Symplectoscyphus trabeculatus, Cantero, 2023

Cantero, Álvaro Luis Peña, 2023, On some benthic hydroids from New Zealand deep waters, with the description of a new species, Zootaxa 5389 (2), pp. 241-252 : 247-250

Symplectoscyphus trabeculatus sp. nov.

( Figs. 5–6 )

Material examined. I666, a mass of stems 20 mm in diameter, with gonothecae (Holotype, NIWA 15839 ) .

Description. A mass of monosiphonic stems and branches 20 mm in diameter. Some anastomoses between branches present. Stems and branches divided into internodes by slightly marked perisarc constrictions. Internodes slightly geniculate. Branching every third hydrotheca, alternate, more or less in one plane. Internodes giving rise to branches with a short apophysis supporting lower-order branch on convex side, below hydrotheca.

Hydrothecae arranged alternately, roughly in one plane, abcaudally curved, usually with an inflexion point where adcauline wall becomes free. Hydrotheca adnate to internode for more than half its adcauline wall. Maximum diameter by the middle, approximately at inflexion point, slightly decreasing towards aperture, more markedly to base. Free part of adcauline wall straight or slightly convex; adnate part somewhat convex. Abcauline wall slightly concave by the middle, but basal half somewhat convex. Hydrothecal aperture directed up- and outwards. Rim of hydrothecal aperture provided with three blunt cusps separated by relatively shallow embayments; adcauline cusp straight. Rim of aperture typically with several short renovations.

Gonothecae ovoid, wall with around 11–12 complete, independent, well-marked rings, not forming an extensive frill outwards and with trabecular structure. Gonothecal aperture circular, placed at end of a relatively large distal funnel, much wider than high.

Measurements (in µm). Internodes: length 665–1125, diameter at hydrothecal base 250–325. Hydrotheca: abcauline length 390–400, free adcauline length 200–240, adnate adcauline length 325–360, adcauline length 500–575, diameter at aperture 200–220, diameter at diaphragm 125–150, maximum diameter 225–250. Gonotheca: height 1150–1200 (including funnel), maximum diameter 600–720, aperture 230–245, funnel height 110–150. Cnidome: larger microbasic mastigophores 11.1±0.3 x 2.8±0.3 (n= 10), range 10.5–11.5 x 2.5–3.0.

Remarks. The general appearance of the colony is bushy, but there is a distinct difference between the basal part of the stems, where the perisarc is quite thick, and their distal parts, where it is much less developed. In some gonothecae the most distal ring is not completely formed, giving rise to a sort of step before the funnel (fig. 6d), which makes the funnel apparently higher than in most gonothecae (fig. 5f–g).

The gonotheca of Symplectoscyphus trabeculatus sp. nov. is clearly different from that present in other species of the genus. Even when the gonotheca is provided with rings, as in a group of Symplectoscyphus species, in Symplectoscyphus trabeculatus sp. nov. the rings are independent, not forming the spiral pattern present in some species, and do not form the outward extension or frill that typically characterises others. Furthermore, the relatively large, conspicuous distal neck bearing the gonothecal aperture may be characterised as relatively low and wide, shorter and wider than in other species of the genus. Finally, the rings are characterised by having a conspicuous trabecular structure (fig. 5h).

The morphologically closer species would be Symplectoscyphus johnstoni ( Gray, 1843) and Symplectoscyphus tuba Totton, 1930 . Symplectoscyphus johnstoni has a somewhat similar hydrothecal shape, but the gonotheca, also ringed, is completely different, elongated and with the aperture on a small conical tube-like neck, eccentrically located on the sloping and flattened distal end.

Symplectoscyphus trabeculatus sp. nov. is allied to S. tuba in the general appearance of the gonotheca. However, in the gonotheca of S. tuba the rings extend outwards, with their flanges upturned, and the neck is higher and markedly widens distally. Symplectoscyphus tuba is also characterised by having long and slender internodes and a hydrotheca adnate for about half its adcauline length.

Ecology and distribution. Symplectoscyphus trabeculatus sp. nov. was collected at a depth of 1165 m, east off Bounty Islands.

Etymology. The specific name trabeculatus is formed with the Latin suffix –atus and refers to the trabecular structure of the gonothecal rings.

Figures

FIGURE 5. (a–h) Symplectoscyphus trabeculatus sp. nov.: a, hydrotheca and origin of branch; b–e, hydrothecae (arrow in c pointing to band of desmocytes); f, gonotheca; g, distal part of gonotheca with detail of funnel; h, trabecular structure of gonothecal rings (arrow). Scale bar: 50 µm (h), 100 µm (e, g), 200 µm (a–d, f); (all photographs from the holotype, NIWA 15839).

FIGURE 6. (a–d) Symplectoscyphus trabeculatus sp. nov.: a, internode with hydrotheca; b, fragment of stem showing hydrothecae and origin of branch; c, fragment of stem showing hydrothecae; d, gonotheca. Scale bar: 250 µm (all drawings from the holotype, NIWA 15839).