One new genus and three new species of plumulariid hydroids (Cnidaria, Hydrozoa, Plumulariidae) from the western Pacific Ocean, with a re-examination of Plumularia insignis Allman, 1883 and related taxa Author Agís, José Ansín Author Ramil, Fran Author Calder, Dale R. text Zootaxa 2016 4169 1 57 86 journal article 10.11646/zootaxa.4169.1.3 dc0eaba4-f442-4ea7-8f4c-b6a389d6e5f8 1175-5326 263049 05BDC917-2890-41BE-B371-5332DB5B7ED9 Schizoplumularia elegans n. sp. ( Figs 6‒9 ; Table 4 ) Material examined. New Caledonia . BIOCAL 1, stn CP 110, 22°12.383'‒ 22°13.315'S , 167°06.434' ‒167°09.936'E, 275‒320 m , 09-IX-1985 : five fragmented colonies to 60 mm high; two colonies with damaged gonothecae. One colony, 120 mm high in two fragments is the holotype ( MNHN-IK-2012-16603 ); remaining colonies are paratypes ( MNHN-IK-2012-16604; RMNH.Coel.42071 ). MUSORSTOM 4, stn CP 171, 18°57.8'S, 163°14.0'E, 435 m , 17-IX-1985 : some badly damaged colonies up to 112 mm high; no gonothecae. (MNHN). MUSORSTOM 4, stn CP 172, 19°01.2'S, 163°16.0'E, 275‒330 m , 17-IX-1985 : one mutilated colony of 70 mm with a few hydrocladia; no gonothecae. (MNHN). MUSORSTOM 4, stn CP 180, 18°56.8'S, 163°17.7'E, 450 m , 18-IX-1985 : five fragmented colonies and a number of pieces, maximal height c. 60 mm ; no gonothecae. (MNHN). CHALCAL 2, stn DW 80, 23°26.70'S, 168°01.80'E, 160 m , 31-X-1986 : one fragment 15 mm high; with damaged gonothecae. (MNHN). Loyalty Islands . MUSORSTOM 6, stn DW 412, 20°40.60'S , 167°03.75'E , 437 m , 15-II-1989 : 100 mm high colony with two fragments of hydrocladia; no gonothecae. ( MNHN ; RMNH one slide). MUSORSTOM 6, stn DW 421, 20°26.27'S, 166°40.17'E, 245 m , 16-II-1989 : 80 mm high colony; no gonothecae. (MNHN). MUSORSTOM 6, stn DW 449, 20°54.40'S, 167°17.75'E, 300 m , 20-II-1989 : one colony 80 mm high in bad condition; no gonothecae. (MNHN). MUSORSTOM 6, stn DW 457, 21°00.42'S, 167°28.71'E, 353 m , 20-II-1989 : single colony 80 mm high and some fragments; no gonothecae. (MNHN). FIGURE 6. Schizoplumularia elegans n. sp. A (SMIB 4, stn DW 53), habit of colony. B‒E, holotype (BIOCAL 1, stn CP 110); B, fragment of colony without apical part; C, apophysis and basal part of a hydrocladium; D, internodes from distal part of a hydrocladium; E, gonotheca. Scales: a‒b, 1 cm. c‒e, 0.1 mm. MUSORSTOM 6, stn CP 464, 21°02.30'S, 167°31.60'E, 430 m , 21-II-1989 : single small colony c. 65 mm high with Kirchenpaueria bonnevieae (Billard, 1906) as epibiontic and a fragment; no gonothecae. (MNHN). MUSORSTOM 6, stn DW 485, 21°23.48'S, 167°59.33'E, 350 m , 23-II-1989 : top part of colony, 45 mm high, plus some detached branches up to 25 mm ; no gonothecae. (MNHN). Norfolk Ridge . SMIB 4, stn DW 53, 23°40.1'‒23°39.5'S, 167°59.9'‒168°00.3'E, 250‒270 m , 09-III-1989 : single c. 80 mm high spirally-built colony; no gonothecae. (MNHN; RMNH one slide). BATHUS 3, stn CP 804, 23º41'S, 168º00'E, 244‒278 m , 27-XI-1993 : one colony 65 mm high; without gonothecae. (MNHN). FIGURE 7. Schizoplumularia elegans n. sp. A‒B, holotype (BIOCAL 1, stn CP 110); A, proximalmost internodes of a hydrocladium; B, fragment of stem. C (MUSORSTOM 4, stn CP 180), branch. Scales: a‒c, 0.1 mm. North New Caledonia . BATHUS 4, stn CP 902, 19º01'S , 163º15'E , 341‒351 m , 04-VIII-1994 : one colony 100 mm high; without gonothecae. ( MNHN ). BATHUS 4, stn CP 906, 19º01'S, 163º15'E, 339‒350 m , 04-VIII-1994 : one colony 120 mm high; without gonothecae. (MNHN). Etymology. The specific name is the Latin adjective elegans , chosen to emphasize the elegant and graceful habitus of the colony. FIGURE 8. Schizoplumularia elegans n. sp. A‒D (SMIB 4, stn DW 53); A, detail of branch; B, apophysis and first internode; C, internodes from distal part of a hydrocladium; D, proximalmost internodes of a hydrocladium. Scales: a‒d, 0.1 mm. Distribution. Schizoplumularia elegans n. sp. was collected at several localities from New Caledonia , the Norfolk Ridge, and the Loyalty Islands , at depths from 160 to 450 m . Description. Hydrorhizae of colonies consisting of a mass of intertwining tubules adhering to sandy sediment, supporting a polysiphonic and forked main axis; main axis sinuous to geniculate in younger parts of colony. Hydrocauli given off from main axis, arranged alternately right and left in one plane. Main axis of colony having same structure as