Second records and redescriptions of two rare thecate hydroids (Cnidaria: Hydrozoa) from the southwestern Pacific Author Galea, Horia R. text Zootaxa 2021 2021-12-20 5082 4 373 383 journal article 2897 10.11646/zootaxa.5082.4.5 e821345c-e11b-4789-b3d7-ccf922a03dd7 1175-5326 5792783 D868FB39-82D3-4413-B0FD-33808CE1CCB3 Carpocladus fertilis Vervoort & Watson, 2003 Figs 1–6 , Table 1 Carpocladus fertilis Vervoort & Watson, 2003: 282 , fig. 67. Material examined. MNHN-IK-2015-3028, KANADEEP 2, Stn. DW 5107, off southern New Caledonia , Mount Munida , 22°59.9’ S , 168°14.4’ E , 30 Sep 2019 , 1151– 1274 m , a ca . 5 cm high cormoid bearing two phylactocarps with female gonothecae. —MNHN-IK-2015-3026, KANADEEP 2, Stn. CP 5095, off southern New Caledonia , Capucine Bassin, 23°38’ S , 167°53.1’ E , 29 Sep 2019 , 1087– 1081 m , a ca . 4 cm high cormoid bearing three phylactocarps with male gonothecae . FIGURE 1. Carpocladus fertilis Vervoort & Watson, 2003 . A. Fertile colony. B–D. Hydrothecae seen frontally (B) and laterally (C, D), with (C) and without (D) a median spine. E. Foramen for the passage of the hydranth, showing spines. Scale bars: E = 100 µm; B–D = 200 µm; A = 1 cm. Description . Colonies up to 5 cm high, arising from rhizoid stolons firmly attached to pebbles ( Fig. 1A ). Stems unbranched, lightly fascicled proximally, unable to support themselves when out of liquid; divided into a proximal, acladiate part of varied length, and a generally longer, distal part bearing alternate hydrocladia; both parts separated by up to five prosegments delimited by deeply-incised hinge-joints, each bearing one or two frontal nematothecae; hinge-joint region distinctly flattened laterally, allowing the colony to swing freely in the water currents; upper part of stem regularly-divided into internodes by means of oblique constrictions of the perisarc; internodes moderatelylong, each with a lateral apophysis in upper half, an axillar nematotheca, and a centrally-placed nematotheca in the lower half ( Fig. 2A ); cauline nematothecae scoop-shaped: axillar ones narrower, lower ones comparatively broader ( Fig. 2B–D ); apophyses short, alternate, given off at an angle of about 60° with the long axis of the internodes, and slightly frontally ( Fig. 2B ); apophyses separated by the corresponding cladia by a slightly oblique node. Cladia unbranched, up to 14 mm long, arching gracefully downward distally; divided into up to 14 internodes by regular, transverse nodes; internodes long, each accommodating a hydrotheca occupying upper 4/5 of their length ( Fig. 2E, H ). Hydrothecae deep, slightly inverted-conical, laterally-flattened, fully adnate, aperture ovoid, distal, slightly tilted forwards ( Figs 1B–D ; 2E–H ); an internal, transverse, upwardly-directed septum projecting into the lower fourth of the lumen, distal edge backwardly-rolled ( Fig. 2K ); above, two lateral, sigmoid septa meeting frontally divide the hydrothecal lumen into a lower third and an upper two-thirds, leaving a V-shaped passage for the hydranth ( Fig. 2K, L ); several short perisarc plugs project into the internode behind the adaxial hydrothecal wall: one prolongs the transverse septum in the opposite direction, another one is given off at junction between the hydrothecal base and the adaxial wall ( Fig. 2K ), and two others are occasionally present behind the adaxial wall (not shown); an additional perisarc plug is to be found proximally on the adaxial side of the cladial internode ( Fig. 2K ); below the intrathecal transverse septum, there is a round hydropore surrounded by whorl of spines ( Fig. 1E ); hydrothecal rim with a broad, median, rounded cusp with thickened perisarc ( Fig. 1B ), and four lateral pairs of triangular cusps, those of the first pair distinctly blunted, and those of the fourth pair partly fused to the lateral nematothecae ( Figs 1C, D ; 2I ); adaxially, hydrothecal rim broadly scooped; most hydrothecae are provided with a slender, horn-like, upwardlycurved, hollow perisarc projection ( Figs 1B, C ; 2E, I ) of varied development (though generally unmistakable) and prolonged proximally into a short, longitudinal, median carina. Three nematothecae associated to each hydrotheca: a mesial one and a pair of laterals; mesial nematotheca originating slightly below the hydrothecal base, long, tubular, adnate for 4/5 of its length, aperture gutter-shaped, rim distinctly crenulate ( Fig. 2K ); lateral nematothecae slightly surpassing the hydrothecal rim, monothalamic, urn-shaped, with deep, adaxial emargination, rim crenulate ( Fig. 2I ). Phylactocarps borne on the proximal-most cormidia ( Fig. 3A ), and given off slightly in front of the cormoid ( Fig. 1A ); up to 9 mm long; first cormidium with a short, lateral, athecate apophysis inserted below the hydrothecal base, thus displacing the mesial nematotheca towards the proximal end of the internode, and