Nemertesia irregularis ( Quelch, 1885 )

Gil, Marta, Ramil, Fran & Agís, José Ansín, 2020, Hydroids (Cnidaria, Hydrozoa) from Mauritanian Coral Mounds, Zootaxa 4878 (3), pp. 412-466 : 446-452

Nemertesia irregularis ( Quelch, 1885)

( Figs. 9 , 10 , 11 ; Table 4 )

Antennularia irregularis Quelch, 1885: 8–9 , Pl. II fig. 4 (Not Antennularia irregularis Fraser, 1938 = Nemertesia fraseri Ramil & Vervoort, 1992 )

Antennularia antennina var. à longs articles: Billard, 1901: 71.

Antennularia antennina var. longa Billard, 1904: 216 ; 1906b: 210, fig. 15B.

Antennularia Perrieri var. antennoïdes Billard 1904: 217 .

Antennularia Perrieri var. antennoïdes ; Billard, 1906b: 212; Arévalo & Carretero, 1906: 82, pl. 13 fig. 3; Fey, 1969: 404.

Antennularia janini Marktanner-Turneretscher, 1890: 259 , pl. VI figs 9, 9A. (Not Nemertesia janini Lamouroux, 1816 = Nemertesia ramosa Lamouroux, 1816 ).

Nemertesia antennina var. irregularis p. p.: Bedot, 1917: 42–43.

Not Nemertesia irregularis: Ramil & Vervoort, 1992:170–173 , fig. 48a; Medel & Vervoort, 1995: 52–56, figs 22, 23c [= Nemertesia perrieri ( Billard, 1901) ].

Nemertesia antennina: Ramil & Vervoort, 1992: 163–169 , figs. 42A–R, 43A–H (part); Ansín Agís, 1998: 437–456, figs. 59A–F, 60A–F, 61A–E (part); Ansín Agís et al., 2001: 193–200, fig. 76–77 (part) [not Nemertesia antennina ( Linnaeus, 1758) ].

Material examined. MAURIT-0911, stn MUDR01 , 16º08´24”N, 16º57´12”W, 488 m, 5-XII-2009: four colonies 13–22 mm high, one with male gonothecae .

MAURIT-0911, stn MUDR02 , 16º08´50”N, 16º57´01”W, 462 m, 5-XII-2009: one colony, without gonothecae .

MSM 16 /3, stn GeoB 14796–5, ROV, 20°14.823’N, 17°40.178’W, 613 m, 3-XI-2010: one colony 39 mm high, with male gonothecae .

MSM 16 /3, stn GeoB 14871–2, 19°08.344’– 19°08.235’N, 16°45.849’– 16°45.664’W, 427–566 m, 9-XI-2010: two colonies 29 and 41 mm high, one colony with female gonothecae .

MSM 16 /3, stn GeoB 14903–1, GKG, 17°32.853’N, 16°39.700’W, 414 m, 15-XI-2010: two colonies on Lophelia pertusa , one with male gonothecae .

Biology. Gonothecae have been found between May and June [ Ramil & Vervoort 1992; Ansín Agís et al. 2001, both as Nemertesia antennina ( Linnaeus, 1758) ]. In our material, the gonothecae were found in November and December. Some colonies were found growing on L. pertusa .

Distribution. Nemertesia irregularis is principally known in the East Atlantic from Glénand Archipelago (Brittany, France) ( Fey 1969, as N. perrieri var. antennoides ), Santander (North Spain) (Arévalo & Carretero 1906, as A. perrieri var. antennoides ), Azores ( Ansín Agís et al. 2001, as N. antennina ), Gulf of Cádiz ( Billard 1906b, as Antennularia perrieri var. antennoïdes ), various localities off the Atlantic coast of Morocco ( Patriti 1970, as N. antennina var. irregularis ; Ansín Agís et al. 2001, both as N. antennina ), Canary Islands ( Billard 1901, 1904, 1906b; Ansín Agís et al. 2001, as N. antennina ), Cape Blanc, Mauritania ( Ansín Agís et al. 2001, as N. antennina ) and Cape Verde Islands (type locality) ( Quelch 1885). The records of N. irregularis in Japanese waters ( Stechow 1909, 1913b; Jäderholm, 1919) should be regarded with caution and need further confirmation.

This species has been collected from depths of 12 to 2450 m ( Ansín Agís et al. 2001). Our material was collected from 414 to 613 m depth.

Description. Hydrorhiza formed by several stolonal tubules growing attached to L. pertusa corals and supporting monosiphonic and unbranched stems. Hydrocauli divided in internodes by transverse nodes, each one with 1–3 apophyses in the distal part and 1–3 nematothecae below the apophyses.

This variability in the number of apophyses per internode is due to the different pattern of ramification along the stem. In the basal part, there is one apophysis per internode (fig. 11C), resulting in the hydrocladia being pinnately disposed and alternately directed left and right. Towards the middle of the stem, there are two apophyses per internode, resulting in opposite hydrocladia with decussate disposition. Finally, in the distal part of the colony, the disposition of apophyses is in verticils of three with decussate disposition, resulting in six rows of hydrocladia around the stem. Each apophysis has a pair of nematothecae at its base, one mamelon on the upper surface and one to seven distal nematothecae, including one, two or even three pairs of nematothecae beyond the mamelon; the number of distal nematothecae, together with the length of apophyses, increases along the stem from basal to distal part of the colony.

