Subphylum Hemichordata Assignment Help

Subphylum Hemichordata Assignment Help are small soft-bodied creatures. Living singly or in group on sandy sea bottoms or in open water .the body and coelom are divided into three regions with paired gill-slits and nervous tissue in both dorsal and ventral epidermis.

Certain tissue as an anterior projection from mouth cavity was formerly interpreted  as a notochord and thus placing the group with phylum chordate. Recent studies cast doubt on such interpretation and so-called earlier notochord is termed the bucal pouch. Now this group is placed under  independent phylum Hemichordata . between hemichordate and chordates there are resemblances in the pharyngeal gill-slits and the collar cord of the nervous system its origin from dorsal epidermis.

 The embryo and early larvae of hemichordate and asteroid echinoderms are much alike in ciliated bands, digestive tracts , from derivation of anus from blastopore and enterocoelous coelom. The  above feSubphylum Hemichordata Assignment Helpatures strongly suggest a common origin.

Classification : busciness assignment help

Phylum  hemichordate is divided into two classes

1: Enteropneusta –burrowing animals, ex-Balanoglossus , Saccoglossus. Ptychpdera.

2: Pterobranchia – encased body

Order 1- Rhabdopleurida. Ex- Rhabdopleura

Order 2 – Cephalodiscida. Ex Cephalodiscus, Atubaria

Subphylum Hemichordata Assignment Help

It lived in a U-shaped burrow and at one opening of burrow fecal casting may be seen . U- tube burrow at other end has opening with a separate branched  opening. It measure 10 cm to 2.5 meter depending on the species . it is bilaterally symmetrical , triploblastic deuterostome with worm –shaped  body divisible into three region –anterior prosoma , middle collar or mesosoma and posterior trunk or metasoma.

Proboscis is conical ,collar is funnel like ,while trunk is cylindrical .heart vesicle central sinus and buccal .diverticulum . it has thick muscular body wall and its cavity or coelom which open by a pair of collar pores on dorsal surface . pharynx and gonads constitute branchiogenital region is composed of genital wing having gonad , branchial region containing paired gills ,and hepatic region having hepatic caecae.

Special features :   Balanoglassus and allied forms have phylogenetic  importance. Certain tissue in the thus placing this group anterior projection from the mouth cavity was formerly interpreted as a notochord and thus placing this group withen the phylum   chordate . recent studies show such structure mainly  as buccal pouch and naw the hemichordate are not included with the chordates but as separate phylum Hemichordata. It show affinities with , chordates (Bateson ,1885) Echinoderms (Metshinkoff,1869) and Annelida (Spangel,1893) . gills-slits, never cord and the so-called notochord are identical with chordates .

Hyman (1959) objected its so-called notochord . blastopore, ciliated bands and enterocoelus coelum are common features both in hemichordates and Echinoderms . it resembles with Annelids also in having segmented body.It may be concluded that invertebrate features out weight the chordate features and hence hemichordates are included in  invertebrates but under separate Phylum Hemichordates .

Identification  : Since the specimen contains short proboscis and all above features, hence it is Balanoglossus . It is bilaterally symmetrical triploblastic deuterostome with. Acorn worm Marin enterocoelous confinfd to head region Several gill-slits, intestine straight solitary