Medusoids in the life cycle of Dentitheca dendritica (Nutting, 1900) and Nemalecium gracile sp. nov. (Cnidaria: Hydrozoa) Author Galea, Horia R. Author Ferry, Romain Author Bertot, Jean-Marie text Zootaxa 2012 3527 43 54 journal article 10.5281/zenodo.282751 67086ae2-8f39-4bc1-b999-afd6edcd4a53 1175-5326 282751 Nemalecium gracile sp. nov. (Figs 2H–N, 3, 4A–D; Table 1 ) Nemalecium lighti — Calder, 1991a : 27, figs 17, 18.— Galea, 2008 ( pro parte ): 24, fig. 4M, O [not fig. 4N = Nemalecium cf. lighti ( Hargitt, 1924 ) ]. not Halecium lighti Hargitt, 1924 , 489, pl. 4 fig. 13. Material examined . Nemalecium gracile — Martinique , Les Abîmes, lat. 14.807514, long. -61.226698, 25 February 2012 , 8 m, sample M257: female colony, ca . 3.5 cm high, with ripe gonophores ( holotype , MHNG- INVE-82194); sample M258: male colony, ca . 3.0 cm high, with ripe gonophores ( paratype , MHNG-INVE- 82195). Martinique , Anse Trois Airs, lat. 14.513223, long. -61.097730, 0 4 February 2012 , sample M147: colony up to 2.4 cm high, with mono- and dioecious stems, on Pinna carnea (Bivalvia) (MHNG-INVE-82196). Martinique , Pointe Lamare, lat. 14.780461, long. -61.211935, 28 January 2012 , 10 m, sample M098: monoecious colony on Halimeda sp. Martinique , Petite Sirène, lat. 14.490951, long. -61.089147, 29 January 2012 , 6 m, sample M114: female colony, ca . 1.2 cm high, on Halimeda sp. Guadeloupe , Stn1. 1, 20 March 2008, several colonies, ca . 5 mm high, some fertile, on Thalassia testudinum . Guadeloupe , Stn. 6, 28 March 2008, numerous colonies, some fertile, up to 0.4 cm high, on T. testudinum . Guadeloupe , Stn. 7, 27 March 2008, a few sterile colony, up to 0.5 cm high, on T. testudinum . Nemalecium cf. lighti (Caribbean) — Guadeloupe , Stn. 6, 23 March 2008: numerous sterile colonies, with both mono- and polysiphonic stems, up to 5.0 cm high, on various algae, concretions and sponge. Guadeloupe , Stn. 7, 25 March 2008: a monoecious colony, ca . 1.8 cm high, on sponge; 27 March 2008 , a 1. Data on stations from Guadeloupe are given in Galea (2008) . few sterile colonies, up to 1.0 cm high, on hydrocoral. Martinique , Les Abîmes, sample M252: colonies on dead gorgonians, up to 2.0 cm high, some stems bearing rare, immature male gonothecae. Nemalecium cf. lighti ( Indonesia ) —Hatta (Rozengain) Island , lat. -4.590954, long. 130.039919, 19 October 2011 , 7 m: portion of a rich colony growing on hydrocoral, with stems up to 1.2 cm high and numerous mature male gonothecae. Derawan Island, lat. 2.284377, long. 118.243072, 18 April 2010 , 15 m: portion of a colony growing on dead gorgonian, stems up to 1.8 cm high, some bearing immature male gonothecae. Alor Island, lat -8.272613, long. 124.400860, 29 October 2010 , 20 m: small colony composed of a few stems detached from substrate, up to 2.2 cm high, some bearing mature male gonothecae. Description . Delicate, upright, unbranched or sparingly branched, coplanar colonies, up to 3.5 cm high, with mono- or slightly polysiphonic stems, arising at irregular intervals from creeping, ramified hydrorhiza (Figs 2H, 3A). Stems and side branches divided into internodes by transverse to slightly oblique nodes; internodes long, slender, slightly geniculate, of approximately the same length (Fig. 2I ); distally with a lateral hydrophore and an upwards-directed apophysis supporting subsequent internode. Hydrophore slightly surpassing level of distal node, bearing a hydrotheca at top (Fig. 2J). Side branches borne on short apophyses given off laterally from hydrophores, just below hydrothecal bases (Fig. 2I 1); first internode comparatively longer than subsequent ones; branching up to 3rd order. Hydrotheca shallow, walls straight, slightly flaring, margin not everted, rather slightly rolled inwardly for a short distance; distinct, large desmocytes as a ring of refringent nodules above diaphragm (Fig. 2J). Renovated hydrothecae occur irregularly; secondary hydrothecae arising at level of diaphragm from within primary hydrothecae; borne on funnel shaped hydrophores of varied length, perisarc annulated basally, smooth elsewhere (Fig. 2I 3–5). Hydranths tall, slender, constantly foraging; distally, a prominent constriction, delimiting