Aquiloniella scabra (Van Beneden, 1848)
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publication ID |
https://doi.org/ 10.1007/s13127-022-00562-y |
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persistent identifier |
https://treatment.plazi.org/id/03AC87AF-FFB9-FFBD-FF20-CA89872A980D |
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treatment provided by |
Felipe |
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scientific name |
Aquiloniella scabra |
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Aquiloniella scabra View in CoL ( Figs. 2B View Fig , 14 View Fig , 19A, C)
Avicularium
Cystid and mandible The small adventitious avicularia are positioned on autozooids both laterally and frontally ( Fig. 14A View Fig ). The cystid of the lateral avicularium is elongate-triangular, expanding distally. The frontal avicularia is “obtuse trapezoidal”. In both cases, the rostrum is triangular, with a pointed tip slightly curved upwards. The postmandibular area is semi-oval, occupied by the frontal membrane connected with the proximal edge of the mandible.
The mandible is triangular with a thickened peripheral sclerite and hook-shaped tip curved downward. It has a narow cavity enclosed between external (upper) and internal (lower) walls ( Figs. 14C View Fig , 19A). The lower mandibular wall presumably bears an oval opening (visible as a dark area in the CLSM stacks) through which the mandible cavity communicates with the avicularian body caity. We were unable to distinguish a hole in the vertical wall in our preparations.
Polypide and muscular system The vestigial polypide consists of a ciliated rudimentary lophohore surrounded by a “voluminous” tentacle sheath whose diaphragmatic muscles form a low “cone” in its uppermost part; the wall of the tentacle sheath also contains at least 11 thin longitudinal muscle fibers ( Fig. 14E, F View Fig ). A round ganglion is situated beneath the rudimentary lophophore ( Fig. 14C, D View Fig ). The distal ends of the longitudinal muscles do not reach the diaphragm ( Fig. 14E View Fig , inset). Three to four striated polypide retractor muscles insert to the lower part of the tentacle sheath and descend towards the basal wall of the cystid ( Fig. 14E, F View Fig ).
The paired smooth abductors are situated in the proximal part of the avicularium ( Figs. 14E, F View Fig , 19A). Each proximal abductor consists of more than 15 tightly packed, long and thin muscle fibers of about the same width and length. Some of them are grouped in “bundles”. They anchor to the proximo-lateral cystid walls behind the posterior regions of the adductor muscles, and distally insert to the frontal membrane within two zones oriented under the obtuse angle in respect to each other.
Two large striated adductors fill most of the body cavity of the avicularium. The area of their proximal attachment is very large and occupies most of the avicularian lateral walls ( Figs. 14C, E, F View Fig , 19A). Each adductor ends with a tendon supposedly inserting in the upper vestibular wall.
Vibracularium (long-bristled avicularium in Winston, 1991)
Cystid and mandible Vibracularia are situated on the basal (abfrontal) side of the colony branches ( Fig. 14B View Fig ). Their number in a colony is low, and, in some colonies, they are absent. A tube-like rhizoid is budded from some vibracularia (although all vibracularia had a pore chamber - potential site of kenozooidal budding).
The vibracularian cystid is triangular, with narrow elongated rostrum and palate. The long and narrow mandible (seta) is slightly curved and slightly exceeds the length of the rostrum ( Fig. 14B View Fig ); the setal length significantly exceeds the length of the avicularian mandible.
The semi-oval postmandibular zone of the vibracularium is occupied by the frontal membrane connected with the views) (inset, diaphragm, longitudinal muscles of tentacle sheath and retractors of vestigial polypide). G Muscular elements of vibracularium (lateral view) (inset, diaphragm and retractors, ring muscle fiber between tentacle sheath and ganglion of vestigial polypide indicated by arrowhead). In E and F dotted line indicates borders of avicularian mandible. Abbreviations: dm, diaphragm, fm, frontal membrane, g, ganglion of vestigial polypide, mab, abductor, mad, adductor, md, mandible, rm, retractor muscles, rt, rudimentary tentacle, s, seta, ts, tentacle sheath, uv, upper vestibular wall widened proximal margin of the seta. The latter consists of three walls—upper, lower, and transverse with a long cavity inside which is connected with the vibracularium body cavity via an oval opening in the transverse wall. The proximal part of the lower wall of the mandible is internal, with the upper vestibular wall lying beneath. Similar to the avicularium, the symmetrical articulation of the seta to the cystid and the symmetrical paired musculature operating the seta enable setal motion in one (vertical) plane.
Polypide and muscular system The vestigial polypide consists of the rudimentary lophophore surrounded by the tentacle sheath, and the ganglion ( Fig. 14D View Fig ). Diaphragmatic muscles form a low “cone” in the distalmost part of the tentacle sheath that also contains up to seven longitudinal muscle fibers in its wall ( Fig. 14G View Fig , inset). The distal ends of the longitudinal muscles reach the diaphragm. Additional annular muscle fiber was detected on the boundary between the tentacle sheath and the ganglion ( Fig. 14G View Fig , inset). A few thin fibers radiate from this annular muscle, but their nature remains unclear. Two striated polypide retractor muscles insert in the lower part of the tentacle sheath ( Fig. 14G View Fig , inset) and anchor on the basal wall of the vibracularium cystid. The diaphragmatic sphincter in the vibracularium is described here for the first time (see also below).
Two small abductors are situated in the proximal part of the cystid. Each abductor consists of more than 15 tightly packed muscle fibers of about the same length. They insert in the frontal membrane within two zones oriented under the obtuse angle in respect to each other. Proximally, they are attached to the lateral walls of the cystid close to and behind the attachment zone of the adductors ( Figs. 14D, G View Fig , 19C). Large striated adductors occupy most of the cystid volume, attaching to its basal and proximo-lateral walls ( Fig. 14D, G View Fig ). Distally, each muscle bundle continues to a tendon supposedly inserting in the upper vestibular wall. The tendons slightly widen near the site of insertion.
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