Plumularia mooreana, Schuchert & C.P. & Ch-, 2013

Schuchert, Peter, 2013, Plumularia mooreana, a new marine hydroid from French Polynesia (Hydrozoa, Cnidaria), Revue suisse de Zoologie 120 (3), pp. 405-413 : 405-410

Plumularia mooreana n. spec.

Figs 1-2

Plumularia strobilophora . – Ryland & Gibbons, 1991: 536, fig. 8. [not Plumularia strobilophora Billard, 1913 ]

HOLOTYPE MATERIAL: University of Florida Natural History Museum UF-7017; field number BMOO-08101; Moorea , 17.55143°S 49.77698°W, 0-2 m depth, collected 06.12.2009, one fertile colony and several stems originating presumably from same colony, some stems with gonothecae, some detached gonothecae present.

PARATYPE MATERIAL: University of Florida Natural History Museum UF-6730; field number BMOO-06413; Moorea , 17.45747°S 149.83277°W, 10-20 m depth, collected 21.11.2009; 2 sterile plumes. – UF-6762; field number BMOO-06722; Moorea , depth 0-3 m, collected 23.11.2009; 5 sterile plumes. – UF-7026; field number BMOO-08110; Moorea , 17.55143°S 149.77698°W; depth 0-2, collected 06.12.2009; several small, sterile plumes.

DIAGNOSIS: Plumularia species with large gonothecae borne on basal part of stem, bearing numerous, scattered nematothecae; walls undulated, distal end broadly truncate, attachment site to stem basilateral. Hydrothecae very shallow, with curved abaxial wall. Lateral nematothecae distinctly funnel-shaped. Plumes small, unbranched.

DESCRIPTION: Relatively small, delicate, pinnate shoots arising from creeping stolons. Stems monosiphonic, regularly and distinctly divided by transverse nodes, each internode with a distal apophysis and two nematothecae: one in the upper axil of apophysis and one in the lower half of segment, on side opposite to apophysis. Perisarc thick at base, thinning out distally.

Hydrocladia alternate, on two opposite sides of the stem, carrying up to four hydrothecae; segmented heteromerously, distinct nodes delimiting main- and intersegments (hydrothecate and ahydrothecate segments), proximal-most segment short and without nematothecae (athecate segment). Main segments elongate, proximal node oblique, distal node straight, with a hydrotheca in middle of segment and three nematothecae: one median inferior and two laterals. Intersegments variable in length, each with one median nematotheca, proximal node straight, distal node oblique. Both types of segments may have indistinct internal, annular ridges close to their ends.

Hydrotheca inclined approx. 45° to main axis of segment, bowl-shaped, shallow, ratio diameter/depth about 2, adcauline wall not completely adnate, abcauline wall thickened and in the majority of the hydrothecae of one plume distinctly convex (bulging), rim smooth to somewhat irregularly undulated, internal wall with a ring of numerous, conspicuous desmocytes (small perisarc knobs).

Nematothecae two chambered, movable, lateral pair conspicuously funnelshaped, with a broad, distal aperture; as high or higher than hydrothecal depth, wall facing hydrotheca depressed.

One to two gonothecae on basal part of stem where no hydrocladia occur; thinwalled, bullet-shaped, base often curved, lateral walls straight to convex, variably undulated (annular bulges/swellings), distal end a large, flat, circular surface. Connection site to stem is basilateral. Numerous (up to 15 seen) nematothecae, more tubular than the laterals associated to the hydrotheca, are scattered over the surface of the gonotheca.

The measurements are given in Table 1.

REMARKS: The following publications were considered to compare the new species to other P. setacea -like hydroids: Allman (1877), Bale (1884), Billard (1913), Calder (1997), Fraser (1937, 1938, 1944, 1948), Hirohito (1995), Jarvis (1922), Mammen (1967), Migotto (1996), Millard (1975), Nutting (1900, 1906, 1927), Ralph (1961), Ryland & Gibbons (1991), Schuchert (2013), Vervoort & Vasseur (1977), Vervoort & Watson (2003), Watson (1973). A complete list of all Plumularia species was obtained from Schuchert (2012).

Plumularia mooreana is a member of the large group of P. setacea -like hydroids (comp. Schuchert, 2013). It is, however, readily distinguished from the nearly cosmopolitan P. setacea through its different gonothecae, the shallower and more tilted hydrothecae, and the funnel-shaped lateral nematothecae.

