Glaciambulata neumayeri Galea, Roder, Walcher, Warmuth, Kohlberg & Fischer

Glaciambulata neumayeri Galea, Roder, Walcher, Warmuth, Kohlberg & Fischer, gen. et sp. nov.

urn:lsid:zoobank.org:act:9DBB7DC2-6BEB-42DF-BFCB-0A3B0193AB41

Figs 1–3

Diagnosis

As for the genus.

Etymology

The species is named after the German Antarctic Station Neumayer III, the platform for all diving operations, from the vicinity of which the new medusa was discovered.

Material examined Holotype

ANTARCTICA: ³, umbrella (U) = 6 mm wide, total diameter of medusa (D) from tip to tip of opposite tentacles = 17 mm, Atka Bay, 7–9 m, -70.533, -8.055, 12 Dec. 2015 (MHNG-INVE-93880), the medusa was attached to the last, hence youngest, stratum of the sub-ice platelet layer.

Paratypes (station data as for holotype)

ANTARCTICA: 1 ³, U = 4 mm, D = 12 mm, 7–9 m, 12 Dec. 2015 (MHNG-INVE-93881); 2 medusae [♀: U = 5 mm, D = 16 mm; ³: U = 4 mm, D = not available (N.A.)], 0 m, 18 Dec. 2015 (MHNG- INVE-93882); 2 medusae (♀: U = 4.5 mm, D = 19 mm; ♀: U = 4 mm, D = N.A.), 12 m, 18 Dec. 2015 (MHNG-INVE-93883); 2 medusae (♀: U = 5 mm, D = 15 mm; ³: U = 4 mm, D = N.A.), 23 m, 18 Dec. 2015 (MHNG-INVE-93884); two medusae (³: U = 4 mm, D = 12 mm; ³: U = 3 mm, D = 10 mm), 5 m, 24 Dec. 2015 (MHNG-INVE-93886); 1 ³ medusa (U = 4 mm, D = 12 mm), 25 m, 24 Dec. 2015 (MHNG-INVE-93885); 1 ♀ medusa (U = 5 mm, D = 16 mm), 25 m, 27 Dec. 2015 (MHNG- INVE-93887).

Description

Medusa up to 19 mm wide from tip to tip of opposite tentacles (Fig. 1 C). Umbrella up to 6 mm in diameter, watch glass-shaped, evenly rounded, without marginal lobes (Fig. 1 D–E). Mesoglea thin, thickening abruptly towards the margin, so as to accommodate a conspicuous belt of chordal cells, on which the tentacles are inserted; belt elongated-ovoid in cross section (Fig. 3 G). Exumbrellar surface smooth, devoid of ribs and grooves; epidermis with scattered nematocysts. Manubrium eight-lobed in proximal half, quadrangular in distal half, projecting beyond aperture of subumbrella; gastric cavity with smooth (Fig. 1 G) to slightly convoluted surface (Fig. 1 F); mouth squared in contracted state (Figs 1 G, 2E–F), and polygonal to almost rounded when distended (Fig. 1 F); 4 simple lips (Fig. 2 E–F), devoid of nematocysts, but containing numerous ciliated cells in epidermis. Eight broad, laterally Fattened radial canals (Figs 1 D–E, 2B), whose position coincides with that of the manubrial lobes, connect to an equally broad, circular canal, with thickened, granular walls (Fig. 2 B), and an oral-aboral Fattened lumen (Fig. 3 G). Centripetal canals absent. Eight well-developed, triangularly-shaped mesenteries connect each manubrial lobe to the subumbrella along each radial canal (Fig. 2 G–H). Tentacles solid, circular in cross section; two types: Fliform and adhesive. Filiform tentacles (Fig. 1 C, E–F) slightly constricted at origin (Fig. 2 A), then swollen and tapering gradually towards their tips; provided with successive, closely-set rings of nematocysts in epidermis throughout their length (Fig. 2 D); very contractile due to the presence of numerous, longitudinal myoepithelial cells; core composed of a mosaic of large, vacuolated cells (best seen in cross section), characteristically stacked along tentacle (particularly obvious in lateral view of tentacle). Adhesive tentacles stout and comparatively shorter than their Fliform counterparts (Fig. 1 F–G), with similar internal structure, but epidermis with only very scattered nematocysts; distal ends with an adhesive pad (Fig. 2 C). Sixteen groups of tentacles originate from the bell margin: 8 are perradial and 8 interradial (Fig. 1 D); each group composed of (at least) three horizontal rows of superimposed tentacles; an aboral view of the exumbrella identiFes each group through the presence of three large, adjacent, Fliform tentacles, pointing both outwards and aborally, and representing the two proximal, aboral rows, their bases forming a triangle (Figs 1 D, 2A, 3C); a third, more distal row, inserts close to lower side of umbrella margin, and is composed of a number of alternating adhesive and Fliform tentacles, the latter being comparatively shorter than their counterparts from the two rows above (Figs 1 F–G; 3D); two adjacent adhesive tentacles in each group are typically perradial (Figs 1 G; 3D); number of additional tentacles in each group varied, and impossible to ascertain due to their crowded condition; however, 2–4 adhesive (exclusive of the perradial ones) and 2–4 Fliform tentacles occur within each octant; the outermost adhesive tentacles (exclusive of the perradial ones) on both sides of each octant bear a free, ecto-endodermal statocyst at their bases (Fig. 3 E–F); consequently, each medusa is provided with 16 of these sensory structures; statocysts small, short-stalked, with single, spherical statolith (Fig. 2 I–K). A conspicuous and continuous cushion of nematocysts (Figs 1 F–G, 2I), the insertion point of which is situated on the inner side of the distalmost row of tentacles, projects into the subumbrella and cups the lower side of the circular canal (Fig. 3 G, n.r.). A velum is absent, with not even a vestige discernible. The gonads develop on each manubrial lobe; 8 broadly ovoid pairs are distinguished; members of each pair are separated by a mesentery (Figs 2 G–H, 3B); male gonads smooth-walled, comprising a translucent, moderately thick layer of sperm cells (Fig. 1 G); female gonads with bumped surface (Fig. 2 G), oocytes rather small and numerous, though their precise number could not be ascertained in Fxed material. Cnidome (measurements given for undischarged capsules): 1) microbasic euryteles [7.69–8.04 µm long (7.87±0.18 µm, n=17), 4.89–5.59 µm wide (5.17±0.18 µm, n=17)], in tentacles and also scattered in exumbrella (Fig. 2 L6–8); 2) two size classes of stenoteles (in exumbrella, tentacles, outer wall of manubrium, gonads, and mesenteries), viz. small, ovoid capsules [8.04–10.13 µm long (9.01±0.62 µm, n=19), 7.34–9.44 µm wide (7.98±0.61 µm, n=19)] (Fig. 2 L4, 5) and large, nearly spherical capsules [12.28–15.73 µm long (14.44±1.22 µm, n=16), 11.88–15.73 µm wide (14.28±1.40 µm, n=16)] (Fig. 2 L1–3). Color: mesoglea and tentacles translucent; walls of radial and circular canals crowded with white pigment granules; gonads, manubrium, and nematocyst ring milky-white.

