5.6. Módulo de Interfaz serie para Periféricos (SPI)
5.6.2. Modos de operación del SPI
The protoehordates are of little economic importance. But they have great phylogenetic
significance to the zoologists. They show great affinities and perhaps, common origin with the living vertebrates. They retain the three basic chordate features (notochord, hollow dorsal nerve cord and pharyngeal gill-slits) throughout life. As such, they are considered most primitive and bo.de,line choiduies closer to the ancestor which prohabh gave rise to the final and the largest jiroap of ehoidates, the vertebrates.
C o m p a r i s o n o f T h r e e P r o t n c h o r t i a t e S u b p h y l a
The earlier arrangement of recognizing the taxonomic status of phylum Protochordata has been given up now-a-days because the three subphyla do not show any intimate relationship.
No doubt they all possess the three fundamental or primitive chordate characteristics (notochord, dorsal hollow nerve cord and pharyngeal gill slits) but they differ from one another in several ways.
Their chief contrasting characters have been summarized in Table 1.
110 i ' Protochordata ; General & Comparative
Table 1. G e n e r a l Comparison of T h r e e Protochordate Subphyla.
C h a r a c t e r s Subphylum I Subphylum I I Subphylum I I I
Hemichordata U r o c h o r d a t a Cephalochordata (Balanoglossus) (Herdmania) f B r a n c h i o s t o m a )
I. Distribution Marine, worldwide Marine, worldwide Marine, worldwide 2. H a b i t s a n d h a b i t a t Solitary or colonial. Solitary or colonial. Solitary, burrowing and
Mostly tubicolous Fixed or free-swimming free swimming
3. Shape Elongated, cylindrical, Degenerate, bag-like Fish-like, laterally compressed wormlike
4. Body divisions Head, neck, trunk Unsegmented without Segmented without distinct
head and tail head
5. P o s t a n a l tall Absent Absent Present
6. F i n s Absent Absent Median fins
7. Test Absent Present Absent
8. Coelom Enterocoelous, divisible Absent, replaced by Reduced by atrial cavity into three body regions atrial cavity
9. Atrial cavity Absent Greatly developed Well developed
10. Notochord Absent, instead stomo- Only in larval tail. Persistent, throughout life.
chord present absent in adult rod-like
11. M u s c l e s Unsegmented Unsegmented Metamerically segmented as.
myotonies 12. Digestive tube Complete, straight or coiled Complete, coiled Complete, straight
13. O r a l hood Absent Absent Present
14. P h a r y n g e a l Large, simple with two Large, complex, with 2 Large, complex with several a p p a r a t u s dorsal linear rows of gill to several pairs of lateral pairs of lateral gill slits
slits gill slits
15. F e e d i n g mechanism Ciliary or filter Ciliary Ciliary
16. R e s p i r a t o r y Absent, Respiration through Absent, Respiration through Absent, Respiration through
organs general surface. body surface body surface
17. H e a r t A dorsal heart present Well developed muscular Heart absent heart
IS. E x c r e t o r y o r g a n s Glomerulus in proboscis Neural gland, pyloric gland Protonephridia
& nephrocytes
19. Nervous system Intraepidermal _ —
20. Sexes Separate United Separate
21. Gonads One to several pairs One pair Numerous pairs metamerically
arranged
22, G o n o d u c t s Absent Present Absent
23. Development Direct or indirect, with or Indirect with retrogressive Indirect with metamorphosis without metamorphosis metamorphosis
93 i ' Protochordata ; General & Comparative
Table 2. Comparison of Habits a n d Habitat.
C h a r a c t e r s Hernichordata (Balanoglossus)
Urochordata (Herdmania)
Cephalochordata (Branchiostoma)
1. O c c u r r e n c e Marine Marine Marine
2. Distribution Worldwide, all seas Worldwide, Indian, Pacific & Worldwide all seas Carribean seas
3. H a b i t a t Marine, shallow Marine, shallow waters with Marine, shallow waters with
coastal waters of rocky bottom. sandy bottoms.
intertidal zones.
