Paralovenia yongalensis Gershwin & Uribe-Palomino
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|Paralovenia yongalensis Gershwin & Uribe-Palomino|
Paralovenia yongalensis Gershwin & Uribe-Palomino sp. n. Figures 5, 6, 7, 8
Holotype: QM G335907. Female, BD ca. 1.47 mm, tentacular bulbs two and two non-tentacular clusters of cirri (Figures 5A, C); near SS Yongala shipwreck, Queensland, Australia, 19.31°S, 147.62°E, 0-28 m, drop net; coll. IMOS-CSIRO, 27 Sep 2016.
Paralovenia with a relatively short, bell-shaped body with a truncated apex; with well-developed spindle-shaped gonads in the distal half of radial canals, not reaching the margin; with two opposite perradial triangular bulbs bearing tentacles, and two similar opposite perradial bulbs each bearing approximately 10-12 cirri; with open statocysts on a broad conical base; nematocysts arranged in flat roundish clusters on the subumbrellar surface.
Description of holotype.
Umbrella bell- to barrel-shaped, broadest about 2/3 of the way down, truncate to slightly indented aborally (Figure 5A); sparsely scattered with minute nematocyst clusters (Figure 6). Oral margin curving slightly inwards possibly due to preservation. Velum narrow.
Tentacles two, opposite, on voluminous, triangular perradial basal bulbs, approximately 250 μm across the base (Figures 5A, C). The tentacles are tightly contracted. The other two perradial bulbs are considerably smaller, and each bears 10-12 solid, straight, thick cirri approximately 300 μm long and decorated with a continuous spiral pattern or a series of fine rings along the whole length (Figures 5A, 7A). One of the cirri in the preserved specimen is coiled and ends in two large, long bean-shaped nematocysts (Figure 7A); the extent to which this coiling is normal in life is unknown.
Other marginal structures: opposite the radial canal associated with one of the tentacle bulbs bearing cirri, there exists a small gelatinous “thorn” projecting outward (Figures 5A, 7A). Under high magnification, this conical structure appears to have a central canal and ends in what appears to be an open statocyst (Figure 7A). Whether this structure exists on the other perradii could not be determined. No ocelli observed.
Stomach small, cruciform at base (Figure 5B), approximately 300 μm in diagonal width, with a short broad tapering manubrium, square in cross section (136 μm long), lacking a gastric peduncle (Figure 5A). Mouth simple without lips, perfectly quadrangular (Figure 5B).
Radial canals four, straight sided throughout length clearly visible from the stomach to the ring canal, approximately 30 μm in diameter and expanded proximally to create mesentery-like connections with the stomach (Figure 5A). Ring canal also straight-sided and of a similar width (Figure 5C).
Gonads four, spindle-shaped, starting approximately half way from the stomach toward the margin, covering 2/5 of the entire length of the radial canal, absent on the distal fifth of the radial canal (Figure 5A). Eggs, in clusters on lumpy follicles 80-90 μm in diameter; easily identified in each of the gonads (Figures 5A, 6).
Near the shipwreck SS Yongala, south-east of Townsville, Queensland, Australia.
No nematocyst preparation was made because the only available specimen is the holotype and it is too small to take sections from without destroying it. Therefore, the following description of nematocysts is based on in situ observation only. Bell nematocysts are mostly in roughly circular clusters up to 30 μm in diameter on the subumbrellar surface. Each cluster consists of 4-20 nematocysts. The nematocysts are oval in shape and approximately 12 μm long and half as wide (Figure 6). Tentacular bulbs: containing bean-shaped nematocysts approximately 15 μm long (Figure 8B). Tentacles: nematocysts are oval shape and they are approximately 7.5 µm long (Figure 8A). Cirri bulbs: the same type of nematocysts were found in the cirri bulbs as those found in the tentacular bulbs (Figure 7B). Cirri: nematocysts were not observed in the majority of the cirri. However, in the coiled cirrus (explained above), the coiled region contained numerous very small nematocysts (ca. 3 µm long) and the terminal end contained two bean-shaped nematocysts approximately four times the size of the other type found more proximally (Figure 7).
The specific name yongalensis is given honouring the area where people lost their lives on board the SS Yongala that sank not far away from Cape Bowling Green, Queensland, in 1911. This area is a popular scuba diving site and it is also the location of one of the IMOS National Reference Stations. This is not to be confused with the town from South Australia of the same name.
The specimen was collected in a vertical drop net from the surface to 28 m in an area of maximum 30 m depth; we therefore do not know its exact location in the water column. The sea surface temperature at the time was 27.5 °C.
Like its congeners, Paralovenia yongalensis has two opposite tentacles and two opposite clusters of short cirri. However, the gonad shape and position immediately distinguish it from the others (Table 2).
Whereas P. bitentaculata Bouillon (1984) and P. latigaster Xu & Huang (2004) both have a deep pyriform bell and long cylindrical gonads, they are distinguished primarily on the number of cirri on each marginal cluster, about six in the former and twelve in the latter, and on the size of the stomach, short in the former and huge in the latter.
The cirri of P. yongalensis are more similar in number to P. latigaster , while the stomach is small, like that of P. bitentaculata ; P. yongalensis differs from both in having a relatively shorter, rounder body, and shorter, more spindle-shaped gonads, tapered at both ends. Moreover, P. yongalensis is approximately the same size as P. bitentaculata .
The cirri are worthy of discussion. Bouillon (1984) described and illustrated the cirri in P. bitentaculata as spiralled in form, while Xu and Huang (2004) do not describe in detail the cirri of P. latigaster . In P. yongalensis , the cirri are straight, solid, relatively thick, with a rounded end, with a series of external rings or a continuous ornamentation spiralling along their length. However, one of the cirri was tightly coiled, so we are unsure whether this coiling is the normal state in life for all the cirri, or for just one in each cluster, or if it was an artefact of preservation.
Interestingly, P. yongalensis has a few flat round clusters of nematocysts on the subumbrellar surface. Neither Bouillon (1984) nor Xu and Huang (2004) mentioned finding this characteristic in the other two species of Paralovenia .
Similarly, the conical statocyst-like structure in P. yongalensis is very interesting to us. Bouillon (1984) stated for P. bitentaculata , "Nous n’avons pas observé d’organes des sens"; we interpret this to mean that he found neither statocysts nor ocelli. However, Xu and Huang (2004) specifically stated that P. latigaster was "without statocysts". The structure that we have observed is extremely small and could be overlooked, but we doubt that all three researchers would have done so. Perhaps more intriguing to us is the fact that open statocysts are typically more “finger-shaped” (e.g., Russell 1953: 13, text fig. 7C), so besides being apparently unique in the genus, this also is a form of statocyst that we have not previously seen.
We recognise the value of providing DNA sequences as molecular evidence to support the description of new species when it is practical. In the present case, all the specimens were preserved in formalin, making successful extraction of DNA unlikely. Moreover, with so few specimens of Melicertissa and only one specimen of Paralovenia , we consider the morphological approach to be the less-destructive method to characterise these two new species.
Finally, while we believe that the fully-developed gonads for both species suggest that they are mature specimens, this hypothesis may be tested using DNA sequencing in future research.
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