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Herdmania – Characteristics, Anatomy (With Diagram), Nervous System

DomainEukaryota
KingdomAnimalia
PhylumChordata
SubphylumTunicata
ClassAscidiacea
OrderStolidobranchia
FamilyPyuridae
GenusHerdmania
AuthorityLahille, 1888

What is Herdmania?

Herdmania is a genus of marine ascidians, belonging to the family Pyuridae. These organisms are invertebrates with a sac-like body structure covered by a tough outer covering called a test. They are filter feeders, drawing in water through an inhalant siphon, filtering out food particles, and expelling the filtered water through an exhalant siphon. Herdmania are commonly found in coastal waters around the world.

  • Herdmania, classified under the genus of ascidian tunicates in the family Pyuridae, is a fascinating marine organism often referred to as the sea squirt due to its unique ability to expel water forcefully when removed from its aquatic environment. Among the species in this genus is Herdmania armata, which is particularly notable.
  • Herdmania is primarily a filter-feeder, a characteristic common among tunicates. These creatures reside in marine environments and are often found in colonies, displaying a gregarious behavior. Their filter-feeding mechanism involves drawing in water through one opening, filtering out microscopic food particles, and expelling the filtered water through another opening, thus facilitating the exchange of nutrients and gases.
  • The presence of Herdmania in marine ecosystems is significant, as they contribute to the ecological balance by participating in nutrient cycling and serving as a food source for various marine organisms. Their unique biological features and ecological roles make Herdmania an intriguing subject of study in marine biology and ecology.

General Characteristics of Herdmania / Shape, Size and Colouration of of Herdmania

Herdmania, specifically Herdmania pallida, exhibits several distinctive anatomical and physiological features that are fascinating to explore. Below are the key characteristics of this marine organism:

  1. Body Structure:
    • Shape and Size: The body of Herdmania pallida is roughly oblong, with the attached end being narrower than the free end. Adult specimens typically measure about 9.5 cm in length, 7 cm in breadth, and 4 cm in thickness. Older and larger specimens can grow up to 13 cm long, 8 cm broad, and 4.5 cm thick.
    • External Openings: The free end of the body has two prominent external openings: the branchial and atrial apertures. The branchial siphon, or incurrent aperture, serves as the mouth, while the atrial siphon, or excurrent aperture, acts as the cloaca.
    • Foot: When present, the foot can extend up to 3 to 4 cm in length, aiding in the organism’s anchorage within sandy substrates.
  2. Color and Surface:
    • Color: In fresh specimens, the body is typically pink. The surface is often marked by bright red patches formed by terminal knobs, or ampullae, in the blood vessels of the test (outer covering).
    • Texture: The test of Herdmania is soft and leathery. While it is more transparent in younger animals, it becomes opaque in adults. The surface is characterized by corrugated lines, both shallow and deep, arranged in a criss-cross pattern.
  3. Siphons and Apertures:
    • Branchial Siphon: This siphon has the branchial or incurrent aperture, surrounded by four lobes or lips.
    • Atrial Siphon: This siphon features the atrial or excurrent aperture, also surrounded by four lobes or lips.
  4. Tunic:
    • Composition and Appearance: The entire body is enveloped in a thick, leathery, and translucent tunic or test, which is formed from a cellulose-like organic substance known as tunicin. The tunic is notably wrinkled and contributes to the organism’s protection and structure.
  5. Feeding and Digestion:
    • Filter Feeding: Herdmania is a filter or ciliary feeder, meaning it filters food particles from the water. The digestive tract is complete, featuring a liver and pyloric glands.
    • Feeding Mechanism: Water enters the body through the branchial aperture, passes through the pharynx where food particles are captured, and exits via the atrial aperture. This process is driven by cilia lining the gill slits, which maintain the water current essential for feeding and respiration.
  6. Respiration:
    • Branchial Sac: Respiration occurs through the branchial sac. The water current, facilitated by cilia, aids in gas exchange as it flows through the pharynx and exits the body.

