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Myoanatomy and serotonergic nervous system of the ctenostome Hislopia malayensis: evolutionary trends in bodyplan patterning of ectoprocta.

Schwaha T, Wood TS, Wanninger A - Front. Zool. (2011)

Bottom Line: The apertural muscles show high similarity within Ectoprocta and always consist of two sets of muscles.Gymnolaemates and Phylactolaemates show clear differences within their digestive tract musculature, the former showing smooth and longitudinal muscles to a much greater extent than the latter.The complex musculature at the lophophoral base appears promising for inferring phylogenetic relationships, but sufficient comparative data are currently lacking.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Vienna, Department of Morphology, Althanstra├če 14, 1090 Vienna, Austria. thomas.schwaha@univie.ac.at.

ABSTRACT

Background: Ectoprocta is a large lophotrochozoan clade of colonial suspension feeders comprising over 5.000 extant species. Their phylogenetic position within the Lophotrochzoa remains controversially discussed, but also the internal relationships of the major ectoproct subclades -Phylactolaemata, Stenolaemata, and Gymnolaemata - remains elusive. To gain more insight into the basic configuration of ectoproct muscle systems for phylogenetic considerations, we analysed the adult myoanatomy and the serotonergic nervous system as well as myogenesis in budding stages of the ctenostome Hislopia malayensis.

Results: In adults, the serotonergic nervous system is restricted to the lophophoral base with a high concentration in the cerebral ganglion and serotonergic perikarya between each pair of tentacles. Prominent smooth apertural muscles extend from the basal cystid wall to each lateral side of the vestibular wall. The musculature of the tentacle sheath consists of regular strands of smooth longitudinal muscles. Each tentacle is supplied with two bands of longitudinal muscles that show irregular striation. At the lophophoral base several muscles are present: (i) Short muscle fibres that proximally diverge from a single point from where they split distally into two separate strands. (ii) Proximally of the first group are smooth, longitudinal fibres that extend to the proximal-most side of the lophophoral base. (iii) Smooth muscle fibres, the buccal dilatators, traverse obliquely towards the pharynx, and (iv) a circular ring of smooth muscle fibres situated distally of the buccal dilatators. Retractor muscles are mainly smooth with short distal striated parts. The foregut consists mainly of striated ring musculature with only few longitudinal muscle fibres in the esophagus, while the remaining parts of the digestive tract solely exhibit smooth musculature. During budding, apertural and retractor muscles are first to appear, while the parietal muscles appear at a later stage.

Conclusions: The apertural muscles show high similarity within Ectoprocta and always consist of two sets of muscles. Gymnolaemates and Phylactolaemates show clear differences within their digestive tract musculature, the former showing smooth and longitudinal muscles to a much greater extent than the latter. The complex musculature at the lophophoral base appears promising for inferring phylogenetic relationships, but sufficient comparative data are currently lacking.

No MeSH data available.


