Protiaropsis anonyma ( Maas, 1905 )

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 257-259

Protiaropsis anonyma ( Maas, 1905)

Fig. 12 A-C

Heterotiara anonyma Maas, 1905: 19 , pl. 3 figs 19-21. – Bigelow, 1909: 216, pl. 41 figs 12-14. – Vanhöffen, 1911: 211, pls 12-13. – Bigelow, 1918: 382. – Bigelow, 1928: 287. – Russell, 1940: 516, figs 5-7. – Kramp, 1959a: 17, 125, fig. 131. – Kramp, 1961: 122. – Kramp, 1965: 41. – Kramp, 1968: 53, fig. 138. – Schmidt, 1973: 22. – Schmidt & Klinker, 1974: 34. – Bouillon, 1980: 314. – Brinckmann-Voss & Arai, 1989: 41, figs 1b, 1e.

not Heterotiara anonyma . – Bigelow, 1913: 25, records North Pacific. [= Bythotiara depressa Naumov, 1960 ]

in part Heterotiara anonyma . – Arai & Brinckmann-Voss, 1980: 69, fig. 40. [in part Bythotiara depressa Naumov, 1960 ]

Protiaropsis anonyma . – Stechow, 1919: 150, new combination. – Schuchert, 2010: 338.

? Kanaka pelagica Uchida, 1947: 103 , fig. 5. – Kramp, 1961: 123. – Kramp, 1968: 58, fig. 153. – Schmidt, 1973: 22, could be a young Heterotiara anonyma . – Bouillon, 1980: 316, could be Heterotiara anonyma .

Examined material: BFLA4037 ; 1 specimen; 26 -MAR-2019; size 12 mm high; part preserved in formalin and deposited as UF-013457, small part in alcohol for DNA extraction; 16S sequence MW528657 .

Observations: Bythotiaridae medusa 12 mm high, bell cylindrical, not compressed laterally, mesoglea thick, especially apical jelly which is about 1/3 of the total bell height; bell margin with regular furrows in which lie the tentacles. Manubrium 2/3 the height of the subumbrella, shaped like inverted cone, section cross-shaped, interradial wall smooth, mouth cruciform, rather small, four red strands run along the interradial corners of the manubrium. Four thin radial canals, no mesenteries; circular canal thin. 10 tentacles, length about half the height of the bell, originating from under circular canals without formation of a distinct tentacle bulb but with an epidermal swelling at the junction of tentacle and circular canal, proximal part of tentacles curving adnate around bell margin in furrows, tapering only slightly distally, ending in bright orange, spherical to ovoid knob, diameter about 0.3 mm. No ocelli.

16S Data: A blastn search in GenBank with the sole 16S ( MW528657 ) gave mostly species of Filifera / Anthoathecata , but all below 90% identity and thus precluding any conclusions on relationships.

Distribution: Widespread in warm parts of the Atlantic, Indian, and Pacific Oceans, usually in depths of 0 to 600 m ( Arai & Brinckmann-Voss, 1980; corrections in Brinckmann-Voss & Arai, 1989). Type locality: Indonesia, 0.2933°S, 129.2418°E, 0-1000 m depth.

Remarks: Most illustrations of this species do not show the terminal swellings of the tentacles (e.g. in Kramp, 1959a, 1968), a typical character of Bythotiaridae medusae. These are almost invariably lost in specimens caught with a plankton net, but they are normally present in this species (see Kramp, 1948, 1965; Schmidt, 1973; Arai & Brinckmann-Voss, 1980).

The size of the examined medusa was at the lower end of the range usually given for this species (12-20 mm, Maas, 1905; Bigelow, 1909; Vanhöffen, 1911). Bigelow (1918) also found somewhat smaller (up to 13 mm) in the nearby Bermuda region, likewise Bouillon (1980) in animals from Papua New Guinea.

The interradial red strands are rather conspicuous in the living and preserved animal ( Fig. 12 A-B), but they have been mentioned only rarely so far. Only Vanhöffen (1911) observed them in an animal caught near the Nias Islands ( Indonesia).

The nematocysts have been described by Russell (1940) and Bouillon et al. (1988a). The species has large desmonemes which are typical for the family Bythotiaridae .

The taxonomic scope of Protiaropsis anonyma is not yet fully clear as there are other similar species, some of which which could prove to be conspecific (see also discussions in Schmidt, 1973).

Protiaropsis minor ( Vanhöffen, 1911) is somewhat smaller (6-12 mm), has perhaps a shorter manubrium, and 16 to 24 tentacles (see description by Pagès et al., 1992). Bouillon et al. (1988a) found both morphotypes in sympatry and kept them distinct.

Kanaka pelagica Uchida, 1947 has eight tentacles but is much smaller (1.8 mm). It was based on a single specimen which was likely a juvenile. Kramp (1953) thought it might belong to P. minor , while Schmidt (1973) and Bouillon (1980) think it is referrable to Protiaropsis anonyma .

Gymnogonium zhengzhongii Xu & Huang, 1994 , is small (2.2 mm), has a short manubrium, and a pair of branched radial canals, resulting in six canals in total. The manubrium of the only observed specimen had gonads. Bouillon et al. (2006: 182) thought that it could belong to Protiaropsis anonyma . As the the species is based on a single specimen, it cannot be excluded that the branched radial canals were a developmental aberration. New material has to prove the validity of the species, but as the type specimen was apparently mature at 2.2 mm, the genus and species should be retained as valid for the moment.

Bouillon (1980) thought that also Bythotiara depressa Naumov, 1960 could be conspecific with P. anonyma as he found intermediate forms. Bythotiara depressa differs from P. anonyma in having an irregularly folded surface of the gonads. Brinckmann-Voss & Arai (1989) examined the problem in detail and they worked out diagnostic differences of the two species (see also Xu et al., 2016). Some of the previous records of P. anyonyma from colder waters of the North Pacific Ocean were actually B. depressa .

All these ambiguities underline the need for a comprehensive dataset of 16S DNA barcodes which will hopefully improve the species delimitations.

Figures

Fig. 12. Protiaropsis anonyma, specimen BFLA4037, bell height 12 mm. (A) Lateral view of animal with amphipod prey in its stomach. (B) Manubrium at other angle, note cruciform base. (C) Bell margin.