What are Aschelminthes?
Phylum Aschelminthes have entire digestive tubes and are pseudocoelomate, bilaterally symmetrical, triploblastic, unsegmented, vermiform, and organ-system grade of construction.
Phylum Aschelminthes characteristics
- Most of them are aquatic, parasitic, or free-living.
- They are unsegmented, bilaterally symmetrical worms.
- The body is flattened or often worm-like, thin, and vermiform.
- While many of them are tiny, even microscopic, others may grow to be a metre or longer.
- They have organ system grade body organisation and are triploblastic and pseudocoelomates.
- Body wall having syncytial or cellular epidermis and a thick scleroprotein cuticle on the outside.
- Except for the front cilia of rotifers, cilia are missing.
- Most of the fibres in muscles are longitudinal.
- The digestive system is complete and straight, with a mouth, a muscular and highly specialised pharynx, a straight, non-muscular intestine, and anus.
- Systems for breathing and moving blood are not present.
- Protonephridia (in certain cases) are a series of canals in the excretory system that are used for osmoregulation. Some people have cloaca.
- The circumenteric nerve ring and the anterior and posterior longitudinal nerves make up the simple nervous system.
- In the form of pits, papillae, bristles, and eyespots, sense organs are present.
- They generally have different sexes and are dioecious, single or twin gonads and ducts.
- There is no asexual reproduction in them.
- Eggs have a chitinous shell with spiral cleavage.
- Typically, they have a simple or complex life cycle without any distinct larval stages.
Classification of the phylum Aschelminthes
Various zoologists have assigned distinct classifications to this phylum since it has a diverse range of different species. Although Storer and Usinger (1971) recognised alternative classifications of Aschelminthes as independent phyla and ranked Aschelminthes as a superphylum, this classification is based on and modified from L. H. Hymann’s (1951) work.
Class 1. Nematoda (Gr., nema=thread+ eidos= form)
- Roundworm that is elongated and may live on land or in water.
- Unsegmented, cylindrical, and lengthy body.
- Body wall having cellular or syncytial epidermis, a thick cuticle, and longitudinal muscles arranged in four bands.
- No cilia, no respiratory and cardiovascular systems.
- The muscular pharynx and stomach complete the digestive system.
- glandular canal or glandular organ excretory system.
- Anterior and posterior nerves are part of the nervous system’s circumenteric ring.
- Simple sense organs
- Males are smaller than females and have penial spicules.
- a single or two gonads. The female genital duct has a different entrance from the male genital ducts, which enter the cloaca.
- Most development is straightforward. No regeneration or asexual reproduction.
- Examples include Trichinella, Necator, Wuchereria, and Ascaris.
Order 1. Enploidea
- Not ringed, it often has cuticular bristles.
- 6 labial papillae on the anterior end.
- One or two circlets of 10 to 12 bristles.
- the anterior muscular and posterior glandular oesophagus.
- cyathiform amphids and two cephalic slits.
- Examples include Synonchus, Anticoma, and Enoplus.
Order 2, Dorylaimoidea
- Zero bristles, smooth cuticle.
- Two 6- and 10-papillae circlets are seen on the anterior end.
- A spear-armed cavity in the buccal cavity.
- The pharynx’s back portion became larger.
- cycliform amphids.
- Dorylamius, Tylencholaimus, and Actinolaimus are among examples.
Order 3. Mermithoidea
- The juvenile stages of smooth, filiform nematodes, which mostly parasitize insects, allow them to live freely as adults in soil or water.
- decreased to six or fewer papillae on the head.
- blind and long pharynx.
- It is a modified form of the blind gut that stores food.
- reduced or cyathiform amphids.
- For instance, there are Mermis, Paramermis, and Aproctonema.
Order 4: Chromadoroidea
- the ringed or smooth cuticle.
- Typically, the cuticle is extensively embellished with bristles, knobs, and punctures.
- has a posterior bulb in the pharynx.
- Amphids either originate from or are spirals.
- Examples include Paracanthonchus and Pacytholamius.
Order 5, Araeolaimoidea
- Sometimes bristles, sometimes smooth cuticles.
- There are labial papillae.
- 4 cephalic bristles on the anterior end.
- loop- or spiral-shaped amphids.
- Plectus, Wilsonema, and Odontophora, as examples.