forcing it to adopt the same shape as the cauline nematothecae ( Figs 4A ; 6A ); phylactocarp composed of a proximal-most, short internode bearing a median nematotheca ( Figs 4A ; 5A, B ; 6A ), followed by a regular succession of up to 16 geniculate internodes forming its rachis ( Fig. 4B ); rachial internodes geniculate, moderately-long, composed of a lateral apophysis supporting a costa (apophyses alternate), an axillar nematotheca, and another nematotheca proximally ( Fig. 6A ); nematothecae scoop-shaped; costae widely-spaced ( Fig. 4B ), phylactocarp open ( Fig. 3 ); costae bifid ( Figs 3C ; 5A ; 6A ), with a basal, smaller hydrotheca ( Fig. 5C ) whose modified mesial nematotheca is displaced proximally; hydrothecate internode prolonged distally by up to six short, collinear internodes, each provided with a single or a pair of elongate nematothecae set laterally; between the mesial nematotheca and the hydrothecal base, a slightly laterally-projecting apophysis supporting the second branch of the costa; second branch with up to four nematothecate internodes ( Fig. 6A ); nematothecae half-adnate, gutter-shaped distally, with crenulate rim ( Fig. 5D ). Gonothecae borne on inconspicuous swellings of the rachial apophyses supporting the costae, the latter arching over the gonothecae; gonothecae fusiform, sexually dimorphic, female ( Figs 4C ; 6D ) comparatively longer and curving away distally ( Fig. 6C ), and with wider distal apertures than the male ones (compare Fig. 4C and B , and 6D and B , respectively); apertures set distally, transverse, circular in shape, prolonged downward as long slits ( Figs 4B, C ; 5E ; 6B, D ). Coenosarc poorly-preserved, the number of tentacles in hydranths and of oocytes in the female gonothecae could not be ascertained. Perisarc of colony straw colored. FIGURE 2. Carpocladus fertilis Vervoort & Watson, 2003 .A–D. Stem internode seen frontally (A); the same, enlarged, to show its nematothecae either frontally (B) or laterally (C, D). E–H. Hydrothecae with (E–G) or without (H) a median spine, seen laterally (E, H), apically (F) and frontally (G). I, J. Hydrothecal aperture seen both laterally (I) and apically (J). K, L. Intrathecal septa seen both laterally (K) and apically (L). Scale bars: A–L = 500 µm. FIGURE 3. Carpocladus fertilis Vervoort & Watson, 2003 .A–C. Phylactocarp with female gonothecae, at various magnifications. Scale bars: C = 500 µm; A, B = 1 mm. FIGURE 4. Carpocladus fertilis Vervoort & Watson, 2003 . A. A stem internode bearing the proximal most cormidium (following cormidia voluntarily removed) supporting a phylactocarp (only its proximal part is shown). B. Central part of the same phylactocarp seen from below, showing its rachis, alternate costae, and male gonothecae. C. Isolated female gonotheca; note its broader aperture compared to its male counterparts. Scale bars: A–C = 500 µm. FIGURE 5. Carpocladus fertilis Vervoort & Watson, 2003 . A. Proximal most part of a phylactocarp, showing the proximal most cladial cormidium, the proximal nematothecate internode, and the first regular rachial internode with male gonotheca, bifid costa and axillar hydrotheca. B. Detail of the origin of a phylactocarp, showing the proximal most cladial hydrotheca, its lateral apophysis, the first (nematothecate only) rachial internode, and the first regular rachial internode. C. Detail of the branching site of a costa, showing the axillar hydrotheca, the peculiar position and shape of its mesial nematotheca, and the apophysis supporting the frontal branch of the costa. D. Nematothecae of a costa. E. Detail of the aperture of a male gonotheca. Scale bars: B–E = 200 µm; A = 500 µm. Remarks . Cormoids in the present material are comparatively smaller ( 4–5 cm high) than in the holotype colony ( 12 cm high). Consequently, their stems are less fascicled, and their cladia shorter (up to 14 mm vs . 25–30 mm long in the holotype ), comprising lesser cormidia (14 vs . up to 35) ( Vervoort & Watson 2003 ). Reportedly, up to 5 internal, incomplete, annular ridges can be found in the internode behind the hydrotheca. Unlike in the present material, the pedicel of the phylactocarp could be quite long, and composed of up to 12 nematothecate internodes, as noted in the holotype . Not stated in the original account, the nematothecae of this species have distinctly crenulated rims. Prior to this study, only the male gonothecae have been described ( Vervoort & Watson 2003 ). However, one of the cormoids examined here bears phylactocarps with female gonothecae. Similar in shape to their male counterparts, but larger, they nevertheless possess comparatively broader apertures apically (compare Fig. 6D and 6B , respectively). TABLE 1 . Measurements of Carpocladus fertilis Vervoort & Watson, 2003 , in µm. N.A. stands for not available. * No distinction was made between the axillar and inferior stem nematothecae.

