Antennella flava, Galea & Maggioni, 2024

Galea, Horia R. & Maggioni, Davide, 2024, On some tropical hydroids (Cnidaria: Hydrozoa), with descriptions of four new species, Zootaxa 5428 (1), pp. 1-57 : 26-28

Antennella flava , sp. nov.

urn:lsid:zoobank.org:act:5667E806-2C12-40C6-82E0-2A8F7B187DCC

Figs 19 , 20 , 32 ; Table 2

Material examined. Holotype: MSNMCoe371 , Indonesia, Bali, Tulamben, dive site known as “ Seraya ”, -8.295692°, 115.612838°, 15–20 m, 23 Apr 2023, fertile colony on Halimeda sp. with stems up to 1 cm high, many bearing gonothecae of both sexes .— Paratype: MSNMCoe372, Indonesia, Bali, Tulamben, dive site known as “Seraya”, -8.295692°, 115.612838°, 20 m, 16 Apr 2023, colony on Halimeda sp. with stems up to 1.1 cm high, some bearing very incipient gonothecae, GenBank: OR872074 (16S), OR872013 (18S), OR872034 (28S). Comparative material [ Antennella secundaria ( Gmelin, 1791) ]: HRG-0124, France, La Ciotat, Mugel creek, 43.164097°, 5.607644°, 0.5 m, 05 Aug 2009, fully fertile colony on alga. —HRG-0153, France, Le Pradet, 43.194122°, 6.023140°, 1 m, 27 Aug 2008, colony with incipient gonothecae on alga.

Description. Colonies arising from branched, anastomosed stolonal fibers creeping on Halimeda sp. (Chlorophyta: Ulvophyceae: Bryopsidales : Halimedaceae ); no nematothecae on hydrorhiza; stems borne on short apophyses given off from hydrorhiza; simple (unramified), up to 1.1 cm high, composed of a proximal, ahydrothecate portion, and a much longer, distal, hydrothecate part, the latter sometimes showing apical stolonization; proximal portion comprising 1–3 internodes of varied length, each bearing a few frontal nematothecae in a row, internodes separated by transverse nodes, except for the distalmost node that is an oblique hinge joint, allowing the stem to move freely in the current; distal cauline part heteromerously divided into a regular succession of hydrothecate and ahydrothecate internodes, proximal most internode always hydrothecate; the latter, with an oblique node proximally and a transverse counterpart distally; ahydrothecate internodes with nodes in the reverse position; oblique nodes always deeply-incised, transverse nodes distinctly marked in front of the stem, fading away backwards; internodes relatively short, ahydrothecate ones as long or slightly longer than the hydrothecate ones; the latter, bearing a hydrotheca (and its associated nematothecae) in their middle portion, leaving distally a free portion of varied length; ahydrothecate internodes with commonly two (exceptionally three) frontal nematothecae, each placed towards one end. Hydrothecae cup-shaped, relatively deep, adnate for about half their length to the internode behind, wall cylindrical in lateral view; abcauline side relatively thickened, of a slightly sigmoid appearance, being concave proximally and convex distally, giving the hydrothecal aperture a slightly flared appearance abaxially; adnate adcauline wall and hydrothecal floor continuous and of a concave appearance, with relatively thickened perisarc; free part of the adaxial wall almost straight; hydrothecal aperture set at a right angle to the long axis of the theca, circular in apical view, rim even; hydropore eccentrically-placed, adjacent to the abcauline wall, where it occasionally forms a small, inner perisarc thickening; four nematothecae associated to each hydrotheca: a mesial, a pair of laterals, and an axillar one; all nematothecae bithalamic and movable, mesial and axillar sessile, laterals borne on well-developed, cylindrical apophyses flanking the hydrotheca; basal chamber taller than the upper chamber; adaxial wall of the latter distinctly lowered, notably in the axillar nematothecae, where it reaches the inner annular thickening separating the two chambers; lateral nematothecae reaching the hydrothecal rim, adaxial wall sinusoid, with a central, rounded cusp separated laterally from the abaxial side by 2 rounded embayments; axillar nematothecae smaller than all their counterparts; cauline nematothecae sessile, similar to the laterals of the hydrotheca, but upper chambers with walls simply lowered on adaxial side. All hydranths retracted within their corresponding hydrothecae, their tentacle number cannot be ascertained. Colonies monoecious, female gonothecae occurring proximally on stems, the male ones more distally; gonothecae sexually dimorphic, though not differing fundamentally in shape; borne laterally, usually singly, from below the hydrothecal bases, on short, cylindrical stem apophyses; a short, intermediate internode (delimited at both ends by transverse nodes) at the base of the gonotheca proper; gonothecae piriform, tapering proximally and there with a distinct bent; distally rounded; female with an articulate, glass-watch-shaped operculum closing a wide, circular aperture; males with comparatively narrower apertures closed by thin perisarc layer; a basal pair of nematothecae in both sexes, thecae similar to the cauline ones, but proportionally bigger. Almost all female gonothecae spent, the structure of the gonophore could not be ascertained. Coenosarc of the colony with numerous, spherical zooxanthellae (with large nuclei surrounded by numerous small chloroplasts filling the whole cytoplasm) and unidentified, formless, vacuolated bodies of unknown nature and function.

