Affinities and Systematic Position of Balanoglossus with Chordate

Affinities with chordates :-

(a) Similarities :-

(i) Pharyngotremy (pharyngeal gill-slits) → Present

(ii) Central Nervous System → Comparable to dorsal tubular nerve cord.

(iii) Stomochord → Comparable to Notochord.

(iv) Enterocoelic coelom → Present.

(b) Objection :-

Features	Balanoglossus	Chordates
Notochord	Not true	True
Morphology	Short, hollow, stifftube	Solid, rod like
Composed of	Tall vacuolated endodermal cell	Arranged  vacuole mesodermal cells
Origin	Endodermal as a buccal diverticulam	Mesodermal
Surrounded by	Besement membrane	Primary & secondary sheathes
Position	Ventral to dorsal blood vessel	Dorsal to dorsal blood vessel
Supporting Function	Absent	Present

Remark :-

(1) Barrington and Hyman called the buccal diverticulam as stomochord instead of notochord. They also rejected the idea of persistant notochord in Balanoglossus.

(2) Central Nervous System :- More similar to invertebrate type (Barrington,1965) than any true chordates, as :

(i) Nerve cord- Intraepidermal.

(ii) Nerve ring- Circumcentric.

(iii) Ventral nerve cord- Solid

(3) Pharyngotremy :- The only Chordates feature might be a convergent feature, as conceived by Beril (1955).

(4) Other Features :- 

(i) Post anal tail- Absent

(ii) Vascular System- Without centralised heart.

(iii) Endostyle- Absent

(iv) Gut- Undifferentiated, without muscular wall, no peristasis.

Remark :-

Resemblances are superficial and such when due to evolutionary convergence in the same track. Features indicate Hemichordates are definition lower in rank than true Chordates ( Uro- & Cephalo-chordates). Hemichordates thus very remotely connected with the central stock from which true chordates descended.

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Affinities and Systematic Position of Balanoglossus With non-chordate

Affinities with non-chordates :-

(B) With Pogonophora :-

(a) Similarities :-

(i) Coelom → Enterocoelic

(ii) Nervous system → Intraepidermal

(iii) Gonads → In trunk region

(iv) Pericardial sac → Present

(b) Dissimilarities :-

Features	Balanoglossus	Pogonophora
Main nervous system  concentrated at	Mesosoma	Protosoma
Coelomoducts	Absent	Present
Alimentary canal	Present	Absent

Remark :-

Young (1983) opposed the resemblances between the two groups (as stated by Barington,1965; Parker and Haswell, 1972; and Mc Ferland et al, 1985), claiming the similarities are superficial.

Affinities with non-chordates :-

(B) With Echinodermata :-

(a) Similarities :-

(i) In Adult Form :-

(i) Coelom → Divisible in 3 successive parts anterior-posteriorly.

(ii) Nervous Plexux → Subepithelial

(ii) In Larval Form :- 

Tornaria resembles Bipinaria in.

(i) Pre-oral ciliated bands → Present

(ii) Cleavage → Holoblastic & equal

(iii) Apical Plate → With a turf of cilia.

(iv) Blastopore → Become Anus in adult.

(v) Enterocoelic coelom → Present.

(b) Dissimilarities :-

(i) In Adult Form :-

Features	Balanoglossus	Echinodermata
Water vascular system	Absent	Present
Pharyngeal gill slits	Present	Absent
Stomochord	Present	Absent

(ii) In Larval Form :- 

Features	Balanoglossus	Echinoderms
Eye-spot in apical plate	Present	Absent
Telotroch	Present	Absent

Remark :-

Based on resemblances; Hemichordates & Echinoderms are thought to be originated from some common remote ancestor (Hymen,1959) and Barrington,1965). H.B fell (1963) denied it on the ground that similarities were due to larval convergence in similar mode of living.

Short type Questions with Answers from Invertebrate

(21) Name two aquatic respiratory structures of the arthropods ? Cite example.

(Ans) :- Gills, lining of the branchiostegite, epipodite.
             Found in Crustaceans.

(22) Name one Poiferan animal where spicules are absent. Mention the subclass of that animal ?

(Ans) :- In Oscarella spicules are absent.
             Subclass- Tetractinellida.

(23) Mention the characteristic features of nervous system of Chiton ?

(Ans) :- Protoneurous condition where the nervous system is without any definite ganglionic function.

(24) State the functions of Tiedman's body & Pollian vessicle ?

(Ans) :- Tiedman's body may produce coelomocytes.
             Pollian vessicle are apparently for fluid storage.

(25) What is Atoll ?