Present study	Vervoort & Watson (2003)
Stem
- internode length	860–920	N.A.
- diameter at nodes	150–190	225–280
- cladial apophysis length	190–220	N.A.
- distance between 2 successive apophyses (same side)	1590–1780	N.A.
- axillar nematotheca, length	175–215	180–195*
- axillar nematotheca, maximum width	80–100	135–150*
- axillar nematotheca, diameter at aperture	25–35	45–55*
- inferior nematotheca, length	170–200	180–195*
- inferior nematotheca, maximum width	110–130	135–150*
- inferior nematotheca, diameter at aperture	75–100	45–55*
Cladia
- internode length	880–1055	820–985
- diameter at nodes	95–120	145–195
Hydrotheca
- total depth	700–800	615–645
- diameter at aperture	280–315	250–280
- spine length	<220	N.A.
- mesial nematotheca, total length	365–380	335–365
- mesial nematotheca, length adnate part	300–315	N.A.
- mesial nematotheca, diameter at aperture (lateral view)	80–95	N.A.
- lateral nematotheca, length	180–190	225–230
- lateral nematotheca, maximum width	85–100	85–90
- lateral nematotheca, diameter at aperture	40–45	28–34
Phylactocarp
- rachial internode length	530–580	N.A.
- rachial internode, diameter at node	195–210	N.A.
- costa, length	<1980	N.A.
- costa, internode length	310–365	N.A.
- costa, length of nematothecae	ca . 280	N.A.
- female gonotheca, length	ca . 1640	N.A. (unknown)
- female gonotheca, maximum width	ca . 485	N.A. (unknown)
- female gonotheca, diameter at aperture (lateral view)	ca . 180	N.A. (unknown)
- male gonotheca, length	1200–1300	1470–1500
- male gonotheca, maximum width	350–385	410–490
- male gonotheca, diameter at aperture (apex, lateral view)	ca . 60	N.A.

The genus Carpocladus was created to accommodate Cladocarpus -like hydroids producing rather complex phylactocarps whose lateral, alternate costae are bifid, each being provided with an axillar hydrotheca between two flanking nematothecate ramuli. In Vervoort & Watson’s (2003) view, their genus showed closer affinities with Cladocarpoides Bogle, 1984 , in which the exceedingly long phylactocarps have costae also provided with a hydrotheca (ending in a “nematophorous spine”), in front of which (between the proximally-displaced mesial nematotheca and the hydrothecal base) arises an antler-shaped, “nematophorous branchlet” or “phylactogonium” ( Bogle 1984 ). Strikingly, the relationships between Carpocladus and Wanglaophenia Vervoort & Watson, 2003 , a hydroid genus forming nearly identical phylactocarps, were not discussed. Given the lack of genetic material, not only of C. fertilis , but also of many Cladocarpus species and members of Cladocarpus -like genera, and the unpredictable relationships between the few species for which genetic data are already available ( Moura et al . 2018 ), it is impossible for the time being to ascertain the validity of the genus Carpocladus , as well as its phylogenetic position within the family Aglaopheniidae . Distribution . Tasman Sea ( Vervoort & Watson 2003 ), off southern New Caledonia (present study). Occurs at depths between 979–1274 m [ Vervoort & Watson (2003) and present study, respectively].