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Internal anatomy

English
Endoskeleton
 
Nervous system Digestive system
Blood and respiratory systems Reproductive system Terminology

As was it already stated before, all arachnids have not the internal skeleton, and internal organs of spider are comprised in shell of exoskeleton. However the last scientific studies have shown that inwardly organism of spider exists the complex structure, consisting of different elements, executing functions strictly as skeleton - endoskeleton.

Endoskeleton. The main elements, forming internal tarantula skeleton, are apodeme (the hollow inside structures), apophysis and entosternum. It above was already mentioned tergal apodeme, middle pressing in residing on prosoma carapace, serving inside revenge for fastening the muscles of sucking stomach (central apodeme). Except it exists else greater amount of other apodeme, serving important elements, linking transverse and longitudinal muscular threads with tarantula exoskeleton.

Except apodeme there is also other element, serving addenda to muscular system, consisting of material like to gristle, which is calls entosternum. Most large entosternum – prosomal entosternum is disposed directly over brain (ganglion) and has the form of horseshoe.

The Nervous system and organs of feelings. The central organ of nervous system of tarantula – ganglion, brain, is disposed in lower part on all length of the prosoma. It has two denominated parts - small upper brain, which gets information from visual and other nerves and lower brain greater size, having star-type form and executing main motor functions. It checks reflex and instinctive beginnings of the tarantula. Besides, ganglion has several ferrous bodies, similar in function to human hypothalamus, secreting regulative hormones.

From the brain to all prosomal organs is pulled the nervous threads, but one central thread goes through pedicel in abdomen.

The organs of feelings of tarantula are formed by the way of differentiation of coverall epithelium cells. On the top of prosoma, beside its front part, inheres towering platform - ocular tubercle, to which are located eight simple eyes (ocella ), connected with brain by means of visual nerves. The tarantula vision very weak, particularly besides burrowing species and the main function of perception of spiders executes the sense of touch.

It above was already mentioned that all tarantula body covered with the hairs. To bases of majority of them are attached nervous completions. These hairs considered being sensors, amongst which stand out two groups – trichobothria and setae, fitting in small hollows of exoskeleton. The main of their part inheres on tarantula pedipalps (also on legs). These hairs catch even most slightest waft of air, experimental way is stated that they perceive fluctuations in atmosphere on distance before one metre!

Besides, tarantulas possess the chemoreception, presented by so-called lyreform organs (sensillae), portioned on the whole body. They present itself microscopic slots in exoskeleton, delayed by fine membrane, which approaches the completion of sensitive nervous cells, perceiving pull exoskeleton that allows to adjust the degree of pressure on it. Some authors stated that they`re mechanoreceptors.

Also all tarantulas have more difficult structured tarsal organs (tarsal), being on pedipalps and first pair of legs, as well as gustatory hutches, disposed on walls of throat.

On the body of tarantula there is else certain amount of microscopic structures, importance which hitherto unknown.

Digestive system of tarantula either as beside other spiders or particularities of its construction is bound in the first place with typical for any spider so-called «external digestion».

The oral cavity is opened beside tarantulas between chelicerae by narrow, expanding to the front tube of gullet (pharynx), which, passing through brain, unites with muscular organ, refereed to as «sucking stomach». It unites the short tube with true stomach, to which, in turn, joins the gut, getting through pedicel pedicel in abdomen. In abdomen formed the network of thread-like organs (the malpighian tubes), uniting with gut. These organs execute the function, similar to buds of human being. Before anus, which opening directly upon spinnerets, inheres the straight line a gut, which at arm's length from anus forms bag-like stercororal pocket.    Thereby, tarantula, by chewing with powerful chelicerae food object (one of the distinguished line of tarantulas from majority of other spiders, which not "chew" food), pump digestive juice in it by sucking stomach, embroiling back already dissolved fluid food (the particles of food have the size beside micron). More large particles are filtered by the multiple setae disposed on the base of chelicerae and сoxa of pedipalp. The liquid food through sucking stomach falls into true stomach, where is partly digests. Main process of digestion occurs in gut at participation with malpighian tubes And hereinafter already digested food agglomerates in stercororal pocket, whence is deleted through anus in the manner of excrements.

Excrements present itself the monotonous globous mass, consisting of difficult for digestion parts of stern object (for instance, insect's chitin or small mammal`s bone), final products of digestion, which tarantula organism cannot digest, a nd superfluous salts.

