Balanoglossus - external characters, T.S. through proboscis, collar & trunk

Balanoglossus 

⚫External Morphology

    (1)It is commonly called as acorn worm.

    (2)The body of Balanoglossus is soft, elongated cylindrical, abundantly coiled and covered with mucus.

    (3)The length of animal varies form 2cm to 2.5cm.

    (4)They are secreted as offensive color.

    (5)The body is bilaterally symmetrical & consists of proboscis, collar or mesosome & trunk or metasome.

    (6)Balanoglossus is a burrowing & exclusively marine animal.

    (7)Balanoglossus is a tubiculus living in U-shaped burrows excavated in sandy bottoms.

⚫T.S. through Proboscis 

    (1)The proboscis forms the anterior of body & is either rounded or conical in shape.

    (2)Body wall represented by epidermis muscle layer & basement membrane.

    (3)The epidermis is single layered.

    (4)A thin nerve layer consist of epidermis.

    (5)The muscle layer consist of thick longitudinal muscle layer & thin circular muscle layer.

    (6)In the center lies a basal organ & central complex made up of glomerulus, buccal diverticulum & vesicle (heart).

⚫T.S. through Collar

    (1)The surface of collar is often marked with elevations, depression & specially circular groove.

    (2)The body wall is represented by single layered epidermis & nervous layer.

    (3)Notochord present only in anterior part.

    (4)Distinct pharynx present perforated by gill slit.

    (5)No skull, Jaw or endo & exoskeleton present.

    (6)Addition to dorsal nerve cord also present.

⚫T.S. through trunk

    (1)Trunk is elongated posterior part of body

    (2)Trunk divided into anterior branchio-genital region, middle hepatic, region, posterior abdominal region.

    (3)It has mid dorsal & mid ventral longitudinal ridges.

    (4)A pair of longitudinal genital ridges extend throughout considerable body part behind & in region of branchial aperture.

    (5)Hepare region is marked externally with irregular elevations due to sacculations produced by projecting hepatic cases of the intestine.