Thamnopteros uniserius Galea

Galea, Horia R. & Maggioni, Davide, 2020, Plumularioid 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 708, pp. 1-58: 46-53

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Thamnopteros uniserius Galea

gen. et sp. nov.

Thamnopteros uniserius Galea   gen. et sp. nov.

Figs 16B View Fig , 20 View Fig ; Table 9


General description as for the genus. Branches with basal prosegment, followed by a regular succession of modules comprising hydro- and nematothecae, each hydrotheca accompanied by a lateral, cladial apophysis; apophyses alternate; hydrothecae truncated cones, with 5 associated nematothecae and 0–1 nematothecae above; cladia with short, proximal, quadrangular segment, followed by an succession of modules, each bearing a tubular hydrotheca and its complement of 5 nematothecae; no nematothecae between successive cladial hydrothecae. All hydrothecae ca ¼ rd adnate, with one mesial, a pair of lateral (often of varied length), and two axillar nematothecae; all nematothecae bithalamic. Gonothecae borne on cladia; piriform, with 3 basal, elongated nematothecae, distally truncate, rim rounded, thickened.


From Latin ‘ ūnus, -a, -um’, meaning ‘one’, and ‘ sěrĭēs ’, meaning ‘row’, to emphasize the unilateral arrangement of branches along the main stem.

Material examined


PACIFIC OCEAN • 1 sterile colony broken into two pieces, basal part ca 8.5 cm high, distal part ca 8.7 cm high; off New Caledonia, stn CP4754; 23°22′ S, 167°54′ E; 1009–1019 m; 25 Aug. 2016; KANACONO leg.; MNHN-IK-2015-611. GoogleMaps  


Colony erect, originally ca 17.2 cm high, now broken into two, almost equal parts, of rigid appearance, with brown perisarc, arising from rhizoid stolon. Stem unbranched, 2.5 mm thick at base, strongly fascicled, displaying superficially a number of tortuous tubes that seem to wrap an internal beam of straight counterparts, as shown by a couple of small, less organized areas on surface that reveal a possible sheath-like general structure. Tubes on stem surface provided with two longitudinal, laterally-set rows of opposite nematothecae along their length. Upper half of stem gives rise unilaterally, at regular intervals, to monosiphonic, Halopteris   -like branches arising from internal beam of component tubes; before each of these tubes becomes free from the fascicled stem, the distal ends of their fused parts become apparent at the surface of the stem for a varied length, displaying on their exposed side two closely-set rows of alternate nematothecae; a short distance (no longer than 1 cm) after diverging from the stem, each tube acquires suddenly a well-organized structure: a basal prosegment is followed by a regular succession of hydrothecae (with their associated nematothecae) and lateral apophyses supporting the cladia. Except for the prosegment, that is delimited at both ends by deeply-incised, very oblique nodes, the remainder of tube is unsegmented. The prosegment bears a hydrotheca devoid of cladial apophyses, its 5 associated nematothecae (1 mesial, far below the base, 1 pair of laterals and 1 pair of axillar), as well as up to 4 nematothecae in two rows above the hydrotheca. Remainder of tube with modules composed of a hydrotheca and its 5 associated nematothecae (as above), an apophysis lateral to it (except for proximalmost hydrotheca that has a pair), as well as 0–1 nematothecae above the hydrotheca. Hydrothecae shifted alternately left and right; truncated cones in shape (broader at base than at aperture), half free from the ‘internode’; abaxial wall straight, free adaxial wall slightly concave, both with quite thick perisarc; mesial nematotheca movable, with wall of upper chamber lowered on adaxial side; lateral nematothecae borne on fairly-developed apophyses fused distally to the hydrothecal wall, as illustrated by a peg-like projection of perisarc, running frontally for a short distance over the hydrothecal wall; lateral nematothecae of varied length, generally short on proximalmost cormidia, and exceedingly long distally; basal chamber very tall, upper chamber shallow, with circular, entire rim; axillar nematothecae bithalamic, wall of upper chamber slightly lowered on adaxial side. Cladial apophyses short, athecate, shifted laterally so that the two rows of hydrocladia they carry form an acute angle between them. Hydrocladia up to 4 mm long, unsegmented, except for a short, proximal, quadrangular segment; cladia comprising up to 10 modules, each with one hydrotheca and its 5 associated nematothecae (as above); there are no additional nematothecae between 2 successive hydrothecae; the lateral nematothecae are generally exceedingly tall and often of unequal length. Gonothecae, likely female, borne on cladia, each inserted laterally between the base of a hydrotheca and its mesial nematotheca through a short apophysis; pedicel of one short, quadrangular piece; gonotheca piriform, with 2–3 proximal, quite long nematothecae, distally truncate, with distinctly thickened, circular rim, apparently without lid.


