LZ Spiders Cnt Eng 190914.Indd

A wide variety of creatures inhabit the forests, tundras and bogs of the Lapland reserve. Each group of animals has its own unique role in a complex hierarchy of ecological relationships. Special place is hold by the most numerous predators in the microcosm – spiders. Spiders of the Lapland reserve Оrder of spiders (Aranei) belongs to the class of the arachnids (Arachnida), subtype chelicerate arthropods (Chelicera- ta), type of arthropods (Arthropoda). At the present moment almost 44 000 species of spiders are known in the world. In number of terrestrial arthropods species, they are second only to related order of acarians (Acarina) and five major insect orders (beetles, butterflies, bugs, Diptera and Hymenop- tera). Spiders have fully inhabited all natural areas and ter- ranean habitat types. Spiders fauna in Russia has more than 2 500 species, and this is not the final number. It is not easy to present a complete portrait of these creatures; we will try to tell at least about several features of them. Unlike millipedes, crustaceans and insects spiders like all the chelicerate arthropods have quite simply organized mouthparts – there are two chelicerae (jaws analogue) and two pedipalps (tentaculites). Chelicerae consist of two segments – a main one and an end one, claw-like embedded in the main segment stria like a pen knife cutting edge. Claw- like segment by the way it is organized resembles a fang – inside is a channel which is used to conduct poison into a kill or an enemy body. However, chelicerae are used by spiders not only to bite an enemy, they also catch and mill kills; it is also of the Lapland reserve a tool to clean the other extremities, dig soil, cut a web while Spiders constructing it and for other needs. Pedipalps unlike chelicerae 1 Lapland state nature biosphere reserve consist of six segments with claws on the top of the latter and digestive system in spider’s prosoma is represented primarily are mainly used as tactile organs, although this is not their sin- by departments responsible for interaction with the environ- gle role. Using pedipalps spiders hold a kill and other objects, ment – esophagus and sucking stomach sucking (spiders do taste and smell, make a web. If fore feet are lost, pedipalps can not swallow food using jaws and throat, but gradually suck it in partially replace them and help moving. Many species of spi- a liquid form using a “vacuum pump” – sucking stomach). ders are able to cast feet. As a lizard’s tail, cast leg continues The rear half of spider’s body, by contrast, has collected moving for a while, distracting potential enemies, and a new almost all organs responsible for internal processes in a body. one grows on its place provided that a spider can still shed. A considerable part of the digestive system, and a chemical Adult males’ pedipalps convert into a copulatory organ. factory: – liver, excretory system, reproductive glands where The latter function of pedipalps is typical namely for spiders The pair of spiders Microlinyphia pusilla: ova and sperm are formed are located here; spinning gland and is not encountered among the other chelicerate arthro- differences between pedipalps of male and female are well seen are located here as well, capable of synthesizing unsurpassed pods. Once upon a time ancestors of male spiders used pedi- in its quality protein building material. If the main in a prosoma palps to transfer bags with semen – spermatophores – and uniting other organ systems (limbs, senses, etc.) – is a brain, passed them to females during a mating ritual. To make car- in abdomen such a center is heart ensuring hemolymph run rying spermatophores more convenient pedipalps have been and metabolism. changing gradually, a claw shifted from the top to the side surface of the last segment, and then acquired a bizarre shape, looking like a syringe capable of injecting semen into female genital pores. Segment itself has increased, acquired a spoon shape, and an onion-like syringe-claw securely storing sperm is located inside a “cup” of a “spoon”. The need for a protective bag – spermatophore – disappeared, and the only thing that reminds about it is that spider’s spermia are not located in semen one by one, but packed by several pieces together. Male pedipalps can often have some additional outgrowths, We will again remember extinct predecessors of spiders. bristles and deepenings of various shapes that fi t together fe- On rear part of a body they had limbs that were inherited male genitals key to a lock. This mechanism of “a lock and from the more ancient progenitors of all arthropods – annelid a key” is an obstacle for interspecifi c hybridization and there- polychaete worms. It must be said that limbs of animals – are fore is an important generic feature. Drawings of the exter- organs