Merga violacea ( Agassiz & Mayer, 1899 )

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 247-249

Merga violacea ( Agassiz & Mayer, 1899)

Fig. 6 A-E

Pandea violacea Agassiz & Mayer, 1899: 160 . – Mayer, 1900: 34, pl. 1 fig. 1. – Bigelow, 1909: 205, pl. 41, figs 10- 11. – Mayer, 1910: 119, text fig. 64, pl. 11 fig. 7, pl. 12 fig. 1.

Mergintha lobiancoi Hartlaub, 1914: 250 , fig. 205. – Kramp, 1953: 265, synonym.

Merga violacea . – Hartlaub, 1914: 249, fig. 204, new combination. – Kramp, 1953: 265. – Kramp, 1959a: 116, fig. 106. – Kramp, 1961: 107. – Kramp, 1968: 41, fig. 104. – Schuchert, 2007: 355, fig. 69.

? not Merga violacea . – Menon, 1932: 7, pl. 1 fig. 10. [? = Pandeopsis ikarii ]

Examined material: BFLA4006 ; 1 specimen; 26 -NOV- 2018; size 12 mm high, 10 mm wide, pink colour; photographed and preserved in ethanol for DNA extraction; 16S sequence MW528650 . – 30-JUN- 2018; 1 specimen photographed; size approximately 7 mm, pink, only 2 rudimentary bulbs between tentacle pairs; not collected . – 09-AUG-2018; 1 specimen photographed; size approximately 10 mm, pink; not collected.

Observations: Typical medusa of the genus Merga , up to 12 mm high, characteristic light pink-purple colour of manubrium and tentacles ( Fig. 6 A-E), without apical process but when fully grown with a thick apical jelly, shallow subumbrellar pockets present. Manubrium about half the height of subumbrella, very wide, connected for about half its length along the radial canals; stomach base and mouth cruciform, mouth rim slightly folded. Gonads on interradial surfaces of stomach, thin, smooth and not folded. Four radial canals broad, connected to stomach in its upper parts as mesenteries. Eight long, tapering tentacles, base laterally compressed and clasping bell margin, may be continued on exumbrella as an atypical, flat, abaxial spur ( Fig. 6B ); large red abaxial ocellus near abaxial end of bulb. Rarely also 9 tentacles observed. Alternating with the tentacles 2-5 small bulbs (max. total 34) with a short, blunt tentacle stump, all the same size and also with a red ocellus. Usually with brown pigment dots in the stomach wall ( Fig. 6C, E ).

Distribution: Circumglobal in tropical to subtropical waters ( Schuchert, 2007). Type locality: Fiji Islands.

16S Data: The partial 16S gene sequence ( MW528650 ) obtained was used to search for similar sequences in GenBank using the blastn function. Other similar sequences found were as expected of Pandeidae species but had only identities below 89%. The similarities with the Pandeopsis species described below were also relatively low (<86%, see also Fig. 8 ).

Remarks: The species has recently been redescribed and discussed by Schuchert (2007), but the problem with the type locality remains unresolved. No type material could be located in the Harvard Museum of Zoology (A. Baldinger, pers. com. June 2019), the museum Agassiz and Mayer were associated with.

Agassiz & Mayer (1899) introduced the name Pandea violacea in a paper reporting on medusae collected in the Fiji archipelago. In the description – no figure was given – they state that they have also found indistinguishable medusae at the Dry Tortugas Islands which they intended to illustrate in a subsequent publication. Notwithstanding, the paper dealt with specimens from Fiji and therefore the Fiji Archipelago should be considered as the type locality of the species. This could be taxonomically important if future genetic studies show that the two populations belong to separate species.

In one of our specimens (BFLA4006), some tentacle bulbs had atypical abaxial spurs formed by thickening of the exumbrellar epithelium ( Fig. 6B ). Several specimens also had brown dots in the stomach wall ( Fig. 6A, C ). There seem to be differences between Pacific and Atlantic individuals, including the colouration (comp. Bigelow, 1909; or Schuchert, 2020: photos of Australian Merga violacea ).

Figures

Fig. 6. Merga violacea. (A-D) Specimen BFLA4006, bell height 12 mm. (A) Lateral view of whole animal, note that the bell is somewhat contracted and more elongate than normal. (B) Bell margin seen from oral, note the flat abaxial spurs above some of the tentacle bulbs (arrow). (C) Lateral view of stomach. (D) Bell margin, note rudimentary bulbs with short tentacle stumps. (E) Lateral view of younger animal observed 30-Jun-2018, size approximately 7 mm.

Fig. 8. 16S rRNA maximum likelihood phylogenetic tree of Pandeidae species obtained with PhyML (GTR+G+I model) and based