertani and Guadanucci 2013). These characteristics have evolved for defense and are irritating to mucous membranes with potential for penetration and thus should be considered as an occupational allergen (Castro et al. 1995). The cuticle can line and extend into other internal structures within the body. For instance, the oral cavity and proximal gastrointestinal tract are often lined with cuticle and this cuticle can extend further into the surrounding organs (often adjacent to or involving ducts and sinuses). Further to this, chitin can serve as tendinous attachments from internal organs and structures to the cuticle. The epidermis is composed of a simple single cell epithelial layer directly below the cuticle (Hadley 1981). Collagen fibers and myofibers can extend directly from the basilar aspect of the epidermis to deeper structures within the limb or body. Figure 8.9 Transverse section of cuticle of an unspecified arachnid species. Hair sensilla (arrows) arise from the cuticle, which is composed of epicuticle (arrowhead), exocuticle (Ex), and endocuticle (En), and is subtended by epidermis (Ep). 200×. Trichrome. The epidermis (also called hypodermis) is arranged as a single layer of columnar cells with basilar oval nuclei. Below the epidermis, there are occasional glands and ducts. Cells with ducts and glands have cytoplasmic vacuoles or granules. In pigmented species and in pigmented areas, there may be pigment deposits within or around the epidermis. White coloration in spiders is caused by the accumulation of guanocytes, which are cells that store guanine crystals. These cells are in the midgut and can form a contiguous layer below the epidermis due to the close proximity of the peripheral portions of the midgut to the epidermis. The guanine crystals in these cells reflect light. This light reflection produces white coloration in regions of the exoskeleton that are transparent. A well‐known example of guanocytes causing white coloration is on the opisthosoma of the common garden spider (Araneus diadematus) (Foelix 2011). Excessive melanin pigmentation within the exocuticle and endocuticle can also occur in response to inflammation. If inflammation is the cause of pigment deposits, bacteria, fungi, or inflammatory hemocytes may be present. Within Araneae, there is an endosternite (also called the cartilage shelf) which is present dorsal to the central ganglion and ventral to the gastrointestinal tract (the mouth, esophagus, and proximal intestines) and dorsal muscle (Figure 8.10). The exact position and length of the endosternite vary within the Arachnida and this feature is also present in Alpigradida, Acarida, Opilionida, Ricinuleida, Scorpiones, Solifugae, and Pseudoscorpionida (Firstman 1973). The endosternite is composed of an eosinophilic to chondroid matrix with lacunae. The lacunae contain vacuoles with peripheralized chondrocytes (Figure 8.11). Myofibers can be attached directly to the cartilage shelf. Skeletal muscle is present dorsal to the endosternite. In some arachnid species, there can be some calcification present within the endosternite (Kovoor 1978). Figure 8.10 Prosoma of a birdeater tarantula (Theraphosa blondi). The endosternite (E) is a rigid shelf in the prosoma to which striated muscle attaches. The sucking stomach (SS) is dorsal to the endosternite, and the aorta (Ao) is dorsal to the sucking stomach. Midgut diverticula (MD) are lateral to the aorta. Coxal glands (CG) are lateral to the midgut diverticula. 9×. HE. Figure 8.11 Endosternite of a birdeater tarantula (Theraphosa blondi). Cells of the endosternite are clustered in lacunae. 400×. HE. Figure 8.12 Cheliceral muscle in an unspecified wolf spider species. Longitudinal (a) and transverse sections (b) of muscle are present. 200×. Masson’s trichrome. The muscle in arachnids is predominantly striated skeletal muscle with nuclei both peripherally and centrally within the fibers (Figure 8.12). Muscle is predominantly found within the prosoma, the proximal limbs and the epidermal layer of the cuticle. Muscles vary in size depending on their location and function. The legs have extensor and flexor muscle at every joint except for the femur‐patella and tibia‐metatarsal joints, both of which lack extensors. The extension of these joints is caused by an increase in hemolymphatic pressure (i.e., hydraulic action). The muscles attached to the cuticle often elongate terminally and are continuous with fine cuticular tubes surrounded by the epidermis (Figure 8.13); this portion of the muscle is referred to by some as a “tendon,” and is prominent in the tarsal claws (Foelix 2011). Figure 8.13 Skeletal muscle of a birdeater tarantula (Theraphosa blondi). Skeletal muscle attaches directly to the internal surface of the cuticle via tendinous extensions (asterisks). Adjacent to areas of attachment are pigmented epidermal cells. Skeletal muscle bundles are separated by hemolymph. 