Salient features and affinities of Onychophora and Hemichordata

• Affinities of Balanoglossus with Annelida & Echinodermata.


Spengel (1893) suggested affinities of Hemichordata (Balanoglossus) with Annelida as follows:-
1. Body vermiform & coelomate.
2. Burrowing habit, tubicolous life & ingesting mud which is passed out as castings through anus.
3. Collar of Balanoglossus is similar to clitellum of earthworm.
4. Proboscis & prostomium is similar & preoral.
5. The arrangement of blood vessel is similar.
6. Dorsal position of heart.
7. Tornaria larva of Balanoglossus shows several structural resemblances with the Trochophore larva of Annelida in being pelagic, ciliated, with apical plate, eye spots, sensory cilia & well developed alimentary canal with similar parts.
Affinities of Balanoglossus with Echinodermata:-
1. Adult resemblances:-
Adult Balanoglossus & echinoderms are structurally quite different. So it is difficult to draw their phylogenetic relationship between themselves. However some resemblances are :-
1. Enterocoelic origin of coelom.
2. Heart vesicles & glomerulus of Balanoglossus are considered homologous to the dorsal sac & axial gland of echinoderm.
3. Nervous system poorly developed & forms epidermal nerve plexus.
4. Proteins & phosphagens present in Balanoglossus closely resemble those of echinoderms.
5. Common habits, echological niches & remarkable power of regeneration.
2. Larval resemblances:-
Tornaria larva of Balanoglossus has striking, structural similarities with Bipinnaria larva of echinoderms.
1. Small, pelagic, transparent & oval.
2. Identical ciliated bands taking up a similar twisted course.
3. Enterocoelic origin & similar development of coelom.
4. Proboscis coelom of Tornaria is comparable to hydrocoel of echinoderm Dipleurula.
5. Deuterostome & digestive tract is complete with mouth & anus & same parts.


• Discuss & comment on echinoderm affinities of Balanoglossus.  Justify its inclusion under the phylum Chordata.


• Echinoderm affinities of Balanoglossus;-
1. Adult resemblances:-
Adult Balanoglossus & echinoderms are structurally quite different. So it is difficult to draw their phylogenetic relationship between themselves. However some resemblances are :-
1. Enterocoelic origin of coelom.
2. Heart vesicles & glomerulus of Balanoglossus are considered homologous to the dorsal sac & axial gland of echinoderm.
3. nervous system poorly developed & forms epidermal nerve plexus.
4. Proteins & phosphagens present in Balanoglossus closely resemble those of echinoderms.
5. Common habits, echological niches & remarkable power of regeneration.
2. Larval resemblances:-
Tornaria larva of Balanoglossus has striking, structural similarities with bipinnaria larva of echinoderms.
1. Small, pelagic, transparent & oval.
2. Identical ciliated bands taking up a similar twisted course.
3. Enterocoelic origin & similar development of coelom.
4. Proboscis coelom of Tornaria is comparable to hydrocoel of echinoderm Dipleurula.
5. Deuterostome & digestive tract is complete with mouth & anus & same parts.
Comment;-
However the Tornaria larva shows presence of apical plate with sensory hairs , eyespots & telotroch which are absent in echinoderm larvae.
The protocoel is single in Tornaria larva but paired in echinoderm larva. This raises the doubts about the echinoderm affinities of Balanoglossus.
Fell (1963) & others believe that their larval similarities are only because of convergent evolution due to same mode of habits & habitats.


Inclusion of Balanoglossus under phylum chordata is not universally accepted.
Among 3 fundamental chordate characteristics the nature of notochord is really questionable. Recent workers do not accept the notochordal nature of buccal diverticulum.
The nervous system, in general, is typically non chordate type excepting the presence of lumen in collar nerve cord.
The only important chordate feature is the gill slits.
However recent DNA analysis such as 18r DNA analysis of enteropneusts suggests that they are closer to the echinoderms than to the chordates.


