Summary
Ototyphlonemertes pallida (Keferstein, 1862) has two statocysts, which are situated just behind the dorsal ganglions on the elongations of the ventral ganglions. Each statocyst consists of one statolith chamber cell, some nerve cells and a number of covering cells and is surrounded by a thick basement membrane. Usually the statolith chamber cell encloses three statolith chambers, which are intercommunicated and surrounded by a double membrane. Each chamber contains a single mobile statolith. Cilia and ciliary structures are lacking. Within the dorsal part of the statocyst some very ramified nerve cells are situated, which form a nerve fibre. In the vicinity of the statolith chamber cell the nerve cells split up into synaptical plates with electric synapses; there are one or several synaptical plates at the level of each chamber. The statolith chamber cell is surrounded by numerous covering cells, which are connected by desmosomes and additionally linked together at the outside in the ventral part of the statocyst. With regard to their structure the covering cells differ greatly from the other cell types, and they do not participate in impulse perception and impulse conduction. There do not exist any closer morphological relations to the statocysts lacking cilia in Coelenterates, Turbellaria, Holothuria, Xenoturbella and Tunicata. The statocyst of O. pallida represents an indigenous structure within the Nemerteans.
Zusammenfassung
Ototyphlonemertes pallida (Keferstein, 1862) hat zwei Statocysten, die unmittelbar hinter den Dorsalganglien auf den verlängerten Ventralganglien liegen. Jede Statocyste besteht aus einer Statolithenkammerzelle, mehreren Nervenzellen und einer Anzahl Hüllzellen und ist von einer dicken Basalmembran umgeben. Die Statolithenkammerzelle umschließt in der Regel drei Statolithenkammern, die von einer doppelten Membran umgeben sind und untereinander in Verbindung stehen. Sie enthalten je einen frei beweglichen Statolithen. Cilien und Ciliarstrukturen fehlen. Auf der Dorsalseite der Statocyste liegen mehrere stark verästelte Nervenzellen, die einen gemeinsamen Strang bilden. In der Nähe der Statolithenkammerzelle spalten sie sich auf und bilden pro Kammer eine oder mehrere synaptische Platten mit elektrischen Synapsen. Die Statolithenkammerzelle wird von zahlreichen Hüllzellen umgeben, die durch Desmosomen fest verbunden und zusätzlich in der ventralen Hälfte der Statocyste an den Außenseiten stark miteinander verzahnt sind. Die Hüllzellen unterscheiden sich im Aufbau deutlich von den beiden anderen Zelltypen und sind nicht an der Reizperzeption oder Reizleitung beteiligt. Zu den cilienlosen Statocysten bei Coelenteraten, Turbellarien, Holothurien, Xenoturbella und Tunicaten-Larven bestehen keine engeren morphologischen Beziehungen. Die Statocyste von O. pallida stellt eine Bildung sui generis innerhalb der Nemertinen dar.
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Abbreviations
- bm:
-
Basalmembran
- d:
-
Dendrit
- de:
-
Desmosom
- dg:
-
Dorsalganglion
- dm:
-
doppelte Membran der Statolithenkammer
- ds:
-
deltaförmige Strukturen
- ep:
-
Epidermis
- es:
-
elektrische Synapse
- hms:
-
Hautmuskelschlauch
- hz:
-
Hüllzelle
- k:
-
Zellkern
- m:
-
Mitochondrium
- ma:
-
abgewandeltes Mitochondrium
- mu:
-
Muskulatur
- n:
-
Nervenstrang
- nv:
-
Neurosekretvesikel
- nz:
-
Nervenzelle
- rs:
-
Rüsselscheide
- sc:
-
Statocyste
- sk:
-
Statolithenkammer
- skz:
-
Statolithenkammerzelle
- sp:
-
synaptische Platte
- st:
-
Statolith
- v:
-
Vakuole
- vg:
-
Ventralganglion
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Brüggemann, J., Ehlers, U. Ultrastruktur der Statocyste von Ototyphlonemertes pallida (Keferstein, 1862) (Nemertini). Zoomorphology 97, 75–87 (1981). https://doi.org/10.1007/BF00310103
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DOI: https://doi.org/10.1007/BF00310103