Zygophylax niger Galea, 2019

Galea, Horia R. & Schuchert, Peter, 2019, Some thecate hydroids (Cnidaria: Hydrozoa) from off New Caledonia collected during KANACONO and KANADEEP expeditions of the French Tropical Deep-Sea Benthos Program, European Journal of Taxonomy 562, pp. 1-70 : 56-61

Zygophylax niger Galea , sp. nov.

urn:lsid:zoobank.org:act:5ED994EF-6147-4508-9C5B-7DDF69E72D8C

Figs 16 F–G, 19; Tables 13–14

Diagnosis

Colonies flabellate, with much branched, heavily-fascicled stems. Division into internodes indistinct, but equivalents of internodes with a proximal cladial apophysis and its associated axillary hydrotheca, two alternate hydrothecae above, and a second cladial apophysis, given off on side opposite to the preceding one; hydrothecae long, tubular, with slightly everted, circular margin, tapering in lower third into long, proximally annulated pedicel. No nematothecae on the hydrothecal apophyses. Gonothecae aggregated into long masses of coppinia around the side branches, but neither fused, nor appressed against each other; long, tubular, walls slightly wrinkled, basally tapering into minute pedicel, distally truncate.

Etymology

From the Latin ‘ nĭgĕr ’, meaning ‘black’ or ‘dark’, to emphasize the color of its colonies.

Material examined

Holotype

PACIFIC OCEAN • a fertile colony, 7.5 × 7.5 cm; off New Caledonia, stn DW4742; 22°53′ S, 167°37′ E; 290–345 m; 23 Aug. 2016; KANACONO leg.; MNHN-IK-2015-478.

Paratype

PACIFIC OCEAN • a fertile colony, 6.5 × 5 cm; off New Caledonia, stn DW4742; 22°53′ S, 167°37′ E; 290–345 m; 23 Aug. 2016; KANACONO leg.; MNHN-IK-2015-480.

Additional material

PACIFIC OCEAN • four colonies (of which the largest is 8 × 8.5 cm), as well as a few smaller fragments, all without gonothecae; off New Caledonia, stn DW4742; 22°53′ S, 167°37′ E; 290–345 m; 23 Aug. 2016; KANACONO leg.; a fragment from one colony was used for DNA extraction, DNA 1396; voucher MHNG-INVE- 120856; barcode identifier MK 073108 ; MNHN-IK-2015-481 • three colonies, 10.5 × 6 cm (now broken into three pieces, without gonothecae), 6.5 × 5 cm (fertile, now broken into two pieces) and 10.5 × 5.5 cm (now broken into three pieces, without gonothecae); off New Caledonia, stn CP4779; 23°02′ S, 168°17′ E; 270–293 m; 28 Aug. 2016; KANACONO leg.; a small fragment detached from one of these colonies was used for DNA extraction, DNA 1395; voucher MHNG- INVE- 120855; barcode identifier MK 073107 ; MNHN-IK-2015-479 • a colony fragment, 6.5× 4.5 cm, without gonothecae; off New Caledonia, stn CP4786; 22°46′ S, 167°42′ E; 350–469 m; 29 Aug. 2016; KANACONO leg.; MNHN-IK-2015-482 .

Description

Colonies flabellate, up to 10.5 cm high, arising from root-like hydrorhiza, firmly attached to the substrate. Main stem branched irregularly, with up to 5 th order side branches; stem and branches heavily fascicled for most of their length, grading to monosiphonic distally; stems up to 3 mm thick basally. Perisarc dark in fascicled parts, brownish in monosiphonic ones. Stem divided into indistinct internodes with the following sequence: a prominent, proximal apophysis (supporting a cladium) and its associated axillary hydrotheca (itself borne on a short, distinct apophysis), followed by two alternate hydrothecae above (each borne on a short stem apophysis), and a second, distal, apophysis (supporting following cladium), together with its associated hydrotheca (itself borne on a stem apophysis). Cladia alternate, monosiphonic, divided through generally indistinct, slightly oblique nodes into moderately-long internodes bearing distally a short apophysis supporting a hydrotheca; apophyses alternate, coplanar; cladia with up to 13 hydrothecate internodes; first internode with a couple of spiral twists basally. Hydrothecae borne on relatively long pedicels, invariably annulated basally (usually two, but up to four annuli observed), but also distally (0–4 annuli), occasionally in middle. Hydrotheca cup-shaped, elongated, proximal ⅓ tapering gradually below, distal ⅔ tubular; aperture circular, rim slightly but distinctly everted, margin smooth; perisarc thin and smooth; hydrotheca delimited basally from pedicel by thin diaphragm. Hydranths with ca 16 filiform tentacles, with no caecum. Nematothecae absent throughout. Gonothecae grouped in certain parts of the colonies, but independent from each other (neither contiguous, nor fused), arising from accessory tubes of the side branches; long, tubular, slightly curved in middle part, tapering below, distally truncate, walls undulated, perisarc rather thick and dark brown. No nematophorous ramuli amongst the gonothecae.