4. Mode of life Solitary, burrowing, Solitary, attached to sub-stratum Solitary, burrows in sand or free nocturnal and sluggish. by broad base, diurnal and swimming, nocturnal, active.
sluggish
5. B u r r o w U-shaped, having at Does not form burrows. Mostly remains burried in sand
least two openings, with anterior body end
lined by sand particles projecting above sand.
cemented together by mucus.
6. Food Micro-organisms and Planktonic microorganisms. Planktonic microorganisms.
organic particles in sand and water.
7. F e e d i n g h a b i t Microphagus Microphagus Microphagus
8. Mode of f e e d i n g Ciliary filter feeding Ciliary filter feeding by Ciliary filter feeding by passing as well as swallowing food-cum- respiratory water food-laden water current with mud. current passing through through perforated pharyngeal
perforated pharyngeal sac sac.
9. W a t e r c u r r e n t Enters branchial sac through Enters branchial sac through Enters branchial sac through mouth and goes outside directly mouth and goes out through mouth, reaches atrial cavity
through gill pores. atriopore. through gill slits and outside
through atriopore.
10. Protective device Secretion of a foul smelling Body surrounded by a Swims actively when disturbed iodoform-like substance. One gelatinous test containing
species is phosphorescent. spicules.
11. Reproduction Only sexual. Sexes separate. Only sexual. Sexes united. Only sexual. Sexes separate. No Also great power of Some reproduce asexually by asexual reproduction.
regeneration. budding.
94 i ' Protochordata ; General & Comparative
1. Alimentary canal
2, Mouth o p e n i n g
3. Buccal cavity
4. Pharynx
14, Digestive glands
Complete, straight narrow canal from mouth to anus.
Wide, circular, permanently open, situated mid-vemrally between proboscis and collar.
Short, without tentacles
Divided by lateral parabranchial ridges into a dorsal branchial portion with gill-slits and a ventral digestive portion.
Absent
Absent
Absent
Dorso-Jaterai U-shaped gill-slits open into branchial sacs which open externally through gill pores.
Not demarcated clearly from intestine.
Straight tube. Anterior or hepatic region sacculated, forming hepatic caeca.
Not differentiated.
Intestine opens at the tip of trunk by a sphinctered circular anal opening.
Absent
Definite glands unknown.
Complete, curved canal with intestinal loop.
Four-sided branchial opening, bordered by four lips, situated on branchial siphon.
It is cavity of branchial siphon, with a circlet of branchial tentacles.
Divided by two ciliated peribronchial ridges into an anterior small prebranchial region and a large posterior branchial sac with gill slits.
Absent
Extendi mid-ventrally along floor of pharynx.
Dorsal lamina present with tongue-like processes or languets.
About 2,00,000 gill-slits open into atrial cavity.
Demarcated from intestine and sphinctered at both the ends.
Forms a looped or U-shaped tube enclosing the left gonad, Ilio-colic ring is absent.
Differentiated and internally ciliated,
Rectum curves do really to open into cloaca by anus bordered by four lips.
Gill slits & anus open into atrial cavity leading to exterior through atrial opening bordered by four lips and situated on atrial siphon.
Liver is composed of two lobes.
Besides a branching pyloric gland in wall of stomach and
Complete, straight canal from mouth to anus.
Wide ante o-vcntral opening, boidwed bv free margin of oral
;al cirri.
«>* /estibuie of oral hood containing wheel organ.
Lateral oblique ciliated peripharyngeal bands demarcate a small antero-dorsal prebranchial region from large posterior branchial sac.
Present between vestibule and pharynx with velar tentacles.
Same as in Hcdmarua,
Ciliated groove present without processes,
150 to 200 pairs of gill slits open into atrial cavity.
Stomach or midgut not demarcated from intestine.
Forms a straight tube internally ciliated containing lateral ciliary tract and ilio-colic ring.
Demarcated and heavily ciliated.
It is a small, circular, sphinctered aperture opening at the base of caudal fin to outside.
Gill slits open into atrial cavity leading outside through atriopore.
Anus does not open into atrial cavity.
A midgut diverticulum is said to function as liver. Pyloric gland is absent.
digestive as well as excretory.
Protochordata : General & Comparative
5. Relation with
7. Division
10. Dorsal lamina
11. P e r i p h a r y n g e a l
12. Relation with
Present inside anterior one-third part oi bronchi ogemtal region of trunk.