• Comment on echinoderm & chordate affinities of Balanoglossus.
• Echinoderm affinities of Balanoglossus;-
1. Adult resemblances:-
Adult Balanoglossus & echinoderms are structurally quite different. So it is difficult to draw their phylogenetic relationship between themselves. However some resemblances are :-
1. Enterocoelic origin of coelom.
2. Heart vesicles & glomerulus of Balanoglossus are considered homologous to the dorsal sac & axial gland of echinoderm.
3. Nervous system poorly developed & forms epidermal nerve plexus.
4. Proteins & phosphagens present in Balanoglossus closely resemble those of echinoderms.
5. Common habits, echological niches & remarkable power of regeneration.
1. Larval resemblances:-
Tornaria larva of Balanoglossus has striking, structural similarities with Bipinnaria larva of echinoderms.
1. Small, pelagic, transparent & oval.
2. Identical ciliated bands taking up a similar twisted course.
3. Enterocoelic origin & similar development of coelom.
4. Proboscis coelom of Tornaria is comparable to hydrocoel of echinoderm Dipleurula.
5. Deuterostome & digestive tract is complete with mouth, anus & same parts.
Comment;-
Fell (1963) & others believe that their larval similarities are only because of convergent evolution due to same mode of habits & habitats.


Chordate affinities of  Balanoglossus:-
Inclusion of Balanoglossus under phylum chordata is not universally accepted.
Among 3 fundamental chordate characteristics the nature of notochord is really questionable. Recent workers do not accept the notochordal nature of buccal diverticulum.
The nervous system, in general, is typically non chordate type excepting the presence of lumen in collar nerve cord.
The only important chordate feature is the gill slits.
Affinities with Urochordata:-
1. Similarity is present in the pharynx & branchial apparatus of both.
2. Development of the central part of the nervous system is quite similar in both.
Remarks:-
The relationship becomes difficult to establish because the chordate nature of hemichordates itself is questionable.
The resemblances are due to the fact that the hemichordates are very remotely connected with the central stalk from which urochordates have descended.
Affinities with Cephalochordata:-
1.  Similarity in the structure & function of branchial apparatus.
2. Arrangement of coelomic sacs are similar.
Remarks:-
Presence of unsegmented muscle fibres in  Balanoglossus & dissimilarities in the developmental history stand as barriers to establish any close relationship between them.


Comment;-
Recent DNA analysis such as 18r DNA analysis of enteropneusts suggests that they are closer to the echinoderms than to the chordates.