In tarantula body there are also possess coaxial glands, disposed in bases of сoxa of leg I and III, importance of which before recent time remain unknown. However in 1991 Taylor and Batt have found out that they secret the liquid, promoting digestion (similarly saliva of human being and animals), as well as executing salt exchanging function in organism of tarantula.

Blood and respiratory systems of tarantulas closely interconnected.

In whole the Spiders is characteristic as pulmonary, so and tracheal breathing. But tarantulas being one of the primitive-organized groups of spiders do not have tracheal system and breaths using two pairs of lungs (named "book lungs" due to it`s structure), openning on lower side of abdomen by longitudal division (stomata, stigmata). Lungs of modern spiders were formed from abdominal gills drumsticks of their water ancestors.

Internal construction of tarantula lungs presents itself the grouped plate-form fine membranes (lamella), reminding pages of ajar book, inwardly which circulates the hemolymph, substituting carbon dioxide by oxygen, got from air. This plates are united between itself by ensemble of very small jumpers.

Different suggestions about respiratory movements besides tarantulas existed among the scientists. Just in 1987 the expieriements of Paul et al. have proved that there are very small fluctuations in walls of "book lungs" which coordinates with change the pressure of hemolymph in circulatory system. But, however, those fluctuations not executing directly respiratory functions.

Anatomy of Tarantula

Blood system not reserved. Bifurcating network of capillaries ends right in bodie tissues, from which the hemolymph seeping back in capillaries. Unlike other Arachnids blood system better all denominated exactly in tarantulas. In tarantula blood system circulates the hemolymph. Carryinging oxygen hemolymph pigment– hemocyanin contains copper (the haemoglobin of human being contains the iron). Four types of hutches also are present In hemolymph – hemocyt, which functions hitherto are not realized.

Hemolymph is painted in sulphur-blue colour and has characteristics of poison. Being introduced in organism of small mammal causes their death (similar characteristics have hemopymph of scorpions).

«Heart» of the tarantula presents itself long tubular organ, passing in higher part on centre of abdomen. It`s may be seing among American tarantulas in the manner of dark dorsal strip on bared part of abdomen. Tarantula heart comprised in pericardium, tubular camera, which covers heart with springy ligaments and organizes circulation of hemolymph inwardly blood-circulatory system. The surface of pericardium is coverred by big amount of nervious filaments not only causing, but also directly adjusting its contraction.

Tarantula heart has four pair of holes ostia along whole length, working as valves, through which under pressure moves hemolymph in both sides.

During pericardium contraction hemolymph moves on three directions – onward (through front aorta), back (through back aorta) and aside. Small capillaries, leaving from back aorta, saturate the organs and abdomen tissues. Entering way back in heart hemolymph moves by pericardium through front aorta and pedicel to prosoma, where it is enters in organs and tissues through arterial capillaries. Hereinafter, gathered in prosoma hemolymph the same way back to abdomen and falls into lungs. Here are goes the saturation of hemolymph by oxygen, after that it enters back in the heart where it stores in pericardium . tгде скапливается в перикарде and then moves for further circulation.

Reproductive system. Internal reproductive organs of male are presented by the paired testicles, which twisted seminal channels unites in united channel near split-like gonopore, opened at underside of the abdomen with, so-called epigastric furrow, lays near the first pair of book lungs. Area infront of epigastric furrow is refered to as epiginum.

Female gonads also are paired. They unite in womb openning with gonopore, which is closed by pleated rise – epiginum. Regardless the oviduct gonoslit oprnning at the epiginal area there are also found the channels, which linked with pocket-like spermatheca, used for accumulation and storing of males semeni (sperm) after copulation. Form and shape of spermatheca is an important taxonomical feature of the species.

Copulative males organ forms on ends of pedipalps only after the last (ultimate) molt than male became mature (adult) .

Copulative organ of male tarantula Nhandu coloratovillosusMutated pretarsus presents itself complex organ and has form of twisted throated bottle. The basal part - bulbum, apical – embolus. Males pedipalpal tarsus abbreviated and have the rolling joint with copulative apparatus. Tibia has special deepenning (alveolus), corresponding to on form of bulbus, in which it inheres (it is puted) in usual condition. At moment of mating copulative organ completely removed from alveolus that is directed onward downwards under angle to the remaining part of the pedipalp. Besides, male tibia of leg I of many species and leg II in some as well of tarantulas has special spurs or hooks (tibial apophyses), used for blocking female helicerae during the copulating process.