in Schizoplumularia vervoorti n. sp. and S. geniculata n. sp. : basal part with a primary axial tube curving away from main axis to form first hydrocaulus; this hydrocaulus with apophyses and hydrocladia disposed alternately left and right in the same plane; remaining hydrocauli originating from secondary axial tubes, given off to left and right of main axis, with apophyses and hydrocladia appearing only after tube curves away from main axis to form a typical hydrocaulus. In distal part of colony, a new secondary axial tube arising from axil of each hydrocaulus and adhering to old secondary axial tubes, these later giving off new hydrocauli as described for the other two species. Hydrocauli always monosiphonic, divided by transverse nodes visible only on apical parts; internodes with a varying number of apophyses, with as many as 10 basally and one or two distally; apophyses arranged alternately right and left in one plane, with one to three nematothecae between two consecutive apophyses on same side. Nematothecae on axis of hydrocauli arranged mostly in a row on one side, only rarely observed on other side. Each apophysis with two axillary nematothecae and one mamelon on upper surface. Hydrocladia heteromerous; basal internode ahydrothecate, bearing a nematotheca on a small proximal elevation and with two internal perisarcal rings near each end; remaining internodes alternately hydrothecate and ahydrothecate, separated by slightly oblique nodes. Ahydrothecate internodes weakly indicated on basal part of hydrocladia, with one nematotheca on a small elevation near basal node. Hydrothecate internodes each with one hydrotheca and three nematothecae: one mesial inferior and a pair of laterals. Hydrothecae situated on basal half of internode, very small, cup-shaped, adcauline wall fully adnate, abcauline wall straight; hydrothecal rim smooth, circular. Number and development of internal perisarcal rings in internodes varied, with up to five observed on hydrothecate internodes: three below, one just proximal to base and one distal to hydrotheca; ahydrothecate internodes with two perisarcal thickenings, one basal and one distal. All nematothecae conical, bithalamic, movable; mesial inferior nematothecae located on an elevation; lateral nematothecae large, mounted on a reduced apophysis. Gonothecae arising from apophyses; all of them tubular to pear-shaped, with a circular terminal aperture closed by an operculum. Variability. Lateral nematothecae were very large (fig. 9A‒B) in colonies from stations MUSORSTOM 6 DW 421 and DW 457, with their lengths varying even on the same hydrocladium. Nodes separating hydrothecate and ahydrothecate internodes were not easily visible on basal parts of some hydrocladia. In material from station DW 53, one hydrocauline internode was observed with a single apophysis as a result of regeneration after rupture. Also in material from stn DW 53, one hydrothecate internode at the proximalmost end of a hydrocladium had two mesial inferior nematothecae. TABLE 4. Measurements of Schizoplumularia elegans n. sp. in µm. BIOCAL 1 MUSORSTOM 6 SMIB 4 stn CP 110 stn DW 485 stn DW 53 First hydrocladial internode, length 110‒140 160‒200 130‒170 Length hydrothecate hydrocladial internodes 360‒440 430‒490 330‒360 Length ahydrothecate hydrocladial internodes 110‒180 180‒250 150‒190 Remarks. Material from the Loyalty Islands (MUSORSTOM 6, stn DW 449), the Norfolk Ridge (SMIB 4, stn DW 53), and BATHUS 3 (stn CP 804) had slightly larger hydrothecae, but the remaining characters are similar to the other examined colonies and therefore we assign it to the same species. Examined material is characterized by large, branched, strongly polysiphonic colonies. Basal parts of the main axis are thick and straight, with long and curved hydrocauli arranged to right and left. In distal parts the main axis is geniculate, and hydrocauli originate from secondary axial tubes, similar to those described for Schizoplumularia vervoorti n. sp. This species nevertheless differs from S. vervoorti in the greater size and greater polysiphonic development of the colony, by the decidedly small size of the hydrothecae, by the position of the hydrothecae on the basal half of the internode, and by the existence of ahydrothecate internodes on the hydrocladia. Some characters of Schizoplumularia elegans n. sp.