Elongated
Attached with the body wall by dorsal and ventral mesenteries.
Absent
Large mid-ventral mouth leads into a short buccal cavity which in turn leads into pharynx.
Simple and uniformly lined by cilia and mucous cells.
Two lateral parabranchiai ridges incompletely divide pharynx into a dorsal respiratory or branchial chamber and a ventral digestive chamber.
Branchial portion of pharynx is perforated by numerous U-shaped gill-slits leading into branchial sacs.
Each sac leads to exterior by a single gillpore.
Absent.
Absent.
Absent.
Pharynx opens directly into intestine
Occupies the major part of body cavity.
Large, sac-like
Attached only mid-ventrally to mantle.
Pharynx suitounued dorso-laterally by the ;
peribranchial cavity which opens to the outside through atrial aperture.
Small, 4-rayed terminal mouth or branchial siphon. Its opening into pharynx is guarded by branched branchial tentacles.
Internal wall complicated and longitudinally folded with cilia and glands restricted into definite tracts.
Differentiated into a small anterior prebranchial zone and a much larger, posterior branchial sac, by two pairs of ciliated peripharyngeal bunds.
Branchial sac of pharynx is perforated by about 200,000 elongated gill-slits or stigmata leading into atrial cavity.
Endostyle is a shallow longitudinal midventral groove on floor of branchial sac. It consists of 5 ciliary tracts alternating with 4 glandular tracts.
A ciliated hyperpharyngeal band or dorsal lamina hangs mid-dorsally bearing tongue-like languets into the branchial sac.
Dorsal lamina and endostyle are connected on either lateral side by a pair of ciliated peripharyngeal bands.
Leads into intestine via oesophagus and stomach.
Occupies nearly one half anterior part of body.
Large, spacious, cylindrical and laterally compressed chamber.
Attached dorsally tb bodywail.
The peribidiichul c.t>u\ or atrium surrounds phaiynx on all sides except the dorsal, its adtopore lies posteriorly.
Large oval mouth bordered by oral hood with buccal cirri and guarded by velar tentacles leads into pharynx through a circular aperture, the enterostome.
Cavity very much complicated with definite ciliary and glandular tracts.
Divided into a small anterior prebranchial zone and the pharynx proper by a pair of ciliated peripharyngeal bands.
Lateral walls of pharynx are perforated by 150 to 200 pairs of vertically oblique narrow gill-slits openings into the atrial cavity.
A hypobranchial tract or an endostyle similar to that of Herdmania is present. It is made of ciliary and alternating mucus-secreting cells,
A prominent ciliated epipharyngeal or hyperpharyngeal groove is present mid-dorsally opposite endostyle. Languets are absent.
Epipharyngeal groove and endostyle are connected anteriorly by a pair of lateral peripharyngeal ciliated bands.
Opens into intestine via short oesophagus and midgut.
(Z-3)
114 i ' Protochordata ; General & Comparative
Table 5. Comparison of Food and Feeding,
C h a r a c t e r s Hernichordata of food particles
5. W a t e r c u r r e n t
Microorganisms and organic particles in sand and water.
Microphagus.
Ciliary filter feeding as well as swallowing mud.
External. Minute food particles trapped outside body by mucus secreted by proboscis.
By lashing of lateral cilia on gill slits of pharynx, a constant, feeding water current enters through mouth.
Mouth —y buccal cavity —»
pharynx —> pharyngeal gill slits
—} branchial sacs —> exterior gill pores
Che mo-receptor cells of pre-oral ciliary organ at the base of proboscis test the quality of food and water entering mouth.
Muscular ventral part of collar regulates feeding current by closing mouth under nervous control.
Endostyle and epipharyngeal groove absent. Food particles move backwards by ciliary action via ventral digestive part of pharynx into oesophagus.
Not known.
Undigested food and sand pass out through anus as castings.
Planktonic microorganisms.
Microphagus.
Ciliary filter feeding.
Internal. Food particles collected inside pharynx by mucus secreted by glandular tracts of endostyle.
Beating of lateral cilia lining stigmata drives a continuous water current into mouth.