Related in: MedlinePlus

Schematic representation of apertural areas of retracted ectoproct zooids with associated muscles. The distal zooidal part points upwards. Epidermal layers are drawn in continuous lines and coelomic epithelia dashed. Tentacles are displayed in dark grey and the diaphragm in orange. (a + b) Apertural muscles in phylactolaemates consist of sparse vestibular dilatators and duplicature bands that either insert at the diaphragm (b) or at the tentacle sheath (a). (c) Cyclostomes possess bundles of vestibular dilatators that extend from the distal bodywall to the diaphragm. Comparable to the duplicature bands, cyclostomes possess an attachment organ built by peritoneal strands. (d - h) Ctenostomes. (d) Paludicelloidean ctenostomes as Paludicella show homologs of phylactolaemate duplicature bands, parieto-vaginal bands, and prominent vestibular dilatators, which are subdivided into the proximal parieto-diaphragmatic muscles and the distal parieto-vestibular muscles. (e + f) Ctenostomes forming elongated peristomes/stolons usually lack parieto-vaginal bands and show a strong separation of parieto-diaphragmatic and distal parieto-vestibular musculature. Alcyonidioideans (g) possess parieto-vaginal bands, whereas hislopioideans (h) lack them. The vestibular dilatators consist of a single portion in hislopioideans. In Alcyonidioideans they are separated into parieto-diaphragmatic and distal vestibular musculature. (i) Cheilostomes possess parieto-vaginal bands and parieto-diaphragmatic musculature as found in ctenostomes. The aperture in cheilostomes is closed by the opercular occlusors - most likely modified distal vestibular muscles. Abbreviations: a - atrium, ao - attachment organ, db - duplicature bands, dvm - distal vestibular muscles, ms - membranous sac, oocl - operculum occlusors, op - operculum, pdm - parieto-diaphragmatic muscles, pvb - parieto-vaginal bands, sph - sphincter, v - vestibulum, vd - vestibular dilatators.
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Figure 7: Schematic representation of apertural areas of retracted ectoproct zooids with associated muscles. The distal zooidal part points upwards. Epidermal layers are drawn in continuous lines and coelomic epithelia dashed. Tentacles are displayed in dark grey and the diaphragm in orange. (a + b) Apertural muscles in phylactolaemates consist of sparse vestibular dilatators and duplicature bands that either insert at the diaphragm (b) or at the tentacle sheath (a). (c) Cyclostomes possess bundles of vestibular dilatators that extend from the distal bodywall to the diaphragm. Comparable to the duplicature bands, cyclostomes possess an attachment organ built by peritoneal strands. (d - h) Ctenostomes. (d) Paludicelloidean ctenostomes as Paludicella show homologs of phylactolaemate duplicature bands, parieto-vaginal bands, and prominent vestibular dilatators, which are subdivided into the proximal parieto-diaphragmatic muscles and the distal parieto-vestibular muscles. (e + f) Ctenostomes forming elongated peristomes/stolons usually lack parieto-vaginal bands and show a strong separation of parieto-diaphragmatic and distal parieto-vestibular musculature. Alcyonidioideans (g) possess parieto-vaginal bands, whereas hislopioideans (h) lack them. The vestibular dilatators consist of a single portion in hislopioideans. In Alcyonidioideans they are separated into parieto-diaphragmatic and distal vestibular musculature. (i) Cheilostomes possess parieto-vaginal bands and parieto-diaphragmatic musculature as found in ctenostomes. The aperture in cheilostomes is closed by the opercular occlusors - most likely modified distal vestibular muscles. Abbreviations: a - atrium, ao - attachment organ, db - duplicature bands, dvm - distal vestibular muscles, ms - membranous sac, oocl - operculum occlusors, op - operculum, pdm - parieto-diaphragmatic muscles, pvb - parieto-vaginal bands, sph - sphincter, v - vestibulum, vd - vestibular dilatators.

Mentions: Apertural muscles are present in all three ectoproct subtaxa, the Phylactolaemata, the Stenolaemata (with the sole extant taxon Cyclostomata) and the Gymnolaemata, which include the Ctenostomata and Cheilostomata. A review of the existing literature shows that their terminology is utterly confusing and inconsistent. Common terms found for apertural muscles are for example "parieto-vaginal muscles" [26], "parieto-diaphragmatic muscles" [31], "parieto-atrial muscles" [32], "parieto-vestibular muscles" [33], "pyramidal muscles" [34] or "longitudinal parietal muscles" [35]. The latter term has been established according to the notion that apertural muscles are derived parietal muscles [28,33] and is also frequently used in more recent compendia on ectoprocts [35-37]. A comparison of these muscles is most easily performed among retracted zooids (Figure 7). In all ectoproct subtaxa, retracted zooids show a distalmost invaginated portion of the cystid wall, termed the vestibular wall, which is separated from the proximally adjoining tentacle sheath by a diaphragm. At the diaphragm a strong sphincter is present in all three subtaxa (Figure 7).


