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.