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IDENTIFICATION OF ARTHROPODA

 

Introduction.

 

Arthropods are the most numerous "phylum" of the animal kingdom: about the  95% of all known species belong to this "phylum". Arthropods can be distinguished from other animals because they are invertebrate and have articulate legs; this character gives the name to the phylum. They have two compound eyes (formed by many eyes called ommatidia) and/or the ocelli (simple eyes). Most of them are oviparous, they lay eggs, but there are also viviparous arthropods procreating living animals and ovoviviparous arthropods, the incubation of eggs is internal and therefore the eggs open just when they are laid. Generally arthropods are subject to the metamorphosis process. The other terrestrial invertebrate animals belong to the phyla Anellida [usually called as worms (1)] and Mollusca (class of Gastropoda).

 

Here it is the list of the most common classes of Italian arthropods with terrestrial species. The name of classes is the Latin one and, when available, there is also the link to the photos (in the legend there are the scientific name of order and suborder  in black; family in blue; genus, species and subspecies in brown, and the common name in green). Photos were taken in Catania and Pedara (Sicily).

 

See also the guide with pictures and the index cards.

 

Crustacea Class

 

Crustacean dermoskeleton (external body layer made of chitin) is strong and generally covered by calcareous (carapace): most of them live in the sea, but some live in rivers, lakes, ponds and there are also terrestrial species. Their body is divided in cephalothorax (thorax and head are fused together) and abdomen; they have two pairs of antennae and are oviparous, generally respiration is brachial. Some orders of this class are: Cladocera (abdomen not segmented, flat body), Isopoda (without carapace, legs are similar, in this order there are many terrestrial species in particular those of family Porcellionidae which can't roll into ball and those of  Armadillidiidae which can roll into ball), Decapoda (with carapace, the first three pairs of legs are fitted to catch and triturate food) these last two orders belong to Malacostraca, the subclass with the most developed crustaceans.

 

See also Crustacea photos

 

Insecta Class

 

It is the most numerous class. Insects can be distinguished from other arthropods because adults have 3 pairs of  legs. It is this class the only with winged animals.

 

Arthropods: go to the insect identification guide

 

Arachnida Class

 

Generally, Arachnids body is divided in two sections: cephalothorax (thorax and head are fused together) and abdomen (in species of Opiliones and Acari these sections are fused together), they have neither wings nor antennae. They have four pairs of legs and two pairs of appendages, chelicerae and pedipalps, usually suited to catch and kill preys, in fact many species are carnivorous. Generally respiration is pulmonary; Arachnids have only simple eyes and are oviparous or viviparous.

Arachnids are divided in different orders, some of which are:

 

 - Acari (mites, ticks): body is not segmented (newly hatched young have only 2-3 pairs of legs), they are very small and many species are parasite. Ticks are in the families Argasidae (without a dorsal shield, parasite of birds) and Ixodidae (with a dorsal shield, parasite of mammals). Some other families are:  Pyrogliphidae (dust mites belong to this family), Tretranichidae (clover mites belong to this family and may infest trees, vegetation and buildings too).

 

 - Araneae (spiders): body is divided in two sections: cephalothorax and abdomen. Some of the most common families of spiders are (for a rigorous  identification we should look at morphological features that are not easy to see in photos so here are only given general indications): Agelenidae (funnel web weavers build web ending in a tube which is their shelter; they have long spinnerets), Araneidae (orb weavers, also called garden spiders, build spiral webs), Clubionidae (sac spiders build a tubular sac opened at both extremities), Linyphiidae (build a web with a shape of a sheet or a dome), Lycosidae (wolf spiders do not build webs, the fourth pair of legs is the longest), Pholcidae (daddy-long-legs, also called cellar spiders, have long legs just like Opiliniones but the body is divided in two sections; they build irregular webs), Salticidae (jumping spiders are quick jumpers; they do not build webs), Theridiidae (combfooted spiders, also called house spiders, have a globular abdomen and build irregular webs), Thomisidae (crab spiders have first pairs of legs longer than other legs; they walk sideways or backwards and do not build webs).

See also Spider photos

 

- Opiliones (harvestmen): cephalothorax and abdomen are fused together; generally legs are long and thin. See also Opiliones photos

 

- Palpigradi (palpigrads): small species (up to 0,28 cm long), the body end with a long thread-like appendage kept vertically when they move. Other species having an appendage are those in the order Thelyphonida (at least 0,3 cm long, not present in Italy) and Schizomida (small species, appendage is short, not present in Italy).

 

- Pseudoscorpionida (pseudoscorpions): they resemble scorpions but are smaller (up to 0,6 cm) and have no tile. See also Pseudoscorpionida photos

 

- Scorpiones (scorpions): body divided in two sections, cephalothorax and abdomen; abdomen is divided in may segments of which the latest are narrow. The last segment ends with a venomous stinger. Pedipalps are very large and end with big chelae. See also Scorpiones photos

 

- Solifugae (solifugids, wind scorpions): they resemble pseudoscorpions but are bigger (at least 0,8 cm long) and pedipalps end with an adhesive organ. In the species of the order Amblypygi (at least 0,5 cm long, not present in Italy) chelicerae are instead small, pedipalps are strong, thorny, without an adhesive organ and fore legs are thin and extremely long.

 

 

Diplopoda Class

 

Millipede body, just like Centipede one,  is divided in two sections: head and trunk, in fact thorax is fused with abdomen. Trunk is divided in many segments with two pairs of legs (a few segments, generally the first and the last ones, may be wingless or with only 1 pair of legs). Antennae are shorter than Centipede ones. They have night habits, respiration is cutaneous or tracheal, in this case a system of small tubes communicating with outside assures the oxygenation of internal tissues. They are oviparous. Chilopoda and Diplopoda are sometimes jointed together into a larger class called Myriapoda.  Some of the commonest orders are: Glomerida (cylindrical, short body, 11-12 segments, the family Glomeridae is in this order), Julida (cylindrical, long body, 40 or more segments, the family Julidae is in this order), Polidesmida (flat body, generally with 20 segments, the family Polidesmidae is in this order).

 

See also Diplopoda photos

 

Chilopoda Class

 

Centipede body is divided in two sections: head and trunk, in fact thorax is fused with abdomen. Trunk is divided in many segments with one pair of legs. Antennae are long. Respiration is cutaneous or tracheal, they are oviparous and have night habits. Some of the commonest orders are: Geophilomorpha (31-177 pairs of legs, the family Geophilidae is in this order), Lithobiomorpha (15 pairs of legs, the family Lithobiidae is in this order), Scolopendromorpha (21-23 pairs of legs, the family Scolopendridae is in this order), Scutigeromorpha (15 pairs of long legs, the family Scuterigidae is in this order).

 

See also Chilopoda photos

 

Pauropoda Class

 

Small arthropods, whitish, with 9 pairs of legs and  branched antennae.

 

Symphyla Class

 

Small arthropods, whitish, with 7-12 pairs of legs and two abdominal appendages.

 

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(1) There are other species called as worms such as those in the phyla Platyhelminthes and Nematoda.

 

Bibliography

 

 

Alessandro Strano