Spines Structures Of The Other Tergal Plates example essay topic

Literature Review about centipedes More than 400 million years ago, not long after animals came to live on land, centipede already knew how to hunt in soil and litter. So, it is hard for me not to respect centipedes.! yen Centipede! | is the common name given to the joint-legged animals that zoologists classify in the class Chilopoda. Although! yenc enti! | means a hundred, centipedes don! |t have 100 feet, the actual range is from 15-191, in fact, none of them has exactly 100 pairs of leg. Indeed, all of them have an odd number of leg pairs.

Till now, only one mutant individual has been found to have an even number of leg pairs (Edgecombe, 2001). After I have read 10 literatures about centipede, I understand more about centipedes and I also have found out some areas that need to have some more research on it. Below, I will mention the taxonomy and morphology of the centipedes, their habitats and living style. Besides, I will also talk about how the differences of the body structures of centipedes help in the classification of different species for itself. I will also mention what I think after I have read all these 10 literature and suggest some research that we can do in the future helping the systematics. Centipedes are in the Phylum Arthropoda, superclass Myriapod a and the class Chilopoda.

There are 5 orders, which are the Scutigeromorpho, Lithobiomorpha, Geophilomorpha, Scolopendromorpha and Craterostigmomorpha. They are commonly living in leaf litter, under bark or logs, and in soil, ranging from sea level to mountaintops. They usually hunt at night. Their natural enemies are some snakes, rats and mites. They always defend themselves from their predator by shedding of legs and regenerating them in the next mount. Other defences include noxious secretions from glands on ventral body surface and producing sticky, silk-like threads from the last legs (Edgecombe, 2001).

Figure 1: The systematics of centipedes (Edgecombe and Giribet, 2002) Centipedes have segmented bodies but no distinct thoracic region as there is in insects. The dorsal surface of the centipede head is covered by a more or less rigid head capsule which bear simple oc elli or paired compound eyes (Verhoeff, 1904). The centipedes also have a pair of antennae, the ratio of length / width of the single articles and the relative length of the whole antenna are characters which separate some families. The morphologically homogeneous antennae carry many hairs and bristles of various shapes and length. Their arrangement relative to each other, and their pattern and density per article seem to be typical for genera, but not for single species (Verhoeff, 1924). Therefore, from the character of the antennae, it can be told which genera should it be in.

The mouth is situated ventrally and is bounded in front by the labrum or upper lip, which is usually divided into a mid-piece with a side-piece on each side. The rigid chitinous plate on the ventral side of the head anterior to the labrum is termed the clypeus. The mouth is bounded laterally by a chitinous! yenpleurite! | on each side. The appendages of the first three segments posterior to the mouth have been modified to form mouthparts and the tergites of these segments have been lost.

The first pair of the mouthparts are the mandibles, each of which consists of a trunk bearing a condyle which articulates with the skeleton of the head capsule and is produced proximally into a curved shank affording attachment for the muscles operating the appendage. The distal end of the mandible is broadened and armed with teeth or comb-like structures (Verhoeff, 1905). The second pair of mouthparts, the first maxillae, are situated ventrally to the mandibles and obscure them when the head is viewed from the ventral side. This pair consists of a basal plate formed from the fused coxae (the basal segment) of each leg and the sternite (the ventral skeletal plate) of the segment and hence called the coxosternite.

The coxosternite bears a pair of conical jointed appendages between which is a second pair of conical processes, the coxae projections. The third pair of mouthparts, the second maxillae, art ly cover the first maxillae and are recognisable leg-like in structure, each coxosternite bearing a telopodite consisting of three segments and an apical claw (Verhoeff, 1905). Up till now, it has been discovered that there may or may not be la bral and epi pharyngeal difference. Sometimes, the differences between single species are greater than that between genera (Verhoeff, 1904). As there is not any information about how the differences of the mouthparts of different species related to the taxonomy of the centipedes, I think there should be more research on this. As I have mentioned before, centipedes are having segmented body.

Each segment is made of a tergite (dorsal shield) and a sternite (a ventral shield). On each tergite, there are spines and the structure and distribution of the spines are not the same for each tergite. As the exoskeletal prominences are some of the best features for distinguishing the genera (Attems, 1926), the spines should be studied carefully. The spines are grouped under two categories, the first one is for simple, rigid, immovable and non-innervated prominences and the second group is for movable, innervated prominences (Wurmli, 1973). The scientist Wurmli has identified the spines by himself according to the information given by Verhoeff in his book in 1905. Under the first group of spines, he identified the short and slender creatures on the tergites as! yen hairs! |; the short, sturdy hairs as! yenSpinulae! |: the long spike-shaped hairs as! yenSpiculae! |; short spike-shaped hairs as! yen short spicula e! |; and the other articulated spines as! yen spines!

|. Under the second group of spines, he identified the setae as! yen bristles! | and the enlarged, thickened bristles as! yens pine bristles! |. All these clear identifications make me feel easier to understand. Wurmli has also drawn some of the spine features, and this also helped me to understand more about the different structures mentioned in Verhoeff's writings.

