Diphasia africana, Gil & Ramil, 2017

Gil, Marta & Ramil, Fran, 2017, The genus Diphasia L. Agassiz, 1862 (Cnidaria, Hydrozoa) in Northwest Africa, Zootaxa 4363 (3), pp. 301-349 : 327-332

Diphasia africana n. sp.

( Figs. 13 , 14 ; Table 7)

Diphasia pectinata: Vervoort, 1959: 255 –256, figs 23–24 [not Diphasia pectinata ( Lamarck, 1816) = Diphasia nigra ( Pallas, 1766) ].

Diphasia margareta: Gili, Vervoort & Pagès, 1989: 99 –100, fig. 24 [not Diphasia margareta ( Hassall, 1841) ].

Material examined. Morocco. MAROC-0411, stn MO09, 35º29´34"– 35º32´40"N, 7º15´13"– 7º18´25"W, 1228– 1198 m, 16-XI-2004: single colony 18 mm high, attached to Nemertesia ramosa , no gonothecae.

Western Sahara. MAROC-0611, stn MO248, 23º26´25"– 23º29´26"N, 16º59´21"– 16º58´29"W, 239– 232 m, 30-XI-2006: ten colonies 33–140 mm high, three colonies with female gonothecae, two with male gonothecae. One colony, 140 mm high and with female gonothecae is the holotype ( MNCN 2.03 /681); remaining colonies are paratypes ( MNCN 2.03 /682; RMNH. COEL.42268; CFM-IEOMA-6217; LZM-16130).

MAROC-0611, stn MO255, 24º08´16"–24º10´25"N, 16º42´26"–16º40´13"W, 271– 230 m, 3-XII-2006: three colonies 26–97 mm high, no gonothecae.

Mauritania. MAURIT-1107, stn MU70, 16º55´14"– 16º58´20"N, 16º48´39"– 16º48´53"W, 755–801 m, 8-XII- 2007: single colony 58 mm high, with male gonothecae, paratype (MNHN-IK- 2014-2196) .

Guinea Bissau. BISSAU-0810, stn BS157, 10º19´36"– 10º18´44"N, 17º10´29" –17º10´12"W, 304–308 m, 28- X-2008: one colony 72 mm high, without gonothecae.

Biology. Our material was collected from muddy bottoms, growing on the axis of Nemertesia ramosa ( Lamarck, 1816) and P. flabellata , or detached from the substrate. The species has been previously found attached to S. cylindritheca ( Vervoort 1959 as D. pectinata ) and on L. myriophyllum and worm tubes ( Gili et al. 1989 as D. margareta ).

Colonies with gonothecae have been found in January and February ( Gili et al. 1989) and April ( Vervoort 1959). We found gonothecae in November and December.

Distribution. Present material collected from Morocco, Western Sahara, Mauritania and Guinea-Bissau between a depth of 230 and 1228 m. The species has been collected from Senegal ( Vervoort 1959 as D. pectinata ) and Guinea-Bissau between a depth of 45 and 439 m ( Gili et al. 1989 as D. margareta ). Nevertheless, there is some confusion about the bathymetric distribution reported by Gili et al. (1989) because the stations this species was collected from are located between 131 and 157 m (Stn P-213) and 4751 m (Stn P-114); the depth of the last station is erroneous because all species studied by these authors were collected from a depth of 0 and 1200 m ( Gili et al. 1989: 67).

Description. Hydrorhiza composed of a framework of stolonal tubules attached to the substratum, supporting an erect monosiphonic and unbranched axis. Axis divided into internodes of different lengths by transverse nodes, with a varied number of hydrothecae disposed in opposite pairs. Hydrocladia inserted under axial hydrothecae, pinnately arranged and slightly directed to the frontal part of the colony. Consecutive hydrocladia separated by one and two pairs of hydrothecae, resulting in the separation of three hydrothecae between two hydrocladia disposed on the same side of the axis. Hydrocladia not divided into internodes, with hydrothecae disposed in sub-opposite pairs on the basal part but opposite distally.