Habit and Habitat of Herdamania

Herdmania, a genus of ascidian tunicates, exhibits specific habits and habitats that are intriguing to study in the context of marine biology. Below are the detailed aspects of the habit and habitat of Herdmania:

  1. Solitary Ascidian:
    • Herdmania is categorized as a solitary ascidian, meaning it generally lives alone rather than in colonies. This solitary nature distinguishes it from some other tunicate species that are more gregarious.
  2. Marine Environment:
    • Exclusive to Marine Habitats: Herdmania is exclusively found in marine environments, indicating its specialization for life in saltwater conditions.
    • Depth Range: This genus is known to inhabit depths ranging from 9 meters to 21.6 meters in the sea. Such a depth range suggests its preference for relatively shallow to moderately deep marine waters.
  3. Sessile Lifestyle:
    • Attachment to Substratum: Adult Herdmania are sessile, meaning they remain fixed in one place. They attach themselves to substrates such as rocks or the sea floor by their base or foot, anchoring themselves firmly.
  4. Feeding Habits:
    • Microphagous Feeding: Herdmania is microphagous, feeding on microscopic animals and plants. This feeding strategy involves filtering tiny food particles from the water, which is facilitated by their specialized feeding structures.
  5. Tunic as Habitat:
    • Shelter for Other Organisms: The tunic, or outer covering of Herdmania, serves as a habitat for various other marine organisms. This protective layer provides a substrate for the growth of other life forms.
    • Common Inhabitants: A green alga often grows on the tunic of Herdmania, sometimes covering the entire animal. Additionally, the tunic can harbor other organisms such as hydroids, anemones, small lamellibranchs (bivalve mollusks), gastropods, and various other marine animals.

General Anatomy of Herdmania with Diagram

Herdmania, an ascidian tunicate, has a unique and intricate anatomical structure that can be divided into distinct parts for detailed study. Below is a comprehensive overview of the general anatomy of Herdmania:

General Anatomy of Herdmania with Diagram
General Anatomy of Herdmania with Diagram
  1. Body Division:
    • Body Proper: This part projects into the seawater and contains all the soft internal organs.
    • Foot: The foot is embedded in the sea bottom and is entirely composed of the test, a protective outer covering.
  2. External Anatomy:
    • Siphons: Herdmania has two projecting siphons, each with annular and longitudinal muscles and guarded by four lips. These siphons serve as entry and exit points for water, facilitating feeding and respiration.
  3. Internal Anatomy (Left Side View):
    • Stomach, Intestine, and Rectum: The digestive system includes the stomach, a looped intestine, and the rectum.
    • Liver: The left lobe of the liver appears as a chocolate-colored body in front of the stomach.
    • Gonads: The left gonad is a lobulated pinkish mass located within the intestinal loop.
    • Endostyle: This structure runs along the ventral margin of the pharynx, playing a role in feeding by secreting mucus to trap food particles.
  4. Internal Anatomy (Right Side View):
    • Neural Gland: Located in the inter-siphonal region, the neural gland is a dark, elevated area.
    • Pericardium and Heart: The pericardium appears as a long, transparent tube containing the heart.
    • Liver: The right lobe of the liver is an oval chocolate-colored mass near the pericardium’s anterior end.
    • Gonads: The right gonad is a lobulated pinkish mass near the longitudinal siphonal muscles.
    • Endostyle: Similar to the left side, it appears as an opaque rod along the ventral margin of the branchial sac.
  5. Branchial Sac:
    • Structure: The branchial sac, when exposed by cutting through the mantle, reveals several important features.
      • Branchial Siphon: Located at the anterior end, this is the incised mouth.
      • Branchial Sphincter: Situated behind the siphon, it is surrounded by a ring of tentacles.
      • Pre-branchial Zone: A smooth area located behind the tentacles, bounded by two peripharyngeal bands.
      • Dorsal Tubercle: Found near the junction of the peripharyngeal bands and the dorsal lamina.
      • Dorsal Lamina: Extends to the anterior margin of the esophageal opening.
      • Internal Surface: The inner surface of the branchial sac displays numerous folds on both sides, enhancing the surface area for filter feeding.
  6. Functionality:
    • Filter Feeding: Herdmania is a filter feeder, using its branchial sac and endostyle to trap and digest microscopic food particles from the water.
    • Respiration: Water flows through the branchial siphon, aiding in gas exchange within the branchial sac before exiting through the atrial siphon.
General Anatomy of Herdmania with Diagram
General Anatomy of Herdmania with Diagram
General Anatomy of Herdmania with Diagram

External Morphology of Herdmania (With Diagram)

Herdmania, a genus of ascidian tunicates, exhibits a distinctive external morphology characterized by various structural features that are essential for its survival in marine environments. Below is an overview of the external morphology of Herdmania:

General Anatomy of Herdmania with Diagram
General Anatomy of Herdmania with Diagram
  1. Body Shape and Color:
    • Shape: The body of Herdmania is oblong and bag-like, often compared to a potato in shape.
    • Color: The organism is typically pink.
  2. Attachment and Foot:
    • Attachment Mechanism: Herdmania can attach itself to substrates such as rocks or molluscan shells using a flat base.
    • Foot Presence: In sandy environments, Herdmania possesses a narrow foot. This foot is absent when the organism is attached to rocks or shells.
    • Division: For individuals with a foot, the body is divided into two parts: the body proper and the foot. The foot measures approximately 3-4 cm in length.
  3. Size Variability:
    • Average Size: The average size of an adult Herdmania is about 9.5 cm in length, though sizes can vary significantly.
  4. Funnels and Apertures:
    • Oral and Atrial Funnels: The free end of the body has two funnels: the oral funnel, which is smaller, and the atrial funnel. Both funnels contain distinct apertures, the oral aperture and atriopore, respectively, each surrounded by four lobes.
    • Tentacular Rings: The bases of both funnels have tentacular rings. The tentacles around the mouth are known as oral or branchial tentacles, while those around the atriopore are called atrial tentacles. Oral tentacles are longer compared to the smaller, vestigial atrial tentacles.
    • Function of Tentacles: The oral tentacles act as a sieve, preventing larger particles from entering the pharyngeal cavity.
  5. Test or Tunic:
    • Composition and Texture: The body of Herdmania is enclosed by a soft, leathery tunic or test.
    • Transparency: The test is transparent in young individuals, becoming opaque in adults. In young stages, a network of blood capillaries is visible through the transparent test.
    • Characteristic Patches: The test features reddish patches caused by ampullae at the terminal ends of blood vessels. These patches are interspersed with white streaks, creating a distinct pattern of eight red patches alternating with eight white streaks from the tips of the funnels to their bases.
  6. Respiration:
    • Accessory Respiratory Structure: The test also functions as an accessory respiratory structure, aiding in gas exchange.
    • Water Current: In living Herdmania, a strong water current is observed entering through the oral funnel and exiting via the atrial funnel.
  7. Orientation and Sides:
    • Mouth and Atriopore: The mouth is located at the base of the oral funnel, indicating the anterior end of the body, while the atriopore is situated within the atrial funnel at the posterior end.
    • Dorsal and Ventral Sides: The dorsal side of the body is marked by the atrial funnel, and the ventral side is opposite to it.

Body Wall of Herdamania

The body wall of Herdmania, an ascidian tunicate, is a complex structure providing protection and support to the organism. Here is a detailed examination of its components and features:

  1. Test (Tunic):
    • Composition and Secretion: The test is the thick, leathery protective covering of Herdmania’s body, secreted by the epidermis of the body wall.
    • Thickness: It ranges from 4 to 8 mm and is composed of tunicin, a cellulose-like substance.
    • Embedded Elements: The test contains various structural elements, including a meshwork of blood vessels, spicules, interlacing fibers, and different cell types.
  2. Cell Types in the Test:
    • Amoeboid Cells: Abundant in the test, these cells play roles in defense and repair.
    • Eosinophilous Cells: These spherical cells contain granules that stain bright red with eosin. They come in two varieties:
      • Larger Variety: Characterized by a big vesicular nucleus.
      • Smaller Type: Features an eccentric nucleus.
    • Granular Cells: Oblong in shape with a large nucleus, these cells are surrounded by nerve fibers and function as receptor cells.
    • Spherical Vacuolated Cells: Contain numerous small vacuoles with an invisible nucleus.
    • Nerve Cells: Small cells with a conspicuous nucleus and 2 to 6 dendrites, involved in transmitting nerve signals.
  3. Structural Features:
    • Blood Vessels: The test is traversed by blood vessels whose terminal ends form vascular ampullae, imparting red-colored patches on the body.
    • Spicules: These are supportive structures found in two forms:
      • Microscleres: Small, with a spherical head and a long body featuring 5 to 25 rings of small spines.
      • Megascleres: Larger, categorized into spindle-shaped and pipette-shaped spicules.
        • Spindle-shaped Spicules: Provided with 20-60 rings of spines, averaging 1.5 mm in size.
        • Pipette-shaped Spicules: Characterized by a large round median swelling and numerous rings of spines, extending up to 3.5 mm in length.
  4. Mantle:
    • Location and Composition: Beneath the test lies the mantle, the true cellular wall surrounding the body, composed of three layers:
      • Outer Epidermis: Made of hexagonal cells.
      • Median Layer: Contains muscles and connective tissue elements.
      • Inner Ectodermal Layer: Lines the atrium with flat cells.
  5. Muscle Structure:
    • Types of Muscles: The mantle contains two sets of non-striated muscles:
      • Longitudinal Muscles: More numerous than the annular muscles.
      • Annular Muscles: Encircle the body.
    • Muscle Fibers: Each muscle is composed of flat ribbon-like cells with a conspicuous nucleus, ensheathed by a connective tissue sheath.
  6. Connective Tissue:
    • Cell Types: The middle layer contains connective tissue cells, mainly amoeboid and vacuolated cells, contributing to the body’s flexibility and strength.
Different types of cells In the test of Herdmania