Tibial apophyses are absent in following genera listed ("A Listing of Male Theraphosids Which Lack Tibial Apophyses" by Lucian K. Ross & Rick C. West, from: BTS Journal No. 20 (3): 81-82):

 

Annandaliella Hirst, 1909 (Selenogyrinae)

Anoploscelus Pocock, 1897 (Eumenophorinae)

Augacephalus Gallon, 2002 (in part): A. junodi (Simon, 1904) (Harpactirinae)

Chilobrachys Karsch, 1891 (Selenocosmiinae)

Citharischius Pocock, 1900 (Eumenophorinae)

 

Coremiocnemis Simon, 1892 (Selenocosmiinae)

Euphrictus Hirst, 1908 (Selenogyrinae)

Heteroscodra Pocock, 1899 (Stromatopelminae)

Heterothele Karsch, 1879 (Ischnocolinae)

Hysterocrates Simon, 1892 (Eumenophorinae)

Ischnocolus Ausserer, 1871 (Ischnocolinae)

Lyrognathus Pocock, 1895 (Selenocosmiinae)

Metriopelma Becker, 1878 (Theraphosinae)

Nhandu Lucas, 1981 (in part): N. carapoensis Lucas, 1981 (Theraphosinae)

Orphnaecus Simon, 1892 (Selenocosmiinae)

Pachistopelma Pocock, 1901 (shield of spines only) (Aviculariinae)

Phlogiellus Pocock, 1897 (Selenocosmiinae)

Phoneyusa Karsch, 1884 (Eumenophorinae)

 

Phormingochilus Pocock, 1895 (Ornithoctoninae)

Plesiophrictus Pocock, 1899 (in part): some males may possess tibial apophyses (Ischnocolinae)

Poecilotheria Simon, 1885 (Selenocosmiinae)

Selenocosmia Ausserer, 1871 (Selenocosmiinae)

Selenotholus Hogg, 1902 (Selenocosmiinae)

Selenotypus Pocock, 1897 (Selenocosmiinae)

Sericopelma Ausserer, 1875 (Theraphosinae)

Stromatopelma Karsch, 1881 (Stromatopelminae)

Theraphosa Thorell, 1870 (in part): T. blondi (Latreille, 1804) (Theraphosinae)

Thrigmopoeus Pocock, 1899 (Thrigmopoeinae)

Xenodendrophila Gallon, 2003 (Stromatopelminae).

 

Main terms used to describe the systematic, taxonomy, anatomy, biology and physiology of tarantulas:

 

 

Abdomen (opisthosoma)

The hindmost of main body divisions of tarantula and insect

Adeagus

The part of the male genitalia which is inserted into the female during copulation and which carries the sperm into the female. Its shape is often important in separating closely related species

Allopatric

Two or more forms of a species having essentially separate distributions

Allotype

A specimen designated from the type series that is the opposite sex of the holotype

Anterior

Concerning or facing the front, towards the head end of the body

Anus

The posterior opening of the digestive tract

Aorta

The anterior, non-chambered, narrow part of the heart which opens into the head

Apodeme (tergal a.)

Place of fastening the internal muscles to spider exoskeleton, residing in deepenning of carapace. In tarantulas apodeme with entosternum form its internal skeleton (endoskeleton)

Apolysis

The word used to describe molting or ecdysis; when a spider sheds its skeleton

Arachnida

A class of arthropods which include the scorpions, spiders, mites, ticks, among others

Arboreal

Living in, on, or among trees

Basal

Concerning the base of a structure - that part nearest the body

Basitarsus

The 1st segment of the tarsus - usually the largest

Bionomics

The study of the habits, breeding, and adaptations of living forms

Book lungs

A respiratory cavity containing a series of leaflike folds

Bulp

The part of a male tarantula`s pedipalp which acts as a container for the sperm and bears the embolus

Carapace (tergum)

Unadulterated dashboard, covering thoracic segment of prosoma

Cephalic

Of or pertaining to the head

Cephalothorax

A body region consisting of head and thoracic segments, as in spiders

Chelicera (pl., chelicerae)

