Peripatus and Affinities First year – semester-I
Presented By B.L.P .LATHA Lecturer in Zoology, S VCR Govt Degree College Palamaner Introduction Onychophora – From Ancient Greek - Onyches means Claws and Pherein- to carry, Commonly known as Velvet worms. Geographical Distribution: In 1930 Onychophora fossils "Aysheaia" were discovered in Cambrian Perio stones. Hence, the Onychophora includes many genera along with Peripatus. We can consider this as a very primitive group. The genus Peripatus is found restricted in the various places of the world such as South Africa, Australia, New Zealand, Tasmania, New Britain, South America and West Indies, Malaya, etc. The following species are available in various countries such as 1.Neo-Peripatus (Peripatus)-Neotropical region (West Indies and America from Mexico) 2.Congo-Peripatus -Congo district in West Africa. 3.Capo-Peripatus- South Africa 4. Melano-peripatus -New Britain 5. Austro-Peripatus- Australia, Tasmania, New Zealand. 6.Typhloperipatus (Himalaya region of India) 7. Chilio-Peripatus Chile. * Now a days - 47 Genera, 155 species available, Length- 0.5 to 20 cm*
It is a best example of Discontinuous Distribution. 2 Introduction
Peripatus, belongs to Phylum Arthropoda. Class Onychophora. Some scientists do not agree to give the status of a class to Onychophora but prefer to consider it as an appendix to Phylum Arthropoda. Because these animals exhibit certain peculiar and unique features which are not shown by a majority of Arthropods. Peripatus was first discovered by Guilding in 1826. By considering the external characters of Peripatus, he considered it is a sluggish locomotion and kept it under Phylum Mollusca. Since the animal bears several "annelidan characters" many scientists grouped it under Phylum "Annelida“ Manton (1970) and other contemporary zoologists have included onychophorans within the Arthropoda as a subphylum or class. But, absence of an exoskeleton and jointed limbs and the primary annelidan characters in Onychophora present serious problems. As a matter of fact, onychophorans are neither annelids nor arthropods but possess distinctive characteristics of their own. Therefore, Onychophora are nowadays considered as a separate phylum. Only in the year 1874 “H. N. Moseley" observed the tracheal mode of respiration and included, is an Arthropoda under class Onychophora. The entire structure, physiology and development of peripatus was clearly worked out by "Adam Sedgwick".
3 STRUCTURE OF PERIPATUS. *Habit, Habitat External Morphology * Body Wall and Body Cavity Digestive System. * Circulatory System Respiratory System * Excretory System Nervous System * Sense Organs Reproductive System * Development Affinities . Habit and Habitat Peripatus is a terrestrial animal, found living in moist places, in crevices of rocks, under bark, stones, logs and other dark and damp places or along stream banks. It is nocturnal in nature and predaceous and carnivorous in feeding habit. Most species of Peripatus are predaceous and feed on small invertebrates, such as snails, insects and worms. A number of species display a particular preference for termites. The genus Peripatus is found in Central America, the Caribbean and northern South America.
5 External Morphology
The body of Peripatus is caterpillar-like, soft, elongated, bilaterally symmetrical, cylindrical and ranges from 1.4 to 15 cm in length. The skin covered by the thin cuticle is soft and has a velvety texture and thrown into a number of fine transverse ridges bearing numerous conical papillae or tubercles armed with little chitinous spines. The ventral surface is nearly always flesh-coloured, while the dorsal surface has a darker colour. But blue, green, red-orange or black colourations are also marked. The entire structure, physiology and development of peripatus was clearly worked out by Adam Sedgwick.