First internode of hydrocladia short and ahydrothecate, separated from apophyses by an oblique node, carrying a single nematotheca in its proximal half and two perisarcal rings, one basal and one distal. Remaining hydrocladia composed of a succession of hydrothecate and ahydrothecate internodes separated by oblique nodes. Hydrothecate internodes with strongly oblique basal and almost straight distal nodes; ahydrothecate internodes reverse. Hydrothecate internode with one hydrotheca in mid-basal position and three nematothecae: one mesial inferior and two laterals. Hydrothecae small and cup-shaped; adcauline wall fully adnate, abcauline wall straight, hydrothecal aperture slightly tilted downwards, rim smooth with slight lateral undulation. Ahydrothecate internodes with one or two nematothecae, two being the most common number. All nematothecae bithalamic and movable. Hydrothecate internodes with one perisarcal ring at its base, whereas in ahydrothecate internodes, there are two, one basal and one distal.

Female and male gonothecae borne on separate colonies, inserted on apophyses near the mamelon by a short pedicel; up to two gonothecae per apophyses may be present. Female gonotheca rounded, narrower in its distal part than at the base, aperture latero-distal, oval-shaped and closed by an operculum attached to the top of the aperture.

Male gonotheca long, narrow and oval-shaped with terminal and circular aperture.

Remarks. Nemertesia irregularis was described by Quelch (1885), and this author, in the original description, stated that N. irregularis is characterised by heteronomous segmentation of hydrocladia with ahydrothecate internodes provided with two nematothecae sometimes replaced by two small ahydrothecate internodes each one with one nematothecae, between two consecutive hydrothecate internodes. Billard (1904), in his description of N. perrieri , indicated the existence of ahydrothecate internodes with two nematothecae as the most frequent disposition, but the presence of two ahydrothecate internodes each one with one nematotheca was also described. On the basis of these descriptions, Ramil & Vervoort (1992) synonymised N. perrieri with N. irregularis and, at the same time, included the varieties of N. antennina and N. perrieri described by Billard (1901, 1904) within N. antennina . Nevertheless, Ansín Agís (1998), after review of the type material of N. irregularis and N. perrieri , stated that, in the former species, the number of nematothecae per ahydrothecate internode varies between one and two nematothecae, but there are always two in the latter species. In addition, in N. irregularis , the lateral nematothecae are clearly longer and show cauline nematothecae under the apophyses, which are lacking in N. perrieri . On the basis of these observations, Ansín Agís (1998) and Ansín Agís et al. (2001) reached the conclusion that N. perrieri is different from N. irregularis and represents a valid species, whereas N. irregularis was placed under the synonymy of N. antennina , together with the varieties described by Billard.

The study of a large amount of Nemertesia material sampled along the Northwest African coast allowed us to verify the existence of morphological differences between male and female gonothecae in this species, which undoubtedly separate the material from N. antennina . In addition, we checked typical colonies of N. antennina collected from Galicia, and we found that the ahydrothecate internodes are always short and provided with only one nematotheca, lateral nematothecae are shorter, cauline nematothecae are absent under the apophyses and the apophyses have similar length all along the hydrocaulus. All these differences, together with the morphology of the male gonotheca, led us to the conclusion that Nemertesia irregularis ( Quelch, 1885) is a valid and different species of N. antennina . Nemertesia antennina var. longa ( Billard, 1904) and Nemertesia perrieri var. antennoides ( Billard, 1904) should be placed in its synonymy but not within N. antennina . We also want to highlight that most of the deep-sea material included by Ramil & Vervoort (1992) and Ansín Agís et al. (2001) within N. antennina belong to N. irregularis .

Our findings are consistent with those obtained by Moura et al. (2012) after molecular analyses of the genus Nemertesia in the East Atlantic and West Mediterranean, which suggests that the current concept of N. antennina includes a species complex. This could mean that N. antennina represents a shallow-water species replaced by N. irregularis in deep waters.

Figures

FIGURE 9. A–F, Nemertesia irregularis (Quelch, 1885) (stn GeoB 14871–2): A, hydrocladium and apophysis with female gonotheca. B, detail of three ahydrothecate internodes. C, apophysis with nematothecae, frontal view. D, female gonotheca, frontal view: E–F, female gonothecae, lateral view. Scales: a–f, 0.5 mm.

FIGURE 10. A–G, Nemertesia irregularis (Quelch, 1885) (stn GeoB 14903–1): A, colony. B, part of hydrocaulus with hydrocladia pinnately arranged. C, part of hydrocaulus with two frontal apophyses. D–E, parts of two hydrocladia. F, male gonotheca. G, part of hydrocaulus with male gonotheca. Scales: a, 1 cm; b–e, 0.5 mm; f–g, 0.3 mm.

FIGURE 11. A–D, Nemertesia irregularis (Quelch, 1885): A (stn GeoB 14903–1), detail of hydrocaulus with decussate pairs of apophyses. B–C (stn MUDR02): B, internode of hydrocaulus with three apophyses. C, hydrocladia pinnately arranged. D (stn MUDR01), detail of hydrocaulus with a pair of apophyses. Scales: a–d, 0.5 mm.