The most characteristic feature of P. mooreana is found in its gonotheca, whose surface is covered with numerous nematothecae ( Fig. 1 B-C). Species belonging to the family Plumulariidae rarely have nematothecae on their gonothecae, a trait that is typical of the Halopterididae ( Schuchert, 1997; the family also includes the genus Polyplumaria , see Peña Cantero et al., 2010). The only known exceptions within the genus Plumularia are P. wasini Jarvis, 1922 , Plumularia australiensis Watson, 1973 , and some populations of P. filicula Allman, 1877 (see Vervoort & Watson, 2003). Plumularia wasini has 2-3 nematothecae on its gonothecae ( Millard, 1975), but is is otherwise rather different from P. mooreana : in having hydrothecae with a relatively long, free adcauline side and a straight abcauline side, a solitary nematotheca behind the hydrotheca, short main segments, gonothecae on hydrocladia, and stem-nematothecae in two rows. Plumularia australiensis closely resembles P. wasini and is therefore distinguishable from P. mooreana using the same characters listed for P. wasini . Plumularia filicula has normally no nematothecae on its gonothecae (comp. Ramil & Vervoort, 1992), but Vervoort & Watson (2003) described material from New Zealand which had a small gonothecae with two nematothecae. As already acknowledged by Vervoort & Watson (2003), the identity of this material is uncertain and it might represent another, undescribed species. The shape of the gonothecae and the hydrothecae of this material are very distinct from P. mooreana and both forms are clearly separable.

Although it is not particularly convex in P. mooreana , a curved outer abcauline hydrothecal wall is also uncommon in the genus Plumularia , being present in only a few congeners, e. g. P. lagenifera Allman, 1885 , P. gaimardi (Lamouroux, 1924) (for a redescription see Schuchert, 2013), and Plumularia caliculata Bale, 1888 . However, all of them have gonothecae that lack nematothecae.

The attachment of the gonotheca in the lower part of the stem is also seen in P. strictocarpa Pictet, 1893 , but the gonothecae of this species have more distinct annular ridges and, again, bear no nematothecae. Moreover, its hydrothecae are different (deeper, straight walls). Both species occur sympatrically, as material of P. stricocarpa was collected concomitantly with P. mooreana (not shown, specimens UF-6820 & UF 7112 of the University of Florida Natural History Museum)

The trophosome of P. mooreana resembles most closely that of P. strobilophora Billard, 1913 , notably regarding the rather shallow, strongly inclined hydrothecae. In the absence of gonothecae, the two species can be difficult to distinguish, and it seems that Ryland & Gibbons (1991) misidentified specimens of P. mooreana as P. strobilophora , although they noted the differences to descriptions given by other authors. In order to make sure that both species are clearly distinct, the type material of P. strobilophora was examined for this study (see below). Apart from the absence of nematothecae on the gonothecae, Plumularia strobilophora differs from P. mooreana in the following details: the first hydrocladial segment (athecate segment) is distinctly longer (comp. Figs 1B and 3A ), there are 2-3 nematothecae on the stem apophyses ( Fig. 3A ), the abcauline hydrothecal wall is either straight or often concave (comp. Figs 2D and 3D ), the portion of the main segments distal to the hydrotheca is distinctly longer (comp. Figs 2A, C and 3B, C ), the intersegments are much longer (comp. Figs 2A, C and 3B, C ), and the gonothecae are much smaller and carried on the stem region provided with hydrocladia.

The conspicuously funnel-shaped lateral nematothecae is another character which distinguishes P. mooreana from all Plumularia species discussed above ( Fig. 2F ).

The distinct ring of desmocytes ( Figs 2A, C, E ) is not unique to P. mooreana , being also present in other species (see Schuchert, 2013). What is rather special, is its position in the upper half of the hydrotheca. Usually it is located near its base and rather inconspicuous.

DISTRIBUTION: French Polynesia (this study), Fiji Islands ( Ryland & Gibbons, 1991); depth 0- 20 m.

Figures

FIG. 1 Plumularia mooreana n. spec. (A) Silhouettes of two plumes: paratype (left), holotype (right). (B) Segment of stem with first, athecate segment of a hydrocladium, FU-6730. (C-D) Gonothecae, holotype. (E) Nematotheca of gonotheca, same scale as B.

FIG. 2 Plumularia mooreana n. spec., scale bar applies to all drawings. (A) Main- and intersegment of hydrocladium, holotype. (B) Abcauline wall of hydrotheca, holotype. (C) Main- and intersegment of hydrocladium, FU-6730. (D) Abcauline wall of hydrotheca, FU-6730. (E) Main segment of hydrocladium, holotype. (F) Lateral nematotheca in adcauline view, holotype.

FIG. 3 Plumularia strobilophora Billard, 1913, syntypes ZMA-4014. (A) Segment of stem with first, athecate segment of a hydrocladium. (B-C) Main- and intersegment of hydrocladium. (D) Hydrotheca. (E) Lateral hydrothecae, same scale as D. (F-G) Female gonothecae, same scale as A. (H) Male (?) gonotheca, same scale as A.