The body wall of Herdmania, with its intricate composition and structure, plays a crucial role in protecting the organism, facilitating respiration, and providing structural support.

Body Divisions of Herdamania

The body of Herdmania, an ascidian tunicate, is divided into two distinct parts: the body proper and the foot. The entire animal is encased in a protective covering called the test. Here is an overview of these divisions, along with their defining features and functions:

Body Divisions of Herdamania
  1. Body Proper:
    • Description: This is the distal, free portion of the body. The branchial aperture, located at the anterior end, marks the front of the animal, while the posterior end is attached to the substratum.
    • Orientation:
      • Anterior End: Marked by the branchial aperture.
      • Posterior End: Attached to the substratum.
      • Dorsal Side: Limited area marked by the atrial aperture.
      • Ventral Side: Extensive area, partly attached to the substratum.
    • Siphons:
      • Branchial Siphon: Short protuberance with the branchial aperture, typically bent outwards and directed laterally, away from the atrial aperture. The average length is about 1 cm.
      • Atrial Siphon: Longer protuberance with the atrial aperture, usually directed upwards. In large-sized animals, it measures about 1.5 cm in length.
    • Apertures:
      • Branchial Aperture: When fully expanded, it has an average diameter of about 2 cm.
      • Atrial Aperture: Smaller in diameter, averaging about 1.2 cm when fully expanded.
    • Tentacles:
      • Branchial Tentacles: Located at the base of the branchial siphon, forming a ring of long tentacles.
      • Atrial Tentacles: Located at the base of the atrial siphon, consisting of slightly serrated folds.
    • Elastic Test: The test covering the siphons is very elastic and can contract to close the apertures in response to disturbances in the sea water.
  2. Foot:
    • Description: The foot varies in character based on the nature of the substratum where the animal resides.
    • Substratum-Dependent Characteristics:
      • Fine Sand: The foot is oval-shaped with a smooth surface, and the test is hard in consistency.
      • Coarse Sand or Broken Shells: The foot has an irregular outline and is softer in consistency.
Calcareous spicules
Calcareous spicules

The body divisions of Herdmania are adapted to its marine habitat, providing both structural support and protection. The body proper, with its siphons and apertures, facilitates feeding and respiration, while the foot aids in attachment to various types of substrata.

Test or Tunic of Herdamania

The test, also known as the tunic, is the external covering of Herdmania, a solitary ascidian tunicate. This structure plays a critical role in the protection, respiration, and sensory functions of the organism. Here is a detailed overview of the test:

General Characteristics

  • Composition: The test is a thick, leathery, and translucent covering composed of tunicin, a polysaccharide similar to cellulose found in plants.
  • Thickness: It typically ranges from 4 to 8 mm in thickness.
  • Origin: The test is ectodermal in origin, meaning it is derived from the outermost layer of cells in the embryo.