Remarks

There is generally one statocyst at the base of each of the outermost adhesive tentacle (exclusive of the perradial ones) in each octant. However, two exceptions to this rule have been observed: 1) a couple of statocysts occurred concomitantly in association with the insertion point of an adhesive tentacle; 2) a statocyst arose at the base of a Fliform, instead of an adhesive, tentacle.

The tentacle arrangement illustrated in Fig. 3 F exempliFes the case of a single specimen provided with a fair number of tentacles, and whose proper observations were possible due to its remarkable state of relaxation. However, the possibility cannot be excluded that, in medusae with a more signiFcant number of tentacles, their arrangement may extend to more than three superimposed rows. Such specimens occur in the present collection, but the number and crowded condition of their tentacles prevented us from making accurate observations without injuring them.

The microbasic euryteles are tear drop-shaped and contain a short shaft with a thread forming four complete coils (Fig. 2 L6, 7). No evaginated capsules were observed in Fxed material, but their discharge was obtained upon a brief treatment with domestic bleach. In this case, a distally-swollen shaft, about as long as the capsule itself, bearing a few prominent spines apically, and with a long, distal thread covered with a succession of minute, closely-set, spirally-coiled spines, appeared (Fig. 2 L8). These capsules proved identical to those described and illustrated by Hesthagen (1971) in Tesserogastria musculosa Beyer, 1959, and are, most probably, of the same type as those found in Ptychogastria polaris Allman, 1878 (Panteleeva et al. 1999).

Through the courtesy of Peter Schuchert of MHNG, the 16S and COI sequences of Glaciambulata neumayeri gen. et sp. nov. will be published on GenBank, once both the generic and speciFc names become available.

Ecology

Individuals were encountered attached upside down to the ice disks of the lowermost stratum of the subice platelet layer. Their distribution was patchy, ranging from areas devoid of animals to densities of up to 200 individuals/m2. The uppermost, Fliform tentacles were typically extended into the underlying water column, undulating under the impact of water motion, while their adhesive counterparts were Frmly attached to the ice discs. The medusae could only be relocated from the ice by melting the substratum. Their mouths were stuck out towards the ice disks, and it is likely that the animals feed by grazing on algae and bacteria. The animals appeared to be incapable of swimming as they would sink immediately when detached from their ice disks. A perceptible movement, i.e. crawling, was not observed in situ, but was nevertheless evident in aquaria, where individuals held for other purposes changed positions within the tanks overnight.

Distribution

Known only from Atka Bay, eastern Weddell Sea (present study).