(Ans) :- Atolls are reefs that encircle a lagoon but not an island. These types of reefs typically slope rather steeply into the deep water at their seaward edge.

(26) Why pulmonatans are so named ? Cite an example.

(Ans) :- In this molluscs true gill absent & respiration is done by pulmonary sac or lung, as the pulmonary sac is respiratory organ so they are named as pulmonatans. Mantle cavity form the pulmonary chamber, the inner surface of which is highly vascularised.

Example :- Achatina fulica

(27) What is Mesenchyme ?

(Ans) :- Embryonic connective tissue ; irregular or amoebocytic cells often embeded in gelatinous matrix, prominant in poriferan animals.

(28) What is Ampulla ?

(Ans) :- Membranous vesicle ; dialation at the end of each semicircular canal containing sessory epithilum, muscular vesicle above tube feet in water vascular system of echinoderm.

(29) What do you mean by Coenosarc ?

(Ans) :- Within the stems of colonial polyp, material that like links the individuals, containing the gastrovascular cavity & surrounded by the perisarc.

(30) What is Kinetodesma ?

(Ans) :- Fibril arising from the kinetosome of a cilium in ciliate Protozoan & passing along the kinetosomes of cilia in that same row is known as kinetodesma. All the kinetosome & kinetodesmata of a row of cilia is named as kinety.

(31) What is Cilium ?

(Ans) :- A hair like vibratil organelle process found on many animal cells. Cilia may be used in moving particles along the cell surface or in ciliate protozoans for locomotion. Each cilium contains nine pairs of longitudinal microtubule arranged in a circle arround a central pair "9+2" tube of microtubules in cilium is it's axoneme.

(32) In which phylum do you find a mantle ? Where does the mantle originate from ?

(Ans) :- In phylum mollusca mantle is found. Two folds of skin, outgrowths of the dorsal body wall, form a protective mantle.
Mantle is responsible for the secretion of the shell.

(33) Name the different types of pseudopodia & state their characters with example.

(Ans) :- (i) Lobopodia- Large blunt extensions of the cell body containing both endoplasm & ectoplasm.

(ii) Filopodia- are thin extensions, usually branching & containing only ectoplasm.

(iii) Reticulopodia- repeatedly region to form a net like mesh.

(iv) Axopodia- Long thin pseudopodia supported by axial rods of microtubules.

(34) Locomotion & function of Chlorogogen cells?

(Ans) :- In annelida coelomic fluid contain four types of corpuscles, chlorogogen cells are one type of coelomic crpuscles.

Function :- Help in removal of excretory products out of body.

Short type Questions with Answers from Invertebrate

(11) In which animal Aristotle's Lantern found ? Mention its function.

(Ans) :- Aristotle's Lantern found in the class Ecinoidea, under the phylum Echinodermata(sea urchin).

Function :- Acts as masticating apparatus to which teeth are attached.

(12) Write the  scientific name of Portugueese-man-of war ? In which phylum does it belong ?

(Ans) :- Physalia physalis (phylum-Cnideria ; class-hydrozoa)

(13) Mention the utility of Byssus threads ?

(Ans) :- Bivalvia having strands of byssus by which the animals are often attached to the substratum or objects. A byssal gland is located in the foot sescretes a fluid protein which passes down a groove along the underside of the foot; the secretion hardens on exposure to sea water.

(14) What is Cnidoblast ?

(Ans) :- A round or oval. epidermal cell with a basal nucleus, typical of cnidaria, that contain nematocyst.

(15) What is Sclerosepta ?

(Ans) :- Each corallite consists of cup. The wall of cup enclosing the aboral position of the polyp is termed as theca. The ridges of the cup are called Skeletal septa or Sclerosepta.

(16) What is Biradial symmetry ? Cite an example of an animal having this type of symmetry.

(Ans) :- The arrangement of body components of an animal such that similar parts are located to either side of the central axis & each of the four sides of the body is identical to the oposite side but different from the adjacent side.
Found in sea walnuts (ctenophora)

(17) Name two free living Platyhelminthes ?

(Ans) :- Planaria, Convoluta, Thysanozoon, Bipalium etc.

(18) Define metamerism ? give an example.

(Ans) :- Metamerism is a serial repetition of similar body segments along the longitudinal axis of the body. Each segment is called metamere or somite. It is found in the phylum Annelida.

(19) Give an example of animals having only polypoid & only medusoid characteristics ? Mention their respective classes.

(Ans) :- Polypoid- Metridium (class- Anthozoa) ;
             Medusoid- Aurelia aurita (class- Scyphozoa)

(20) Write the function of Madriporite ?