the hypostome region from the rest of the body; body with a short, distal, slightly swollen digestive region, bright yellow in life, and a much longer, non digestive part below, nearly transparent in life ( Fig. 3 A, insert); hypostome region conical, bearing terminally the mouth, encircled by a row of 22–26 filiform tentacles ( Fig. 3 B), characteristically irregularly raised ( Fig. 3 A, insert); normally two conspicuous nematodactyls; between tentacle bases, large glandular cells ( Fig. 3 E), these also scattered over the hydranth body as ovoid, granular patches ( Fig. 3 B, g.c.); nematodactyls curved inwards towards hypostome from diametrically opposite sides or nearly so; each armed along either side with a row of 12–13 large pseudostenoteles ( Fig. 3 F). Nematocysts ( Fig. 4 A–D): 1) pseudostenoteles, 2) microbasic mastigophores typical of the haleciid hydroids, 3) microbasic euryteles resembling the microbasic mastigophores, but comparatively wider, and 4) ovoid rhopaloid heteronemes with oblique shaft (for measurements, see Table 1 ). Colonies and individual stems either mono- or dioecious. Gonothecae given off from primary hydrophores below hydrothecal bases (Fig. 2K, L, N, 3H–J), occasionally from the stolon. Gonothecae of both sexes similar, tubular, tapering gradually basally, walls undulated, distally truncate to watch glass shaped. Gonophores one per gonotheca, budded off from a blastostyle ending in a conspicuous apical plate, all enveloped together in an ectodermic mantle ( Fig. 3 J). Gonophores of cryptomedusoid type ; large, ovoid, with thick mesoglea; an eccentric, moderately long, club shaped spadix ( Fig. 3 P) surrounded by a compact mass of gametes, living only a reduced subumbrellar cavity ( Fig. 3 J); basally a fairly developed velum; bell aperture surrounded by a belt of spherical (8.5–17.0 µm wide), solid, refringent corpuscles arranged in 1–3 concentric rows ( Fig. 3 L and insert); subumbrella provided with conspicuous transverse myoepithelial cells ( Fig. 3 O); there are no radial or circular canals, no tentacles, no mouth, and no sense organs. Female gonophore with ca . 30–35 polygonal eggs with large nuclei ( Fig. 3 H). Elongating blastostyle, followed by the mantle withdrawal allow the gonophore to be progressively liberated ( Fig. 3 K) through the rupture of a rounded, apical "lid" of the gonotheca (fig. 2M). Spawning and fertilization could not be observed in either sex. Discussion . The material assigned to Nemalecium lighti ( Hargitt, 1924 ) by Calder (1991a) shows striking resemblances to the present species. The shape and size of the internodes, the primary hydrophores surpassing the level of the distal node, as well as the size of the pseudostenoteles, strongly suggest that it is conspecific with N. gracile (see also Table 1 for comparison). The same is partly true for the material studied earlier by Galea (2008) . Indeed, upon its reexamination, it was found that it is actually composed of two species, one of which is N. gracile . Distinction between them is easier, especially when living specimens are examined, given the present material from Martinique . Nemalecium gracile has very long, nearly transparent (except for the digestive part, with a conspicuous bright yellow tinge), constantly foraging hydranths, whose tentacles are typically raised at different levels (see insert of Fig. 3 A). In contrast, the second species2 has shorter, nearly immobile, milky white hydranths (except for their digestive part, which is pale yellow), with all tentacles always raised at the same level. Microscopically, both species are especially distinguished through the shape and size of their internodes (compare Fig. 2I 1–5 and 2P, Q), as well as the cnidome composition (compare Fig. 4 A–D and E–H). FIGURE 3 . Nemalecium gracile sp. nov. —living colony (A) and hydranth (insert) showing the typical bright yellow tinge of the digestive region and the tentacles raised at different levels; fixed hydranth showing the hypostome (h.) encircled by the row of filiform tentacles (f.t.), the digestive (d.r.) and non-digestive (n.d.r.) regions, as well as ectodermic glandular cells (g.c.); detail of the non-digestive region (C) showing