The anterior pair of appendages in arachnids, the fangs

Chitin

The tough horny material, chemically known as a nitrogenous polysaccharide, which makes up the bulk of the arthropods cuticle

Cladogram

A diagram showing nothing more than the sequence in which groups of organisms are interpreted to have originated and diverged in the course of evolution

Class

A division of the animal kingdom lower than a phylum and higher than an order, for example the class Arachnidae

Clypeus

Triangle-like lowest part of the tarantula carapace, just above the labrum. Clearly shown in Brachypelma emilia with dark colored triangle in cephalic area of carapace

Coxa

The basal segment of the arachnid leg, which attaches to its cephalothorax

Cuticle

The outer noncellular layers of the arachnid integument secreted by the epidermis

Cymbium

The upper segment of male pedipalp of spider, representing itself complex copulative organ type which alongside with spermatheca shape of female is of taxonomic importance under tarantula species determination

Dimorphism

A difference in size, form, or color, between individuals of the same species, characterizing two distinct types

Dorsal

On or concerning the back or top of an animal

Ecdysis

The moulting process, by which a young arachnid changes its outer skin or pupal case

Endemic

Restricted to a well defined geographical region

Embolus

Segment of spider pedipalp of mature male residing on cymbium and used as copulative apparatus which transfers a pserm in female`s tarantula

Endoskeleton

In a complicated way outline system inwardly organism of spider, executing functions of "skeleton"

Epigastric furrow

A slit between the two forward pair of book lungs, that is the opening of of the genital aperture

Exoskeleton

External "skeleton" of tarantula

Exuvium, exuvia

The cast-off outer skin of an arthropod

Family

A taxonomic subdivision of an order, suborder, or superfamily that contains a group of related subfamilies, tribes and genera. Family names always end in -idae

Fang

An apical segment of tarantula`s chelocerae used to inject venom into prey items

Femur

The 3rd (counting out from the body) and often the largest segment of the insect leg

Foregut

The anterior part of the alimentary canal from the mouth to the midgut

Fossorial

Adapted for digging

Fovea (thoracic fovea)

An indentation in the carapace of a tarantula

Fuscous

Smokey grey-brown in colour, normally applied to wings

Ganglion

A nerve mass that serves as a center of nervous influence, tarantula "brain"

Genus

A group of closely related species (plural: genera). The name of the genus is incorporated into the scientific names of all the member species

Hemolymph

The blood plasma or liquid part of the blood, though generally synonymous for blood of arachnids

Habitus

Body-build, general appearance

Homologous

Organs or parts which exhibit similarity in structure, in position with reference to other parts, and in mode of development, but not necessarily similarity of function, are said to be homologous

Holotype

The type specimen of a species is the actual tarantula from which the original description of that species was produced. If several specimens were used for this purpose, one of them should have been designated as the type. Because the type can be of only one sex, it is usual to designate a certain individual of the opposite sex as the allotype. The original type specimen is then called the holotype

Homonym

A scientific name which has been given to two different species. When such an instance comes to light one of the species must be given another name

Host

The organism in or on which a parasite lives

Instar

Age of spider, definied gap between any two moults. A newly-hatched insect or atachnid, which has not yet moulted is said to be a first-instar nymph or larva. The adult (imago) is the final instar in insects or males of tarantulas

Labellum

The expanded tip of the labium

Labium

The 'lower lip' of the insect mouth-parts, formed by the fusion of two maxilla-like appendages

Labrum

The 'upper lip' of the mouth-parts

Lateral

Concerning the sides

Malpighian tubes

Excretory tubes of insects arising from the anterior end of the hindgut and extending into the body cavity

Maxilla

One of the two components of the insect and arachnid mouth-parts lying just behind the jaws. They assist with the detection and manipulation of food and are often drawn out into tubular structures for sucking up liquids

Metatarsus

The basal segment of the tarsus or foot: usually the largest segment

Moult

To moult is to shed the outer covering of the body - the exoskeleton

Nocturnal

Active at night

Ocular tubercle

A triangular area, usually quite distinct from the rest of the head with domes that a tarantula`s eyes can see through

Ocellus (Plural Ocelli)

One of the simple eyes of insects, usually occurring in a group of three on the top of the head, although one or more may be absent from many insects