Cnidome ( Fig. 20I ): large, ovoid pseudostenoteles [(16.6–17.4) × (6.2–6.8) µm, some seen discharged], banana-shaped microbasic mastigophores [(5.9–6.2) × (2.1–2.2) µm, none seen discharged], and small, eggshaped microbasic heteronemes with a distal, eccentric, small prominence [(4.1–4.7) × (2.8–3.1) µm, none seen discharged].

Color in life ( Fig. 19 ): yellow, due to the presence of zooxanthellae in the coenosarc.

Remarks. The new species comes close to A. secundaria ( Gmelin, 1791) , but the intense, unmistakable yellow color of its stems is distinctive, while Mediterranean (type locality) specimens of the latter are translucent-white in life (Galea, pers. obs.). Antennella flava sp. nov. is also genetically divergent from all other halopteridid species (including A. secundaria , with which it forms a sister-group relationship) and other A. secundaria -like specimens ( Fig. 32 ).

Morphologically, however, there are almost no salient features allowing a reliable distinction between A. flava and A. secundaria . However, the examination of two samples of A. secundaria from southern France (HRG-0124 and -0153) revealed that the lateral nematothecae have the adaxial walls of their upper chamber simply lowered, not adopting a marked sinusoid shape as in the new species. Schuchert (1997: 15) also noted that his NE Atlantic specimens of A. secundaria had the “inner side of the wall of upper chamber lowered almost to bottom”, Peña Cantero & García Carrascosa (2002: fig. 18F) depicted lateral nematothecae with adaxially lowered walls in their Mediterranean material, and Medel & Vervoort (1995: 35, fig. 14B) described and illustrated nematothecae “with shallow adcauline embayment” in specimens from around the Strait of Gibraltar.

When fixed material of A. flava is examined, the abundant presence of zooxanthellae in the coenosarc indicates that living stems must show some coloration. On the other hand, the examination of the Mediterranean material at hand, however, demonstrated that A. secundaria does have zooxanthellae, as well, but their number is comparatively lower, and the pigment they produce does not confer the stems a notable coloration in life.

There are two Australian records of short-stemmed A. secundaria -like congeners exhibiting either a “golden yellow” ( Watson 2002: 347) or a “golden brown” ( Watson 2005: 537) coloration when alive. Their relationship to the new species could not be established strictly based on morphological grounds.

Etymology. From the Latin flavus, -a, -um, meaning yellow, to describe its color in life.

Distribution. Only known from Bali, Indonesia.

Figures

FIGURE 19. Antennella flava, sp. nov. Holotype colony in situ (A), shortly after collection (B), and detail showing zooxanthellae and vacuolar inclusions in the coenosarc (B, insert).

FIGURE 20. Antennella flava, sp. nov. Portions of stems in lateral (A, B) and frontal (C) views. Stem (D), mesial (E), lateral and axillar (F) nematothecae. Female (G) and male (H) gonothecae. Cnidome (I). From samples MSNMCoe371 (A, G, H), MSNMCoe372 (B–F). Scale bars: 10 µm = I; 200 µm = A–H.

FIGURE 32. Phylogenetic hypothesis of the family Halopterididae based on the 16S rRNA region. Numbers at nodes represent BPP and MLBS, respectively. N.B.: According to Galea et al. (2021: 341), Antennella varians (Billard, 1911b) MF784528 should be correctly regarded as A. billardi Galea (in Galea et al.), 2021. Sequences MF784526 and MF784531, identified in GenBank as Halopteris sibogae (Billard, 1913) (Galea et al. 2018: fig. 9), should bear the recently-introduced taxon name, H. longibrachia Calder & Faucci, 2021.