highly vacuolated endodermal cells; detail of a filiform tentacle showing large, endodermal chordal cells (D); insertion of the filiform tentacles (f.t.) around the hypostome, showing conspicuous glandular cells (g.c.) in between; nematodactyl (n.d.) armed with pseudostenoteles (p.s.) and filiform tentacles (f.t.) richly recovered with microbasic mastigophores (m.b.m.) (F); detail of a nematodactyl showing a discharged pseudostenotele (G); female (H) and male (I) gonothecae from dioecious stems; gonotheca and male gonophore, showing the blastostyle (b.) ending in an apical plate (a.p.) and budding off the gonophore, all being covered with a mantle (m.); the slightly eccentric spadix (s.) is distinguished from the mass of sperm cells (s.m.) through its darker tinge (J); male medusoid getting free from its mantle (m.), which remains attached to the blastostyle (b.) (K); newly released male medusoid (L), showing the conspicuous belt of refringent corpuscles (insert); fixed male medusoid seen with transmitted (M) and incident (N) light, showing the velar aperture (left) and the striated subumbrellar ectoderm; detail of the myoepithelial fibers of the subumbrellar ectoderm (O); slightly squashed preparation of a male medusoid showing the spadix (sp.) and a number of pseudostenoteles (p.s.) disseminated among the mass of gametes (P). Scale bars: 30 µm (O), 50 µm (D, E, G, and insert of L), 100 µm (F), 200 µm (P), 300 µm (C, J, M, N), 500 µm (A, B, K, L), 1 mm (H, I). FIGURE 4 . Cnidome of Nemalecium gracile sp. nov. (A–D) and Nemalecium cf. lighti (Hargitt, 1924) from the Caribbean (E–H) and Indonesia (I–L): pseudostenoteles (A, E, I), microbasic mastigophores (B, F, J), microbasic euryteles (C, G, K), and unidentified rhopaloid heteronemes (D, H, L). The type material of N. lighti , the sole nominal species belonging so far to that genus, was not examined and specimens from the type locality (Puerto Galera, Mindoro Oriental, Philippines ) were unavailable for this study in order to confirm the identification of the second Caribbean species. However, material belonging to Nemalecium originating from three remote ( 700–1500 km distant) Indonesian localities (Alor, Derawan, and Hatta islands) is housed in the private collection of the senior author and was therefore available for comparison with the original description of N. lighti by Hargitt (1924) and with the Caribbean specimens in hand. The materials from Alor and Derawan agree well with the description of the type of N. lighti (especially in the colony structure and the length of their internodes3), and they are most probably conspecific. In contrast, the colony from Hatta, growing over a gorgonian, has a different appearance and seems to display a few distinctive features, such as a tendency to form widely-spaced, mostly unbranched, rather stout stems, with irregular internodes (Fig. 2X ), while the specimens from Alor and Derawan form characteristically more crowded stems, branched strictly in one plane, and provided with typical collinear internodes (Fig. 2U, V). In contrast, the cnidome seems uniform in all three sets of material4. 2. A living colony from Guadeloupe is illustrated in Galea (2010) , p. 6, fig. 1A. 3. Material with a similar trophosome was reported on by Pennycuik (1959) from Queensland, Australia . 4. This should be checked again using living material so as to obtain fully discharged capsules. TABLE 1 . Comparative measurements of Nemalecium (in µm, unless otherwise stated) based on specimens from literature data and the present study. N.I. signifies that information was not indicated by the authors cited. N.B.: Male and female gonothecae of the Caribbean specimens assigned to Nemalecium cf. lighti were not fully formed and their dimension are expected to be above the range given herein.

Geographical distribution Reference Colony - height (mm) - appearance	Nemalecium gracile sp. nov Western Atlantic Martinique Bermuda Present study Calder (1991a), as N. lighti 35 20 coplanar N.I.	Nemalecium cf. lighti Western Atlantic Guadeloupe Brazil Present study Migotto (1996) 50 54 coplanar N.I.	Indo-Pacific Indonesia Present study 20 coplanar	Australia Pennycuik (1959) N.I. N.I.
