Plumularia roxanae, Galea, 2020

Galea, Horia R., 2020, Plumularia roxanae, a new epiphytic hydroid (Cnidaria: Hydrozoa: Plumulariidae) from the Indo-Pacific, Revue suisse de Zoologie 127 (2), pp. 367-376 : 367-375

Plumularia roxanae sp. nov.

Figs 1-2 ; Tables 1-2

Holotype: MHNG-INVE-137167 ; INDONESIA, Bali, Pererenan beach ; -8.650831°, 115.119820°; 13 Jan. 2020; fertile colony on red alga.

Paratypes: MHNG-INVE-137168 ; INDONESIA, Bali, Pererenan beach ; -8.650831 °, 115.119820 °; 13 Jan. 2020; fertile colony on red alga . – MHNG- INVE-137169 ; INDONESIA, Bali, Pererenan beach ; -8.650831 °, 115.119820 °; 13 Jan. 2020; fertile colonies on 3 fragments of red algae.

Diagnosis: Small-sized, epiphytic Plumularia arising from stolon with perisarcal spurs, giving rise to monosiphonic stems divided homomerously by transverse nodes into rather short, collinear internodes, each with a subterminal cladial apophysis provided with an inconspicuous adaxial mamelon and a pair of axillar nematothecae; cladia heteromerously segmented by alternating straight and oblique nodes into short, ahydrothecate internodes occasionally provided with a nematotheca, and up to three, comparatively longer hydrothecate internodes accommodating a centrally-placed hydrotheca and its three associated nematothecae; hydrotheca deep, saccate, partly adnate, distal portion distinctly constricted through the hypertrophy of the free adaxial wall that adopts a triangular shape, considerably reducing the thecal lumen; abaxial wall slightly convex; gonothecae in two closely-set, parallel rows along the stem, borne on the cladial apophyses, minute, ovoid, thick-walled.

Etymology: It is my great pleasure to dedicate this new species to the memory of my late mother, Roxana S. Galea (née Florescu, 5 Oct. 1946 – 18 Jan. 1994), a Romanian biologist, who passed on to me her interest for natural sciences.

Description: Colonies epiphytic on algae, composed of numerous erect cormoids arising from creeping, branching, flattened stolonal tubes firmly attached to substrate; lumen with two lateral rows of perisarcal spurs; a wide flange of thinner perisarc flanking outer lateral sides. Stems short, up to 5 mm high, with thick and firm perisarc, gradually thinning out distally; monosiphonic, divided by means of transverse nodes into a regular sequence of collinear, rather short internodes, length slightly increasing gradually towards tips of cormoids; each internode with two internal perisarc ridges (one above proximal node, the second below the distal node) and a subterminal cladial apophysis; apophyses alternate along the stem, the two rows either in one plane in some specimens or variably shifted on to the anterior side of the colony in others; apophyses well-developed, each with a subterminal, internal perisarc ridge, an inconspicuous mamelon (reduced to a mere pore) with small, circular aperture on adcauline side, and a pair of axillar nematothecae, one to each lateral side; distal node straight. Cladia given off at an angle of about 45° with the long axis of the stem; up to 1 mm long, divided heteromerously by an alternation of deeply-incised, straight and oblique nodes delimiting a- and hydrothecate internodes; first cladial internode ahydrothecate; all ahydrothecate internodes short, with proximal node straight and distal node oblique, with two internal perisarc ridges (one proximal, one distal) and, occasionally, with a nematotheca in middle of upper side; hydrothecate internodes, up to 3 per cladium, comparatively longer than their ahydrothecate counterparts, slightly sigmoid in overall shape, with proximal node oblique and distal node straight, a centrally-placed hydrotheca (together with its 3 associated nematothecae), occupying more than half the length of the internode, and two internal perisarc ridges near both ends. Hydrotheca deep, saccate, adnate for about 2/3 to its corresponding internode; abaxial wall thick, slightly convex proximally; free adaxial wall exceedingly hypertrophied, adopting a triangular shape, free angle upturned; adnate adaxial wall moderately thick, forming an L-shaped perisarc thickening at junction with the hydrothecal base, the latter pierced by circular foramen for the passage of the hydranth; hydrothecal aperture facing nearly upwards, rim entire, circular in apical view; mesial nematotheca well below the hydrothecal base, mounted on small prominence of the internode; lateral nematothecae borne on indistinct apophyses and hidden by the free portion of the adaxial wall when the hydrotheca is seen frontally, and typically inclined over this side of the thecal wall; hydranths able to completely retract into their corresponding hydrothecae, with ca. 12 filiform tentacles in a whorl around a dome-shaped hypostome. All nematothecae of the colony movable, elongate-conical in shape and bithalamic; lower chamber comparatively taller than upper one, the latter with the wall slightly lowered on adaxial side. Gonothecae in two parallel, closely-set rows along the stem, arising singly from the anterior side of each cladial apophysis; likely male in the present material, with a homogenous, granular content; elongate-globular, thick-walled, with smooth outer surface, apically with a small funnel-shaped aperture in some specimens, delimited basally by transverse, thick diaphragm from a short, tubular pedicel.