Hydrothecae tubular, adnate by 2/3 of its total length and curved outwards. Free part of the adcauline wall short, straight, or slightly concave distally; adnate part slightly concave. Abcauline wall characterized by a strongly developed internal perisarcal ledge curved upwards; at the level of the internal ledge, the abcauline wall curving abruptly upwards. Hydrothecal rim smooth, with a semicircular adcaulinar sinus and closed by a single operculum attached to the sinus. Aperture of the hydrothecae mostly directed upwards and perpendicular to the hydrocladia (fig. 13C). Renovations of the hydrothecal margin frequent and sometimes numerous, considerably enlarging the free part of the hydrothecae (fig. 14B).

Female and male gonothecae borne in different colonies and inserting in both axis and hydrocladia under a pair of hydrothecae; female bigger than male. Female gonotheca pear-shaped, with apical part rounded and narrowing basally. Gonothecal wall with four poorly developed longitudinal ridges, each one with only one well-developed spine on the distal part. Apical part of the gonotheca with an internal marsupium communicated with the proximal gonothecal cavity by a circular aperture; two lateral funnels originating from both sides of the marsupium reach the gonothecal wall, forming a pair of lateral openings for larval release (fig. 13D–E).

The male gonothecae are narrow at the base, widening to the distal part, which is quadrangular in the crosssection and provided with four spines, one at each corner surrounding a central aperture located at the end of a conical elevation. The spines vary in length and morphology (fig. 14C–D).

Remarks. The presence of an internal marsupium with two lateral apertures for larval release includes this species in the D. margareta group. However, D. africana n. sp. differs from D. margareta on the basis of the morphology of the female gonothecae, which have poorly developed external ridges and only one spine at each ridge; similar female gonothecae have also been described by Vervoort (1959) in Senegal. In the male gonothecae, the conical elevation on which the aperture is located appears more developed in Diphasia africana n. sp.; similar male gonothecae have been observed by Gili et al. (1989) in colonies collected from Guinea-Bissau. In addition, the hydrothecae are more abruptly curved upwards, and the proportion of adnate to free parts of the hydrothecal adcauline wall is higher in this species. The same differences are observed in Diphasia saharica n. sp.; however, in this case, we must also add the absence of an internal ledge on the abcauline hydrothecal wall and the ramification pattern of the colony of Diphasia saharica n. sp. The morphology of the female gonothecae, the quadrangular cross-section of the distal part of the male gonothecae, and the unbranched habitus of the colonies separate Diphasia africana n. sp. from Diphasia leonisae n. sp.

MAROC-0611 Diphasia pectinata Stn MO248 ( Vervoort 1959) Sertularia nigra Pallas, 1766: 135 –136.

Sertularia pinnata Pallas, 1766: 136 –137.

Sertularia pectinata Lamarck, 1816: 116 ; Billard, 1907: 218.

Diphasia pinnata: Hincks, 1868: 255 –257, pl. LII; Philbert, 1934: 6 –7, pl. II, figs 1–8; Millard, 1975: 261; Cornelius, 1979: 265 –267, fig. 12; Cornelius, 1995: 47 –49, fig. 9.

Not Diphasia pectinata: Vervoort, 1959: 255 –256, figs. 23–24 (= Diphasia africana n. sp.).

Material examined. Meteor Bank. METEOR 42/3, stn 519, 30º06.1´N, 28º24.5´W, 410–418 m, 14-IX-1998: single colony 120 mm high, with male gonothecae.

Biology. Diphasia nigra has been reported on bivalve shells and presumably occurs on other similar substrates ( Cornelius 1979, 1995). Dense populations spreading on wide areas were found near Roscoff ( Teissier 1965). Fertile colonies have been reported from April to September ( Cornelius 1979, 1995). The only colony examined by us was collected in September.

Distribution. This species has been reported in the British Isles ( Hincks 1868; Cornelius 1979, 1995), Roscoff and Glenan Islands (Northwest France) ( Teissier 1965; Fey 1969), the north side of the Bay of Biscay ( Browne 1907), and Santander and A Coruña (North Spain) ( Rioja 1905) at a depth of around 60–146 m ( Teissier 1965; Cornelius 1979, 1995; Alvarez 1993). Diphasia nigra has also been reported in South Africa by Busk (1851), but Millard (1975) regarded this record as doubtful. Our material was obtained from the Meteor Bank and was collected at a depth of 410– 418 m.