• Comment on the phylogenetic status of Peripatus./Discuss on the systematic position of Peripatus.
Peripatus have both annelidan & arthropodan characteristics. Therefore they are regarded to be intermediate stage or connecting link between Annelida & Arthropoda.
However they appear to be more closely allied to arthropods than to annelids. They may represent an offshoot from near the base of the arthropod line. Based on such phylogenetic considerations, Manton & other contemporary zoologists have included onychophorans (Peripatus) within the Arthropoda as a subphylum or class.
But absence of exoskeleton, & jointed limbs & the presence of primary annelid characters in Onychophora create serious problems. Others claim that Peripatus is definitely an annelid.
In fact, onychophorans are neither annelids nor arthropods but possess distinct characteristics of their own. Hence now a days, Onychophora is considered as a separate phylum.
The modern view holds that Onychophora is not an evolutionary link between Annelida & Arthropoda but a distinct surviving branch. This is supported by the discovery of a mid-Cambrian fossil, Aysheaia  which closely resembles the modern Onychophora.
• Onychophora exhibits both arthropod & annelid characters along with its own
peculiarities- Explain.
Arthropod characters of  Onychophora:-
1. Presence of antennae.
2. Body is covered with chitinous cuticle.
3. Appendages are provided with claws.
4. Jaws are modified appendages, provided with striped muscles.
5. Locomotion by definite legs having definite musculature.
6. Presence of haemocoel.
7. Dorsal tubular heart with lateral ostia.
8. Presence of tracheal respiratory system.
9. Coelom reduced to small cavities that surround the excretory & reproductive ducts.
10. Peculiar salivary gland supposed to be modified nephridia.
11. Brain is large & typically arthropodan.
12. General structures of the reproductive organs & development mainly arthropodan.
Annelid characters of Onychophora;-
1. Vermiform body with truncated extremities.
2. Absence of true head.
3. Outer body covering is cuticle, skin thin & flexible.
4. Muscles separate in identical way.
5.  locomotion slow & by peristalsis as in an earthworm.
6. Simple & straight alimentary canal.
7. Paired, segmentally arranged nephridia.
8. Presence of cilia in excretory & reproductive ducts.
9. Structure of eye same as in polychaetes.
10. Slime & coxal glands correspond with similar glands of chaetopods.
Onychophoran characteristics:-
The following features are peculiar to Onychophora in which they differ from other phyla:-
1. Body shows no or indistinct segmentation.
2. Texture of skin. A rough cuticle covered with numerous velvety processes not known in other phyla.
3. Antennae not homologous to the antennae of other arthropods.
4. 3 segmented head of Peripatus shows a condition mid way between that of Annelida & Arthropoda.
5. Restriction of jaws to a single pair. Movement of jaws is antero-posterior.
6. Presence of non jointed legs with claws.
7. Irregular distribution of spiracles or tracheal openings.
8. 2 ventral nerve cords widely separated & without true ganglia.
9. Structure of eye less complicated.
10. Distribution of reproductive organs.


• Write in details the arthropodan affinities of Peripatus.
Arthropod characters of  Onychophora:-
1. Presence of antennae.
2. Body is covered with chitinous cuticle.
3. Appendages are provided with claws.
4. Jaws are modified appendages, provided with striped muscles.
5. Locomotion by definite legs having definite musculature.
6. Presence of haemocoel.
7. Dorsal tubular heart with lateral ostia.
8. Presence of tracheal respiratory system.
9. Coelom reduced to small cavities that surround the excretory & reproductive ducts.
10. Peculiar salivary gland supposed to be modified nephridia.
11. Brain is large & typically arthropodan.
12. General structures of the reproductive organs & development mainly arthropodan.


• Make a note on the geographical distribution of Peripatus..
The genus Peripatus is found restricted in various places of world such as South America & West Indies, South Africa, Australia, New Zealand, Tasmania, New Britain, , Malaya, Equatorial Africa & Chile.
Some common forms of Peripatus are:-
1. Neo-Peripatus:- (Peripatus):- West Indies & America
2. Congo-Peripatus:- (Mesoperipatus Evans):- Congo & Caribbean islands.
3. Eo-Peripatus:- (Eoperipatus Evans):- Malaya
4. Capo-Peripatus:- (including Peripatopsis Pocock & Opisthopatus Purcell):- South Africa
5. Melano-Peripatus;- ( Paraperipatus Willey):- New Britain.
6. Austro-Peripatus:- (Peripatoides Pocock & Ooperipatus Dendy):- Australia, Tasmania, New Zealand.
7. Chilio-Peripatus:- (Opisthopatus Bouvier), Chile.

Type study of Non-chordata :- Cockroach

• Describe the circulatory system of Periplaneta.


The circulatory system of Periplaneta is of open type as the blood or haemolymph flows freely within the body cavity or haemocoel. There is a heart & aorta but no capillaries & veins.
Circulatory system consists of  haemocoel, heart & haemolymph.


