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Abstract Rotifers possess complex morphologies despite their microscopic size and simple appearance. Part of this complexity is hidden in the structure of their organs, which may be cellular or syncytial. Surprisingly, organs that are cellular in one taxon can be syncytial in another. Pedal glands are widespread across Rotifera and function in substrate attachment and/or egg brooding. These glands are normally absent inAsplanchna, which lack feet and toes that function as outlets for pedal glandular secretions in other rotifers. Here, we describe the ultrastructure of a pedal gland that is singular and syncytial inAsplanchnaaff.herricki, but is normally paired and cellular in all other rotifers.Asplanchnaaff.herrickihas a single large pedal gland that is active and secretory; it has a bipartite, binucleate, syncytial body and a cytosol filled with rough endoplasmic reticulum, Golgi, and several types of secretory vesicles. The most abundant vesicle type is large and contains a spherical electron‐dense secretion that appears to be produced through homotypic fusion of condensing vesicles produced by the Golgi. The vesicles appear to undergo a phase transition from condensed to decondensed along their pathway toward the gland lumen. Decondensation changes the contents to a mucin‐like matrix that is eventually exocytosed in a “kiss‐and‐run” fashion with the plasma membrane of the gland lumen. Exocytosed mucus enters the gland lumen and exits through an epithelial duct that is an extension of the syncytial integument. This results in mucus that extends from the rotifer as a long string as the animal swims through the water. The function of this mucus is unknown, but we speculate it may function in temporary attachment, prey capture, or floatation.
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Ultrastructure and Function of the Stalk Gland Complex of Pompholyx faciemlarva (Rotifera: Monogononta)
ABSTRACT Many planktonic rotifers carry their oviposited eggs until hatching. In some species, the eggs are attached to the mother via secretions from her style gland, which forms a thread that extends from her cloaca. In species ofPompholyx, the mother possesses the rare ability to change the tension on the secreted thread, which alters the proximity of the egg with respect to her body. In this study, we used behavioral observations, confocal microscopy, and transmission electron microscopy to study the functional morphology of the stalk gland, which secretes a similar thread to the style gland. Our observations reveal that six longitudinal muscles insert on a stalk‐gland complex, which is a combination of a two‐headed gland and an epithelial duct that connects to the posterior cloaca. The gland secretes a single, long, electron‐dense thread that traverses the duct and attaches to the egg surface through the cloaca. Three retractor muscles insert on the stalk gland and function to pull the entire complex anteriorly, thereby increasing tension on the thread and moving the egg close to the mother's body. A set of three (two pairs and a single dorsal) protractor muscles antagonize these actions, and their contraction pulls the gland complex close to the cloaca, thereby releasing tension on the thread and allowing the egg to distance itself from the mother. The stalk gland complex does not appear to be homologous to the style glands of other rotifers, but we hypothesize that it functions as a form of maternal protection as is the case with style glands.
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- Award ID(s):
- 2051684
- PAR ID:
- 10554843
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Morphology
- Volume:
- 285
- Issue:
- 11
- ISSN:
- 0362-2525
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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