Order 6. Monhysteroidea
- Cuticles that are smooth or somewhat ringed and often have bristles.
- bristles on the anterior end are 4, 6, or 8.
- spherical amphids.
- Examples include siphonolaimus and cyclolaimus.
Order 7. Desmoscalecoidea
- Cuticle with a thick ring and noticeable bristles all over or in a small region.
- 4 bristles on the anterior end.
- Crescent-shaped amphids
- marine nematodes
- Desmoscolex, Tricoma, and Greeffiella, for instance.
Order 8. Rhabditoidea or Anguilluloidea
- independent or parasitic.
- the smooth or ringed cuticle.
- The pharynx often has swelling anterior to the nerve ring and a posterior bulb.
- Caudal glands are absent.
- Pocket-sized amphids.
- Rhabditis, Diploscapter, and Diplogaster, as examples.
Order 9. Rhabdiasoidea
- Nematodes have a distinct pharyngeal bulb that is smooth.
- Hermaphrodites are also capable of pathogenicity.
- animal phases of parasitism.
- Males and females may emerge from free-living stages.
- Rhabdias and Entomelas are two examples.
Order 10. Oxyuroidea
- pharynx with the posterior bulb valvulated.
- Long, pointed tail; female; terminal elements of the female system often strongly muscled.
- Male has one or two equally sized spicules.
- Typically, a cuticular brusa is formed by caudal alae.
- Examples include Enterobius or Oxyuris.
Order 11. Ascaroidea
- three pronounced lips around the mouth.
- The pharynx is not vulvulated whether the posterior bulb is present or absent.
- Pharynx, intestine, or sometimes both with caeca.
- zero buccal capsule.
- Females have blunt tails, while males lack caudal alae and have two spicules that are almost equal in size.
- For instance, Ascaris
Order 12. Strongyloidea
- lips are absent, but the mouth often has a leaf crown.
- No bulb in the pharynx.
- Typically, females have an ovijector.
- Male with a normally 13-rayed copulatory brusa supported by muscles.
- Strongylus, Necator, and Ancylostoma, for instance.
Order 13: Spiruroidea
- Typically, the mouth has two lateral lips; sometimes there are four or six tiny ones.
- Without a bulb, the pharynx is anteriorly musculoskeletal and posteriorly glandular.
- Males lack brays; spicules are uneven and different.
- Examples include Thelazia, Oxyspirura, and Rictularia.
Order 14. Dracunculoidea
- lacking cuticularized buccal capsules or distinct lips.
- Without a bulb, the pharynx is anteriorly musculoskeletal and posteriorly glandular.
- The vulva is normally found behind or close to the centre of the body, but it is not functioning.
- Males lack brusa but have equal filiform spicules.
- Examples include Micropleura, Philometra, and Dracunculus.
Order 15. Filarioidea
- a lipless, worm-like shape.
- buccal capsules that are small or simple.
- The pharynx has posterior glands and anterior muscles.
- There is no pharyngeal bulb.
- Females have an anterior vulva.
- Lacking brusa, spicules that are uneven and different.
- Wuchereria and Loa Loa are two examples.
Order 16.Trichuroidea or Trichinelloidea
- Front of the body is filiform.
- sans lips, a mouth.
- thin pharynx.
- provided by a cirrus, and just one spicule if any are present.
- Trichinella and Trichuris, for instance,
Order 17. Dioctophymoidea
- moderately to very lengthy.
- 6, 12, or 18 papillae surround an open mouth without lips.
- Bulbless, elongated pharynx.
- Male without rays but with a muscular brusa
- Dictyophyme, Hystrichis, and
Class 2: Nematomorpha (Greek: nema=thread + morphe= form) or Gordiacea
- Hair worm is a freshwater species. Nectonema is the only marine genus.
- a very long, narrow, cylindrical body.
- body wall with tiny papillae and a thick cuticle.
- single-layered, cellular epidermis.
- In larvae, the digestive system is fully developed; in non-feeding adults, it deteriorates. Cloaca is there.
- Parenchyma mostly fills the pseudocoel.
- no respiratory, digestive, or circulatory systems.
- has a nervous system that includes a midventral nerve cord and the circumenteric nerve ring.
- pairings of gonads and gonoducts. Also leading into the cloaca are oviducts.