(Ans) :- Sieve like structure that is the intake for the water vascular system of echinoderm.In echinodermata a sieve like, button shaped process on the aboral surface of the body; through its opening the water vascular system is connected to the water outside.

Short type Questions with Answers from Invertebrate

(1) What is Cytopharynx ?

(Ans) :- In some Protozoan cells, a short passage like region through which food passes after being ingested at the cytostome.

(2) What is Pseudocoelom & where it is found ?

(Ans) :- A small second body cavity (the first being the gut) which occupies a space between the mesoderm of the body wall & the endoderm of the gut. There are no mesentaries suspending the internal organs & no muscular layers around the gut.
Found in Nematohelminthes.

(3) What is Amoeboid movement ?

(Ans) :- Movement in the fashion of Amoeba i.e. by Pseudopodia.

(4) What is contractile vacuole? Mention its function ?

(Ans) :- An organelle which appears to function in removal of excess water from the cells of Protozoa. The contractile vacuole expands as it fills with water from the cytoplasm & contracts as this water is emptied to the extertior.

Function :- They are responsible for osmoregulation, i.e. maintenance of a constant water potential inside the body.

 

(5) What is Tracheoles ? Where they are found ?

(Ans) :- One of the circular tubes that make up the respiratory system of an insect. The tracheae ramify throughout the body, terminating in fine, intracellular branches called Tracheoles.

(6) What is stone canal ? Where it is found ?

(Ans) :- In Echinoderm a canal with walls strengthened by calcarious matter that connect the madriporite with water vascular system.

(7) In which animal group Choanocytes are found ? Mention their function.

(Ans) :- One of the flagellated collar cells that line cavities & canals of sponges are called choanocytes.
In Poriferan animal Choanocytes are found.

Functions :- (a) Flagella of choanocytes maintain a current of environmental water through the canals(keep the water moving). (b) Trap & phagocytize food particles that are carried in the water.

(8) What is Medusa ?

(Ans) :- Medusa are usually free swimming stage in the life cycle of Cniderians. Medusa have bell shaped or umbrella shaped bodies & tetramerous symmetry, the mouth is usually centered on the concave side & tentacles extend from the rim of the umbrella.

(9) Name the different types of gills found in crustaceans?

(Ans) :- (a) Podobranch- attached with coxopodite of the thoracic appendage.
            (b) Arthrobranch- Attached with arthroidal membrane.
            (c) Pleurobranch- Attached with the lateral wall of the thorax.

(10) What is Radial Symmetry ? give example.

(Ans) :- Radial symmetry applies to the forms that can be devided into similar halves by more than two planespassing through the longitudinal axis.

Example :- Spongs, Hydra, Jellyfish etc.

     

Affinities and Systematic Position of Balanoglossus with non-chordate

Affinities with non-chordates :-

(B) With Phoronida :-

(a) Similarities :-

(i) In Adult Form :-

(i) Body → Worm like

(ii) Mode of Feeding → Ciliary

(iii) Sense Organ → Absent

(ii) In Larval Form :-

(i) Body → Spindle shaped; Transparent; Free-swimming;

(ii) Pre-oral cilia → Present

(iii) Coelomic Compartment → Five

(iv) Apical Plate → With a turf of cilia and eye spots.

(v) Blastopore → Become Anus in adult.

(b) Dissimilarities :-

(i) In Adult Form :-

Features	Balanoglossus	Pheronida
Body	Divisible into 3 parts	Not so
Pharyngeal gill slits	Present	Absent
Stomochord	Present	Absent
Sexes	Separate	Not Separate

(ii) In Larval Form :- 

Features	Tornaria	Actinotrocha
Ciliated bands	Pre-oral & Pre-anal	Along the arms
Arm like Projection	Absent	Present
Coelom formation	Enterocoelic	Schizocoelic

Remark :-

Similarities are so superficial that Balanoglosssus can not be grouped with Phoronids; as suggested by Goodrich at al.

Affinities and Systematic Position of Balanoglossus

Affinities with non-chordates :-

(A) With Annelida :-

(a) Similarities :-

(i) In Adult Form :-

(1) Body → elongated; vermiforms; coelomate;

(2) Heart → dorsal to gut.

(3) General Sense Organ → Absent

(4) Collar → Resembles to clitellum.

(5) Blood Vessel → Similar pattern.

(ii) In Larval Form :-

  

Tornaria of Balanoglossus resembles Trochophore larva of anelids in :

(1) Body → Transparent and spindle-shaped.

