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The digestive tract of actinotroch larvae (Lophotrochozoa, Phoronida): anatomy, ultrastructure, innervations, and some observations of metamorphosis

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Abstract:

The digestive tract of actinotroch consists of the vestibulum, oesophagus, stomach with stomach diverticulum, midgut, and proctodaeum. Monociliate muscle cells resting on the basal lamina of the oesophagus form its circular musculature. The epithelium of the cardiac sphincter contains axonal tracts and neurosecretory cells. Glandular, secretory, and digestive cells form the epithelium of the stomach and stomach diverticulum. The epithelium of the midgut is biciliate. The proctodaeum is divided into two parts, differing in fine structure and function. Individual serotonian and FMRFamide neurons and fibers occur in the oesophagus, cardiac sphincter, and midgut, as well as surrounding the anus. In larvae of Phoronopsis harmeri Pixell, 1912 during metamorphosis, the larval oesophagus gives rise to the juvenile oesohagus, the upper portion of the stomach stretches and transforms into prestomach, the stomach diverticulum moves into the stomach and then is digested, the larval stomach becomes the juvenile stomach, the midgut gives rise to the pyloric region, and the proctodaeum transforms into the ascending branch of the juvenile digestive tract. The data do not support the views that the proximal part of adult digestive tract forms from the ectodermal epithelium of the dorsal and ventral epidermis of the larva or that the telotroch enters the intestine during metamorphosis.

Le système digestif des larves actinotroques consiste en un vestibule, un œsophage, un estomac avec un diverticule gastrique, un tube digestif moyen et un proctodéum. Des cellules musculaires monociliées reposant sur la lamelle de base de l’œsophage forment sa musculature circulaire. L’épithélium du sphincter cardiaque contient des tractus axonaux et des cellules neurosécrétrices. Des cellules glandulaires, sécrétrices et digestives forment l’épithélium de l’estomac et du diverticule gastrique. L’épithélium du tube digestif moyen est bicilié. Le proctodéum se divise en deux parties qui diffèrent par leur structure fine et leur fonction. Des neurones et des fibres individuels à sérotonine et à amide FMRF se retrouvent dans l’œsophage, le sphincter cardiaque et le tube digestif moyen, ainsi qu’autour de l’anus. Chez les larves de Phoronopsis harmeri Pixell, 1912 durant la métamorphose, l’œsophage de la larve se transforme en œsophage juvénile, la portion supérieure de l’estomac s’étire et se transforme en pré-estomac et le diverticule gastrique se déplace dans l’estomac et est ensuite digéré, l’estomac larvaire devient un estomac juvénile, le tube digestif moyen produit la région pylorique et le proctodéum se transforme en branche ascendante du tube digestif juvénile. Les données n’appuient pas les propositions voulant que la partie proximale du tube digestif de l’adulte se forme à partir de l’épithélium ectodermique des épidermes dorsaux et ventraux de la larve et que la télotroche pénètre dans le tube digestif durant la métamorphose.

Document Type: Research Article

Publication date: 2010-12-01

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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