1. Haemocoel:-
Body cavity of cockroach is known as haemocoel as it remains filled with haemolymph (blood).
The coelom is divided into 3 main sinuses by a dorsal & ventral horizontal diaphragm:-
1. Pericardial sinus (surrounding the heart & aorta).
2. Perivisceral sinus (surrounding the various visceral organs)
3. Perineural sinus ( surrounding the ventral nerve cord).
2. Heart:-
1. Position:- the heart is present along the middorsal line of the body. It extends from the tip of the head up to the abdominal end.
2. Attachment:- The heart remains attached with the dorsal body wall dorsally & the dorsal diaphragm ventrally by a sets of alary muscles. The alary muscles hold the heart in position.
3. Structure:- The heart of cockroach is an elongated muscular tube. It consists of 13 segmentally arranged funnel shaped chambers.
In between the 2 chambers a pair of ostia are present.
3. Haemolymph:-
The haemolymph or blood of cockroach consists of clear colourless plasma & haemocytes. The haemocytes remain suspended into the plasma.
The haemocytes are of 3 types - prohaemocytes, transitional haemocytes & large haemocytes.
According to Jones, haemocytes may be classified into 2 broad categories- plasmocytes & coagulocytes.
• Course of circulation:-
Course of blood flow may be summarized as follows-
Heart  (via anterior aorta) to sinuses of head region to perineural sinus (via ventral diaphragm) to perivisceral sinus (via dorsal diaphragm) to pericardial sinus (via ostia) to heart.
• Mechanism:-
The circulation of the blood is controlled by the contraction & relaxation of the alary muscles. In fact the alary muscles control the opening & closer of ostia.
• Functions:-
As the blood lack respiratory pigments it doesn’t carry respiratory gases. Rather it
1. Acts as the reservoir of water.
2. Transports food materials, hormones, excretory products etc.
3. Maintains the hydrostatic pressure of the body.
4. Performs blood coagulation & wound healing.


• Describe the male reproductive system of Periplaneta sp.  


Male reproductive system of Periplaneta  includes a pair of testis, vasa differentia, an ejaculatory duct, mushroom gland, phallic gland, genital pouch & external genitalia.
Testis:-  
Male gonads are a pair of testis.
Position;- Each testis lies dorso laterally in the 4th & 5th abdominal segments, being embedded in fat body.
Structure:- Each testis is 3 lobed & consists of numerous small, whitish, transparent follicles.
The follicles discharge sperms into the vasa differentia.
Vasa differentia:- 
The paired thin, thread like vasa differentia one from each testis run posteriorly & downwards to open into the ejaculatory duct.
Ejaculatory duct;-
It is an elongated, wide duct.
Position;- Ejaculatory duct is median in position & it runs backward in the abdomen & opens out by gonopore.
Function;- The glandular wall of this duct secretes the middle layer of spermatophore.
Utricular /Mushroom shaped gland:-
It is a large, whitish accessory reproductive gland. 
Position;- Situated at the junction of vasa differentia & ejaculatory duct.
Structure;- It has a mass of glandular tubules which are of 3 kinds.
1. Peripheral long tubules or utriculi majors.
2. Central short tubules called utriculi breviores.
3. Behind the short central tubules are some short but more bulbous, opaque white tubules, forming seminal vesicles.
Phallic gland;-
It is a large, multilobed, leaf like or club shaped gland.
Position;- Phallic gland is situated below the ejaculatory duct.
Function:- It secretes the outer layer of spermatophore.
Genital pouch:-
It lies at the hind end of the abdomen bounded dorsally by 9th & 10th terga & ventrally by 9th sternum.
It contains dorsal anus, ventral genital pore, & gonapophyses.
External genitalia:-
In the genital pouch, surrounding male genital pore, are present phallic organs or gonapophyses which help in copulation.
These consists of 3 small, irregular, chitinous plates known as phallomeres.