(2) Habit → Free-swimming

(3) Ciliated bonds → Transverse

(4) Apical Plate → With a tuft of cilia and eye spots.

(b) Dissimilarities :-

(i) In Adult Form :-

Features	Balanoglossus	Annelids
Body	Unannulated	Annulated
Pharyngeal gill slits	Present	Absent
Stomochord	Present	Absent
Excretory  organ	Glomerulus	Nephridia

(ii) In Larval Form :- 

Features	Tornaria	Trochophore
Cleavage	Equal	Spiral
Blastula	Hollow	Solid
Coelom formation	Enterocoelic	Schizocoelic

Remark :- 

Dissimilarities are much more prominent than superficial similarities. Balanoglossus, thus, could not be grouped together with Annelids.

Types of Coelom

A true coelom is lined on all sides by mesoderm which gives rise to muscles that surround the gut aas well as underlying the body wall. This allows more efficient digestion because food can be pushed through the digestive tract by muscles.

True  Coelom :- 

Schizocoeloms are found in animals known as Protostomates.

Enterocoeloms are found in animals known as Deuterostomates.

Protostomia :-

Cleavage is spiral. In spiral cleavage the first two divisions of the egg are equal, but the rest are unequal. These results into some small and some large cells, as it can be seen. The blastopore forms the mouth. The body cavity is formed by Schizocoely- Schicoely means that the body cavity is formed from blocks of mesoderm around the gut that enlarge and hollow out. The end result is a pair of coelomic cavities. Cleavage is determinate. This means that the fate of each individual cell is already established when it is formed. Each cell can only develop into a specific cell type.

Deuterostoma :-

Cleavage is radial- Each cell division is equal and result in cells of all the same size. The blastopore does not form the mouth, it usually forms the anus. The body cavity is formed by enterocoely. Enterocoely is the formation of the body cavity by out pocketing of the primitive gut that break off and form the coelom. Cleavage is indeterminate. This means that the fate of each individual cell is not determined when it is formed and each cell can form one of many cell types. There are cavities , coeloms. that form and lie both outside (extraembryonic) and inside (intra-embryonic) the embryo during development. The intra-embryonic coelom is the cavity that lies within the developing embryo that will form the 3 major body cavities : Pericardial, Pleural. Peritoneal. The coelom forms very early in embryogenesis and is much later partitioned inferiorly by the diaphragm and pleura-peritoneal membrane ; and superiorly initially by the pleuro-pericardial fold between the heart and lungs. The intraembryonic coelom communicated through coelomic portals (at the level of midgut herniation) with the extraembryonic coelom. All cavities are fluid filled and developing organs push against a wall of the cavity, generating a double coat (serosal/adventital) surrounding an organ (for example the lungs). The serous membrane is the epithelium (squamous) and its associated underlying loose connective tissue.

Protostomes  Vs  Deuterostomes :-

In echinoderms and chordates, for example, the anus forms first, and then the mouth. In animals belonging to several other important phyla, on the other hand, such as arthropodes, annelids and molluscs, the mouth forms first, followed by the anus. For this reason arthropods, annelids and molluscs are sometimes called Protostomes (Greek : proto = the first ; stoma = mouth ). It is also possible to take an most echinoderm or chrodate embryos at the 2-cell or 4-cell stage of development, separate the cells, and still have each cell continue on to develop into a complete, variable organism. This is not possible with protostome embryos. If they are separated at this stage, the cells will not develop into complete, viable organisms. For this reason, protostomes are said to display determinate cleavage, and deuterostomes are said to have indeterminate cleavage. You will be introduced in lecture and in subsequent laboratory exercises to other important developmental characteristics that distinguish protostomes from deuterostomes.

Advantage of a coelom :- 

(i) The hydrostatic skeleton a fluid body cavity provides a more rigid structure than mesoderm for muscles to pull against and thus be a more efficient skeletal support system.

(ii) Circulatory system : absorbed nutrients can be circulated around the body and metabolic wastes can be carried to the body surface more efficiently by fluid than by solid mesoderm.

Result- Faster locomotion and larger body size possible.

Advantage  of Pseudocoelom :- 

In evolution, the pseudocoelom is a blatocoel (the space in the blastula) that is retained to adulthood. In addition to having a body cavity, organisms with pseudocoeloms also have a complete digestive tract separate opening for food to enter and undigested material to leave. This makes digestion and feeding more efficient because the animal can eat before it has finished digesting its previous meal. Organisms that have pseudocoeloms are not a monophyletic group (in other words, the pseudocoelom is a homoplasious character that occured more than once).