Internodes
- length	625–1165 308–802	445–555 280–780	335–675	380–470
- diameter at node	75–135 45–89	110–175 95–175	100–160	107–154
Hydrotheca and hydranth
- diameter at rim - diameter at base	155–170 124–166 135–155 98–144	155–175 122–205 135–145 117–192	150–170 135–150	150–170 N.I.
- height	30–40 21–28	35–40 17–52	40–45	ca . 30
- hydrophore length	35–50 N.I.	0 (sessile) 0 (sessile)	0 (sessile)	0 (sessile)
- tentacle number Cnidome - pseudostenoteles	22–26 ca . 25 26.3–30.0 × 26.5–29.1 × 11.6–13.1 12.3–13.3	ca . 28 21–24 38.4–42.1 × 37.0–39.0 × 13.7–16.8 15.0–17.0	ca . 28 39.5–42.1 × 13.7–15.3	N.I. N.I.
- microbasic mastigophores	7.4–8.1 × 2.1 6.5–7.3 × 1.7–2.0	6.8–7.4 × 2.1 7.0–8.0 × 2.0–2.5	6.3–6.8 × 1.8–2.1	N.I.
- microbasic euryteles	7.4–8.4 × N.I. 2.6–2.9	7.4–8.1 × N.I. 2.9–3.2	8.4–8.9 × 3.1–3.7	N.I.
- rhopaloid heteronemes	5.8–6.3 × N.I. 3.9–4.2	4.5–5.0 × N.I. 2.6–2.9	4.5–5.0 × 2.4–2.6	N.I.
Female gonotheca
- length - maximum diameter	1180–1670 N.I. 465–525 N.I.	1790–1890 N.I. 500–575 N.I.	N.I. N.I.	N.I. N.I.
Male gonotheca
- length	1060–1400 ca . 1300	1400–1585 1300–1900	ca . 1545	N.I.
- maximum diameter	390–465 ca . 515	425–560 385–800	ca . 435	N.I.
Female gonophore
- length - maximum diameter - egg number	1025–1305 N.I. 355–400 N.I. 30–35 N.I.	N.I. N.I. N.I. N.I. N.I. N.I.	N.I. N.I. N.I.	N.I. N.I. N.I.
Male gonophore
- length - maximum diameter	730–1085 N.I. 255–340 N.I.	1195–1220 N.I. 305–415 N.I.	ca . 760 ca . 325	N.I. N.I.

There is increasing evidence that we are most probably dealing with more than one species of Nemalecium in the Indo-Pacific, some materials having been likely erroneously assigned earlier to the binomen N. lighti , as exemplified by the specimens from Papua New Guinea studied by Bouillon (1986). His material displays some obvious morphological differences compared to the type of N. lighti described by Hargitt (1924) , such as the presence of very long, slender internodes, similar to those of N. gracile . In addition, Di Camillo et al . (2008) mentioned an as yet unnamed species inhabiting the "shady crevices of the corals" in North Sulawesi, while Gravier-Bonnet & Bourmaud (2006) found another species "colonizing walls and tips of large grey sponges" in Juan de Nova Island , as well as two additional species occurring in the Maldives ( Gravier-Bonnet & Bourmaud 2012 )5. We conclude that a comprehensive study of Nemalecium , based on abundant, fertile material, is imperative, though out of the scope of the present paper. Subtle morphological differences could, indeed, be noted only if living material is studied, including the precise identification of the nematocyst types upon obtaining fully discharged capsules. On the other hand, comparison of the second species of Nemalecium from the Caribbean (Fig. 2P, Q) with the materials from Alor and Derawan indicate that they are indistinguishable morphologically from each other, a conclusion equally supported by their respective cnidomes (compare Fig. 4 E–H and 4I –L). Therefore, we tentatively assign the second Caribbean Nemalecium to Hargitt's (1924) species, pending reexamination of the type of N. lighti . It is curious to note that the cnidome of Nemalecium was underestimated in earlier accounts (Bouillon 1986, Calder 1991a , Migotto 1996 ). In addition to the conspicuous pseudostenoteles and the numerous microbasic mastigophores, it appears to comprise at least two additional, less abundant types of capsules: a microbasic eurytele similar in length to the mastigophores, but comparatively wider ( Fig. 4 C, G, K), and an unidentified rhopaloid heteroneme, possibly a microbasic eurytele ( Fig. 4 D, H, L). Pseudostenoteles are found not only in the nematodactyls ( Fig. 3 F, G), but occur also in the coenosarc of the trophosome, as well as in the gonophores, where they are more easily seen in the male medusoids as large capsules (p.s.) scattered among the mass of sperm cells ( Fig. 3 P). The microbasic mastigophores (m.b.m.) heavily arm the filiform tentacles of the hydranths ( Fig. 3 F), but are equally found in the coenosarc and the exumbrella of the medusoid. The microbasic euryteles occur in the coenosarc of the trophosome, as well as in the gonophore mantle, while the heteronemes are found in the coenosarc and the spadix of the medusoid. Based on the cnidome composition alone, especially on the shape and size of the pseudostenoteles, it is obvious that N. gracile could be readily distinguished, through its comparatively smaller capsules (Calder 1991 and the present study), from the Indonesian (present study), Papua New Guinean (Bouillon et al . 