6 Dorsal, Lateral and Ventral view of Peripatus Adam Sedgwick
7 The entire body of Peripatus may be divided into an indistinctly marked off head and an elongated trunk. 1. Head: The head of Peripatus bears a pair of eye, a pair of antennae, a pair of jaws or mandibles, and a pair of oral papilla. . The eyes are simple and dorsal in position. . One pair of antennae represents the first pair of appendages. The free end of each antenna is covered by a sheath of spiny tissue. . One pair of jaws or mandibles constitute the second pair of appendages. . These are present deep inside the mouth cavity. Each jaw is small, muscular, stumpy and provided at its free end with a pair of sharp cutting blades. The jaws appear to be used for tearing the food. . Third paired appendage is a pair of oral papillae. The oral papillae are placed at the sides of the head, one on each side. . On the terminal end of each oral papilla is situated an aperture of a special kind of gland called slime glands.
. Mouth is situated on the ventral side immediately behind the oral papillae .
8 Dorsal and ventral view of peripatus
9 2. Trunk: The trunk possesses appendages or legs which vary in number from 14 to 43 pairs, depending on the species and the sex. . Each leg is a large, hollow, conical, un-jointed protuberance bearing a pair of terminal claws. It bears two sickle-shaped claws and two, three or four papillae. . The trunk is devoid of exoskeletal coverings and its skin is thrown out into a number of ridges, along which wart-like papillae are placed.
10 Legs consist of two main divisions - the leg and the foot. Each leg is a large, hollow, conical, un-jointed protuberance bearing a pair of terminal claws . At the distal end of each leg on the ventral side are three to six transverse spiniferous pads, on which the leg rests when walking. The entire surface of the leg consists of numerous papillae. The foot is attached to the distal end of the leg. It bears two sickle-shaped claws and two, three or four papillae.
11 Body Wall The body wall is dermomuscular, consisting of cuticle, epidermis, dermis and muscles. The cuticle is ridged and covered with microscopic small and large tubercles which give it a velvety texture which is unknown in other animals. Body Cavity The body cavity is a haemocoel. It is lined with epithelium and consists of four compartments—one central, two laterals and one pericardial. The central compartment- the largest and contains the alimentary canal, the reproductive organs and the slime glands. The lateral compartments- are much smaller than the central and they extend within the legs. The pericardium contains a peculiar cellular tissue
12 Slime Glands A pair of slime glands is situated, one on either side of the body cavity. The slime glands are tubular and their ducts are considerably dilated to form the large slime reservoirs. These glands open on the terminal ends of the oral papillae and secrete an adhesive slime for entangling the prey. This secretion hardens very rapidly into threads in the air.
Digestive System The digestive system consists of alimentary canal and digestive glands. The alimentary canal is straight. Stars from Mouth- foregut of a pharynx and oesophagus-midgut composed of stomach, intestine-hindgut or rectum- Anus. The anus opens on the ventral side at the posterior end of the body.
13 Salivary glands: A pair of salivary glands opens into a median dorsal groove in the pre oral cavity. Each salivary gland is slender, tubular and elongated. The salivary glands extend from third to tenth and sometimes up to thirty-first segment. The two salivary ducts fuse to open within the pre oral cavity. In some forms, a reservoir is also present.
Circulatory System The heart placed on the dorsal surface of the gut. The heart is tubular and contractile, lies within the pericardial sinus. It is provided with a pair of lateral ostia in each segment. No other definite blood vessel is found. The blood is colourless and contains phagocytic amoebocytes.
14 Respiratory System It consists of air tubes called tracheae or tracheal tubes. The tracheae are delicate, un-branched or rarely branched tubes. They are lined by a thin chitinous layer exhibiting faint transverse striations. The tracheae extend throughout the body and communicate to outside through minute spiracles. The spiracles are minute openings. These are present in large numbers all over the surface of the body between bands of tubercles. The spiracle opens into a very short atrium, at the end of which arises a tuft of minute tracheae. By means of tracheal tubes the air is conveyed to all parts of the body for respiration.
Excretory System The excretory organs are nephridia. The nephridia are segmentally arranged pairs of coiled tubes. Each segment contains a single pair of nephridia located in the ventrolateral sinuses. The first three pairs of nephridia are poorly developed consisting of a vesicle and duct. The anterior nephridia are modified as salivary glands and the posterior nephridia are modified as gonoducts in the female.