Order

A subdivision of a class or subclass containing a group of related families

Oviparous

Producing eggs which are hatched outside the body of the female

Palp

A segmented leg-like structure arising on the maxilla or labium. Palps have a sensory function and play a major role in tasting food

Patella

Fourth segment of leg of spider (spider`s knee)

Pedicel

Section of body of spider, connecting prosoma with opisthosoma

Pedipalp

The second pair of appendages of an arachnid

Pharynx

The anterior part of the foregut between the mouth and the esophagus

Phylum (pl., phyla)

A major division of the animal kingdom, containing various suborders and classes etc

Pilose

Densely clothed with hair

Plumose

With numerous feathery branches: applied especially to antennae

Posterior

Concerning or facing the rear

Predator

An animal that attacks and feeds on other animals, usually smaller and weaker than itself

Pretarsus

Seventh the terminal segment of the leg bearing the pretarsal claws. Most authors not confesses it as independent segment and includes in tarsus

Proximal

Concerning the basal part of an appendage - the part nearest to the body

Pubescent

Covered with short, soft hair

Race

A variety of a species; a subspecies

Rastellum

Spines that overhang the chelicerae of mygalomorph spiders, except Tarantulas

Reticulate

Covered with a network pattern

Rostrum

A beak or snout, applied especially to the piercing mouth-parts of bugs and the elongated snouts of weevils

Rudimentary

Poorly or imperfectly developed

Sclerite

Any of the individual hardened plates which make up the exoskeleton

Sclerotization

The hardening and darkening processes in the cuticle (involves the cuticle with a substance called sclerotin)

Scopula

A small tuft of dense hairs of uniform lengh. In tarantula presents on the underside of apical legs segments and allows to climb

Segment

One of the rings or divisions of the body, or one of the sections of a jointed limb

Setae

A bristles, term for arthropod "hairs"

Sigilla

Indentations on a spider`s sternum

Species

The basic unit of living things, consisting of a group of individuals which all look more or less alike and which can all breed with each other to produce another generation of similar creatures

Spermatheca

A small internal receptacle of the female tarantula in which sperm may be stored - a sperm storage

Spermatophore

A packet os sperm

Spiderling

A baby tarantula

Spine

A multicellular, thorn like process or outgrowth of the integument not separated from it by a joint

Spinnerets

Appendages on the rear of a tarantulas that are used to spin webbing

Striae

Grooves running across or along the body

Stridulation

The production of sounds by rubbing two parts of the body together

Stadium (pl., stadia)

The time interval between molts in a developing insect. The same term as Instar in tarantulas

Stage

A distinct, sharply differentiated period in the development of an insect, e.g., egg stage, larval stage, pupal stage, adult stage; in mites and ticks, each instar

Sub-species

A sub-division of a species, usually inhabiting a particular area: visibly different from other populations of the same species but still able to interbreed with them

Suture

A groove on the body surface which usually divides one plate or sclerite from the next

Synonym

One of two or more names which have been given to a single species. The earliest name usually (should) takes precedence

Tarsus (pl., tarsi)

6th segment of leg of spider. 2d, 3d, 4th and 5th pair of segments consists of two pseudosegments – basitarsus and telotarsus. Some authors consider its last segment, in such event it precedes metatarsus (leg consists of 7 segments)

Tergum

The dorsal surface of any body segment

Terrestrial

Tarantula that lives on or in the ground

Tibia (pl., tibiae)

The forth leg segment between the femur and the tarsus

Tibial spurs

Hooks on most male tarantulas` tibias that are used to secure a female`s fangs while mating

Trochanter

The second segment of the leg, between coxa and femur: often very small and easily overlooked

Tubercle

A small knob like or rounded protuberance

Type

The type specimen of a species is the actual insect from which the original description of that species was produced. If several specimens were used for this purpose, one of them should have been designated as the type. Because the type can be of only one sex, it is usual to designate a certain individual of the opposite sex as the allotype. The original type specimen is then called the holotype

Urticating hairs or bristles

Barbed hairs on most New World tarantulas` opisthosoma that they flick off by rubbing by their hind legs

Venter, ventral

Undersite, a "belly" of tarantula

   

In conclusion I will note two main particularities, typical for all spiders of fauna of the world – ability to make web and to grow due to a periodical change of the exoskeleton (molting).

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