1986), and Brazilian ( Migotto 1996 ) materials, as well as from the Caribbean specimens provisionally assigned to N. lighti . The swimming gonophores of N. gracile are morphologically similar to, and exhibit apparently the same expulsion mechanism from the gonotheca as those described earlier by Gravier-Bonnet & Migotto (2000) for N. cf. lighti 6. Gross differences rely in the number of eggs (possibly 7 30–35 vs . 40–62) and the shape of the marginal corpuscles (rounded vs . irregular). Similarities between the medusoids of Nemalecium and those belonging to other hydrozoan families have been discussed at length by the above-mentioned authors. Due to their apparent mineral composition and their shape and size possibly being influenced by physicochemical parameters, it is unclear whether these corpuscles are good indicators for the separation of species. Morphological differences have been observed, for instance, between specimens from Reunion and Brazil , as noted by Gravier-Bonnet & Migotto (2000) . Moreover, corpuscles with heterogenous morphology may occur within the same species, as illustrated by Antennella sp. from Reunion Island ( Bourmaud & Gravier-Bonnet 2005 ). On the other hand, the number of eggs should be, in theory, species-specific, but there are contrary evidences demonstrating that it can vary depending on environmental factors in at least two documented cases: Macrorhynchia philippina and an as yet unidentified Rhizogeton from the Indian Ocean (Bourmaud & Gravier- Bonnet 2004). 5. Due to complete absence of formal descriptions and illustrations, all these "species" records are considered with some reservation, and are listed herein for information only, pending detailed taxonomical studies that clarify their identities. 6. According to Gravier-Bonnet & Migotto (2000) , slight differences were observed between the specimens from São Sebastião and those from Reunion Island, suggesting that they were probably dealing with two different species. 7. Egg number could not be evaluated with certainty in non-spawned medusoids. Their number was estimated in nonreleased gonophores, through the transparency of the gonothecal wall. Attempts to estimate their number in dissected, formalin-fixed gonophores proved inconclusive. Since neither swimming of the gonophore, nor the spawning could be observed in N. gracile , it is assumed that the role of the subumbrellar myoepithelial cells is to favor peristaltic movements of the bell allowing the gametes to be liberated out of the gonophore, while the contractions of the velum would help the medusoid to swim and spread its gametes in the water column. Ecology . Nemalecium gracile occurs on Halimeda sp., on the leaves of Thalassia testudinum , on some bivalve shells ( e.g. Pinna carnea ), and on artificial inert substrates ( e.g. fishing wires). In contrast, N. cf. lighti of the tropical western Atlantic is found on a larger variety of substrates, mainly sponges and (dead) gorgonians, but also on mineral concretions, worm tubes, various artificial inert substrates, or the algae Tricleocarpa sp. and Amphiroa sp., as well as Halimeda sp. Geographical distribution . Bermuda ( Calder 1991a ), Guadeloupe ( Galea 2008, pro parte ), Martinique (present study), possibly Belize ( Calder 1991b, as N. lighti , presumably the specimens growing on T. testudinum ). The species is expected to occur in the whole Caribbean basin and northwards to Bermuda , and possibly to the neighboring Gulf of Mexico (though not listed by Calder & Cairns 2009 ). Etymology . The specific name gracile , Latin , meaning “slender” or “thin”, makes reference to the delicate appearance of the colonies and the features of their internodes.