Nemertesia caboverdensis, Gil & Ramil & Agís, 2020

Gil, Marta, Ramil, Fran & Agís, José Ansín, 2020, Hydroids (Cnidaria, Hydrozoa) from Mauritanian Coral Mounds, Zootaxa 4878 (3), pp. 412-466 : 439-441

Nemertesia caboverdensis n. sp.

( Fig. 5 ; Table 2 )

Nemertesia belini: Ansín Agís, 1998: 457–460 ; figs. 62–63; Ansín Agís et al., 2001: 200–204, figs. 78–79 (not Nemertesia belini Bedot, 1916 ).

Material examined. Cape Verde Islands. CANCAP, stn 6.072, 15º54´N, 23º06´W, 110 m, 13-VI-1982: six colonies 26–171 mm high, without gonothecae; paratypes (RMNH-Coel. 28754; LZM-UV slide R. 332) .

CANCAP, stn 6.074, 15º55´N, 23º04´W, 91 m, 13-VI-1982: one colony 53 mm high, no gonothecae; paratype (RMNH-Coel. 28762).

CANCAP, stn 6.076, 15º55´N, 23º05´W, 92 m, 13-vi-1982: one colony 69 mm high, without gonothecae; paratype (RMNH-Coel. 29101).

CANCAP, stn 6.078, 15º55´N, 23º06´W, 185–190 m, 13-vi-1982: one colony 92 mm high, with gonothecae; holotype (RMNH-Coel. 28788).

Etymology. The specific name, caboverdensis , refers to the locality from which this new species was obtained: Cape Verde Archipelago.

Biology. Gonothecae were found in June ( Ansín Agís 1998; Ansín Agís et al. 2001).

Distribution. Only recorded in four localities of Cape Verde Islands, between depths of 91 and 190 m ( Ansín Agís 1998; Ansín Agís et al. 2001).

Description. Hydrorhiza tubular, adhering to substrate, giving rise to several monosiphonic, unbranched hydrocauli, divided into internodes by straight nodes, distinctly visible along the entire stem, especially in distal part. Each internode provided with two opposite apophyses in basal part of stem and a verticil of four apophyses in distal part, with decussate disposition; moreover, each axial internode carries several nematothecae distributed under the apophyses. Length of apophyses varies, short basally and long distally; each apophysis with two axillar nematothecae, a mamelon on its upper surface and an unpaired distal nematotheca. Long apophyses may have, after the mamelon, a pair of proximal nematothecae and up to three unpaired distal nematothecae.

In basal half of stem, the apophyses are short and each hydrocladium starts with a short ahydrothecate internode, provided with a single nematotheca. In distal half, with long apophyses, first internode of hydrocladium is hydrothecate because of the fusion of the first ahydrothecate internode with the apophysis. Hydrocladia composed of succession of hydrothecate internodes with slightly oblique nodes, each with one hydrotheca on distal third, two to four mesial inferior nematothecae, a pair of lateral nematothecae and occasionally a supracalycine nematotheca. Hydrothecae cup-shaped, adcauline wall fully adnate, abcauline wall straight, with the aperture perpendicular to longitudinal axis of hydrocladia; rim smooth.Ahydrothecate internodes occur but distributed without any regularity, bearing one to three nematothecae, usually as the result of node formation in basal part of succeeding hydrothecate internode; in this case, the hydrotheca occupies a central position on the internode. All nematothecae bithalamic and movable, with long and narrow basal chamber.

Gonothecae inserted on apophyses, ovoid, narrowing basally into a short pedicel. Aperture latero-terminal, broadly oval. Only one type of gonothecae observed; sex unknown.

A colony from Stn 6.078 showed two secondary hydrocladia arising from the interior of a hydrotheca or a small apophysis below the hydrotheca of a primary hydrocladium (fig. 5E).

Remarks. Review of the type material of N. belini and study of the samples identified as N. belini by Ansín Agís (1998) and Ansín Agís et al. (2001) led us to the conclusion that they are different species.Although this species was not collected in our surveys, for comparative purposes, we have also included a description of this material.

Comparison of these colonies with the type material of N. belini showed a fair similarity in morphological traits, both with respect to trophosome and gonosome. Moreover, this material also shows wide variations related to the length of apophyses, segmentation of the stem and hydrocladia, and number of nematothecae per hydrocladial internode. This variability is consistent with that described by Bedot (1916) for N. belini .

Nevertheless, we found differences that, in our opinion, justify its specific separation. In N. caboverdensis n. sp., hydrothecae are disposed in distal third of internodes and its aperture is almost perpendicular to the longitudinal axis of hydrocladia, whereas in N. belini , hydrothecae are located in basal half of internodes and its aperture is clearly tilted to abcauline side (adcauline wall longer than abcauline one) (fig. 4F, G). The number of supracalycine nematothecae is also different: one to three in N. belini , two being the more common number ( Bedot 1921b) versus zero to one in the N. caboverdensis n. sp., one being the most common; moreover, in N. caboverdensis n. sp., the nematothecae are longer (see Table 2 ). In addition, N. caboverdensis n. sp. has ahydrothecate internodes irregularly distributed along hydrocladia, whereas in N. belini , hydrocladia are composed of a succession of hydrothecate and ahydrothecate internodes as standard morphology.

Material from CANCAP stn 5010, collected in the Azores area and reported by Ansín Agís (1998) and Ansín Agís et al. (2001) within N. belini , must be reviewed before its definitive identification. Some features of this colony, such as the hydrothecal aperture tilted in abcauline direction and the length of its nematothecae clearly smaller, suggest that could be a different species.

Differences with N. freiwaldi n. sp. are discussed below.

Figures

FIGURE 5. A–E, Nemertesia caboverdensis n. sp., holotype (stn 6.078; A), colony. B, detail of colony, frontal view. C, hydrocladium, lateral view. D, gonotheca, frontal view. E, branched hydrocladium. Scales: a, 1 cm; b–e, 0.2 mm.