Eucheilota menoni Kramp, 1959

Peter Schuchert, 2017, Systematic notes on some leptomedusa species with a description of Neotima galeai n. spec. (Hydrozoa, Cnidaria), Revue suisse de Zoologie 124 (2), pp. 351-375 : 366-367

Eucheilota menoni Kramp, 1959

Eucheilota menoni Kramp, 1959b: 248 , fig. 14a-b. – Kramp, 1961: 175. – Kramp, 1968: 82, fig. 221. – Bouillon, 1984: 57. – Bouillon et al., 1988: 217, fig. 12, nematocysts. ‒ Bouillon & Barnett, 1999: 89, fig. 80.

? Mitrocomium assimile Browne, 1905b: 137 , pl. 1 fig. 3.

? Lovenella assimilis . – Kramp, 1961: 177. – Kramp, 1968: 80, fig. 216. – Bouillon, 1984: 76, nematocysts. – Bouillon et al., 1988: 220, nematocysts. – Brylinski et al., 2016: 21, fig. 2.

Lovenella assimilis . ‒ Bouillon & Barnett, 1999: 89, Fig. 87.

Material examined: Holotype of Eucheilota menoni , 1 female medusa, NHMD-98221; Nancowry Harbour, Nicobar Islands, Galathea station 319; 06.05.1951 ; det. P. L. Kramp. – MHNG-INVE-29469, about 60 mature medusae; collected at several stations between Auckland and Leigh , New Zealand; February 1997 ; originally in formaldehyde, pigment almost entirely lost. – MHNG- INVE-33457, 8 specimens; Narrow Neck Beach , Hauraki Gulf, New Zealand, 36.8123°S 174.8025°E, 0 m depth; 03.07.2002 ; 7 specimens originally in formaldehyde, pigments now faint, one specimen preserved for DNA extraction giving sample DNA072 ; 16S KY363960 . – 10 mature medusae, not in permanent collection; same locality as before but collected 26.07.2002 ; preserved in 95% ethanol; pigments and statocysts preserved; DNA of one individual sample 1131; 16S sequence KY363961 . – Several specimens, not in permanent collection; Motutapu Island, Hauraki Gulf, New Zealand, 36.7443°S 174.9044°E, depth 0-3 m, 30.06.2002; specimens used for examination lips. Manubrium without spots of dark pigment. Radial canals four, narrow. Gonads large for the bell-size and already present in small animals (1 mm), covering distal half of radial canals and reaching to level of circular canal; thick, cushion-shaped and projecting deeply into subumbrella, surface smooth, usually without adaxial furrow except in a few animals (and only in 1-2 of the four gonads). Observed egg numbers per gonad about 40. Marginal tentacles 4, between each pair of tentacles 3 small, rudimentary bulbs without tentacles. Tentacles with solid endodermis. Tentaculate bulbs with 3-8 lateral cirri, no cirri on rudimentary bulbs. Tentacular bulbs on abaxial side with a large, conspicuous, black pigment spot. Per quadrant 2-3 statocysts, thus 8-12 in total, each with 1-3 concretions, mostly 2 or 3.

Medusa buds never present.

Nematocysts (preserved material): atrichous isorhizas in tentacles, almond-shaped, size very variable and perhaps 2 size classes, (2.5-3.5)x(7.5-11) μm; mainly in tentacle bulbs, large, curved holotrichous isorhizas, end opposite thread opening pointed, spines of thread tiny and hardly visible under light microscopy, capsule size (4-5.5)x(25- 26) μm. Presence of other types cannot be excluded for the examined material (2 medusae).

Distribution: Indian Ocean, Red Sea, western Pacific, eastern Pacific ( Altuna, 2009), perhaps introduced in the north-eastern Atlantic ( Altuna, 2009; Brylinski et al., 2016). Type locality: Nancowry Harbour, Nicobar Islands.

Discussion: The material from New Zealand was identified as E. menoni because DNA sequences of part of the present material have already been published under this name and also because it mostly matched the diagnosis given in Bouillon & Barnett (1999). However, the identity is not entirely clear and it could as well be attributed to Lovenella assimilis ( Browne, 1905) as has been argued in detail by Brylinski et al. (2016). Eucheilota menoni and Lovenella assimilis are indeed rather difficult to separate ( Bouillon, 1984). Bouillon has reportedly seen both species in Papua New Guinea and he summarised the diagnostic differences of Lovenella assimilis and E. menoni as follows (in brackets the condition observed in the present material): - 12 to 20 statocysts versus 8 only (8-12)

- no black pigment on the manubrium versus black dots on manubrium (no dots on manubrium)

- gonads with a longitudinal furrow versus smooth gonads (smooth)

- gonads reaching to bell margin versus gonads reaching close to bell margin (to bell margin).

Lovenella assimilis has two concretions per statocyst ( Browne, 1905b). Kramp (1959b) could not observe the concretions in his material of E. menoni , but in Kramp (1961) he states that there is one concretion only. It could be that he took this from Menon (1932) who described a similar medusa that Kramp thought to be E. menoni . The NZ animals had 1-3 concretion, mostly 2-3.

Browne’s type material of Lovenella assimilis could not be obtained for study, but it is clear from Browne (1905b) that he had a preserved medusa that had lost its pigmentation. This makes L. assimilis de facto a “ species inquirenda ”, a species that is currently not unambiguously identifiable.

The nematocysts of these two nominal species have been documented by Bouillon (1984), Bouillon et al. (1988), Hirano & Yamada (1985), and Altuna (2009). Comparing the results is inconclusive and the interpretation of the capsule types is occasionally subjective.

Bouillon also observed medusa buds in both morphotypes, something never observed by other authors.

To conclude, the present material is not unambiguously attributable to either E. menoni or L. assimilis and this is also the case for the European material described by Altuna (2009) and Brylinski et al. (2016). As already concluded by the latter authors, it is likely that both nominal species as used today are in fact conspecific. Another possibility is that there are more than two species involved and that they all intergrade morphologically. In order to resolve the ambiguity, more specimens of both morphotypes obtained from the western Indian Ocean must be examined morphologically and genetically.

It might seem surprising that two nominal species that are hardly distinguishable have been attributed to two different genera. The medusae of the genus Lovenella differ from Eucheilota by their number of statocysts, 16-32 versus 4-12 ( Kramp, 1968; Bouillon et al., 2006). This seems rather arbitrary, but the separation stems from Lovenella Hincks, 1868 being polyp-based, while Eucheilota McCrady, 1859 is based on a medusa. A re-assessment of the classification is clearly needed ( Cornelius, 1995), and Lovenella should be regarded a synonym of Eucheilota .

Family Malagazziidae Bouillon, 1984 Genus Octophialucium Kramp, 1955