Remarks: Upon a comparison with all shallow-water, small-sized (generally not surpassing 1 cm high), shortcladiate, nominal species of Plumularia Lamarck, 1816 from the tropical Indian and western Pacific oceans ( Table 1 ), it appears that the material at hand is distinctive, mainly through the shape of its hydrothecae. Similar gonothecae are only found in P. floridana Nutting, 1900 , a species of circumtropical occurrence, described under various names ( Calder, 1997: 15).

The epiphytic hydroid erroneously assigned ( Watson, 2011: 78) to Monotheca hyalina ( Bale, 1882) by Vervoort & Watson (2003) resembles the present species, notably in the structure of the colony and the shape of hydrotheca, but shows several differences: 1) its stolon is devoid of perisarc spurs; 2) there is only one axillar nematotheca associated to the cladial apophyses of the stem; 3) the hydrothecae are devoid of the characteristic thickening of the free adaxial wall; 4) its (female) gonothecae are much bigger, ca. 1 mm high, as deduced from their fig. 90I, and they are piriform, with an apical, broad, circular aperture closed by an operculum. For these reasons, their record is not included in the synonymy of the present species, pending the discovery of colonies belonging to the opposite (female) sex.

Distribution: Known only from Bali, Indonesia, but presumably spread throughout the archipelago.

Figures

Fig. 1. Plumularia roxanae sp. nov. (A) Portion of cormoid. (B) Detail of a portion of stem with proximal parts of four successive cladia. (C) Detail of a stem internode, showing centrally an apophysis and the proximal part of the corresponding cladium. (D) Proximal most hydrotheca. (E) Distalmost hydrotheca, note the absence of the distal part of its corresponding internode. (F) Portion of fertile stem with rows of gonothecae. (G) Gonotheca. (H) More detailed view of a gonotheca, showing apical

Fig. 2. Plumularia roxanae sp. nov. (A) Portion of ramified stolon, showing internal spurs. (B) Two stem internodes and proximal parts of their corresponding cladia. (C) Portion of stem with gonotheca. (D) Detail of stem internode. (E, F) Two hydrothecae seen laterally, note differences in the adaxial perisarc thickening. (G) Hydrotheca seen from above, note the position of lateral nematothecae. (H) Base of hydrotheca with mesial nematotheca. (I) Distal part of hydrotheca with lateral nematotheca. (J) Cladial ahydrothecate internode. (K) Gonotheca. Scale bars: 50 μm (D, H-K), 100 μm (E-G), 200 μm (B, C), 300 μm (A).

Tables

Table 1. Measurements of Plumularia roxanae sp. nov., in μm.

Stem
- internodes, length	220-285
- internodes, diameter at node	45-95
- cladial apophyses, length	40-45
Cladia
- ahydrothecate internodes, length	65-95
- hydrothecate internodes, length	255-300
- diameter at transverse node	30-40
Hydrotheca
- abaxial wall, length	180-195
- free adaxial wall, length	75-85
- adnate adaxial wall, length	110-120
- diameter at rim	100-115
Nematothecae
- axillar, length	60-65
- axillar, diameter at rim	ca. 25
- of ahydrothecate internodes, length	ca. 40
- of ahydrothecate internodes, diameter at rim	ca. 25
- mesial, length	ca. 55
- mesial, diameter at rim	ca. 25
- lateral, length	55-60
- lateral, diameter at rim	ca. 35
Gonotheca
- length	195-220
- maximum width	135-140
- pedicel, length	45-50
- pedicel, width	40-45