Herdmania: Blood vascular system

• Herdmania is a genus of sea squirts, or ascidians, belonging to the family Pyuridae.

Habitat and Distribution

• Herdmania are marine animals found in the littoral and shallow waters of tropical and subtropical regions.
• They are widely distributed in the Indo-Pacific area, including the coasts of India, Australia, and Japan.
• They are sessile animals, attaching themselves to rocks, coral reefs, or other submerged objects.

Morphology

• Herdmania are typically spherical or oval in shape, with a tough outer covering called the tunic.
• The tunic is usually translucent or opaque and may be colored, often with shades of red, orange, or yellow.
• Two siphons are visible on the surface: the branchial siphon (inhalant) and the atrial siphon (exhalant).
• The branchial siphon is located at the anterior end, while the atrial siphon is usually on the dorsal side.
• The size of Herdmania varies, but they usually range from a few centimeters to about 10 centimeters in diameter.

Anatomy

Tunic

• The tunic is the outermost layer, composed mainly of tunicin, a type of cellulose.
• It protects the animal and provides support.
• The tunic may be smooth or covered with small projections or encrustations.

Mantle

• Beneath the tunic is the mantle, a body wall that contains muscle fibers, blood vessels, and nerves.
• Contraction of the mantle muscles helps in expelling water from the body.

Siphons

• The branchial siphon draws water into the branchial sac.
• The atrial siphon expels water after it has passed through the branchial sac.
• Sphincter muscles around the siphons control the opening and closing.

Branchial Sac (Pharynx)

• The branchial sac is a large, perforated structure that occupies most of the body cavity.
• It is lined with numerous stigmata (gill slits) through which water passes.
• Cilia lining the stigmata create a water current, drawing water in through the branchial siphon and out through the atrial siphon.

Digestive System

• Food particles are filtered from the water as it passes through the branchial sac.
• The particles are trapped in mucus secreted by the endostyle, a longitudinal groove on the ventral side of the branchial sac.
• The mucus, with trapped food, is moved by cilia to the dorsal lamina and then to the esophagus.
• The esophagus leads to the stomach, where digestion begins.
• The intestine is a coiled tube that extends from the stomach to the anus, which opens into the atrial cavity near the atrial siphon.

Circulatory System

• Herdmania has an open circulatory system.
• A tubular heart is located near the stomach.
• The heart periodically reverses the direction of blood flow.
• Blood passes through sinuses and lacunae in the tissues.
• The blood contains vanadocytes, cells that contain vanadium.

Nervous System

• The nervous system is simple, consisting of a cerebral ganglion located between the siphons.
• Nerves extend from the ganglion to various parts of the body.
• Sensory receptors are present around the siphons.

Excretory System

• Excretion occurs through nephrocytes, specialized cells that accumulate waste products.
• These cells are found in various parts of the body, including the mantle.

Reproductive System

• Herdmania are hermaphroditic, possessing both male and female reproductive organs.
• The gonads (ovary and testis) are located in the mantle.
• Fertilization is usually external, with sperm and eggs released into the water.

Life Cycle

• The life cycle of Herdmania includes a free-swimming larval stage known as the tadpole larva.
• The tadpole larva resembles a vertebrate tadpole, with a notochord, dorsal nerve cord, and tail.
• The larva swims for a short period before attaching to a substrate and undergoing metamorphosis.
• During metamorphosis, the tail is resorbed, the notochord disappears, and the body reorganizes into the adult form.

Feeding

• Herdmania are filter feeders.
• They filter microorganisms and organic particles from the water.
• Water enters through the branchial siphon, passes through the branchial sac, and exits through the atrial siphon.
• Food particles are trapped in mucus and transported to the digestive system.

Respiration

• Gas exchange occurs in the branchial sac as water passes over the stigmata.
• Oxygen is absorbed from the water, and carbon dioxide is released.

Significance

• Herdmania are important members of marine ecosystems.
• They contribute to nutrient cycling through filter feeding.
• They are also used in scientific research, particularly in studies of development and evolution.
• Some species may have pharmacological potential.