Internal anatomy

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.

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) .

Mutated 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:

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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