Pandeopsis ikarii ( Uchida, 1927 )

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 249-252

Pandeopsis ikarii ( Uchida, 1927)

Fig. 7 A-C

Tiaranna ikarii Uchida, 1927a: 208 : fig. 35.

Pandeopsis ikarii . – Kramp, 1961: 444. – Kramp, 1965: 39, synonymy. – Kramp, 1968: 41, fig. 105. – Schuchert, 1996: 73, fig. 43a-b. – Buecher et al., 2005: 43 . – Kubota et al., 2011: 57, figs 1-3. – Suehiro & Kubota, 2015: 73, fig. 1, pl. 1.

Pandeopsis scutigera Kramp, 1959b: 232 , fig. 7, Gulf of Thailand. – Kramp, 1961: 113, 444. – Kramp, 1968: 41, synonym.

? not Pandeopsis ikarii . – Bouillon, 1980: 336. – Bouillon, 1985: 257, fig. 6, life cycle. [? = Pandeopsis prolifera n. spec.]

Examined material: BFLA4088 ; 1 specimen; 07 -MAY-2019; size 2.5 mm, faintly greeninsh gastrodermis, no dots on manubrium seen; preserved in ethanol for DNA extraction; 16S sequence MW528673 . – 08-AUG-2018; 1 specimen photographed; size approximately 5 mm, greenish manubrium, dots present; not collected.

MHNG-INVE-0092017 ; Japan, Mie Prefecture, Toba City; WGS84 34.4781, 136.8670; collector and donor Takanori Suehiro; year 2015; 12 medusae cultivated from a polyp stage collected on sand, age about 3 months, examined alive and preserved, size 4 mm, 12 tentacles; 16S sequence MG136757 .

Observations: Sample BFLA4088, bell height 2.5 mm, bell top rounded, lower lateral walls straighter, mesogoea thick, at apex nearly 1/2 of bell height, smooth. Manubrium large, base square-shaped, wide upper half, narrower lower part with cross-shaped section, mouth drawn out into four lips with smooth rim; colour greenish, no pigment dots; wall of upper half of manubrium apparently with layer of numerous developing oocytes ( Fig. 7A ). Radial canals forming mesenteries along upper half of manubrium, smooth, greenish. Eight tentacles, long, tapering, with red abaxial ocellus at base. Eight adradial rudimentary bulbs with a very short, stump-like tentacle, with abaxial red ocellus ( Fig. 7B ). Individual collected 08-AUG-2018 similar but larger (5 mm), with dots on manubrium ( Fig. 7D ).

16S Data: An blastn search with the partial 16S gene sequence ( MW528673 ) was used to search for similar sequences in GenBank. The closest match with 3.5 % sequence divergence was with sequence MG136757 obtained from a Pandeopsis ikarii sample from Japan (see also Fig. 8 and the discussion of the next species).

Distribution: Japan, Philippines, Gulf of Thailand, Java Sea, New Zealand, Indian Ocean, Red Sea. Type locality: Seto (Wakayama), Japan.

Remarks: This is the first record of this species for the Atlantic Ocean. Notably sample BFLA4088 ( Fig. 7 A-C) matched very well the existing descriptions of this species given above in the synonymy. The only difference being the absence of pigment dots on the stomach wall. They might develop later only (comp. Suehiro & Kubota, 2015). Another observed specimen ( Fig. 7D ) had such spots, but as no sequence information is available for this specimen the identification remains somewhat uncertain.

Pandeopsis ikarii has been widely reported in the Indian- and Pacific Oceans, but some of these records might belong to a distinct species. Bouillon (1980: 336) observed that his animals from the Bismarck Sea had a dense proliferation of medusa buds on the manubrium and developed up to 14 tentacles. The budding was sometimes already present in young animals with four tentacles only. The maximal size was up to 10 mm, thus quite larger than usually reported (4.5 mm in Kramp, 1968). Another detail mentioned by Bouillon is a band of chordoid cells along the four corners of the manubrium ending in nematocysts clusters, an element neither observed here nor mentioned in other descriptions of the species. The budding was also observed by Navas (1971, cited in Bouillon, 1980) in animals collected in the Indian Ocean, but not by any other observer. Dr Shin Kubota (pers. com.) informed us that he never observed medusa buds in Japanese P. ikarii . It is therefore very likely that Bouillon’s material belonged to another species, perhaps even Pandeopsis prolifera n. spec described below.

Figures

Fig. 7. Pandeopsis ikarii. (A-C) Specimen BFLA4088, size 2.5 mm, presumable incipient oocytes are visible in the stomach wall. (D) Specimen collected 08-AUG-2018, size 5 mm, the identification is somewhat unreliable as there is no sequence data available.

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