Plumularia insignis Allman, 1883

Agís, José Ansín, Ramil, Fran & Calder, Dale R., 2016, 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, Zootaxa 4169 (1), pp. 57-86 : 73-77

Plumularia insignis Allman, 1883

( Figs 10‒11 ; Table 5 )

Plumularia insignis Allman, 1883: 21 , pl. II, figs. 1‒4; Billard, 1908: 759; Billard, 1910: 32, fig. 14; Van Praët, 1979: 924, fig. 96.

? Plumularia insignis: Millard, 1977: 42 , fig. 12D‒E; Stepanjants, 1979: 117, pl. XXII, fig. 2; Blanco, 1994: 239, fig. 30; Genzano, 1995: 6; Das, 2007: 16; Gul et al., 2015: 6.

Plumularia abietina Allman, 1883: 21 , pl. III.

Plumularia insignis abietina: Billard, 1908: 759 .

Plumularia insignis var. abietina: Billard, 1910: 35 ; Bedot, 1921: 28; Van Praët, 1979: 925.

Plumularia flabellum var. abietina: Stechow, 1923: 226 .

? Plumularia sp. Naumov & Stepanjants, 1962: 100, fig. 19.

Not Plumularia cf. insignis: Vervoort & Watson, 2003: 394 , fig. 95G‒I.

Material examined. Plumularia insignis : fragments of syntype material at the Museum national d’Histoire naturelle, Paris; Challenger Expedition Stn. 145, 46º40’S– 37º50’E, 567 and 274 m depth, 27-12-1873, off Prince Edward Island ( South Africa). MNHN-IK-2012 -16036, three slides:

L. 1278. Fragment of a polysiphonic branch 14 mm long, with hydrocladia arising from axial tube; secondary tubes with nematothecae.

L. 1279. Five hydrocladia.

L. 1280. Branch fragment 17 mm long, with polysiphonic basal part and hydrocladia arising from axial tube.

Plumularia abietina: fragments of syntype material at the Museum national d’Histoire naturelle, Paris; Challenger Expedition, Prince Edward Island ( South Africa). MNHN-IK- 2012 - 16035, two slides:

L. 1179. Six hydrocladia.

L. 1281. Fragment of distal part of a branch, 11 mm long; monosiphonic; with four gonothecae; a second fragment 5 mm long, with one apophysis, one hydrocladium and one gonotheca.

Distribution. Plumularia insignis is known with confidence only from Prince Edward Island ( South Africa) at depths of 274 and 567 m (Allman 1883). Records from Kerguelen (Millard 1977; Naumov & Stepanjants 1962, as Plumularia sp.), southwestern Atlantic (Stepanjants 1979; Genzano 1995), Bangladesh (Das 2007) and Pakistan (Gul et al. 2015) are considered here as dubious and the material reported from New Zealand waters by Vervoort & Watson (2003, as Plumularia cf. insignis ) is excluded (see Discussion).

Description. Type material of Plumularia insignis . Fragment of hydrocaulus polysiphonic proximally, becoming monosiphonic distally. Main tube divided into internodes by straight nodes, with nodes visible only on monosiphonic parts; each internode with two apophyses, one near mid-region and another near distal node; nematothecae two, one near proximal node and another just above first apophysis. Apophyses bearing hydrocladia directed alternately left and right, arising only from main tube; each apophysis with one mamelon having a welldeveloped circular aperture and three or four nematothecae: two axillary and one or two above mamelon; two perisarcal thickenings sometimes apparent. Internode at proximal end of hydrocladium ahydrothecate, with one nematotheca on a small elevation basally, and with two perisarcal rings, one at each end. Rest of hydrocladium comprising a succession of hydrothecate and ahydrothecate internodes, separated by oblique nodes. Hydrothecate internodes with one hydrotheca in mid-region and with three nematothecae: one mesial inferior and two laterals. Hydrotheca cup-shaped, deep; adcauline wall fully adnate; abcauline wall straight; margin circular, smooth, perpendicular to hydrocladial axis. Mesial inferior nematotheca on a small elevation, sometimes surpassing hydrothecal base. Lateral nematothecae on small apophyses placed below hydrothecal margin, but extending some distance beyond orifice. Mesial and lateral nematothecae with distal chamber slightly scooped. Number of perisarcal rings variable, with between two and six per internode along the same hydrocladium; when six thickenings apparent, two located below hydrotheca, three behind, and one above; when two appear, one present at each end. Ahydrothecate internodes each with one nematotheca basally on a small elevation, and two perisarcal thickenings at ends, these strongly developed on proximal parts of hydrocladium and weakly developed on distal parts. All nematothecae bithalamic, movable. Nematothecae of apophyses larger that those of hydrocladial internodes.

Type material of Plumularia abietina . Fragment of hydrocaulus monosiphonic, divided into internodes by transverse nodes; each internode with two apophyses bearing hydrocladia, one near mid-region and another just beneath distal node on opposite side; cauline nematothecae two per internode, one immediately above basal node and another over first apophysis. Apophyses alternately placed left and right, each with one well-developed mamelon, two axillary nematothecae, and one or two unpaired nematothecae distal to mamelon; one perisarcal ring may occur near the node. Hydrocladia inserted on apophyses, arranged alternately to left and right, segmented heteromerously. First internode of hydrocladium always ahydrothecate, with one nematotheca on a small elevation on basal part and with two perisarcal rings, one at each end. Hydrothecate internodes with one hydrotheca and three nematothecae: one mesial inferior and two laterals. Hydrotheca cup-shaped, placed centrally, with adcauline wall fully adnate, abcauline wall straight; hydrothecal margin smooth, circular, perpendicular to hydrocladial axis. Mesial inferior nematotheca on a small elevation, reaching or sometimes surpassing hydrothecal base. Lateral nematothecae each borne on a small apophysis located under hydrothecal margin, extending well beyond orifice.

