The portion of the dorsal nerve cord in the collar region of Balanoglossus is the dorsal tubular nerve cord. The reference is to the presence of a notochord-like structure in the head of the animal. Hemichordates are worm-like animals whereas urochordates are bag-like in shape. Hemichordates are nearest to Urochordata, as they exhibit many close resemblances with them. Affinities of Hemichordata (here Balanoglossus) is mainly seen with Chordata.Due to their peculiar anatomical organisation and embryology, the Hemichordata (or Balanoglossus) have been considered closer to the Chordata as well as most non-chordate phyla by different workers … b)   Differentiation of alimentary canal into oesophagus, stomach and intestine. 5) The coelom of annelid is schizocoelic while that of Balanoglossus is enterocoelic. In urochordates, the adult body is covered by a tunic or test. The ventral nerve cord of Balanoglossus never exists in chordates. Helpfull entry but illustrations were required, its really helped me in making notes………….thank uu, oh thank u so much………………. Answer (1 of 1): Affinities with Hemichordata:Amphioxus resemble with hemichordates in having similar:1. Superficial resemblances in ciliary feeding and respiratory mechanism (no gill slits in molluscs) have no phylogenetic significance. Both the structures are related and combine vascular and excretory functions. The most striking similarity of this group with Balanoglossus is its method of formation of mesoderm and coelom. 3. It is supported throughout its length by the dorsal and ventral mesentries. The main objectives are: Hemichordata shows following affinities with Annelida which was first suggested by Spengel in 1893: Thus, compared to their differences, similarities of the two groups are only superficial and quite insignificant indicating probably a convergent evolution due to similar habits and habitat. The hydrocoel opens to exterior by pore as the protocoel and mesocoel does in Balanoglossus. 819-821. Affinities of Hemichordata with Chordata| Annelida & Echinodermata. In 1814, Sedgwick and Huxley suggested the affinities of Enteropneusta (Hemichordata) with the vertebrates and it was in 1885 Bateson considered this group as a subphylum of the phylum Chordata. Due to these similarities Hemichordata had been considered as a subphylum of the phylum Chordata till recently, representing its lowest group, and probably having a common ancestry. Unlike that of the chordates, the so-called ‘notochord’ is very short, confined to proboscis and without any supporting function. This structure, as predicted by Newman, has ceased to be regarded as notochord due to the following reasons: (1) The notochord is never formed as a diverticulum. The buccal cavity is usually lined with ectoderm. Relationships between creatures are postulated mainly on grounds of comparative anatomy and development. The fact that only a few invertebrate groups are enterocoelomate suggests that Pogonophora appears to be fairly closely related to hemichordates. They are, as mentioned above, closer to invertebrate phyla Echinodermata and Phoronida in their morphology and development than to the Chordates. Affinities of Phylum Chaetognatha: The Chaetognaths were first discovered by Slabber in 1769. 4. We do not support piracy. Hemichordates thus very remotely connected with the central stock from which true chordates descended. The paired sacs given off from the stomach of phoronids are compared with buccal diverticulum of Balanoglossus. Echinoderms and Hemichordates have free-swimming larval forms, but in Chaetognaths, development is direct, i.e., larval form is absent. 8) The pre-oral coelom of tornaria is absent in trochophore. 4. They are: 1. 1. Urochordates-Affinities Affinities of Urochordates . Proboscis coelom opening to outside by proboscis pore of tornaria comparable to hydrocoel of echinoderm dipleurula. The annelidan aflffmities of Balanoglossus have, therefore, been given up. Presence of dorsal and ventral fins. Both have common habits, ecological niches and remarkable power of regeneration. J.F. Digestive System of Balanoglossus (Hemichordata) Alimentary Canal. In spite of these similarities following differences present between these two groups show that these groups are not closely related: 2)   Presence of lateral nerve cord in Phoronis. Instead of being solid and made of vacuolated cells, it is hollow and lined by epithelial cells. Affinities # Branchiostoma with Mollusca: Molluscs and Branchiostoma differ widely. Affinities of Balanoglossus: The position of Hemichordata, in the scheme of classification of animals, has been controversial. They were supposed to possess the notochord, the gill-slits, and the dorsal tubular nerve cord which are three unique characters of … (b)  It has some relation to the skeletal function. Though that has not been confirmed. Annelids do not have pharyngeal gill-slits, stomochord or buccal diverticulum and dorsal tubular nerve cord found in. Affinities # Balanoglossus with Chordata: Similarities: 1. Echinoderms and hemichordates are similar in having enterocoelus coelom which is divided into three different parts filled with sea water to serve hydraulic mechanism. Hyman (1959), however, placed them near Echinodermata and gave Hemichordata a status of an independent phylum. Entrocoelic coleom.5. (2) Gill-slit. This simple organism shows affinities with several diverse groups. Urochordates are hermaphrodites whereas sexes are separate in cephalochordates. There is close similarity in gill-slits of Balanoglossus and Amphioxus. 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