Structural Components

  1. Matrix:
    • Description: The matrix is a gelatinous substance that forms the bulk of the test.
    • Composition: It is primarily made up of tunicin, which gives the test its characteristic properties.
  2. Cells:
    • Origin: These cells are mesodermal in origin, having migrated into the test from the middle layer of the embryo.
    • Types: The test contains several types of cells, each with distinct functions:
      • Large Eosinophilous Cells: These cells have bright red staining granules.
      • Small Eosinophilous Cells: Smaller in size, also containing red staining granules.
      • Small Amoeboid Cells: Mobile cells that can change shape.
      • Granular Cells: Cells with granules in their cytoplasm.
      • Round Vacuolated Cells: Cells with numerous small vacuoles.
      • Nerve Cells: Cells with several processes, involved in sensory functions.
      • Squamous Epithelial Cells: Flat cells forming a protective layer.
  3. Interlacing Fibrils:
    • Description: These fibrils form a fine network within the test.
    • Resemblance: They resemble smooth muscle fibers, providing structural support and elasticity.
  4. Calcareous Spicules:
    • Description: The test contains numerous calcareous spicules, which are needle-like structures.
    • Types: There are two main types of spicules in Herdmania:
      • Spindle-Shaped Spicules: These have equidistant rings of minute spines along their length.
      • Pipette-Shaped Spicules: These have a large round median swelling and numerous rings of spines.
    • Function: These spicules provide structural support and contribute to the rigidity of the test.
  5. Blood Vessels:
    • Network: The test is traversed by a network of blood vessels.
    • Vascular Ampullae: These blood vessels end in bulb-like dilations called vascular ampullae, which are visible as bright red patches on the test.
    • Functions: The blood vessels and ampullae transport blood, supply nutrients to the test, and act as accessory respiratory organs. They also serve as sensory receptors.

The test of Herdmania is a multifunctional structure that not only protects the animal but also plays a role in respiration and sensory perception. Its complex composition, including a matrix, various cell types, interlacing fibrils, calcareous spicules, and a network of blood vessels, underscores its importance in the overall physiology of the organism.

Test or Tunic of Herdamania

Spicules of Herdamania

Spicules are an integral part of the body structure of Herdmania, a type of ascidian tunicate. These spicules provide structural support and protection, contributing to the rigidity and defense mechanisms of the organism. The spicules in Herdmania are calcareous, meaning they are composed of calcium carbonate. They are found in two distinct types: microscleres and megascleres.

Spicules of Herdamania

Types of Spicules

  1. Microscleres:
    • Location: Microscleres are exclusively found in the test, or tunic, of Herdmania.
    • Structure: Each microsclere consists of a rounded, knob-like head and an elongated, tapering body.
      • Head: Generally smooth, occasionally with a few spines.
      • Body: Characterized by rings of spines, typically 5 to 20, which are evenly spaced and point towards the head of the spicule.
    • Size: The size varies depending on the growth stage. On average, they measure about 50 microns, but can be as large as 80 microns.
  2. Megascleres:
    • Varieties: There are two kinds of megascleres in Herdmania:
      • Spindle-Shaped Spicules
      • Pipette-Shaped Spicules
    • Spindle-Shaped Spicules:
      • Location: These spicules are distributed throughout the body, often found in connective tissue sheaths and arranged in linear rows resembling strings.
      • Structure: Like microscleres, they have numerous rings of spines (20 to 60), all pointing in the same direction.
      • Size: Typically, they measure about 1.5 mm, but can grow up to 2.5 mm.
      • Distribution: They are particularly dense around the stomach, gonads, bases of siphons, and in the mantle, but sparse at the base of longitudinal muscles.
    • Pipette-Shaped Spicules:
      • Location: These spicules are found in various organs, particularly in the mantle around the gonads and liver lobes.
      • Structure: Characterized by a large spherical swelling in the middle, giving them a pipette-like shape. They often bend, forming U or V shapes.
      • Size: These are larger than spindle-shaped spicules, often reaching up to 3.5 mm in length.
      • Spines: They also have rings of spines and are covered with connective tissue sheaths.

Functions of Spicules

  • Structural Support: Both types of spicules provide skeletal support to the body, helping to maintain the shape and integrity of various organs.
  • Attachment: Many spicules project into the test, anchoring it firmly to the mantle. This prevents the mantle from detaching when it contracts.
  • Vascular Support: Spicules surrounding blood vessels help stiffen their walls, preventing collapse and ensuring proper blood flow.

