Excretory system in herdmania
According to Das (Dass, 1936) the only definite excretory organ of Herdmania pallida is the neural gland. It is a light brown ellipsoid or oval, 4 mm long and 1 mm thick structure. It is embedded in the middle surface of the mantle and just above the neural ganglion or brain. It consists of a number of branched peripheral tubules originating from some central tubules, which open into a longitudinal canal running its entire length. Further forward, the canal forms a small, narrow duct that passes through the middle of the anterior nerves and opens by a ciliated funnel at the base of the dorsal gullet in the parietal region. The excretory cells are actually the kidney cells of the blood (nephrocytes). They mainly store waste substances such as xanthine and urate particles, which are discharged into the prebranchial zone of the pharynx through the opening of the duct of the nervous gland.
According to Julin 1881, Bacq, Florkin and Das (Dass, 1956) the nervous gland also secretes a hormone which controls ovulation, development and metamorphosis. Thus the nervous gland is considered a homolog of the pituitary gland.
nervous system in herdmania
The adult nervous system is very simple and lost. In this, there is a pink, elongated, about 4 mm long, solid nerve ganglion embedded in the mantle between the two vents, which is the so-called brain or cerebral ganglion. In most tunicates, it is located on the posterior side of the nervous gland. But in Hadmania (family Pyuridae, fam. pyuridae) it is located just below the nervous gland. The brain is made up of a network of bipolar and multipolar nerve cells and multi-branched nerve fibers. It controls the reflexes of the body. From the brain to the front, 3 nerves go to the chloem-vinal, and 2 nerves go to the sacral canal at the back.
SENSE ORGANS IN HERDMANIA
There is a lack of specialized sensory organs. However, many single simple structures or clustered cells with nerve endings represent receptors.
Tangoreceptors : These cells, which are sensitive to touch, are scattered along the ends of the canals covering the entire nonvascular regions of the chord, over the tentacles and the vascular tubules.
Photoreceptors : Sensitive to light, red pigmented granules, these pigmented cells or ocelli are located at the ends of the venules and above the vascular tubules.
Rheoreceptors: Sensitive to water currents, these cells line the anterior margins of the canals.
Thermoreceptors: These cells, sensitive to temperature, form the lining of the canals.
Chemoreceptors : Sensitive to chemicals, includes tentacles and dorsal gullets.
Due to their rich nerve supply, the chyme tentacles are considered to be olfactory in nature. They check the properties of water and the quantity of food particles entering the ferrix.
(b) Dorsal tubercle
It is a small sensory structure suspended from the mid-dorsal side in the anteriorcolumn region, just ahead of the junction of the peripharyngeal bands and the dorsal lamina. It consists of two conical, spiral-coiled lobes or lobes. On each lobe there is a spirally coiled, ciliary narrow and open channel running from the base to the summit. The two channels are connected at a broad, convex base, resembling a dome of dorsal canal. The floor of the dorsal gullet is covered with a ciliated columnar epithelium rich in nerve supply. The dorsal gullet performs the function of smelling and tasting the water entering the pharynx and thus performs both olfactory and taste sensory functions.