than can in the course of evolution be easily subjected nal sex organs are the basis for description of spider species to amazing modifi cations and can switch to completely differ- in the scientifi c literature. ent roles than in the beginning. This happened to abdominal Eyes of remote ancestors of spiders were faceted, complex, legs of ancient chelicerates: a part of them, which served for consisting of many simple eyes, just as of modern insects. Look of the spider-wolf Alopecosa aculeata seems quite sensible movement and breathing in water (they settled gill branches) However, after inhabiting ground ways of two groups of an- persistently kept on perform a respiratory function when ani- cestor diverged – if insects preserved faceted eyes, individual mals began to inhabit ground. For this purpose, pits and later facets of chelicerates were divided and gave start to forma- nests for respiratory legs were formed in abdomen to protect tion of simple eyes. It should be noted that such eyes often them from drying in air. Thus limbs transformed into lungs. give to an image of spider a remarkable resemblance to verte- It distinguishes spiders from insects and strangely reminiscent brates, unattainable for other arthropods. of terrestrial vertebrates: only they and we have lungs. How- Figure 8 is amusingly repeated manifold in a structure ever, with decrease in body size insect respiratory system – of spiders. This is known by everyone amount of walking legs, the trachea – is more suitable and many groups of spiders which distinguishes most arachnids; and a number of eyes switched to it partially or completely, and very small species (although some species of spiders, especially those living generally lost their respiratory organs and breathe through in caves can have reduced amount of eyes by one pair or more, the whole body surface. until complete absence of eyes). Even body shape of a spider Hind abdominal legs of ancient pre-spiders fulfi lled anoth- resembles an eight, consisting of the anterior part – prosoma er role. Spinning glands appeared namely here. What was their and posterior – abdomen. Prosoma is a half of body that is re- initial function is diffi cult to say; possible for making a shel- sponsible for interaction with the outside world. For a reason ter or protective canopy for eggs laying. Over time, the main a head and sense receptor of bilateral animals with a front end body of the glands moved to abdomen, only glands outputs of the body (as opposed to radially symmetrical animals, like left on shortening legs; number of legs segments was reduced sea stars) have developed namely in the front, in the direction to two or three, and the legs themselves displaced to the end of movement. This process reached its logical end at spiders: of abdomen. Thus spinnerets were formed, by the way an ini- the front half of the body has not only main sense receptors, tial number of them was equal to eight (four pairs)! Howev- of the Lapland reserve but limbs, and a nervous system inside a prosoma coordi- er, amount of spinnerets of modern spiders reduced up to 6, nates everything, it is concentrated in a rather complicated 4 or 2; it is enough to create webs. One pair of spinnerets Spiders for invertebrate brain, more perfect than, say, insects. Even The spider-wolf Trochosa spinipalpis, side-view of some spiders species is still very elongated and resembles 2 ABCGheritage – Our common arctic heritage digestive system in spider’s prosoma is represented primarily small legs, often used in addition to creating web as sense by departments responsible for interaction with the environ- of touch. Position of spinnerets on the end of the body, even ment – esophagus and sucking stomach sucking (spiders do a hind one, has proved to be very successful: they are able to not swallow food using jaws and throat, but gradually suck it in move as hand fi ngers, abdomen can also be moved from side a liquid form using a “vacuum pump” – sucking stomach). to side, moving the entire “palm with fi ngers” like a painter’s The rear half of spider’s body, by contrast, has collected brush. Amount of waking legs appeared to be abundant, there- almost all organs responsible for internal processes in a body. fore a rear pair is used, in addition to walking, to pull a web and A considerable part of the digestive system, and a chemical make manipulations with it. So it is not a surprise that with factory: – liver, excretory system, reproductive glands where such a set of “tools: and freedom of movement spiders have ova and sperm are formed are located here; spinning gland developed and improved their web making abilities. Suitable are located here as well, capable of synthesizing unsurpassed body structure served as a basis for further evolution.

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