Myoanatomy and serotonergic nervous system of the ctenostome Hislopia malayensis: evolutionary trends in bodyplan patterning of ectoprocta.

Schwaha T, Wood TS, Wanninger A - Front. Zool. (2011)

Schematic representation of apertural areas of retracted ectoproct zooids with associated muscles. The distal zooidal part points upwards. Epidermal layers are drawn in continuous lines and coelomic epithelia dashed. Tentacles are displayed in dark grey and the diaphragm in orange. (a + b) Apertural muscles in phylactolaemates consist of sparse vestibular dilatators and duplicature bands that either insert at the diaphragm (b) or at the tentacle sheath (a). (c) Cyclostomes possess bundles of vestibular dilatators that extend from the distal bodywall to the diaphragm. Comparable to the duplicature bands, cyclostomes possess an attachment organ built by peritoneal strands. (d - h) Ctenostomes. (d) Paludicelloidean ctenostomes as Paludicella show homologs of phylactolaemate duplicature bands, parieto-vaginal bands, and prominent vestibular dilatators, which are subdivided into the proximal parieto-diaphragmatic muscles and the distal parieto-vestibular muscles. (e + f) Ctenostomes forming elongated peristomes/stolons usually lack parieto-vaginal bands and show a strong separation of parieto-diaphragmatic and distal parieto-vestibular musculature. Alcyonidioideans (g) possess parieto-vaginal bands, whereas hislopioideans (h) lack them. The vestibular dilatators consist of a single portion in hislopioideans. In Alcyonidioideans they are separated into parieto-diaphragmatic and distal vestibular musculature. (i) Cheilostomes possess parieto-vaginal bands and parieto-diaphragmatic musculature as found in ctenostomes. The aperture in cheilostomes is closed by the opercular occlusors - most likely modified distal vestibular muscles. Abbreviations: a - atrium, ao - attachment organ, db - duplicature bands, dvm - distal vestibular muscles, ms - membranous sac, oocl - operculum occlusors, op - operculum, pdm - parieto-diaphragmatic muscles, pvb - parieto-vaginal bands, sph - sphincter, v - vestibulum, vd - vestibular dilatators.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Figure 7: Schematic representation of apertural areas of retracted ectoproct zooids with associated muscles. The distal zooidal part points upwards. Epidermal layers are drawn in continuous lines and coelomic epithelia dashed. Tentacles are displayed in dark grey and the diaphragm in orange. (a + b) Apertural muscles in phylactolaemates consist of sparse vestibular dilatators and duplicature bands that either insert at the diaphragm (b) or at the tentacle sheath (a). (c) Cyclostomes possess bundles of vestibular dilatators that extend from the distal bodywall to the diaphragm. Comparable to the duplicature bands, cyclostomes possess an attachment organ built by peritoneal strands. (d - h) Ctenostomes. (d) Paludicelloidean ctenostomes as Paludicella show homologs of phylactolaemate duplicature bands, parieto-vaginal bands, and prominent vestibular dilatators, which are subdivided into the proximal parieto-diaphragmatic muscles and the distal parieto-vestibular muscles. (e + f) Ctenostomes forming elongated peristomes/stolons usually lack parieto-vaginal bands and show a strong separation of parieto-diaphragmatic and distal parieto-vestibular musculature. Alcyonidioideans (g) possess parieto-vaginal bands, whereas hislopioideans (h) lack them. The vestibular dilatators consist of a single portion in hislopioideans. In Alcyonidioideans they are separated into parieto-diaphragmatic and distal vestibular musculature. (i) Cheilostomes possess parieto-vaginal bands and parieto-diaphragmatic musculature as found in ctenostomes. The aperture in cheilostomes is closed by the opercular occlusors - most likely modified distal vestibular muscles. Abbreviations: a - atrium, ao - attachment organ, db - duplicature bands, dvm - distal vestibular muscles, ms - membranous sac, oocl - operculum occlusors, op - operculum, pdm - parieto-diaphragmatic muscles, pvb - parieto-vaginal bands, sph - sphincter, v - vestibulum, vd - vestibular dilatators.
Mentions: Apertural muscles are present in all three ectoproct subtaxa, the Phylactolaemata, the Stenolaemata (with the sole extant taxon Cyclostomata) and the Gymnolaemata, which include the Ctenostomata and Cheilostomata. A review of the existing literature shows that their terminology is utterly confusing and inconsistent. Common terms found for apertural muscles are for example "parieto-vaginal muscles" [26], "parieto-diaphragmatic muscles" [31], "parieto-atrial muscles" [32], "parieto-vestibular muscles" [33], "pyramidal muscles" [34] or "longitudinal parietal muscles" [35]. The latter term has been established according to the notion that apertural muscles are derived parietal muscles [28,33] and is also frequently used in more recent compendia on ectoprocts [35-37]. A comparison of these muscles is most easily performed among retracted zooids (Figure 7). In all ectoproct subtaxa, retracted zooids show a distalmost invaginated portion of the cystid wall, termed the vestibular wall, which is separated from the proximally adjoining tentacle sheath by a diaphragm. At the diaphragm a strong sphincter is present in all three subtaxa (Figure 7).

