- Affinities of Balanoglossus with Annelida & Echinodermata.
- Body vermiform & coelomate.
- Burrowing habit, tubicolous life & ingesting mud which is passed out as castings through anus.
- Collar of Balanoglossus is similar to clitellum of earthworm.
- Proboscis & prostomium is similar & preoral.
- The arrangement of blood vessel is similar.
- Dorsal position of heart.
- 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.
- Adult resemblances:-
- Enterocoelic origin of coelom.
- Heart vesicles & glomerulus of Balanoglossus are considered homologous to the dorsal sac & axial gland of echinoderm.
- Nervous system poorly developed & forms epidermal nerve plexus.
- Proteins & phosphagens present in Balanoglossus closely resemble those of echinoderms.
- Common habits, echological niches & remarkable power of regeneration.
- Larval resemblances:-
- Small, pelagic, transparent & oval.
- Identical ciliated bands taking up a similar twisted course.
- Enterocoelic origin & similar development of coelom.
- Proboscis coelom of Tornaria is comparable to hydrocoel of echinoderm Dipleurula.
- 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;-
- Adult resemblances:-
- Enterocoelic origin of coelom.
- Heart vesicles & glomerulus of Balanoglossus are considered homologous to the dorsal sac & axial gland of echinoderm.
- nervous system poorly developed & forms epidermal nerve plexus.
- Proteins & phosphagens present in Balanoglossus closely resemble those of echinoderms.
- Common habits, echological niches & remarkable power of regeneration.
- Larval resemblances:-
- Small, pelagic, transparent & oval.
- Identical ciliated bands taking up a similar twisted course.
- Enterocoelic origin & similar development of coelom.
- Proboscis coelom of Tornaria is comparable to hydrocoel of echinoderm Dipleurula.
- Deuterostome & digestive tract is complete with mouth & anus & same parts.
- Comment on echinoderm & chordate affinities of Balanoglossus.
- Echinoderm affinities of Balanoglossus;-
- Adult resemblances:-
- Enterocoelic origin of coelom.
- Heart vesicles & glomerulus of Balanoglossus are considered homologous to the dorsal sac & axial gland of echinoderm.
- Nervous system poorly developed & forms epidermal nerve plexus.
- Proteins & phosphagens present in Balanoglossus closely resemble those of echinoderms.
- Common habits, echological niches & remarkable power of regeneration.
- Larval resemblances:-
- Small, pelagic, transparent & oval.
- Identical ciliated bands taking up a similar twisted course.
- Enterocoelic origin & similar development of coelom.
- Proboscis coelom of Tornaria is comparable to hydrocoel of echinoderm Dipleurula.
- Deuterostome & digestive tract is complete with mouth, anus & same parts.
- Similarity is present in the pharynx & branchial apparatus of both.
- Development of the central part of the nervous system is quite similar in both.
- Similarity in the structure & function of branchial apparatus.
- Arrangement of coelomic sacs are similar.
- Comment on the phylogenetic status of Peripatus./Discuss on the systematic position of Peripatus.
- Onychophora exhibits both arthropod & annelid characters along with its own
- Presence of antennae.
- Body is covered with chitinous cuticle.
- Appendages are provided with claws.
- Jaws are modified appendages, provided with striped muscles.
- Locomotion by definite legs having definite musculature.
- Presence of haemocoel.
- Dorsal tubular heart with lateral ostia.
- Presence of tracheal respiratory system.
- Coelom reduced to small cavities that surround the excretory & reproductive ducts.
- Peculiar salivary gland supposed to be modified nephridia.
- Brain is large & typically arthropodan.
- General structures of the reproductive organs & development mainly arthropodan.
- Vermiform body with truncated extremities.
- Absence of true head.
- Outer body covering is cuticle, skin thin & flexible.
- Muscles separate in identical way.
- locomotion slow & by peristalsis as in an earthworm.
- Simple & straight alimentary canal.
- Paired, segmentally arranged nephridia.
- Presence of cilia in excretory & reproductive ducts.
- Structure of eye same as in polychaetes.
- Slime & coxal glands correspond with similar glands of chaetopods.
- Body shows no or indistinct segmentation.
- Texture of skin. A rough cuticle covered with numerous velvety processes not known in other phyla.
- Antennae not homologous to the antennae of other arthropods.
- 3 segmented head of Peripatus shows a condition mid way between that of Annelida & Arthropoda.
- Restriction of jaws to a single pair. Movement of jaws is antero-posterior.
- Presence of non jointed legs with claws.
- Irregular distribution of spiracles or tracheal openings.
- 2 ventral nerve cords widely separated & without true ganglia.
- Structure of eye less complicated.
- Distribution of reproductive organs.
- Write in details the arthropodan affinities of Peripatus.
- Presence of antennae.
- Body is covered with chitinous cuticle.
- Appendages are provided with claws.
- Jaws are modified appendages, provided with striped muscles.
- Locomotion by definite legs having definite musculature.
- Presence of haemocoel.
- Dorsal tubular heart with lateral ostia.
- Presence of tracheal respiratory system.
- Coelom reduced to small cavities that surround the excretory & reproductive ducts.
- Peculiar salivary gland supposed to be modified nephridia.
- Brain is large & typically arthropodan.
- General structures of the reproductive organs & development mainly arthropodan.
- Make a note on the geographical distribution of Peripatus..
- Neo-Peripatus:- (Peripatus):- West Indies & America
- Congo-Peripatus:- (Mesoperipatus Evans):- Congo & Caribbean islands.
- Eo-Peripatus:- (Eoperipatus Evans):- Malaya
- Capo-Peripatus:- (including Peripatopsis Pocock & Opisthopatus Purcell):- South Africa
- Melano-Peripatus;- ( Paraperipatus Willey):- New Britain.
- Austro-Peripatus:- (Peripatoides Pocock & Ooperipatus Dendy):- Australia, Tasmania, New Zealand.
- Chilio-Peripatus:- (Opisthopatus Bouvier), Chile.
Spengel (1893) suggested affinities of Hemichordata (Balanoglossus) with
Annelida as follows:-
Affinities of Balanoglossus with
Echinodermata:-
Adult Balanoglossus & echinoderms are structurally quite
different. So it is difficult to draw their phylogenetic relationship between
themselves. However some resemblances are :-
Tornaria larva of Balanoglossus has striking, structural similarities with Bipinnaria larva of
echinoderms.
Adult Balanoglossus & echinoderms are
structurally quite different. So it is difficult to draw their phylogenetic
relationship between themselves. However some resemblances are :-
Tornaria larva of
Balanoglossus has striking, structural similarities with bipinnaria larva of
echinoderms.
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.
Adult Balanoglossus & echinoderms are
structurally quite different. So it is difficult to draw their phylogenetic
relationship between themselves. However some resemblances are :-
Tornaria larva of
Balanoglossus has striking, structural similarities with Bipinnaria larva of
echinoderms.
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:-
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:-
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.
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.
peculiarities- Explain.
Arthropod characters
of Onychophora:-
Annelid characters of
Onychophora;-
Onychophoran
characteristics:-
The following
features are peculiar to Onychophora in
which they differ from other phyla:-
Arthropod characters
of Onychophora:-
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:-
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