15 16 Coxal/Crural glands: A series of paired glands are present in the lateral compartments of the body cavity. Their ducts open on the lower surface of the legs just outside the apertures of the excretory ducts. Its are only present in male. Anal glands :A pair of anal glands having uncertain function opens close to the anus. These are probably modified excretory organs.
Nervous System: A ladder-like appearance Reproductive System: The males are usually smaller than females, unisexual. Development: Oviparous and viviparous. The fertilization is internal and the egg develops within the uterus.
17 Affinities of Peripatus Some scientists do not agree to give the status of a class to Onychophora but prefer to consider it as an appendix to Phylum Arthropoda. Because these animals exhibit certain peculiar and unique features which are not shown by a majority of Arthropods. Class Onychophora includes primitive worm like, Arthropods. The study of this Class infers the Annelid and ancestry of Arthropod, Some authors say it as connecting link or living link. * Therefore, It is a connecting link between Annelids and Arthropods. Peripatus exhibits close affinities with the Annelids on one hand and with Arthropods on the other. Peripatus is a unique organism. It forms a connecting link between Annelids are Arthropods. It exhibits several important Annelida characters and some Arthropodan characters. In addition to these, peripatus exhibits some peculiar characters not shown by either Annelids or Arthropods.
18 Affinities
Annelidan characters Arthropodan characters 1.The body is in Vermiform. 1. Body is covered with chitinous cuticle. 2. Absence of distinct head region 2. Antennae are present.
3. Structure of the eye is same as in 3. Presence of Moulting of cuticle . polycheates. 4. Presence of thin transparent cuticle on 4. Appendages are modified into jaws the body and skin is thin and flexible. 5. Presence of Oral papilla 5. Presence of a pair Salivary glands.
6. Legs are hollow stumpy (short) and un 6. The appendages (legs) are provided jointed resemble the parapodia with claws.
7. body wall is dermomuscular. 7. Coelome contains colorless blood (Haemocoel).
8. The Presence of muscular pharynx 19 Affinities Annelidan characters Arthropoda characters 9. Alimentary canal is simple and straight 8. Smooth muscle (Striped/ involuntary) is found in jaws(Mandible). 10.Voluntary or Non-striped muscles are 9. Respiration is by trachea. present.
11. Slime glands and Coxal glands 10.Presence of tubular heart Positioned correspond with similar glands of dorsally which is with valvular Ostia Chaetopoda. with. 12. Presence of paired Nephridia in every 11. Nephridia open into Coelome through segment nephrostome.
13. Presence of salivary glands which are 12. Presence of tubular gonads around modified Nephridia the gut.
14. Genital ducts are ciliated.
20 Special Characters of Peripatus
1. Body has Velvety skin which is known as Velvet worm. 2. Presence of superficial segmentation of the body. 3. Antennae, Papillae, Jaws are not like the first three pair of appendages of Arthropoda. 4. Simple trachea which open all over the body and open out with diffused stigmata. 5. Presence of a ladder like Nervous system.
21 Summery
Discontinuous distribution 14-41 pairs of legs with two claws Mandible muscles are striped but others are non striped. Velvet worm, insectivorous A pair of Simple eyes Excretion is conducted by paired nephridia. Caterpillar, Nocturnal Body wall is Oviparous, dermomuscular(endodermis) almost all species are Viviparous. Terrestrial animal The haemocoel is divided into 3 vertical Gonads occupy most compartments. of the body cavity Elongate, Cylindrical, Delicate Alimentary canal is long or straight . Unisexual, Internal fertilization No external segmentation but with Heart is dorsal tubular ,has a valvular The genus Peripatus transverse circles around the body ostia, and colorless blood. was established in with tubercles No blood vessels. 1826 by Guilding, who first obtained specimens of it from St. Vincent in the Antilles. Legs without Joints. Slime ,salivary, Coxal glands are present. *************************** 22