• Describe briefly the female reproductive system of Periplaneta sp.
The female reproductive system of Periplaneta sp. consists of a pair of ovary, oviducts, vagina, genital pouch, collaterial glands, spermatheca & external genitalia.
Ovaries:-
No.:- A pair of yellow coloured ovaries present.
Position:- They lie in 2nd to 6th abdominal segments one in either side of hindgut, embedded in fat bodies.
Structure:- Each ovary consists of  8 elongated tapering, beaded, blind tubes called ovarioles.
Each ovariole include the following parts:-
1. Terminal filament:- Anterior most, tapering thread like continuation of the connective tissue layer. It serves to suspend the ovariole in the haemocoel.
2. Germarium:-The anterior 1/3 part is the germarium containing only the primordial germ cells & oogonia.
3. Vitellarium:- It is the posterior part containing ova in various stages of development & maturation. The wall of ovariole encloses each ovum in a follicle. These follicles gives a beaded  appearance to ovariole.
4. Egg chamber:- The vitellarium opens posteriorly into a small, thick, oval egg chamber. It contains a single, large, mature ovum at a time.
5. Stalk or pedicel:- The egg chamber continues posteriorly into thin walled, hollow stalk or pedicel. It opens into the lateral oviduct.
Oviduct:-
The stalk of 8 ovarioles on one side join to form an oviduct which is lateral, small & with muscular wall.
Vagina:-
Both the lateral oviduct unite to form a broad median common oviduct called vagina.
It opens by the female gonopore into the genital chamber.
Genital pouch/ Gynatrium:-
A large boat shaped structure whose floor is formed by 7th sternite, roof & sides are formed by the 8th & 9th sternite.
It can be divided into a genital chamber  (vagina opens)& an oothecal chamber (oothecae are formed) .
Collaterial glands:-
There is a pair of white, much branched collaterial glands behind & above the ovaries. Left gland is opaque & more developed while the right one is transparent & less developed. They open into genital pouch through separate openings.
Their secretion forms the ootheca around groups of eggs.
Spermatheca:-
The spermatheca consists of a left sac like & right filamentous caecum. It opens in the genital pouch at the tip of a small spermathecal papillae.
Spermatheca receives spermatozoa during copulation.
External genitalia:-
A sclerite around the female genital pore is called valvular plate. Besides 3 pairs of plate like chitinous gonapophyses are present between the female genital pore & anus.
These assist in copulation, in laying eggs & in the formation of ootheca.


• Give an account of the digestive system  in  Periplaneta sp.
The digestive system of Periplaneta sp . consists of the alimentary canal & digestive glands.
1. Alimentary canal:-
It is a long & somewhat coiled tube divisible into 3 regions; foregut, midgut & hindgut.
1. Foregut:-
It includes mouth, mouth cavity, pharynx, oesophagus, crop & gizzard.
1. Mouth:-
True mouth is a small opening at the base of the preoral cavity.
2. Mouth cavity;-
 Mouth cavity is a small, ill defined space  in front of mouth, surrounded by mouth parts.
Food is crushed & acted upon by the salivary secretion here.
3. Pharynx:-
It is short & tubular & its cuticular lining is more folded posteriorly.
4. Oesophagus:-
From pharynx arises a long, straight, laterally compressed tube, the oesophagus.
5. Crop:-
It is a large, thin walled, muscular, pear shaped sac after the oesophagus.
It serves as a reservoir of food.
6. Gizzard:-
It is a small, cone shaped, muscular & thick walled chamber behind the crop. It consists of 2 parts:-
1. ) Armarium:-
It possesses internally 6 highly chitinised plates called teeth. Behind the teeth there are thin, less chitinised plates which bear cushion like pads covered with backwardly directed bristles.
The teeth help in grinding & the bristles help in straining the food.
2. ) Stomodaeal valve:-
The hind part of the gizzard projects into midgut as a funnel called stomodaeal valve.
It prevent regurgitation of food from midgut into gizzard.
2. Midgut:-
It is a short narrow tube of uniform diameter. It is internally lined by glandular epithelium & serves as true stomach.
1. Hepatic caeca:-
Near the junction of fore & midgut there are 8 hollow slender tubes called hepatic caeca. They secrete digestive enzymes.
2. Malpighian tubules:-
At the junction of midgut & hindgut there are 80 to 90 thread like, yellow coloured blind tubules, called malpighian tubules.
They are generally excretory in function.
3. Hindgut:-
Relatively broader posterior part divisible into 3 regions-
1. Ileum:-
Narrow & short tube behind the midgut. Its lumen has epithelial lining.
2. Colon:-
This is longer, wider & slightly coiled tube behind the ileum.
3. Rectum:-
Colon continues into a small, sac like rectum. Rectal glands are present in the rectal wall for absorbing water. It opens to the outside through anus.


