Pegantha martagon Haeckel, 1879

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 322-324

Pegantha martagon Haeckel, 1879

Fig. 53 A-C

Pegantha martagon Haeckel, 1879: 332 .

Polycalpa zonaria Haeckel, 1879: 327, Mediterranean.

? Pegantha simplex Bigelow, 1904: 260 , pl. 5 figs 19-20. – Bigelow, 1909: 83.‒ Bigelow, 1918: 395, synonym of P. martagon .

Pegantha martagon . ‒ Mayer, 1910: 443, figs 295-296. – Bigelow, 1909: 83, pl. 18 figs 1-8. ‒ Bigelow, 1918: 396. ‒ Kramp, 1955a: 160. ‒ Kramp, 1957: 67, pl. 6 fig. 1, revision. ‒ Kramp, 1959a: 64, 197, fig. 302. ‒ Kramp, 1961: 274. ‒ Kramp, 1968: 127, fig. 342. ‒ Segura-Puertas, 1984: 45, pl. 14 fig. 1. ‒ Pagès et al., 1992: 41, fig. 49. – Larson et al., 1989: 789, fig. 1A.

Examined material: BFLA4070 ; 1 specimen; 11-APR- 2019; size 10 mm, 10 tentacles; preserved in alcohol for DNA extraction; 16S sequence MW528666 . – BFLA4109 ; 1 specimen; 03-JUN-2019; size 8 mm, 8 tentacles; part preserved in formalin and deposited as UF-013796 , small part in alcohol for DNA extraction; 16S sequence MW528676 . – BFLA4336 ; 1 specimen; 07-FEB-2020; size 6 mm, 9 tentacles; preserved in alcohol for DNA extraction; 16S sequence MW528708 . – 26-FEB-2018; 1 specimen photographed, not collected, 9 tentacles.

Observations: Medusae hemispherical or slightly wider than high, diameter 6-10 mm, 8-10 tentacles and marginal lappets ( Fig. 53A, C, E ), stomach wide, up to 2/3 of bell diameter, no gastric jelly cone ( Fig. 53B, E ), without manubrial pockets, peripheral canals originating below tentacles ( Fig. 53C ), first descending parallel along the peronial fold, then along lappet periphery, rather thin (1/6 of lappet width), width constant. Marginal lappets rectangular to rounded, with 4-5 otoporpae ( Fig. 53B ), these short, max. twice the size of the width of the peripheral canals. Statocysts near otoporpae, about as many as otoporpae. Tentacles curved, tapering, held at approximately 45° upwards, proximal end pointed and horizontal; below tentacles a slight furrow in the exumbrella with the peronium ( Fig. 53A ).

16S Data: The three obtained haplotypes have only low sequence divergences ( Table 1 , Fig. 48 ), but there was no significant relationship to a sequence of P. martagon from the Eastern Pacific (GenBank MG979374 , Fig. 48 ).

Distribution: Widely distributed in the tropical and subtropical parts of the Atlantic and Indo-Pacific Ocean ( Bigelow, 1909; Kramp, 1959a; Bouillon, 1978c; Bleeker & Van der Spoel, 1988; Navas-Pereira & Vannuci, 1991; Bouillon & Barnett, 1999; Segura Puerta et al., 2003, 2009; Oliveira et al., 2016), surprisingly also in the cold waters around South Georgia and in Antarctic waters ( Kramp, 1959a; Toda et al., 2008). Occurs in shallow waters, occasionally from 100 to 300 m depth ( Kramp, 1957). Type locality: China Sea.

Remarks: Our samples had apparently not yet developed gonads, being thus not fully mature. The observed tentacle numbers of 8-10 were lower than the 16 given in Kramp (1959a, 1968), but this is a maximal number and most animals have actually only 10-13 tentacles and lappets ( Bigelow, 1909; Kramp, 1957, 1959a). According to Bigelow (1909) and Kramp (1959a: 64), the final tentacle number (10-11) is attained early in development, though during further growth some few tentacles and lappets may occasionally be added.

Kramp (1957) observed that the lateral portions of peripheral canal in the lappets are broader than the transverse portions along the bell margin. This was not seen in the present material ( Fig. 53 C-E).

Pegantha simplex Bigelow, 1904 – a nominal species based on a type specimen from the Maldive Islands – was later synonymized with Pegantha martagon by Bigelow himself ( Bigelow, 1909, 1918). We think that Bigelow’s specimen from the Maldives nevertheless deviates quite strongly from the scope of P. martagon as described by later authors (see synonymy above). It was a small (3 mm) medusa but with fully developed, pendant-saclike gonads. It had 8 tentacles/lappets and reportedly 25 statocysts per lappet, more than twice the number usually seen in P. martagon . Later, Bigelow (1909) reexamined this material and had to revise this number. The contraction of the alcohol preserved material feigned the presence of more statocysts. Actually, also Haeckel (1879) in his first description reported 13-15 statocysts per lappet. Because he also had preserved material, Bigelow (1909) assumed that he was likewise mistaken. The gonads of P. martagon are variably described as a simple ring at the periphery of the stomach, or as irregularly lobed, pendant sacs. While it is possible that these two stages are only different developmental stages, we nevertheless suspect that the wide variation of the current concept of P. martagon indicates that it comprises several species. Our 16S sequences are very different from a tentatively identified P. martagon from California found parasitizing a planktonic polychaete Tomopteris ( Bentlage et al., 2018) .

Figures

Fig. 53. Pegantha martagon. (A-B) Sample BFLA4109, diameter 8 mm. (A) Aboral view, the annular, more opaque structure was interpreted as food debris at the periphery of the stomach, the bright oval element is an out of focus crustacean. (B) Lateral view, note the clearly visible otoporpae and crustacean on the exumbrella. (C-D) BFLA4070, 10 mm. (C) Oral view. The bright, granular material is interpreted as partially digested food which fills the stomach and also the peripheral canal. Note also the closed mouth and the folds of the mouth margin. (D) Lateral view of bell margin. (E) BFLA4336, 6 mm, lateral view, the white matter in the gastric system is likely digested food.

Fig. 48. Maximum likelihood phylogenetic tree of Narcomedusae obtained with PhyML (GTR+G+I 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%). Sequence labels start with the GenBank numbers (except for identical haplotypes) permitting the retrieval of more information. Some proveniences were obtained from Lindsay et al. (2017) or through personal communications. Red ODEHOV DUH QHZ VHTXHQFHV IURP WKLV VWXG\. &RORXUHG ER[HV LQGLFDWH IDPLO\ DI¿OLDWLRQV DFFRUGLQJ WR WKH FXUUHQWO\ XVHG V\VWHP. (") 'HQRWHV SRVVLEOH PLVLGHQWL¿FDWLRQV.