Mantle or Body Wall of Herdamania

The mantle, also known as the body wall, is a vital component of Herdmania’s anatomy, located beneath the test or tunic that covers the entire organism. It plays crucial roles in providing structural support, facilitating movement, and housing important internal organs. Here’s a detailed look at the structure and functions of the mantle:

  1. Location and Attachment:
    • The mantle is situated beneath the test, attached only at the branchial and atrial apertures, where it forms the branchial and atrial siphons.
    • These siphons allow for the intake and expulsion of water, crucial for respiration and feeding.
  2. Composition:
    • The mantle is composed of three distinct layers:
      • Outer Ectoderm: This layer is made up of flat, hexagonal cells. It extends inside at the pericardium, branchial, and atrial apertures, forming the stomodaeum and proctodaeum.
      • Inner Ectoderm: Consisting of flat polygonal cells, this layer lines the atrium, the large cavity within the mantle that contains water.
      • Middle Mesoderm: Situated beneath the outer ectoderm, this layer comprises connective tissue, muscle fibers, blood sinuses, and nerve fibers.
  3. Muscle Fibers:
    • The middle mesoderm contains unstriped muscle fibers, arranged in three main sets:
      • Annular Muscles: Found around the branchial and atrial siphons, these muscles are arranged in several rings, aiding in the opening and closing of the siphons.
      • Longitudinal Muscles: Extending from the branchial and atrial apertures, these muscles fan out towards the middle of the body on each side, assisting in movement and contraction.
      • Branchioatrial Muscles: Located between the two siphons, these muscles contribute to the overall flexibility and mobility of the organism.
  4. Function:
    • The mantle serves several essential functions, including:
      • Providing structural support and shape to the body.
      • Facilitating movement and contraction, especially in opening and closing the siphons.
      • Housing internal organs, such as the pharynx, stomach, and reproductive structures.
      • Acting as a protective barrier against external threats and environmental factors.
Mantle or Body Wall of Herdamania

Nervous System of Herdmania (With Diagram)

The nervous system of Herdmania is relatively simple yet essential for its survival and response to environmental stimuli. Here is an overview of the key components and functions of its nervous system:

Nervous System of Herdmania
  1. Location of Nervous System:
    • In the adult Herdmania, the nervous system includes a brain or nerve ganglion, which is approximately 4 cm long.
    • The brain is situated in the mantle mid-dorsally between the two siphons.
    • In the Pyuridae family to which Herdmania belongs, the brain lies below a neural gland, although in most ascidians, the brain is dorsal to the neural gland.
  2. Structure of the Brain:
    • The brain contains bipolar and multipolar nerve cells.
    • It gives off three nerves towards the branchial siphon and two towards the atrial siphon.
    • The brain is considered the degenerate remains of the anterior part of a well-developed nervous system found in the larval stage.
  3. Neural Complex:
    • The neural ganglion or brain, the neural gland, and the dorsal tubercle together form the neural complex.
  4. Receptors:
    • While Herdmania lacks specialized sense organs, various cells throughout its body serve as receptors for different stimuli:
      • Red pigmented cells on the margins of siphons and vascular ampullae act as photoreceptors, sensitive to light.
      • Sensory cells in the test, siphon margins, and tentacles function as tangoreceptors, sensitive to touch.
      • Cells on the siphon margins are rheoreceptors, sensitive to water currents.
      • Cells lining the siphons are thermoreceptors, sensitive to temperature changes.
      • The tentacles and dorsal tubercle serve as chaemoreceptors, detecting chemical stimuli.
  5. Dorsal Tubercle:
    • Found in the pre-branchial zone near the junction of the dorsal lamina with the peripharyngeal bands, the dorsal tubercle has a broad base with two spirally coiled lobes.
    • Each lobe contains three coils and is covered with ciliated cells.
    • The dorsal tubercle is richly supplied with blood sinuses and nerves, functioning as an olfactory and gustatory organ.
Nervous System of Herdmania
Nervous System of Herdmania

Digestive System of Herdmania (With Diagram)

The digestive system of Herdmania is integral to its survival, consisting of the alimentary canal and digestive glands. Here is an in-depth look at the components and functions of its digestive system:

Digestive System of Herdmania (With Diagram)
  1. Alimentary Canal:
    • The alimentary canal is coiled, beginning from the mouth and ending in the anus.
    • It includes the following parts:
      1. Mouth:
        • Located at the top of the branchial siphon, serving as the anterior end of the body.
        • Guarded by four lips (lobes) of the test.
        • Leads into the branchial siphon.
      2. Branchial Siphon:
        • A narrow, tubular cavity lined by ectoderm, also known as the stomodaeum or buccal cavity.
        • Contains a ring of branching tentacles acting as a sieve for food particles.
      3. Pharynx:
        • Divided into the prebranchial zone and branchial sac.
        • The prebranchial zone is the anterior region with smooth walls.
        • The branchial sac is the larger, posterior part of the pharynx.
        • Contains rows of stigmata (perforations) for water exchange, surrounded by cilia.
        • The lining of the pharynx has longitudinal folds and contains a dorsal lamina and an endostyle.
      4. Oesophagus:
        • A short, bent tube with ciliated grooves directing food into the stomach.
      5. Stomach:
        • Wider than the oesophagus, with thin walls and a tubular, branching pyloric gland.
        • Opens into a thin-walled intestine.
      6. Intestine:
        • Consists of two parallel limbs forming a U shape.
        • Joins a short, ciliated rectum opening into the cloaca.
  2. Digestive Glands:
    • Herdmania has two main digestive glands:
      1. Liver:
        • A dark brown bilobed organ lying against the stomach.
        • Formed of fine tubules embedded in connective tissue.
        • Secretes powerful enzymes like amylase, protease, and weak lipase, along with bile pigments.
      2. Pyloric Gland:
        • Located in the walls of the stomach and intestine.
        • Branched structure with ductules opening into the intestine.
        • Secretes a pancreatic-like fluid and possibly acts as an excretory organ.
Digestive System of Herdmania (With Diagram)
Digestive System of Herdmania (With Diagram)

Food, Feeding and Digestion

Herdmnia’s feeding habits, methods, and digestive processes are critical for its survival. Here’s a detailed overview:

  1. Food:
    • Herdmania feeds on various microorganisms and organic matter, including protozoans, decaying animal pieces, zooplankton, and algae.
  2. Feeding:
    • Feeding is primarily facilitated by ciliary action due to its sedentary lifestyle.
    • Cilia bordering the stigmata create a constant current of water that enters the mouth, passes through ciliated epithelium into the pharynx, and exits through the stigmata into the atrial cavity, eventually exiting through the atrial aperture.
    • The current of water carries in minute organic food particles, which settle on the pharyngeal walls.
  3. Endostyle and Mucus Secretion:
    • Gland cells in the endostyle secrete mucus, which is not carried forward by cilia but lashed out transversely from the endostyle by its cilia.
    • Food particles on the pharyngeal wall are caught in the mucus and transported upwards along the pharyngeal wall to the dorsal lamina.
    • The dorsal lamina’s cilia convert the food-laden mucus into a string, which is then carried into the oesophagus and stomach.
  4. Digestion:
    • The liver secretes a yellowish-brown digestive fluid into the stomach, containing enzymes like amylase for carbohydrates, protease for proteins, and a weak lipase for fats.
    • The pyloric gland, an accessory digestive organ, is likely pancreatic in nature.
    • Digestion primarily occurs in the stomach, with absorption in the intestine.
  5. Excretion:
    • The ciliated rectum expels coiled excreta with significant force, shooting it out about 10 cm through the atrial siphon.
Digestive System of Herdmania (With Diagram)

References

  • http://www.soghracollege.com/img/Lectures%2023-05-20/Zoology%20(Urochordata-2)%20B.ScPart%202.pdf
  • https://www.eshiksha.mp.gov.in/mpdhe/pluginfile.php/53465/mod_resource/content/1/etxt%20deepali.pdf
  • https://www.notesonzoology.com/phylum-chordata/herdmania/nervous-system-of-herdmania-with-diagram-chordata-zoology/7286
  • https://www.notesonzoology.com/phylum-chordata/herdmania/digestive-system-of-herdmania-with-diagram-chordata-zoology/7298

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What is Karyotyping? What are the scope of Microbiology? What is DNA Library? What is Simple Staining? What is Negative Staining? What is Western Blot? What are Transgenic Plants? Breakthrough Discovery: Crystal Cells in Fruit Flies Key to Oxygen Transport What is Northern Blotting? What is Southern Blotting?
What is Karyotyping? What are the scope of Microbiology? What is DNA Library? What is Simple Staining? What is Negative Staining? What is Western Blot? What are Transgenic Plants? Breakthrough Discovery: Crystal Cells in Fruit Flies Key to Oxygen Transport What is Northern Blotting? What is Southern Blotting?
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