2. Digestive glands:-
The salivary glands, the inner lining of midgut & hepatic caeca are the digestive glands of cockroach.
A pair of salivary glands on either side of the crop are found associated with the alimentary canal.
Each gland consists of 2 leaf like, diffused lobes & a reservoir. They with their ducts form the salivary apparatus.
Each salivary gland consists of secretory lobules or acini. Each acinus is formed of 2 types of cells- zymogenic cells & ductule containing cells. Both of them secrete saliva.
The inner lining of mid gut & hepatic caeca also produce digestive juices.


• Describe the respiratory organs & mechanism of respiration in Periplaneta sp.
The respiratory system of Periplaneta is well developed & elaborate to compensate the absence of respiratory pigment in the blood.
The respiratory system consists of spiracle/stigmata, tracheae & tracheoles.
1. Spiracle/ Stigmata:-
No. &  position:-
10 pairs of spiracles or stigmata are present on the lateral side of the body arranged segmentally. 2 pairs present on thorax & 8 pairs on abdomen.
Structure:-
Each spiracle is a slit like aperture guarded by bristles or hair to keep out dirt. It is surrounded by an annular sclerite, the peritreme. It has a simple valve which can be closed or opened to regulate the flow of  air.
Each spiracle internally leads into a short tracheal chamber or atrium from which arises a main tracheal trunk.
2. Tracheae:-
Haemocoel contains a network of  elastic, closed, branching & silvery white tubes called tracheae.
The wall of each trachea consists of 3 layers- taenidia/ intima, basement membrane, & epithelium.
There are 3 pairs of longitudinal tracheal trunks- 1 dorsal, 1 ventral, & 1 lateral in position. All these trunks are connected by transverse commissures, forming a network  which reaches to every part of the body.
3. Tracheoles:-
The profusely branching tracheae anastomose & penetrate to all parts of the body. The ultimate finer branches are called tracheoles. Tracheoles come in contact with the individual body cells. Their cavity are intracellular & lined by trachein protein. Tips of tracheoles are usually filled with a fluid in which O2 dissolves & diffuses to tissues.
Mechanism of respiration:-
Alternate contraction & relaxation of the tergo-sternal muscles causes exhalation & inhalation of air through tracheae as well as spiracles.
The 1st thoracic & 1st abdominal pairs of spiracles remain open all the time while the remaining 8 pairs open only during inspiration.
Air enters the spiracles during inspiration & comes to the tracheae, then comes to the tracheoles which contains fluids. Now  the O2 get dissolved in the fluid & reaches to the tissue cells.
Some of the CO2 leaves the body through tracheae & spiracles. But the major portion of CO2 leaves through the cuticular covering of the body.


1. Name the major endocrine glands of Periplaneta sp.
Corpora allata (JH) & corpora cardiaca.
2. What is mushroom/ utricular gland? State its function.
It is a large, whitish accessory reproductive gland. 
Position;- Situated at the junction of vasa differentia & ejaculatory duct.
Structure;- It has a mass of glandular tubules which are of 3 kinds.
Utriculi majors, utriculi breviores & seminal vesicles.
Function:-
1. Secretion of utriculi majors form the inner layer of spermatophore.
2. Secretion of utriculi breviores nourishes the sperms.
3. Seminal vesicles are meant for storage of sperm.