Annular thickenings as many as six per internode. Mesial and lateral nematothecae with distal chamber slightly scooped. Nematothecae of apophyses larger that those of hydrocladial internodes. Ahydrothecate internodes with one nematotheca on basal part, arising from a small elevation; perisarcal thickenings two, with one at each end. All nematothecae bithalamic, movable.

Gonothecae large, tubular, widening towards distal end; aperture tilted, closed by a semicircular operculum; in lateral view, gonotheca narrow over apical part.

Remarks. Examination of type materials of Plumularia insignis Allman, 1883 and P. abietina Allman, 1883 revealed no significant morphological differences between them except for the former, having a polysiphonic stem. As for that character, we emphasize that our description of P. abietina is based on the material examined by us, namely six isolated hydrocladia (L.1179) and two monosiphonic fragments of the distal part of two branches (L.1281); in the original description, Allman (1883: 21) stated that the colony is polysiphonic. In consequence, both possessed the same colony structure, with similar branching patterns. Trophosomal morphology and measurements were also identical. We therefore uphold the conclusion that they are conspecific. Billard (1908), acting as First Reviser, assigned precedence to the name P. i n s i g ni s over P. abietina (as well as over P. f l ab e l l um Allman, 1883, which he believed was conspecific). The presence of a polysiphonic stem having a main tube provided with lateral apophyses that support hydrocladia fits well within the current concept of the genus Plumularia Lamarck, 1816 .

We consider other records of P. insignis in the literature to be questionable because of differences in colony morphology from the type material examined here. Hydroids referred to P. i ns i gn i s by Millard (1977) from Kerguelen had hydrocladial internodes that were nearly all hydrothecate. Ahydrothecate internodes were rare, sporadic, and normally linked to regeneration processes following damage. Segmentation of hydrocladia was also mostly homomerous in specimens examined by Naumov & Stepanjants (1962, as Plumularia sp.) from the Kerguelen Islands. The same character was reported by Stepanjants (1979) in colonies from Patagonia, although gonothecae were similar to those described in P. abietina by Allman (1883). Colony ramification in material examined by Millard (1977) included lateral branches originating from secondary tubes (see Millard 1977: fig. 12D), and a hydrocladium originating from the same tube was always present below each branch. Millard considered this character, not previously described, to be peculiar to the Kerguelen material. A similar pattern of ramification from accessory tubes was also described by Vervoort (1972) and Blanco (1976) in hydroids identified as Nemertesia ramosa Lamouroux, 1816 . Both of those records were later referred to P. insignis by Stepanjants (1979) and Ramil & Vervoort (1992). Finally, P. insi gni s has been reported from the southwestern Atlantic (Genzano 1995), Bangladesh (Das 2007) and Pakistan (Gul et al. 2015) but all without description of the colonies. In our opinion, hydroids from these studies merit re-examination before they can be assigned with confidence to P. insignis .

The specimen included provisionally in P. insignis by Vervoort and Watson (2003, as Plumularia cf. insignis ) is clearly not referable to that species. It differs in having two hydrothecae per internode, hydrothecae that are very deep and with the abcauline wall slightly concave, and an additional unpaired nematotheca at the base of the hydrotheca.

Figures

FIGURE 10. Plumularia insignis Allman, 1883. Syntype material; A: colony (after Allman 1883). B: fragment of a polysiphonic axis with two apophyses and proximalmost internodes of a hydrocladium. C: part of a hydrocladium, with detail of hydrothecate and ahydrothecate internodes. Scales a: 2 cm. b ‒ c: 0.1 mm.

FIGURE 11. Plumularia insignis Allman, 1883. Syntype material of Plumularia abietina Allman, 1883; A: colony (after Allman 1883). B: fragment of axis with an apophysis and proximalmost internode of a hydrocladium. C: part of a hydrocladium, with detail of hydrothecate and ahydrothecate internodes. D: gonotheca, frontal view. E: gonotheca, lateral view. Scales a: 2 cm. b ‒ e: 0.1 mm.

Tables

TABLE 5. Measurements of Plumularia insignis Allman, 1883 and Plumularia abietina Allman, 1883 in µm.

	P. insignis	P. abietina	P. abietina
	L.1279	L.1179	L.1281
First hydrocladial internode, length	220‒270	150‒170
Diameter at node	100‒110	100‒110
Hydrothecate internode, length	510‒610	460‒520
Ahydrothecate internode, length	130‒180	140‒160
Diameter at node	80‒110	80‒110
Hydrotheca
Abcauline wall, length	220‒330	250‒290
Adcauline wall, length	190‒270	210‒260
Diameter at rim	150‒190	180‒200
Mesial nematotheca, length	100‒110	100‒110
Diameter at rim	50	50
Lateral nematotheca, length	90‒100	90‒100
Diameter at rim	40‒50	50‒60
Gonotheca, length			1860‒2160
Maximun diameter			620‒710