Till now, the study on the spines structure were based on the sixth and seventh tergal plates. For this, Wurmli has once pointed out in his paper in 1973 that it was not sufficient to describe the situation of the sixth and seventh tergal plates only because, according to Verhoeff's! SSDornenregel!" , in English, it means! SS they carry more prominences!" , but unfortunately, he did not do anything about the spines! | structures of the other tergal plates afterwards.

In his book, he has pointed out the reason he said this was because he knew that the tergite armour can vary during post embryonic development (Wurmli, 1973). Due to the reasons he mentioned in his work, I think that there should be more research done on the spines structure. Beside of the reasons given by Wurmli, I also think that doing more research on the spine structure is a good idea, as I suspect that the structures given by Verhoeff and Wurmli may not be very accurate. This is because during the time when they wrote their article, they could only use the light microscope. Under the light microscope, the magnification would not be enough to observe the specimen clearly, especially for the spines which are very tiny features. So, nowadays, with the condition that we already have scanning electronic microscope (SEM) and transmission electronic microscope (TEM), I think we should redo the investigation of the structure of the spines in detail again.

Both electronic microscopes can give clearer picture of the specimen, in fact, they can also show the very tiny structures of the spines which could not be shown under the light microscope. Therefore, I think if we can use the advanced technology we have today and investigate the structure of the spines, there may be some new contributions to the systematics of centipedes. For the legs, they consist of six basic segments, the coax, trochanter, pre femur, femur, tibia and tarsus are terminated by an apical claw and are inserted laterally into the pleural region. A marked exception to the normal constructional pattern of the trunk segments is seen in the first and to a lesser extent the last segments. The legs of the first trunk segment form large poison claws, variously termed prehensors, toxicognaths, maxilliped es and forcipules. The last term will be used here.

The forcipules reach forward under the head and partially cover the mouthparts forming part of the feeding apparatus. The forcipular tergite may be free or fused with the tergite of the second trunk segment; the sternite is invariably fused with the coxae to form the forcipular coxosternite. The anterior boarder frequently bears spines or teeth (Verhoeff, 1904). In conclusion, after I have read these 10 literatures, I really doubt that how can they draw that detailed diagrams in their papers by using just a simple light microscope. I think that nowadays, we already have such an advanced technology, so why not use them to do more research on the centipedes, may be there are more undiscovered features which would help the systematic.

So, I think there should be more studies on two areas: the structure and distribution of spines and how the differences between the mouthparts of different species related to the taxonomy of centipedes. I am sure there will be some interesting features on the centipedes that have not been discovered yet, and these discoveries may more or less contribute to the systematics of centipedes or even the Phylum Arthropoda.

Bibliography

Attems. C (1926).
The Myriopoda of South Africa. Annals of the South African Museum 26: 36-48 Edgecombe. G. (2001).
Centipedes: The Great Australian Bite. Nature: 40-51. Edgecombe, G.D. and Giribet, G. (2002).
Myriapod Phylogeny and the Relationships of Chilopoda. Verhoeff. K. W (1904).
Gesellschaft nuturforschender Freunde, Berlin. Sitz ung 13: 245-285. Verhoeff. K. W (1905).
Uber Scutigeriden. Zoologischen Anzeige r 13: 74-119. Verhoeff. K. W (1924).
Chilopoda. Results of Dr. E. Mj oberg's Swedish Scientific Expedition to Australia 1910-1913 39: 1-64.
Verhoeff. K. W (1937).
Chilopoden aus Malacca, nach den Objucten des Raffle Museum in Singapore. Chilopoden aus Malacca 13: 198-200,268-270. Wurmli. M. (1973).
Zur Systematik der Scutigeriden Euro as and Kleinasiens. Vor arbeiten zu einer Mon ographie der Scutigeromorpha 1: 399-408. Wurmli. M. (1973).
Pes varus pachy pus n. gen. n. sp., eine neue Scutigeriden aus Australien. Zoologist 192: 140-141 Wurmli. M. (1977).