Aequorea macrodactyla (Brandt, 1835)

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 : 368-369

Mesonema (Mesonema) macrodactyla Brandt, 1835: 221 . ‒

Brandt, 1838: 359, pl. 4 figs 1-3.

Polycanna purpurostoma Agassiz & Mayer, 1899: 169 , pl. 8

figs 26-28.

Aequorea maldivensis Browne, 1905a: 732 , pl. 56, figs 4-12.

Mesonema macrodactylum . ‒ Maas, 1905: 40, pl. 8 fig. 52.

Aequorea macrodactylum . ‒ Bigelow, 1909: 174, pl. 36. ‒ Bige-

low, 1928: 313, pl. 43 fig. 7.

Aequorea pensilis .– in part Russell, 1953: 355, fig. 220C-D, 225, pl. 33 figs 1-5 [not Aequorea pensilis ( Haeckel, 1879) ]

Aequorea macrodactyla . – Kramp, 1959 a: 167, fig. 235. – Kramp, 1961: 207, synonymy. ‒ Kramp, 1965: 87, fig. 8. ‒ Kramp, 1968: 98, fig. 267. – Pagès et al., 1992: 26, fig. 26. – Cornelius, 1995: 208, fig. 48D-E. ‒ Bouillon & Barnett, 1999: 79, fig. 71. ‒ Mizrahi et al., 2015: 59, fig. 1A-D.

? Aequorea macrodactyla . – Nogueira et al., 2016: fig. 1.

Material examined: NIWA 119801; 8 medusae; from sediment trap in 360 m depth deployed north of Hauraki Gulf, New Zealand, - 35.0867°S 174.8833°E, sampling period 28.11. 1996 to 05.02.1997; very well-preserved in formalin, 7-30 mm diameter, gonads developed after reaching bell diameters of 20 mm.

Diagnosis: Umbrella diameter when mature 20-75 mm, central jelly thick, lens-shaped, margin thin; with conical jelly filling stomach (1/2 subumbrella height); velum spanning about 1/5 of umbrellar opening. Stomach about 2/3 as wide as umbrella, funnel-shaped, mouth region much folded, about as many folds as radial canals. 60-100 (max. 150) radial canals; gonads extending along radial canals from close to circular canal to base of the stomach (and conical jelly). Much fewer tentacles than radial canals, only 10-30 marginal tentacles of variable lengths, all with conspicuous bulbs of variable sizes, also many bulbs without tentacles, but many radial (>50%) canals end in no bulbs. Marginal bulbs characteristically broad and with rounded abaxial keel clasping the bell margin, with excretory papilla on subumbrellar side. Statocysts below circular canal, numerous, 1-3 between two radial canals, 2-5 concretions per statocyst. Colours: stomach wall pink, gonads greyish-blue or violet (after Kramp, 1965, 1968; Pagès et al., 1992; own observations).

Polyp stage unknown. Nematocysts see Russell (1939, as A. pensilis ).

Distribution: Circumglobal, widely distributed in tropical and temperate regions of the Indo-Pacific, less common in the Atlantic Ocean, perhaps introduced in the Mediterranean ( Kramp, 1965; Pages et al., 1992; Mizrahi et al., 2015; Nogueira et al., 2016, the latter with a map and many references of records). Type locality: Equatorial Pacific.

It is rather frequent at depths from the surface to 2000 m, but even sampling with cable lengths of 4000 m yielded specimens ( Kramp, 1965).

Remarks: The relatively low tentacle number combined with the diagnostic broad marginal bulbs with an abaxial keel ( Fig. 17 C-D) allows a reliable identification of this species, notably to separate it from A. pensilis ( Haeckel, 1879) and A. krampi Bouillon, 1984 . Identifying Aequorea species is currently rather difficult (comp. e.g. Arai & Brinckmann-Voss, 1980; Gershwin et al., 2010) and a taxonomic revision based on a worldwide study comparing morphotypes and DNA markers is highly desirable.

Aequorea macrodactyla has been recorded from New Zealand before ( Kramp, 1965; Bouillon & Barnett, 1999), but the good preservation of the specimens permitted the illustration of some structural details ( Fig. 17 A-D). As in other Aequorea species, the stomach is very wide but relatively shallow and it almost covers the conical jelly that hangs down from the subumbrella like a gastric peduncle.

Figures

Fig. 17. Aequorea macrodactyla, bell diameter about 26 mm, about 70 radial canals, after preserved specimen. (A) Lateral view, left half shown as with umbrella cut away. (B) Oral view. (C) Bell margin seen from outside, note characteristic shape of tentacle bulb. (D) Bell margin seen from inside the bell, note the excretory papilla (arrow, ep). Other abbreviations: cc ‒ circular canal, ex ‒ exumbrella, statocyst, v ‒ velum.