Diphasia attenuata var. robusta Billard, 1924

Gil, Marta & Ramil, Fran, 2017, The genus Diphasia L. Agassiz, 1862 (Cnidaria, Hydrozoa) in Northwest Africa, Zootaxa 4363 (3), pp. 301-349 : 307-309

Diphasia attenuata var. robusta Billard, 1924

( Fig. 3 ; Table 2)

Diphasia attenuata: Billard, 1906: 195 –198, fig. 13 [not Diphasia attenuata ( Hincks, 1866) ]. Diphasia attenuata var. robusta Billard, 1924: 62 –64; Patriti, 1970: 44, fig. 58; Ramil & Vervoort, 1992: 198 –200, fig. 5A, B; Medel & Vervoort, 1998: 13 –14, fig. 1.

Material examined. Morocco. CCLME-1205, stn BT571, 35º03´32"– 35º01´58"N, 6º15´13" –6º15´48"W, 47 m, 12-VII-2012: two colonies 31–39 mm high, no gonothecae.

Additional material. MNHN.L453, TALISMAN, stn. 23, Cap Blanc du Nord, 120 m, 18-VI-1883: one slide with one hydrocladia of 14 mm high, without gonothecae, syntype material.

LMZ-104, BALGIM expedition, stn DR113, 35º45.4´N, 06º04.8´W, 144 m, 11-VI-1984, as Diphasia attenuata var. robusta : one slide with a fragment of 15 mm high from the distal part of the colony, no gonothecae.

LMZ-145, BALGIM expedition, stn DR113, 35º45.4´N, 06º04.8´W, 144 m, 11-VI-1984, as Diphasia attenuata var. robusta : one slide with one hydrocladia of 17 mm high, without gonothecae.

Biology. This species was found growing on Sertularella gayi (Lamouroux, 1821) on rock and shell bottoms ( Billard 1906).

Distribution. Diphasia attenuata var. robusta was collected from various stations located between Cap Spartel, northern Morocco, and Cap Bojador, Western Sahara ( Billard 1906, 1924; Patriti 1970; Ramil & Vervoort 1992). Our material was recorded within this area, south of Larache. In addition, a single hydrocladium that originated undoubtedly from a living colony was reported by Medel & Vervoort (1998) at Cape Verde Islands.

Previous records have set the depth range of D. attenuata var. robusta between 102 ( Billard 1906) and 470– 520 m ( Medel & Vervoort 1998). The latter authors have stated that the deepest limit for the species is 890 m, but we could not trace the origin of this record. The CCLME material was collected at a depth of 47 m, which is the shallowest record for this variety.

Description. Colony composed of a monosiphonic axis provided with pinnately arranged hydrocladia, all in the same plane. Hydrothecae usually disposed in opposite or sub-opposite pairs on the axis and hydrocladia. Subopposite pairs are more common in the basal part of the colony, but we also observed the same disposition in the distal part of some hydrocladia.

Hydrothecae tubular and curved outwards at an angle of ca. 45° and adnate one-third to half of the adcauline wall. Free part of the adcauline wall rather long and straight. Abcauline wall concave and with the perisarc slightly thickened at the level of the flexure but without internal perisarcal ledge. Hydrothecal rim smooth with a large adcauline sinus; hydrothecal aperture tilted in the abcauline direction and closed by an operculum composed of a single flap, attached to the adcauline sinus (fig. 3B). Hydrothecal border usually with renovations. Gonothecae not observed.

Remarks. The description of our material is consistent with the description of Diphasia attenuata var. robusta Billard, 1924 , and its comparison with part of the syntype material showed that they are identical in morphology and size.

This variety differs from the nominal species Diphasia attenuata ( Hincks, 1866) mainly by its size (clearly bigger with respect to both colony and hydrotheca measurements), but also by the absence of intrathecal adcauline laminae, presence of one and two axial pairs of hydrothecae between two successive ramifications, and a noticeable thickening of the abcauline hydrothecal wall ( Billard 1924) (fig. 3D).

The same differences were reported by Ramil & Vervoort (1992) and observed in our colonies. We agree with Ramil & Vervoort (1992) in considering that these differences would justify its separation from the nominal species, but the absence of gonothecae in the studied material prevent us from classifying this variety to the specific level.

CCLME-1205 TALISMAN

Stn BT574 MNHN.L453 Diphasia fallax: Hincks, 1868: 249 –251, pl. XLIX, fig. 2; Nutting, 1904: 109–110, pl. XXIX, figs. 2–6; Fraser, 1944: 242–244, pl. L, fig. 227; Vervoort, 1972: 103–105, figs. 30d, 31; Cornelius, 1979: 260–263, fig.9; Cornelius, 1995: 44–46, fig.8; Schuchert, 2001: 93–94, fig. 78 A–C.

Remarks. Diphasia fallax was not represented in the material studied in this report, but we include it in the key of identification because the species is known from the eastern North Atlantic.

Diphasia fallax is a cold-temperate North Atlantic species, reported from Arctic Seas to northern parts of British Isles ( Cornelius 1979, 1995), Iceland ( Schuchert 2001), Greenland ( Broch 1918; Schuchert 2001) and the Atlantic coast of North America from Canada to Charleston ( Nutting 1904; Fraser 1944). The records from The Netherlands were considered doubtful by Vervoort & Faasse (2009).

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.