PHYLUM :- CHORDATA (Notochord, dorsal tubular nerve cord present and gill slits present).

Group :- ACRANIATA (No head, cranium or brain)

Sub-phylum :- UROCHORDATA (Marine. Body covered by a thick test. Notochord present only in larval tail)

Class :- ASCIDIACEA (Test with scattered muscles. Many pharyngeal gill-slits. Bottom-dwelling).

Order :- ENTEROGONA  (Neural gland ventral to nerve ganglion. Gonad one).

Genus : Herdmania


  • Different species of Herdmania (=Rhabdocynthia) are widely distributed in
    the Pacific, Atlantic and Caribbean seas, besides Indian Ocean.


  • Solitary, sedentary and sometimes living as commensal in association with
    gastropod shells, specially over Xaneus pyruns (Shankh) and Xaneus angulatus (Conch).


  • It is commonly called as Monoacidian or Sea squirt. Das S.M. (1936) wrote a memoir on this animal.
  • It is more or less like a purse or large oval potato, measuring 6.5 to n.8 cm in length and 5.2 to
    6.9 cm in breadth.
  • Body dark brown, reddish brown or yellowish brown in colour and regionated into soft body proper and foot.
  • Foot large, dirty, rough, leathery and with a number of foreign objects. It forms one-third of the body.
  • Body enclosed in a thick, tough and supporting transparent test or tunic in the form of a thick translucent protective investment meant for respiration and reception of stimuli. It is composed of
    polysaccharide, called as tunicin, and protein.
  • Without cutting the animal open at the free end, body is drawn to form 1.0 cm long branchial or incurrent siphon and 1.5 cm long atrial or excurrent siphon. The incurrent opening of mouth is somewhat laterally placed, while the excurrent opening is directed upwards. Branchial and atrial apertures are found  on branchial and
    atrial siphons respectively.
  • Body proper lies within test.
  • Herdmania is hermaphroditic and protogynous.
  • Fertilization external. Development includes a fully formed larva, called ascidian tadpole larva. It contains all the chordate characters i.e., notochord and nerve chord, etc.
  • Metamorphosis is retrogressive in which notochord, nerve cord, tail and tail fins are degenerated. By the time adult is formed, all chordate characters disappear.


  • Herdmania in adult form is devoid of any chordate characters which are exhibited only by its tadpole larva. Animal has also a peculiar symmetry; branchial aperture marks the anterior end and opposite end is the posterior end. The atrial aperture indicates dorsal side and the area diagonally opposed to it represents ventral side. Such abnormal symmetry is brought about by metamorphosing larva into sedentary adult. 


  • The animal contains soft transluscent body and atrial and branchial apertures, at the same level and all above features, hence it is Herdmania.


  • https://en.wikipedia.org/wiki/Ascidia
  • Book of Practical Zoology VERTEBRATE by S.S.LAL – Rastogi Publications.

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