Aglaura hemistoma Péron & Lesueur, 1810

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 332

Aglaura hemistoma Péron & Lesueur, 1810

Fig. 58 A-D

Aglaura hemistoma Péron & Lesueur, 1810: 351 . – Haeckel, 1879: 275, pl. 16 figs 3-4. – Vanhöffen, 1902: 78, synonymy. – Bigelow, 1909: 119, pl. 2 fig. 6, synonymy. – Mayer, 1910: 398, fig. 254, pl. 46 figs 4-5, pl. 49 figs 3-7, pl. 50 fig. 11. – Kramp, 1959a: 192, fig. 291 – Kramp, 1961: 251. – Kramp, 1965: 127, distribution. – Kramp, 1968: 122, fig. 331. – Bouillon, 1978a: 162, cnidome. – Fagetti, 1973: 41, pl. 4 fig. 13. – Goy, 1979: 284, fig. 25. – Pagès et al., 1992: 44, fig. 53. – Bouillon et al., 2004: 241, fig. 152G. – Nagata et al., 2014: 316 , figs 36-37.

Lessonia radiata Eydoux & Soulyet, 1852: 643 , pl. 2 fig. 16, Pacific Ocean.

Aglaura Peronii Leuckart, 1856: 10 , pl. 1 fig. 5, Mediterranean. ‒ Haeckel, 1879: 275, synonym.

Aglantha globuligera Haeckel, 1879: 272 , pl. 16 fig. 8, Canary Islands. ‒ Kramp, 1959a: 192, synonym.

Aglaura nausicaa Haeckel, 1879: 274 , pl. 16 fig. 1, Mediterranean.

Aglaura laterna Haeckel, 1879: 274 , pl. 16 fig. 2, Canary Islands.

Stauraglaura tetragonima Haeckel, 1879: 277 , pl. 16 figs 10- 11, coast of Australia. – Kramp, 1961: 264, probably A. hemistoma .

Aglaura prismatica Maas, 1897: 24 , pl. 2 figs 4-5, Gulf of Panama, Pacific Ocean. – Maas, 1906 a: 97, pl. 3 fig. 12.

Aglantha octogona Bigelow, 1904: 257 , pl. 7 fig. 9, Maldives.

Aglaura ciliata Perkins, 1906: 118 , Tortugas.

Examined material: BFLA3808 ; 4 specimens observed, one collected; 19-OCT-2018; size 2 mm; preserved in alcohol for DNA extraction; 16S sequence MW528640 . – BFLA4214 ; 1 specimen; 27-AUG-2019; 2 mm; parts preserved in formalin ( UF-013830 ) and in alcohol for DNA extraction; 16S sequence MW528686 . – 20-AUG-2019; 1 specimen photographed; size 3 mm; not collected.

MHNG-INVE-0031745 ; Mediterranean , Bay of Villefranche-sur-Mer, 43.6860°N 7.3170°E, depth 0-70 m; collection date 03-MAY-2001; numerous specimens collected, some preserved in formalin, one used for DNA extraction, 16S sequence KP776748 .

Observations: Specimens from Florida with bell size of 2 mm, cylindrical shape, aboral side with funnellike depression ( Fig. 58C ), wall very thin, velum broad, with slender gastric peduncle of 2/3 of subumbrellar height ( Fig. 58D ). Manubrium protruding through velar opening ( Fig. 58 A-D), bipartite, upper part saclike, lower half with cruciform cross-section, ending in four-lipped mouth ( Fig. 58B ), margins smooth, not crenulated. Gonads eight sausage-shaped apendices in a whorl attached at junction of manubrium to peduncle ( Fig. 58 A-C). Eight radial canals, thin and very transparent. Seven or eight statocysts ( Fig. 58B ) on bell margin and about 70 thin tentacles. Mostly colourless, but interference effects often cause iridescence in rainbow colours ( Fig. 58A, D ).

16S Data: The two haplotypes of this study differed in 0.9% of the base pairs, while the minimal differences to other population were 2 to 5 % ( Table 1 ). In a maximum likelihood tree (not shown) obtained by comparing it to the Trachymedusa 16S dataset of Bentlage et al. (2018) and additional trachyline sequences from GenBank, all Aglaura hemistoma clustered as a monophyletic group.

Distribution: Widely distributed and common in the warm and temperate parts of the Atlantic-, Indian-, and Pacific Oceans, usually between about 40°N and 40°S including also the Mediterranean, usually in large numbers ( Kramp, 1965; Fagetti, 1973; Bouillon, 1978b; Goy, 1979; Navas-Pereira &Vannuci, 1991; Pagès et al., 1992; Nagata et al., 2014). Type locality: Mediterranean Sea, near the town of Nice.

Remarks: Although Aglaura hemistoma has numerous synonyms, it is taxonomically rather unproblematic. Providing a tabular comparison of the nominal Aglaura species , Vanhöffen (1902) concluded that they are mostly developmental stages or variants of A. hemistoma . Moreover, A. hemistoma has a very thin jelly which gets deformed quite drastically when preserved ( Bigelow, 1909). Our own observations on material from the Mediterranean showed that the bell actually elongates considerably in formalin. Some authors may have misinterpreted this fixation effect as a diagnostic trait and it explains the number of synonyms. The few available 16S sequences are also relatively similar ( Table 1 ).

Figures

Fig. 58. Aglaura hemistoma. (A-B) Sample BFLA3808, bell size 2 mm, oblique views from oral side. The statocysts can be seen in B as tiny, bright spots along the ball margin. (C) Animal photographed 20-AUG-2018, bell size 3 mm. (D) BFLA4214, bell size 2 mm, lateral view.