Cyclotron sp.
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publication ID |
https://doi.org/ 10.4202/app.00553.2018 |
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DOI |
https://doi.org/10.5281/zenodo.10999703 |
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persistent identifier |
https://treatment.plazi.org/id/332187DE-FFC8-FFE0-8E23-FA54FF0A4FF4 |
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treatment provided by |
Felipe |
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scientific name |
Cyclotron sp. |
| status |
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Fig. 7 View Fig .
Material.—Two separated valves (ZPAL Cr.11/ph095, ZPAL Cr.11/ph102), Furongian, Olenus Biozone, Dębki 2 borehole, northern Poland.
Description.—The specimens of Cyclotron sp. occur as single valves with partly preserved shell layer covered by the inner lamella (here meaning the lower cuticle or surface of the shield expanding between margin and body proper). In the dorsal part of the inner lamella, several small rod-like internal invaginations occur ( Fig. 7 View Fig ) bearing attached remains of putative muscle strands. They are interpreted here as the apodemes, serving as a site of insertion for muscles running into the limbs. In extant arthropods, apodemes are infoldings of the cuticle and may occur as rods, flanges or nodes (e.g., Manton 1964; Moore and McCormick 1969; Coleman 2002; Brusca and Brusca 2003; Oliveira and Meyer 2013). In some cases, as on the distal ends of the appendages of onychophorans, a small slit-like pore still indicates the invagination ( Oliveira and Mayer 2013).
Right and left phosphatocopid valves with apodemes have been found separately in the same sample. The sizes of the valves are identical and the apodemes are in corresponding positions. Hence, the valves are interpreted as belonging to the same specimen or at least to the same ontogenetic stage. In both valves, apodeme pairs occur in the same position, corresponding to the limb insertions ( Fig. 7A View Fig 1 –A View Fig 3 View Fig , B 1 –B View Fig 3 View Fig ). Possibly they represent attachment places of the antenna, mandible and three post-mandibular limbs. In both valves at the point of the mandible muscles insertion, only a relatively wide proximal part of the cuticle invagination is preserved ( Fig. 7A View Fig 2, B 2 View Fig ). There are also two smaller extensions of the cuticle close to the posterior margins of the valves without preserved apodemes, which may also represent the places where additional limbs arise. The insertion of the antennula is not preserved, as it inserts on the antero-lateral slope of the hypostome.
The apodemes are approximately 100–110 μm long extending medially with rounded hook-like apices. All apodemes are oriented almost perpendicular to the internal surface of the cuticle and are gently inclined posteriorly. On the dorsal apodeme surfaces there are narrow keels ( Fig. 7A View Fig 3 View Fig , B 1 View Fig ). On the proximal part of the ventral surfaces small cavities, c. 20–23 μm in diameter, occur ( Fig. 7A View Fig 4 View Fig , A 5 View Fig , B 3 – B View Fig 7 View Fig ). The fragmentarily preserved, inferred muscles from the appendages are attached inside these cavities ( Fig. 7A View Fig 4 View Fig , A 5 View Fig , B 4 –B View Fig 7 View Fig ). Each muscle bundle is composed of numerous muscle fibres of nanomicron-scale ( Fig. 7A View Fig 4 View Fig , A 5 View Fig , B 4 –B View Fig 7 View Fig ). Some muscles are partly covered by a putative phosphatised bacterial film ( Fig. 7B View Fig 6 View Fig ).
The two sides of the apodemes differ morphologically; whereas their anterior sides are smooth ( Fig. 7B View Fig 1 View Fig , B 3 View Fig ), their posterior sides exhibit small elongate transversal grooves ( Fig. 7A View Fig 3 View Fig , B 8 View Fig ).
In addition, in the antero-dorsal part of the valves, small structures (remains of labral muscles?) occur that probably belong to the hypostome-labrum complex ( Fig. 7A View Fig 6 View Fig , B 9).
On the inner surface of the cuticle layer, close to the dorsal marginal area and between the apodeme structures, two scar-like structures are developed as small nodes ( Fig. 7A View Fig 2 View Fig , A 3 View Fig , B 2 View Fig ).
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