Diameter at node	35‒55	35‒60	35‒50
Hydrotheca Length abcauline wall Length adcauline wall	25‒40 30‒40	35‒45 35‒45	50‒60 50‒65
Diameter at rim Mesial nematotheca, length Diameter at rim	45‒50 50‒60 30‒35	45‒55	60‒65 50‒60 30‒35
Lateral nematotheca, length Diameter at rim Supracalycine nematotheca, length	70‒100 35‒40 50‒60	70‒80 30‒35
Diameter at rim Gonotheca, length Greatest diameter	30‒35 500‒550* 210
* Only three measurements.

FIGURE 9. Schizoplumularia elegans n. sp. A‒B, internodes with long nematothecae from same hydrocladium (MUSORSTOM 6, stn DW 457); A, proximalmost internode of a hydrocladium; B, penultimate internode of same hydrocladium. C, holotype (BIOCAL 1, stn CP 110), gonotheca. Scales: a‒c, 0.1 mm. resemble those of Plumularia spiralis Billard, 1911 , but in that species the colony has the normal morphology seen in species of Plumularia Lamarck, 1816 , with hydrocauli arising from a hydrorhiza and not from a polysiphonic main axis. The hydrocaulus of S. spiralis is monosiphonic with a characteristic zig-zag shape, hydrocladia are homomerously segmented, and hydrothecae are larger. In the heteromerous segmentation of hydrocladia, in overall measurements, in disposition of hydrothecae and nematothecae on internodes, and in shape and small size of hydrothecae, colonies of this species come close to Plumularia tenuissima Totton, 1930 , but there are important differences that separate the two species. Type material of P. tenuissima , a polysiphonic fragment 1 cm high that is branched and rebranched in one plane ( Totton 1930 ), clearly differs from the ramification pattern of Schizoplumularia elegans , in which the main axis may be forked or unforked but the only lateral ramifications are represented by the typical lateral hydrocauli, always monosiphonic and unbranched. In addition, in P. tenuissima the hydrocladia are alternate on distal parts of branches but become sub-opposite and decussate in other parts and the basalmost ahydrothecate internode of hydrocladia is fused with the apophyses; both features of Totton’s species resemble the genus Nemertesia Lamouroux, 1812 . The same opinion was already advanced by Vervoort & Watson (2003) when describing new material of P. tenuissima from New Zealand . Part of the material studied by Vervoort & Watson (2003) was also examined during this work (RMNH-Coel. slides 2100, 2195, 2196, 3030). These colonies are polysiphonic and bear hydrocladia on the main axis. Ramifications arise from apophyses on secondary tubes. They seem to conform with diagnoses of Plumularia rather than Schizoplumularia . While trophosomes of both species are similar, their gonothecae differ, with those of P. tenuissima having an oblique aperture while the aperture is terminal in Schizoplumularia . Moreover, ramification of their colonies is very different. Plumularia brachiata Totton, 1930 (= Plumularia mula Totton, 1936 ) also shows some similarities with S. elegans , but its ramification pattern is similar to that of P. tenuissima .