Gills in invertebrates

Gills in annelida , arthropoda and mollusca for zoology post graduate students

1. Dr Shampa Jain Professor Dept of Zoology Govt Science College Jabalpur Gills in Inv e rtebrates and their mechanism

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. Gills in Arthropoda 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. Crustacea 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.

5. Mechanism of Respiration 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.

6. Gills in Mollusca 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 .

7. 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 g ills disappear and the mantle forms a lung for aerial respiration.

8. 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.

9. 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. OL-Outer gill lamina, IL- Inner gill lamina S- shell

10. 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

11. 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 M-Mantle

12. 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.

13. Secondary or adaptive gills 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- Anal gills- In Doris, a rosette of delicate feathered and retractile secondary gills surround the anus at posterior end of the body.

14. Continued………. Cerata 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.

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

16. References Modern text book of zoology “ Invertebrates” by R L Kotpal

17. THANK YOU