Digestive system consists of an alimentary canal and digestive glands. Alimentary Canal: The alimentary canal is a straight tube from mouth to anus. It is lined by. The lancelets, also known as amphioxi (singular, amphioxus), consist of about 32 species of fish-like marine. The common lancelet, Branchiostoma lanceolatum, has been recorded from the . The digestive system of Branchiostoma consists of an alimentary canal and.
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Phagocytic intracellular digestion in amphioxus (Branchiostoma)
Since the blood of Branchiostoma lacks any respiratory pigment and also occurs in lymph-spaces in the fins and meta-pleural folds, it is doubtful whether the pharynx has any role in oxygenation.
The food particles are filtered from the respiratory water current that passes in through the mouth and go out through the atriopore via the gill-slits. At the posterior end of the buccal cavity is present a circular, membranous velum. Placozoa Trichoplax Cnidaria jellyfish and relatives. A similar endostyle is found in urochordates and in the ammocoete larva of lampreys, but the larval endostyle is lost during metamorphosis of lamprey, it contributes to the formation of a thyroid gland in the adult.
The pointed anterior end projects forward as snout or rostrum. It is not photosensitive in nature.
Cross section through the pharyngeal region: The tree of life reflects the branching pattern of speciation The nephridia, called protonephridia, are situated on the dorsolateral wall of the pharynx.
An endostyle is a ciliary and glandular groove present on the floor of the pharynx. Such anterior prolongation of the notochord beyond the brain is associated with its burrowing habit. Proboscis, collar and trunk.
Lancelet – Wikipedia
It is schizocoelic in annelids and enterocoelic in Branchiostoma. Ap, atriopore; Ir, ileo-colon ring; Lu, lumen; As, apical side. The number of gill-slits is about pairs. Surrounding the notochordal sheath there is a non-cellular gelatinous layer containing few fibres.
Here, in Branchiostoma belcheriusing a special tissue fixation method, we show that some epithelial cells, especially those lining the large diverticulum protruding from the gut tube, phagocytize food particles directly, and Branchiostoma can rely on this kind of phagocytic intracellular digestion to obtain energy throughout all stages of its life.
Behind the ileocolon ring, the, intestine proceeds backwards as a straight hindgut which opens through the anus.
Digestive System of Branchiostoma (With Diagram) | Chordata | Zoology
The pharynx and oesophagus constitute the foregut. Ikuta T, et al.
The gill-bars are provided with cilia. The Hesse organs also known as dorsal ocelli consist of a photoreceptor cell surrounded by a band of microvill and bearing melanopsin, but half enveloped by a cup-shaped pigment cell.
Akphioxus diverticulum extends shstem on the right-hand side of the pharynx for about one-third of the length of the pharynx. Because of remote phylogenetic connection all these groups are expected to share some common features. From the foregoing discussion on the anatomy and affinities of Branchiostoma, the systematic position appears to be uncertain.
Further the embryonic development of Branchiostoma is of indeterminate type. Zhang Y, et al. The main bodies of the cells lie outside of the pigment cup, while the cilia extend into the pigment cup before turning and exiting.
Digestive System Of Amphioxus PowerPoint PPT Presentations
Ciona intestinalis ParaHox genes: The edges of the velum bear 12 or more slender, ciliated velar tentacles which normally project backwards forming a strainer. The afferent and efferent nerve fibres in the atrium presumably play the important role in feeding.
The giant cells are absent between segments.
Analysis of a repulsive axon guidance molecule, draxin, on ventrally directed axon projection in chick early embryonic midbrain. Yang P, et al. The wheel organ produces a vortex of water current which is drawn in towards the mouth.
Phylum Chordata The chordates are a group of particular interest to us as we belong to it, being members of the subphylum Vertebrata. Stumpp M, et al.