125×. HE. The digestive system is composed of the luminal alimentary tract and the digestive ceca (also called midgut diverticula). The luminal alimentary tract is composed of the preoral cavity (formed by the coxa of the pedipalps), pharynx, esophagus, stomach, midgut, and hindgut. The midgut is the only portion of the alimentary tract without an inner cuticle lining, and as such is the primary site of food absorption. The majority of arachnids are liquid feeders so they lack specific mouthparts; however, many use the chelicera, characteristic of the class, for prey manipulation and to extract fluid for digestion. Cheliceral manipulation ranges from piercing in Acari, to envenomation in Araneae, to crushing in Solifugae. The preoral cavity, typically located within the prosoma, encompasses the chelicarae and pedipalps, which manipulate food material into the oral cavity, which leads to the pharynx and esophagus. The esophagus is continuous with the sucking stomach, which leads to the midgut, which is composed of a midgut tube and numerous prosomal and opisthosomal diverticula (also called digestive ceca). Prosomal diverticula extend into the legs in some species. At the junction between the midgut and hindgut in arachnids (except for solifuges), there is a blind‐ended pouch called the stercoral sac (also called cloaca). Malpighian tubules (excretory organ) terminate in the stercoral sac (when present) or at the midgut–hindgut junction. The oral cavity within Arachnida is predominantly located between the chelicerae. It is proposed that hair sensilla lining the preoral cavity are associated with taste (Foelix 2011). The preoral cavity, oral cavity, and pharynx are lined by a thick sclerotized cuticle with a subjacent pseudostratified epithelium. Some species have a prominent labrum over the dorsal opening of the mouth; Ricinulei has a specialized cuticular plate dorsally over the oral cavity called the cucullus (Talarico et al. 2011). There are minimal or no pores within alimentary cuticles. On the ventral aspect of the preoral cavity and oral cavity are setae‐like protrusions or “teeth,” which help filter liquified ingesta (Figure 8.14). The pharynx begins after the oral cavity. The pharynx has a variable shape on transverse section, with some species having a distinct “horseshoe” shape in Ricinulei (Talarico et al. 2011) or a “Y” shape in Solifugae (Klann and Alberti 2010). The cuticle luminal lining of the pharynx is thick and very sclerotized, with a thick epithelium. Additional setae‐like protrusions can be seen on the ventral aspect. Dorsal to the luminal pharynx is a relatively large pharynx dilator striated muscle which is responsible for the pumping action that transports liquified ingesta through the esophagus. Figure 8.14 Oral cavity setae of a zebra tarantula (Aphonopelma seemanni). Setae‐like protrusions over the epithelium help filter ingesta. 200×. HE. Figure 8.15 Esophagus of Asian jungle scorpion (Heterometrus sp.). The esophagus is a chitin‐lined, luminal structure surrounded by neuropil that runs horizontally through the brain, dividing the brain into the supraesophageal ganglion (dorsal to the esophagus; not pictured) and the subesophageal ganglion (ventral to the esophagus; pictured). 20×. HE. The esophagus is a narrow, chitin‐lined luminal structure that leads to the sucking stomach and lies dorsal to the endosternite. It is lined by a circular striated muscle that is attached to the basilar aspect of the esophageal cuticle. The esophagus passes horizontally through the central nervous system (CNS), diving the CNS into the sub‐ and supraesophageal ganglia, such as described for Solifugae (Klann and Alberti 2010) (Figure 8.15). The esophagus terminates in the sucking stomach, which is the main pump for food intake. The lumen of the sucking stomach has a larger diameter than the esophagus but is often collapsed in histologic section in a resting state (this resembles a “collapsed square”). The lateral and dorsal walls are attached to large muscle bundles; the muscular attachments to the lateral walls are attached to the endosternite (Figure 8.16). The sucking stomach is bordered dorsally by the aorta. When these muscles contract, the stomach luminal diameter expands greatly, acting as suction for liquefied ingesta (Foelix 2011). The sucking stomach ends at, and empties into, the midgut tube at the caudal end of the prosoma. The midgut tube has numerous branches called midgut diverticula or digestive ceca. These diverticula fill the majority of the opisthosoma and are present in smaller numbers in the prosoma (Ruppert et al. 2004).
8
Arthropoda: Arachnida
8.1 Introduction
8.1.1 Taxonomy
8.1.2 Life History
8.1.3 Relevance for Conservation, Agriculture, Trade, Etc.
8.2 Gross Anatomy
8.2.1 Dissection
8.3 Histology (Table 8.1)
8.3.1 Body Wall/Musculoskeletal
Organ system
Organs
Body wall/musculoskeletal
Cuticle, epidermis, endosternite, skeletal muscle
Digestive
Oral cavity, pharynx, esophagus, sucking stomach, midgut tube, midgut diverticula, hindgut
Excretory
Malpighian glands (kidneys), coxal glands, stercoral sac
Circulatory
Heart, pericardial sac, arteries, sinuses
Immune
Hemocytes
Respiratory
Book lungs, tracheoles
Nervous
Supraesophogeal ganglia, subesophageal ganglia, optic lobe, peripheral nerves
Reproductive
Male
Testes, palpal bulb
Female
Ovary, uterus
Special senses
Ocelli, cuticular sensilla
Special organs
Venom gland, silk gland
8.3.1.1 Cuticle
8.3.1.2 Epidermis
8.3.1.3 Connective Tissues
8.3.2 Digestive System
8.3.2.1 Oral Cavity
8.3.2.2 Pharynx, Esophagus, and Sucking Stomach
8.3.2.3 Midgut Tube and Midgut Diverticula
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