Remarks

The gonosome of the new species shows striking resemblances to that of Z. polycarpa Vervoort & Watson, 2003 , a species discovered from off Three Kings Island, New Zealand. Indeed, coppinia of

both species are composed of loosely-packed, separate, elongated, tubular gonothecae, and are devoid of nematophorous structures. However, Z. polycarpa possesses sessile, and comparatively shorter and broader hydrothecae, not perfectly symmetrical, but rather convex, especially on adaxial side ( Vervoort & Watson 2003).

The differences to Z. niger sp. nov. of the congeners displaying both hydrothecae borne on long pedicels and separate, loosely-aggregated gonothecae, are summarized in Table 14 .

The trophosome of Z. tottoni Rees & Vervoort, 1987 , a species from off Oman with a so far unknown gonosome, shows a few similarities to that of Z. niger sp. nov., notably the mode of branching of its stems, the shape of its hydrothecae, and the presence of rather long hydrothecal pedicels. However, the latter does not possess proximally the distinctive basal annuli, its hydrothecae are comparatively shorter and narrower, and there is one nematotheca on frontal side of each apophysis supporting a hydrotheca ( Rees & Vervoort 1987).

Distribution

Only known from off New Caledonia (present study).

Molecular study

For 30 samples described in this study it was possible to obtain about 600 bp of the mitochondrial 16S gene sequence that could be compared in a maximum likelihood tree ( Fig. 20 ). All sequences were initially compared to all GenBank sequences using BlastN ( Johnson et al. 2008). This allowed to control whether each new sequence was, indeed, of hydrozoan origin, and concomitantly identified closelyrelated sequences that proved important for subsequent comparisons. A total of 90 sequences were thus aligned and used to determine the optimal probabilistic model of sequence evolution, as well as to make the phylogenetic analyses. The optimal substitution model suggested was GTR+I+G. There was no need to remove regions with uncertain alignments, as there were few such regions, and their exclusion did not alter the results significantly. The resulting maximum likelihood tree has numerous unresolved basal nodes, but several families appear in well supported clades (> 70% bootstrap support: Syntheciidae , Symplectoscyphidae , Lafoeidae , Sertularellidae , Staurothecidae , and Zygophylacidae ). The family Sertulariidae sensu Maronna et al. (2016) appears also as clade, but with insufficient bootstrap support (58%).

Taxonomically noteworthy results are as follows:

- two species of Caledoniana and two of Solenoscyphus are more closely-related to the Staurothecidae than to Sertulariidae . Only Solenoscyphus decidualis mapped outside the Solenoscyphus and Staurothecidae clades, but without any supported relationship to other taxa;

- Billardia hyalina and B. subrufa (Jäderholm, 1904) ( FN424117 ) are deeply embedded in the well supported Syntheciidae clade;

- the four Hincksella species dealt with herein do not group into a common clade, but are scattered over the whole tree. The type species of the genus ( H. sibogae ; see Totton 1930) associates with Zygophylax , but the node support is not significant;

- Dictyocladium reticulatum clusters with the Symplectoscyphidae ;

- Symplectoscyphus acutustriatus sp. nov. is deeply embedded in the clade Sertularellidae and not in Symplectoscyphidae , the parent taxon of the genus Symplectoscyphus .

Figures

Fig. 16. A.? Symplectoscyphus acutustriatus Galea, sp. nov., holotype colony, MNHN- IK-2015-460. — B.? Symplectoscyphus elongatulus Galea, sp. nov., holotype colony, MNHN- IK-2015-463. — C. Symplectoscyphus paulensis Stechow, 1923, colonies from sample MNHN- IK-2015-393. — D. Symplectoscyphus cf. tropicus (Hartlaub, 1901), colony from sample MNHN-IK-2015-394. — E. Tuberocaulus scorpioides (Vervoort, 1993) gen. et comb. nov., colony from sample MNHN-IK-2015-400. — F–G. Zygophylax niger Galea, sp. nov., holotype colony (F) and detail of its coppinia (G) from sample MNHN-IK-2015-478. Scale bars: A, G = 5 mm; B–E = 1 cm; F = 2 cm.

