Classification and characteristics of Herdmania
Classification of Herdmania:
Phylum: Chordata
Group: Acraniata
Sub-Phylum: Urochordata
Class: Ascidiacea
Order: Enterogona
Genus: Herdmania
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| Herdmania classification characteristics |
Geographical distribution of Herdmania
Different species of Herdmania (Rhabdocynthia) are widely distributed in the Pacific, Atlantic, and Caribbean seas, besides the Indian Ocean.
Habit and habitat of Herdmania
Solitary, sedentary, and sometimes living as commensal in association with gastropod shells, especially over Nancus pyruns (Shankh) and Xancus angulatus (Conch)
Comments regarding Herdmania
(1) It is commonly called Monoacidian or Sea squirt. Das S.M. (1936) wrote a memoir on this animal.
(2) It is more or less like a purse or large oval potato, measuring 6.5 to 11.8 cm in length and 5,2 to 6.9 cm in breadth.
(3) Body dark brown, reddish brown, or yellowish brown in color and regional into the soft body proper and foot.
(4) Foot large, dirty, rough, leathery, and with a number of foreign objects. It forms one-third of the body
(5) 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 polysaccharides, called tunicin, and protein.
(6) Without cutting the animal open at the free end, the body is drawn to form a 1.0 cm long branchial or incurrent siphon containing mouth and a 1.5 cm long atrial or excurrent siphon. The incurrent opening of the mouth is somewhat laterally placed, while the excurrent opening is directed upwards. Branchial and atrial apertures are found on branchial and atrial siphons respectively.
(7) Body proper lies within the test.
(8) Herdmania is hermaphroditic and protogynous.
(9) Fertilization external. The development includes a fully formed larva, called the ascidian tadpole larva. It contains all the chordate characters i.e., notochord and nerve chord, etc.
(10) Metamorphosis is retrogressive in which notochord, nerve cord, tail, and tail fins have degenerated. By the time adulthood is formed, all chordate characters disappear.
Special features of Herdmania
Herdmania in adult form is devoid of any chordate characters which are exhibited only by its tadpole larva. The animal has also a peculiar symmetry; the branchial aperture marks the anterior end and the opposite end is the posterior end. The atrial aperture indicates the dorsal side and the area diagonally opposed to it represents the ventral side. Such abnormal symmetry is brought about by metamorphosing larvae into sedentary adults. Identification: Since the animal contains a soft translucent body and atrial and branchial apertures, at the same level and all the above features, hence it is Herdmania.
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