Excretory System in Various Arthropods

Learn about the comparison of excretory system in various Arthropods.

Comparison: Arthropod # Macrobrachium:

1. The excretory or­gans consist of a pair of cream coloured antennary glands with their ducts, a median renal sac and a transverse commu­nicating duct. It also per­forms the function of os­moregulation (Fig. 46A).

2. The antennary gl­and is placed in the coxa of the second antenna. It consists of three parts.

(a) A small end sac.

(b) A glandular mass. These two extract excre­tory products which are carried to the exterior th­rough the bladder.

(c) The bladder occu­pies the innermost region and is drawn into a narr­ow tube to open to the ex­terior through the renal aperture on the inner side of the coxa. The gland is also called green gland.

3. The renal sac is a thin-walled median stru­cture lying just above the stomach. It is connected with each antennary gl­and by a narrow duct ant­eriorly. The two ducts are again connected by a narrow transverse duct. Posteriorly, the renal sac ends blindly at the region of the gonad. The renal sac acts as a temporary reservoir for waste products.

4. No other renal organs

5. The thick chitinous layer of the integument is a nitrogenous product secreted by the ectoderm and is cast off in each mo­ult. Moulting is consider­ed as a special mechani­sm to get rid of nitroge­nous wastes.

Comparison: Arthropod # Periplaneta:

1. The excretory or­gans consist mainly of nu­merous Malpighian tubu­les and nephrocytes (Fig. 46B).

2. The Malpighian tu­bules are thread-like ye­llow structures of variab­le number present at the junction of the stomach and the intestine. Each tubule is a hollow struc­ture opening into the lumen of the intestine and the wall is made of a sing­le layer of glandular epi­thelium. Nitrogenous was­tes are absorbed by the cells from the haemocoelomic fluid and the same are discharged into the lumen of the tubule which in turn conveys the wastes into the lumen of the in­testine.

3. No such structure.

4. Certain cells (nephrocytes) associated with the fat bodies and the hypodermis also serves as excretory organs.

5. The thick chitinous layer of the integument is a nitrogenous product secreted by the ectoderm and is cast off in each mo­ult. Moulting is consider­ed as a special mechani­sm to get rid of nitroge­nous wastes.

Comparison: Arthropod # Palamnaeus:

1. The excretory organs consist of a few Malpighian tubules and a pair of coxal glands (Figs.46C and 47C).

2. The Malpighian tubu­les are delicate tubes and are two pairs in number, attach­ed to the intestine. Each tubu­le is a hollow structure open­ing into the lumen of the int­estine and the wall is made of a single layer of glandular cells. Nitrogenous wastes are absorbed by the cells from the haemocoelomic fluid and the same are discharged into the lumen of the tubule which in turn conveys the wastes into the lumen of the intestine.

3. No such structure.

4. A pair of coxal glands is found near the bases of the 3rd walking legs in the 5th segment of the prosoma. These are derived from coelomoducts and function as excretory organs. In the em­bryo of scorpion, the coelomoducts are found in the 3rd, 4th, 5th, 6th and 8th seg­ments.

All of them disappear in the adult stage except those in the 5th segment which persist as coxal glands. Each coxal gland consists of an end sac, a colied tube and a bladder opening to the ext­erior by a duct at the base of the 3rd walking leg.

(a) A diverticulum or lymphatic organ, possibly excretory (phagocytic) in function, lies on each side of the abdomen connected with the coxal gland of the side.

5. The thick chitinous layer of the integument is a nitrogenous product secreted by the ectoderm and is cast off in each mo­ult. Moulting is consider­ed as a special mechani­sm to get rid of nitroge­nous wastes.