Bottom Line: The apertural muscles show high similarity within Ectoprocta and always consist of two sets of muscles.Gymnolaemates and Phylactolaemates show clear differences within their digestive tract musculature, the former showing smooth and longitudinal muscles to a much greater extent than the latter.The complex musculature at the lophophoral base appears promising for inferring phylogenetic relationships, but sufficient comparative data are currently lacking.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Vienna, Department of Morphology, Althanstra├če 14, 1090 Vienna, Austria. thomas.schwaha@univie.ac.at.

ABSTRACT

Background: Ectoprocta is a large lophotrochozoan clade of colonial suspension feeders comprising over 5.000 extant species. Their phylogenetic position within the Lophotrochzoa remains controversially discussed, but also the internal relationships of the major ectoproct subclades -Phylactolaemata, Stenolaemata, and Gymnolaemata - remains elusive. To gain more insight into the basic configuration of ectoproct muscle systems for phylogenetic considerations, we analysed the adult myoanatomy and the serotonergic nervous system as well as myogenesis in budding stages of the ctenostome Hislopia malayensis.

Results: In adults, the serotonergic nervous system is restricted to the lophophoral base with a high concentration in the cerebral ganglion and serotonergic perikarya between each pair of tentacles. Prominent smooth apertural muscles extend from the basal cystid wall to each lateral side of the vestibular wall. The musculature of the tentacle sheath consists of regular strands of smooth longitudinal muscles. Each tentacle is supplied with two bands of longitudinal muscles that show irregular striation. At the lophophoral base several muscles are present: (i) Short muscle fibres that proximally diverge from a single point from where they split distally into two separate strands. (ii) Proximally of the first group are smooth, longitudinal fibres that extend to the proximal-most side of the lophophoral base. (iii) Smooth muscle fibres, the buccal dilatators, traverse obliquely towards the pharynx, and (iv) a circular ring of smooth muscle fibres situated distally of the buccal dilatators. Retractor muscles are mainly smooth with short distal striated parts. The foregut consists mainly of striated ring musculature with only few longitudinal muscle fibres in the esophagus, while the remaining parts of the digestive tract solely exhibit smooth musculature. During budding, apertural and retractor muscles are first to appear, while the parietal muscles appear at a later stage.

Conclusions: The apertural muscles show high similarity within Ectoprocta and always consist of two sets of muscles. Gymnolaemates and Phylactolaemates show clear differences within their digestive tract musculature, the former showing smooth and longitudinal muscles to a much greater extent than the latter. The complex musculature at the lophophoral base appears promising for inferring phylogenetic relationships, but sufficient comparative data are currently lacking.

No MeSH data available.


Related in: MedlinePlus