- Grasshoppers, crickets, and other insect parasitic juveniles
- For instance, there are Gordius, Paragordius, and Nectonema.
Order 1. Cordioidea
- Bristles for swimming are lacking.
- Parenchyma fills the pseudocoel.
- gonad pairs.
- Gordius and Paragordius, for instance.
Order 2. Nectonematoidea
- Two rows of swimming bristles are placed.
- Pseudocoel that is empty
- a single gonad.
- Marine dress
- Consider the nectomema.
Class 3. Rotifera (L., rota= wheel + ferre= to bear)
- These are tiny creatures that may be found in streams, lakes, and ponds. Oceans seldom have what are known as “wheel bearers.”
- Anterior end of the body wall with ciliated corona (wheel organ) utilised for eating and motility. Body wall hardened into stiff plates or lorica.
- Toes and sticky glands are present on the post-anal foot.
- Transverse and longitudinal muscle strands and bands make up the body’s musculature.
- the interior cuticle of the mastax, the digestive system’s grinding organ,
- two protonephridia and two protonephridial tubes, which drain into bladders, make up the excretory system.
- three main ganglia and nerves make up the nervous system.
- antennas, eyespots, and other sensory organs.
- Females are larger than males. Common parthenogenesis
- No larval stages; female oviparous.
- For instance, Rotaria, Asplanchna, and Philodina.
Order 1. Seisonacea
- Long neck and a lean body.
- Corona is a little
- gonad pairs.
- found on crustaceans as commensals.
- For instance, seasoning
Order 2: Budelloidea
- Typically, a corona has two trochal discs.
- More than two pedal glands.
- Degenerate male; paired germovitellaria in female.
- Forms that swarm or crawl
- Other examples are Rotaria or Rotifera, Philodina, and Mniobia.
Order 3. Monogonontea
- forms that swim or are sessile.
- Degenerate or undersized males.
- typically just one testis in males.
- Females only have one germovitellaria.
- Mytilina and Limnias, as examples.
Class 4. Gastrotricha (L., gaster= stomach + trichos= hair)
- freshwater, marine, or microscopic.
- Cuticle-covered body wall with small, curving dorsal spines.
- The ventral surface of the corona is devoid of cilia for movement.
- Forked posterior end with attachment glands and sticky tubes.
- There are six pairs of longitudinal muscles in the body.
- bristles around the mouth.
- The pharynx is muscular and triradiate.
- the two protonephridia of the excretory system.
- The nervous system consists of two lateral nerves and a saddle-shaped ganglion.
- Whether monoecious or dioecious, parthenogenetic females are common.
- direct development Young and old are similar.
- For instance, take Chaetonotus and Macrodasys.
Order 1. Macrodasyoidea
- worm-like marine formations.
- several tubes of adhesive.
- Absence of protonophelia
- Among them is Macrodasys.
Order 2. Chaetonotoidea
- On vegetation, freshwater forms are the majority.
- tubes for adhesive on the tail.
- a protonephridia pair.
- Parthenogenesis, or parthenogenesis,
- As for Chaetonotus and Neodesys, as examples,
Class 5. Kinorhyncha (Greek: more + rhynchos = beak)
- marine, worm-like in size.
- body is superficially divided into 13 or 14 overlapping rings (Zonites).
- There are spiny cuticles on the body’s surface but no cilia.
- mouth cone or protruding, scalid-covered head.
- a pair of sticky tubes on the ventral surface’s front side.
- Pseudocoel with amoebocyte-containing fluid.
- Each zonite has a nerve ring, a ventral cord, and a ganglion. in some eye spots.
- Salivary glands finish the digestive system.
- Gonads are described as two tubular sacs.
- Male penial spicules.
- intrinsic feminization. a transformation including numerous larval stages.
- There are many juvenile phases in development.
- Echinoderes and Pycnophyes, for instance.
Order 1. Homalorhagida
- Both the head and the neck protrude.
- Trachydemus, as an example.
Order 2. Cyclorhagida
- Only the protruding head ring is present.
- Consider echinoderms.
- Kotpal RL. 2017. Modern Text Book of Zoology- Invertebrates. 11th Edition. Rastogi Publications.
- Jordan EL and Verma PS. 2018. Invertebrate Zoology. 14th Edition. S Chand Publishing.