Nephridium

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Related to nephridia: Malpighian tubules, parapodia

nephridium

[nə′frid·ē·əm]

(invertebrate zoology)

Any of various paired excretory structures present in the Platyhelminthes, Rotifera, Rhynchocoela, Acanthocephala, Priapuloidea, Entoprocta, Gastrotricha, Kinorhyncha, Cephalochorda, and some Archiannelida and Polychaeta.

Nephridium

an excretory organ that is characteristic of invertebrates. The nephridium regulates osmotic pressure, extracts and removes harmful metabolites from the body, and sometimes transports gonad products. The most primitive nephridia are those of flatworms, rotifers, gastrotrichs, nemerteans, and some polychaetes. These nephridia, which are called protonephridia, are branched tubules of ectodermal origin. They are closed at the internal ends by terminal cells, or solenocytes, and open to the exterior by means of excretory pores, or nephridiopores. Upon losing its solenocytes and opening into the coelom, the protonephridium is transformed into a metanephridium (primarily in annelids). In some annelids the nephridium coalesces with the mesodermal ciliated gonad funnels, or coelomo-ducts, forming an organ of mixed origin, the nephromyxium.

A. V. IVANOV

References in periodicals archive ?

And also the nephridia are present only as rudiments.

Both authors indicated a proandric condition (later not confirmed) and did not observe nephridia.

Michaelsen (1918: 332), in synonymizing the genus Brachydrilus under Tritogenia, accepted duplication of nephridia as the exclusive generic character for this genus, and wrote '.

Michaelsen (1928a: 7) described Microchaetus melmothanus, with the gizzard in segments 6-7 (characteristic for Tritogenia), although not observing nephridia.

more than one pair of nephridia small and fairly simple in constitution .

A new family Tritogeniidae for the genera Tritogenia and Michalakus, earlier accredited to the composite Microchaetidae (Annelida: Oligochaeta)

Thus, digestive gland tubules, intestine, nephridia, gills, gonad, and connective tissue of the mantle were the main sites invaded.

During an initial stage, gills, nephridia, connective tissue of mantle, gonad, and digestive system were infiltrated by hemocytes, and a few neoplastic cells were apparent (Fig.

Gonad atrophy caused by disseminated neoplasia in Mytilus chilensis cultured in the Beagle Channel, Tierra del Fuego Province, Argentina

These sacs (thread glands in Wilson, 1932) are destined to become the first nephridia in the adult worm, derived from the ventral epidermis of the larva.

By the time the rudiment fully encircles the hindgut, not only are the nephridia, chaetae, and uncini present, but also the segmental body wall musculature, chaetal musculature, and future coelomic lining have formed (Fig.

At the same time, the trunk begins to straighten out: as the sock unrolls, the digestive tract is pulled down and enclosed, with the anterior nephridia and juvenile musculature adopting their appropriate positions (Fig.

The first chaetigerous segment inherits the third pair and the longest pair of nephridia (4), which probably become fused, as adults have only one pair of nephridia in each abdominal segment.

Unusual development of the mitraria larva in the polychaete Owenia collaris

The early development of the nephridia in amphioxus: introduction and part I, Hatschek's nephridium.