The document discusses the different types of respiratory structures called gills found across various animal phyla. It describes the gills in annelids like Arenicola and Amphitrite, which are branched structures located on certain body segments. In arthropods, book gills are described in Limulus, while crustaceans have three main types of gills. Molluscs generally have ctenidia or true gills, and details are provided on their structure and location in different classes like gastropods and bivalves. Alternative respiratory structures called adaptive or secondary gills are also briefly discussed in some mollusc groups.

1. Dr Shampa Jain
Professor Dept of Zoology
Govt Science College Jabalpur

2. Gills – In Annelida
• gills found in Arenicola and
Amphitrite .
• Arenicola commonly known as
lugworm .
• It lives in mud or sand in U and J
shaped burrows lined by mucus .
• Middle region consist of 13 segments
each bearing parapodia and branched
gills.
• Gills act as respiratory surfaces and a
water is maintained through the
burrow.
• In Amphitrite first three segment bear
paired dorso -lateral branched gills.

3. Different types of gills found in different
groups of Arthropoda are as follows :
Chelicerata -
 Merostomata – In Limulus , the respiratory
organs are book gill.
 Which occur five posterior segments of mesosoma.
 They become modified as gills.
 On each appendage are found , some 1,500
thin walled lamellae.
 The lamellae lie parallel to each other
resembling a pages of a book,
 They are characteristically known as book gills.
 The beating of appendages causes a current
of water to pass over the book gills.
 The respiratory pigment is hemocyanin.

4.  Gills are the organs of respiration in most crustaceans .
 In decapoda fully develop gills are found.
 For example in palaemon there are 8 gills present inside each gill chamber.
 They may be of three types based on their place of origin and attachment.
 Podobranch or foot gill
 Arthrobranch or joint gill
 Pleurobranch or side gill
 In palaemon gills are phylobranchs i.e. they have a central axis bearing
biserially arranged main branches which are themselves sub branched.

6.  The scaphognathite of each maxilla lies anteriorly inside the gill
chamber.
 By its constant vibrating movements, it bales out water from the
anterior open end of gill chamber.
 Action of scaphognathite is supplemented by the exopodites of
maxillipedes.
 Current of water flows over the lining of branchiostegites , gills and
epipodites which are richly supplied with blood, so that ,exchange of
gases takes place.
 Oxygen ,dissolved in water, is taken in by blood and carbon di oxide
from blood diffuses out in water.

7.  True gills or ctenidia
 Most of the mollusc are aquatic and respire by means of gills or ctenidia.
 A ctenidium consist of a horizontal main axis attached to the body and
bearing on alternately arranged, delicate , flexible, respiratoy lamellae or
filaments.
 Surface epithelium of gills usually covered by cilia.
 Number form and position of ctenidia
 In class Monoplacophora 5 pairs of unipectinate gills, composed of finger
like lamellae, are present in pallial groove.
 In class Amphineura mantle cavity is primarily posterior and the gills are
true ctenidia.

8. Continued ……..
 In class Gastropoda, gills are shifted to the front of the body with
mantle cavity, as a result of torsion .
 In sub class Prosobrenchiata most Prosobranchs (e.g. Haliotis )retain
a single pair gills, these gills have primitive bipectinate condition.
 In remaining Prosobranchs, Mesogastropoda (e.g.Pila) right gill has
complete disappeared. A single gill carrying a single row of leaf lets on
its right side.
In sub class Opisthobrenchia, In Aplysia, single ctenidium is still
retained on the right side.
In sub class Pulmonata gills disappear and the mantle forms a lung for
aerial respiration.

9. Continued……..
 In class Pelecypoda have the
most complex molluscan gill.
 Besides respiration, gills make
important organs for nutrition.
 In sub class Protobrenchia (Nucula)
gills are relatively smaller their
filaments form small, compressed
and triangular leaflets, free from
one another.

10. Continued……..
 In sub class Filibrenchia, gill filaments become
elongated and thread like (Amusium ).
 In Arca each gill filament is bent upon itself to
form an elongated V .Thus each gill forms a W in
section and consist of two V shaped demibranchs
 In Mytilus , the adjacent filaments of each
demibranch are loosely united to each other, side
to side by groups of large , stiff and interlocking
cilia.

11. Continued……..
 In sub class Eulamillibranchia
( Unio, Anodonta )ciliary inter- filamentar
junctions are replaced by vascular
cross connections with narrow
openings between them.
VM-Visceral mass
OL-Outer lamina
IL-Inner lamina
ILJ-Inner lamellar junction
S-Shell
M-Mantle

12. Continued………..
 In sub class Septibranchia(Poromya and
Cuspidaria), gills degenerate , being replaced
by a horizontal perforated muscular
septum , extending from the base of foot
to the mantle.
 Septa move up and down so that the
water current enters through inhalant siphon.
BS-Branchial septum
SBC-Supra branchial chamber
P-Perforation
F- Foot

13. Mechanism of ctenidial respiration
 Movement of cilia are responsible for continuous renewal of water
over the gills .
 Ctenidium receives venous blood from the body through an
afferent branchial vein , and after becoming oxygenated in the
filaments , it is sent back to heart through an efferent branchial
vein.
 Water flows over the gills in a direction opposite to that taken by
blood within the filaments..
 Oxygen of water passes through the wall of gill filament : in return
carbon dioxide passes in to the water.

14.  In certain Molluscs, true ctenidium
is absent and other morphological
different structures develop called
as secondary gills or adaptive gills.
Adaptive gills are three types-
In Doris, a rosette of delicate
feathered and retractile secondary gills
surround the anus at posterior end of the body.

15. Continued……….
In Aeolis, numerous simple or pinnately
branched secondary gills or cerata are
carried upon dorsal surface of the body.
They are richly vascular ,presents a variety
and beauty of forms.

16. Continued……
 Pallial gills
 In Patella , a series of adaptive gills
occur in a row on each lateral
side in the pallial groove .

17. References
Modern text book of zoology
by R L Kotpal