Description. Detached colony composed of a robust, rigid and polysiphonic primary axis from which several branches with irregular disposition arise. Main axis covered by a tangled mass of secondary tubules that hide the axial hydrothecae, which causes them to be totally buried within the stem. Branches formed by an erect, robust, polysiphonic and unbranched stem, carrying axial hydrothecae in widely separated opposite pairs together with hydrocladia. Hydrothecae and hydrocladia borne only on the axial tube; the axial tube presents a cone-shaped cross-section, with an evenly convex frontal side that spreads out in a well-formed abfrontal carina (figs. 15C, 22A). Secondary tubules are strongly developed on the abfrontal side along the carina, while the frontal side remains free of secondary tubules along almost its entire length; only the smallest and youngest branches are monosiphonic. Axial hydrothecae disposed laterally close to the convex frontal side. The hydrocladia, thinner than the axis, arise behind the axial hydrothecae on the lateral sides of the abfrontal carina and are slightly tilted in the abfrontal direction; they are pinnately arranged left and right, with two pairs of hydrothecae between two consecutive hydrocladia and four hydrothecal pairs separating two hydrocladia on the same side of the axis. Crosssection of the hydrocladia also cone-shaped, and arrangement of the hydrocladial hydrothecae in opposite pairs similar to those described for the stem.

Hydrothecae narrow, tubular and adnate by almost its entire length but gently curving outwards; distal edge of the adcauline wall almost touching the base of the next hydrotheca but not overlapping it (fig. 15D). Abcaulinar wall with thin perisarc and without any internal fold. Hydrothecal aperture smooth, semicircular, directed upwards and closed by a single-flap operculum attached to a small adcauline sinus.

Male gonothecae, the only one observed in the material, borne on hydrocladia on a short pedicel, arising upwards and frontally between two hydrothecae of the same pair. They are small, oval and tapering towards the base; aperture terminal, circular and located at the end of a short cone surrounded by five blunt spines (fig. 15E–G).

Remarks. This well-known species shows the female gonothecae provided with an internal marsupium with two lateral funnels that end on two elongated lateral apertures for larval release ( Philbert 1934); consequently, it should also be included in the D. margareta group. Nevertheless, D. nigra differs from all other species of this group on the basis of the morphology of the colony, with a large, straight and rigid axis; pinnately arranged hydrocladia along the branches; adnate but gently curved tubular hydrothecae disposed in opposite pairs almost touching vertically; the brown or black color of the preserved colonies seems characteristic for this species ( Cornelius 1979, 1995). Moreover, the morphology of the female gonothecae, without either external ridges or spines ( Philbert 1934) but with four longitudinal grooves meeting distally ( Cornelius 1979, 1995), keeps it separate within the group. The morphology of the axial tube and hydrocladia and development of the polysiphonic condition described here also seem characteristic for D. nigra . Medel & Vervoort (1998: Fig. 3 ) described within D. margareta some colonies collected at Cape Verde Islands that had female gonothecae with indistinct ribs and without spines, reminiscent of D. nigra ; nevertheless, the morphology of the hydrothecae approaches this form to Diphasia leonisae n. sp., but not this species. We consider it necessary to study new material before reaching a definitive conclusion about the identity of the Cape Verde material.

METEOR BANK Stn 519

Hydrotheca, length adnate part adcauline wall 520–570 length free part adcauline wall 40–50

length abcauline wall 520–600 diameter rim 110–160

Male gonotheca, total length 630–700 maximal diameter 380–440

Figures

FIGURE 3. Diphasia attenuata var. robusta Billard, 1924. A–C, stn, BT574; A, colony; B, two pairs of hydrothecae from hydrocladium; C, part of axis with insertions of hydrocladia.D, MNHN.L453, part of hydrocladium.Scales: a, 1 cm; b–d, 0.5 mm.

FIGURE 14. Diphasia africana n. sp. A–D, stn MO248. A, part of colony showing insertion of three hydrocladia; B, part of hydrocladium; C–D, male gonothecae. Scales:a, 1 mm; b–d, 0.5 mm.

FIGURE13. Diphasia africana n. sp. A–E, stnMO248; A, colony; B, part of hydrocladium; C, three pairs of hydrothecae; D– E, female gonothecae.Scales: a, 3 cm; b–e, 0.5 mm.