Proboscidactyla gemmifera ( Fewkes, 1882 )

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 263

Proboscidactyla gemmifera ( Fewkes, 1882)

Fig. 15 A-F

Willia gemmifera Fewkes, 1882b: 300 , pl. 1 fig. 24.

Proboscidactyla gemmifera . – Browne, 1905: 727.

Dyscannota gemmifera . – Mayer, 1900: 47, pl. 8 fig. 17.

Proboscidactyla ornata var. gemmifera . – Mayer, 1910: 192, fig. 101a, pl. 21, figs 1-3.

Material examined: BFLA4285 ; 1 specimen; 06-DEC- 2019; size 3 mm, 19 tentacles, with medusa buds; preserved in alcohol for DNA extraction; 16S sequence MW528699 . – BFLA4321 ; 1 specimen; 24-JAN-2020; size 2.5 mm, 17 tentacles, with medusa buds; preserved in alcohol for DNA extraction; 16S sequence identical to MW528699 . – BFLA4338 ; 1 specimen; 07-FEB- 2020; size 3 mm, 18 tentacles, with medusa buds; preserved in alcohol for DNA extraction; 16S sequence identical to MW528699 . – 24-JAN-2020; 1 specimen photographed, not collected; 3 mm, 14 tentacles, with medusa buds.

Observation: Medusae as described for P. ornata but somewhat smaller, 2.5-3 mm, though none of them appear sexually mature, tentacle numbers 14-19, more nematocyst patches on exumbrella, these often quite irregular and some not in linear arrays, no dark pigment in gastrodermis of tentacle bulbs. The most notable difference is the presence of four blastostyles ( Fig. 15C ) at each of the proximal-most branching points of the radial canals. Blastostyle resembling a polyp with one short capitate tentacle (visible in Fig. 15A, C ) and bearing one to several medusa buds of different development stages.

16S Data: See Table 1 and Fig. 16 .

Distribution: NE Atlantic from Cape Hatteras to Florida, likely more widely spread but identifications are unreliable (see P. ornata ). Type locality: USA, North Carolina, Beaufort Inlet.

Remarks: Although the three samples used to obtain 16S sequence data were collected at different dates they all proved to be identical and clearly distinct from P. ornata ( Fig. 16 ). This clade seems to be about equally distant from P. ornata as it is from the Pacific P. flavicirrata Brandt, 1835 . This evident barcoding gap argues for it representing a distinct species.

The observed morphological differences to the sympatric P. ornata are listed above. It must be noted that P. gemmifera were found during the winter months, while the mature P. ornata were seen from March to June.

Proboscidactyla gemmifera was described based on a single medusa which was probably not fully developed as it had only eight tentacles ( Brooks, 1880; Fewkes, 1882b). Mayer (1900, 1910) later supplemented more detailed descriptions of more advanced specimens from Florida. These descriptions do not agree with our specimens concerning the position of the blastostyles. Fewkes and Mayer found them at the junction of the radial canal to the manubrium, while in our samples they were located at the first bifurcation of the radial canals ( Fig. 15A ). This is not necessary a significant difference. Kramp (1957, 1962) found the blastostyles in every possible position along the radial canals, this in various populations from the Pacifc (identified as P. ornata ). He regarded this variation as without any systematic importance.

Uchida & Sugiura (1975) examined the medusa bud development in a Japanese form of P. ornata and found that the position of the blastostyles is variable, depending on the developmental age (size) of the medusa. Smaller ones had them at the corners of the stomach, larger ones at the branching points. They also found that sexually mature medusae can continue budding medusae.

Although with some hesitation, we therefore referred our medusae to Proboscidactyla gemmifera .

Figures

Fig. 15. Proboscidactyla gemmifera. Note that the usage of a flash brightens very much the exumbrellar nematocysts. (A) BFLA4338, diameter 3 mm. (B) Medusa photographed 24-JAN-2020, not collected, diameter 3 mm.(C) BFLA4285, lateral view, diameter 3 mm, arrows point to blastostyles (D) BFLA4285, oral view. (E) BFLA4321, aboral view. (F) BFLA4321, lateral view of bell margin, diameter 2.5 mm, note regular arrangement of exumbrellar nematocysts patches.

Fig. 16. 16S maximum likelihood phylogenetic tree of Proboscidactylidae and related taxa obtained with PhyML (GTR+G model) and based on about 600 bp positions of the mitochondrial 16S gene. Node-support values are bootstrap values of 100 pseudoreplicates (shown only if> 70%).All sequence labels start with the GenBank numbers permitting the retrieval of more information. Red labels are new sequences from this study. All samples are based on medusae.