The new species differs from Thamnopteros valdiviae (Stechow, 1923)   in having: 1) all Halopteris   - like branchlets given off unilaterally from the stem, instead of pointing in all directions around it; 2) undivided axes and cladia; 3) cladia missing an intervening nematothecate internode between the proximalmost, quadrangular segment and the remainder of cladium; 4) hydrothecae with an even rim, not sinuated laterally; 5) bithalamic instead of scale-shaped axillar nematothecae.


Only known from its type locality, off New Caledonia (present study).

Genetic results

The newly sequenced specimens were used to build updated phylogenetic hypotheses for the families Aglaopheniidae   , Plumulariidae   , and Halopterididae   , based on the 16S rRNA region ( Figs 21–23 View Fig View Fig View Fig ). Overall, all families showed a pervasive polyphyly of genera, as previously demonstrated by other studies using the same DNA region (e.g., Galea et al. 2018; Moura et al. 2018), but non-monophyly was also commonly observed using multi-locus approaches ( Maronna et al. 2016). Therefore, a thorough integrative morpho-molecular revision is needed to better define the generic and specific boundaries in these plumularioid families.

In the Aglaopheniidae   tree ( Fig. 21 View Fig ), the newly produced sequences represent the first genetic data for the analysed species, except for Gymnangium expansum ( Jäderholm, 1903)   , which clusters with a conspecific sequence. Sequences of the recently-described Cladocarpus pennatus Galea, 2020   cluster in a monophyletic group, divergent from all other Cladocarpus   sequences, and the same happens for

Aglaophenia digitulus Vervoort & Watson, 2003   , highlighting the peculiar nature of these species and their possible belonging to other genera. Finally, Cladocarpus keiensis Schuchert, 2003   clusters with C. unilateralis Schuchert, 2005   and C. bocki Jäderholm, 1919   , and all together form a fully-supported monophyletic group with 3 species of Streptocaulus   , suggesting that the scope of these genera is in need of a revision.

Regarding the Plumulariidae   ( Fig. 22 View Fig ), the newly-produced sequence of Dentitheca habereri ( Stechow, 1909)   clusters with a conspecific sequence from Japan, and this species is closely-related to D. contraria   comb. nov. (confirming the assumption based on morphological grounds alone, see above), even though with low nodal support, and with D. dendritica ( Nutting, 1900)   . Sequences of Schizoplumularia   are sister to the group composed of the species of Dentitheca   mentioned above, and the two species, Schizoplumularia elegans Ansín Agís et al., 2016   and S. helicoidalis   sp. nov. do not form a monophyletic group in our phylogenetic hypothesis. Sequences of Schizoplumularia   spp. and D. contraria   comb. nov. were also produced for the first time with this work.

Finally, the sequence of Corhiza pauciarmanta Ansín Agis et al., 2009   , in the Halopterididae   tree ( Fig. 23 View Fig ), forms a fully supported group with Antennella kiwiana Schuchert, 1997   and A. siliquosa (Hincks, 1877)   , and represents the first genetic data obtained for both genus and species.