Mouth - 4
Ciliary filter feeding.
y secretion of miu ous m lit. endostyle on the
Vv heel organ on roof of oral hood causes a constant flow of sea water through mouth.
Same as in Herdmania
Branchial tentacles act as chemoreceptors and also as strainers to prevent entry of impurities and larger food particles. Ciliary beating is under nervous control.
Mucous-entangled food particles from ventral endostyle are shifted dorsally along pharyngeal wall to dorsal lamina and driven backwards into oesophagus by ciliary action.
Unwanted current and larger particles thrown out of mouth by producing a strong reverse current by muscular contraction.
Undigested food expelled out forcefully, through atrial aperture, by sudden contraction of body musculature.
Buccal cirri and velar tentacles serve as sieves as well as chemoreceptors preventing entry of larger food and sand particles.
Ciliary beating is under nervous control.
Sheets of food particles entrapped by mucus secreted by endostyle move dorsally to epipharyngeal groove and passed as a narrow food cord into oesophagus by ciliary action.
Periodically, the atriopore closes and atrial flood suddenly contracts regurgitating water current and large food particles forcefully through mouth.
Undigested food is thrown out directly to outside through anus.
f Z-3)
115 i ' Protochordata ; General & Comparative
Table 6. C o m p a r i s o n of Excretory System.
Characters Hemichordata U r o c h o r d a t a C e p h a l o c h o r d a t a
(Balanoglossus) (.Herdmania) (,Branchiostoma)
1. M a i n e x c r e t o r y Excretory organ is the proboscis Excretory organ is the neural gland Main organs are 90 to 100 pairs of o r g a n gland or glomerulus projecting lying mid-dorsally embedded in mantle protonephridia present segmentally one
into proboscis coelom. above the nerve ganglion. above each gill slit.
2. S t r u c t u r e Glomerulus consists of tubular Neural gland consists of peripheral and Each nephridium consists of lower projections lined by peritoneum central tubules leading into a small duct vertical limb terminating blindly, and and containing blood. opening anteriorly by a large ciliated
funnel at the base of dorsal tubercle.
an upper horizontal limb opening by a small nephridiopore into atrium.
3. Solenocytes There are no solenocytes. There are no solenocytes. Both limbs give out several small branches each receiving a tuft of flame cells or solenocytes.
4. Physiology of The peritoneal cells of The excretory cells or nephrocytes Nitrogenous wastes diffuse from excretion glomerulus extract from Mood collect waste products, and discharge surrounding blood and coelomic fluid
the excretory particles, discharge through aperture of the duct into into solenocytes, discharge into atrium them into proboscis coelom and prebranchial zone of pharynx. through nephridiopores and pass out of
finally to the exterior through body through atriopore with the
proboscis pore. outgoing water current.
5. Secretion of h o r m o n e s
Unknown. Unknown. Neural gland secretes a hormone
controlling opposition, development and metamorphosis, and is considered homologous to vertebrae pituitary gland.
6. H a t s c h e k ' s rKphridium
Not found. Not found. A nephridium of Hatschek lies in roof
of oral hood. Its structure and function are similar to those of a piotoncphridium.
7. B r o w n f u n n e l Not found. Not found. Two sac-like brown funnels situated dorsally upon pharynx are also considered to be excretory.
8. R e n a l p a p i l l a e Not found. Not found. Groups of cells or renal papillae present on atrial floor are also considered to be excretory.
Table 7. C o m p a r i s o n of Nervous System.
C h a r a c t e r s Hemichordata U r o c h o r d a t a C e p h a l o c h o r d a t a (Balanoglossus) (Herdmania) fBranchiostoma )
1. G r a d e of n e r v o u s Primitive, resembling that of Adult nervous system simple and Simple but better developed than system coelenterates or echinoderms. degenerate. in Balanoglossus and Herdmania.
2. S t r u c t u r e Consists of subepidermal plexus Consists of a solid nerve ganglion Consists of a hollow tube or nerve of nerve fibres and cells, forming lying just below the nerural gland cord lying mid-dorsally above the two def'nite strands or nerve cords, mid-dorsally in the mantle notochord.
one mid-dorsal and other between the two siphons. A nerve mid-ventral. cord is also present in the larva.