Fig. 20 (opposite page). 16S maximum likelihood phylogenetic tree of selected Leptothecata species obtained with PhyML(GTR+G+I model) and based on 622 aligned basepair positions of the mitochondrial 16S gene. Node-support values are bootstrap values of 100 pseudoreplicates (shown only if> 70%). Species treated in this study are in bold. Some family clades with sufficient bootstrap support discussed in the present study are highlighted in blue boxes. N.B.: Two species names were not used as given in GenBank (FJFJ550462 and FN424141), and the reasons are given in the Material and methods section.

Tables

Table 14 (continued on next page). Species of Zygophylax with long hydrothecal pedicels and non-fused gonothecae, and their differences to Z. niger Galea, sp. nov.

Species name	Main distinguishing morphological features
Z. abyssicola ( Stechow, 1926)	Species not illustrated ( Rees & Vervoort 1987). Hydrothecae biseriate, alternate, shifted on unilaterally, borne on long pedicels; very elongated, ca 2.5 times as long as wide. Gonothecae individualized, borne on short, smooth pedicels; with 2–3 broad rings, distally truncated and provided with 2 opposite apertures, each borne on a short, wide lateral tube; a network of mesh-like, branched, nematophorous tubes amongst gonothecae ( Stechow 1926)
Z. bifurcata Billard, 1942	“apophyses and their hydrothecae […] directed obliquely forward. Hydrothecal pedicels long, with wrinkled to indistinctly ringed portions […]”. Hydrothecae moderately-long, tapering in lower half, occasionally asymmetrical. “ Nematothecae, where present, invariably found on hydrothecal apophyses ”. Gonothecae “contiguous but not fused […] elongate-ovate, constricted basally, with short pedicel, apical portion with two diverging funnels pointing in opposite directions, each with rather wide, slit-shaped opening”. Nematophorous tubules, dichotomously-branched, curving over the gonothecae ( Rees & Vervoort 1987)
Z. concinna ( Ritchie, 1911)	“The hydrothecae […] lie in one plane […]. Each hydrotheca rests on a well-marked projection from stem or branch. On this is perched a long, cylindrical stalk […] half or a little more than half the length of the hydrotheca. The hydrothecae are deep, tubular, and cyathiform, the abcauline profile forming a simple convex curve, the adcauline a compound curve, first convex, then concave”. Nematothecae absent ( Ritchie 1911). “The gonangia are ovate with undulated edges, truncated at the distal end, and tapering towards the proximal extremity. […] In frontal aspect each gonangium is a little narrowed in near the distal end and then widens outwards forming a conspicuous round projection or shoulder at each side of the top where the gonangium reaches its maximum width. These shoulders are produced slightly downwards into truncated processes, each of which ends in a small circular aperture directly facing towards the proximal extremity of the gonangium ” ( Briggs 1922)
Z. convallaria ( Allman, 1877)	“Hydrothecae usually borne on one side of hydrocaulus, facing a plane perpendicular to the plane of the branches […] “ bending near distal end to varied extent, occasionally at a right angle […]. Nematothecae present on tubes of stem and branches, on apophysis or on rare occasions on the internodes” ( Hirohito 1995). Gonothecae independent from each other, “anchor-shaped, apex with two downwardly directed flukes, at the of which is an opening. Protective ramules with some nematothecae occasionally present” ( Rees & Vervoort 1987)
Z. elongata Ramil & Vervoort, 1992	“Hydrothecae […] directed frontally, tubular, placed on pedicel of considerable length […]. Adcauline hydrothecal wall distinctly convex and abcauline wall concave, giving hydrotheca a characteristic, curved appearance. […] Nematothecae inserting on apophyses, one on each side of hydrothecae, on base of side-branches (hydrocladia) and dispersed on axis and secondary tubules. […] Gonothecae separate, without adnate walls, ovoid, apically with bifurcate process, bifurcations ending in gonothecal apertures, two for each gonotheca” ( Ramil & Vervoort 1992)
Z. infundibulum Millard, 1958	“The two rows of hydrothecae on stem and branches not in the same plane, but shifted on to the anterior surface and forming a sharp angle (about 15-40°) between them”. Hydrotheca “elongated, curving upwards in the distal part, with abcauline wall convex, and adcauline wall convex in proximal two-thirds and concave in distal third. […] One nematotheca on the apophysis next to each hydrothecal pedicel” ( Millard 1958). “Gonothecae not adpressed, narrow at base and widening distally, then divided into two outwardly curved necks bearing the terminal apertures. Protective tubular structures numerous, arising amongst the gonothecae and rising above them, completely obscuring them and forming a bristly coat to the coppinia; each branching irregularly and bearing many nematothecae similar to those of the trophosome” ( Millard 1980).