3. B r a i n Brain is lacking. Nerve ganglion is the so-called Anterior end of nerve cord slightly brain or cerebral ganglion. dilates, forming the so-called brain
or cerebral vesicle.
4. N e r v e s Definite nerves lacking. Nerve ganglion sends 3 nerves to There are 2 pairs of sensory branchial siphon and 2 nerves to cerebral nerves, followed by atrial siphon. No spinal nerves several pairs of spinal nerves, each present. with separate dorsal and ventral
nerve roots.
5. A u t o n o m i c system Lacking. Lacking. Present,
(Z-3)
Protochordata : General & Comparative
IMPORTANT QUESTIONS
Long Amw$r Typ* Qum&ms
1, Differentiate between the habits tod habitats of Balanoglossus, Herdmania and Branchiostoma.
2 Compare the circulatory, excretory and nervous systems of Babmoghssus with that of an ascidian and a laacelet, 3, Describe the alimentary canal and associated glands of Branchiostoma and compare it with that of a hemichondate and a
urochordate.
4, Describe the structure and function of pharynx to Herdmania and compare it with that of Bakmugbasus and Branchiostoma.
5, Compare the food and feeding of the three Protochardate subphyla, Short Antwer Type Questions
1. List the three common chordate character*.
2. What are Protoehordates? Discuss their significance.
3. Give a general comparison of the three Protochardate subphyla.
» Multiple Choke Questions
1, The post-anal tail is present in :
(a) Hemichordates (b) Urochordates (c) Cephalochordates (I) All Protoehordates 2, Test is present in :
(a) All protoehordates (b) Hemichocdate (c) Urochordates (d) Cephalochordates 3, Metaroerically segmented muscles are present in ;
(a) AH protoehordates (b) Hemichordates (c) Urochordates (d) Cephalochordates 4, Development in Urochordata is :
(a) Direct
(b) Indirect with retrogressive metamorphosis (c) Indirect without metamorphosis
(d) Indirect with metamorphosis 5, In Amphioxus rectum is :
(a) Not differentiated
(b> Differentiated and sparsely ciliated (c) Differentiated but not ciliated (4) Differentiated and heavily ciliated 6, In Urochordata, the pyloric gland is :
(a) Digestive as well as excretory (b) Only digestive
(c) Only respiratory (d) Only excretory
7, In Balanoglossus each branchial sac opens to t i e exterior :
(a) Directly (b) By a single gill pore (c) By a single gill slit (d) Through the pharynx 8, In Hentmunia the opening of branchial siphon into the
pharynx is guarded by :
10,
I t .
12.
13.
14,
(a) Branched branchial tentacles (b) Branched and ciliated tentacles (c) Unbranched tentacles
(d) Unbranched pharyngeal tentacles
In Amphioxus reverse current is caused by the closing of :
(a) Atriopore (b) Anns (c) Oral hood (I) Mouth In Urochordata and Cephalochordata t i e course of feeding current is :
(a) Mouth stigmata - > atrium atriopore - e x t e r i o r (b) Mouth - » pharynx ->atrium -*extenor
(c) Mouth -^pharynx ->atrium ->atriopore - + exterior (d) Mouth —•pharynx —>stigmata -> atrium - » atriopore
—> exterior
In Hcmichordata the function of excretion is chiefly performed by
(b) Liver (d) Neural gland
brown funnels situated near the
(a) Pyloric gland (c) Proboscis gland In cephalochordates pharynx are ;
(a) Respiratory (b) Excretory (c) Circulatory (d) Sensory Autonomic nervous system is present to : (a) All Protoehordates (b) Urochordata (c) Hernichordata (d) Cephalochordata In Cephalochordates ;
(a) Only cerebral nerves are present (b) Only spinal nerves are present (c) Nerves are absent
(d) Both cerebral and spinal nerve are present
ANSWERS
1. (c) 2 . (c) 3. (d) 4 . (b) 5, (d) 6 . (a) 7 . (b) 8 . (a) 9 . (a) 10. (d) 11. (c) 12. (b) 13. (d) 14. (d).
(Z-3)