Diphasia rosacea ( Linnaeus, 1758 )

Gil, Marta & Ramil, Fran, 2017, The genus Diphasia L. Agassiz, 1862 (Cnidaria, Hydrozoa) in Northwest Africa, Zootaxa 4363 (3), pp. 301-349 : 341-343

Diphasia rosacea ( Linnaeus, 1758)

( Fig. 20 ; Table 13)

Sertularia rosacea Linnaeus, 1758: 807 .

Diphasia rosacea: Hincks, 1868: 245 –247, pl. XLVIII, fig. 1; Nutting, 1904: 107 –108, pl. XXVIII, figs. 4–5; Fraser, 1944: 247 –248, pl. LII, fig. 233; Naumov, 1969: 358 –359, figs. 221–222; Ramil & Vervoort, 1992: 213 –214, fig. 56B; Cornelius, 1995: 54 –55, fig. 11; Schuchert, 2001: 95 –96, fig. 80.

Not Diphasia rosacea: Vervoort, 1959: 257 –258, fig. 25.

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 7 mm high, attached to Halecium sp., no gonothecae.

MAROC-0411, stn MO14, 35º31´08"–35º29´25"N, 6º27´51"–6º27´17"W, 720–724 m, 18-XI-2004: single colony 10 mm high, with female gonothecae.

Aditional material. Norway. Hordaland. Nr.6921, AppellØf Expedition, loc: Bergen skjaergaard, (no further information provided as to the exact location, depth or date): eight colonies 30–40 mm high, five with female gonothecae and two with male gonothecae.

Nr.10813, AppellØf Expedition, loc: Bergen skjaergaard, stn. 65, 75 m, 1899: six colonies 25–40 mm high, one with female gonothecae and one with male gonothecae.

Nr.13667, AppellØf Expedition, loc: Knappene, Solsvik, VI-1903: five colonies 24–29 mm high, four with female gonothecae and one with male gonothecae.

Nr.13668, loc: Bognestraumen, Manger, 30–50 m, IV-1912: one colony 25 mm high with gonothecae.

Nr.48108, W. T. Rees Expedition, loc: Vatlestraumen, Fana, stn. 46–48, 15– 25 m, 31-III-1962: four fragments 10–13 mm high, two with male gonothecae.

Nr.48109, W. T. Rees Expedition, loc: Vatlestraumen, Fana, 30–40 m, 15-VIII-1962: two fragments 5–6 mm high, no gonothecae.

British Isles. Liverpool. Nr.3755, Porf. W. A. Herdman Expedition: three colonies 28–35 mm high, one colony with female gonothecae, two with male gonothecae.

Biology. Well-distributed along the European continental shelf in European waters, especially in Laminaria zones, gravel bottoms and in places with strong water movement ( Hincks 1868; Rees & Thursfield 1965; Cornelius 1995). Diphasia rosacea has been found growing on a wide range of substrates, such as stones, algae ( Corallina , Delesseria ), sponges, shells, bryozoans, the bivalve Aequipecten opercularis ( Linnaeus, 1758) and hydroids like tubularids, D. alata, Sertularia cupressina Linnaeus, 1758 , Thuiaria hartlaubi ( Nutting, 1904) and Nemertesia antennina ( Linnaeus, 1758) ( Hincks 1868; Ritchie 1912; Leloup 1952; Teissier 1965; Fey 1969; Ramil & Vervoort 1992).

Fertile material collected in February, March, April–June, July and September ( Teissier 1965; Ramil 1988; Cornelius 1995; Schuchert 2001). We found colonies with gonothecae in August and November.

Distribution. Diphasia rosacea is widely distributed in the Arctic Seas and North Atlantic Ocean. The species has been reported in the White and Barents Seas ( Naumov 1960), Norway and Iceland ( Vervoort 1946; Schuchert 2001) to the Gibraltar region ( Ramil & Vervoort 1992) in the Northeast Atlantic, and from Canada to Nantucket (Massachusetts) in the Northwest Atlantic ( Schuchert 2001). The species has also been reported in South Africa and Tristan da Cunha by Naumov (1969), but we could not trace the origin of these data. The material studied by us was obtained from the Norwegian and English coasts and the Atlantic side of Morocco.

The record of D. rosacea from Guinea ( Vervoort 1959) was excluded by Ramil & Vervoort (1992) and another from South Africa ( Busk 1851) was transferred by Millard (1961) to Diphasia attenuata ( Hincks, 1866) .

Its bathymetric range extends from the intertidal zone ( Lewis 1964; Ramil 1988) to 521 m ( Ramil & Vervoort 1992). Our records of D. rosacea in Northwest Africa extend its bathymetric distribution to 1198–1228 m.

Description. Colonies composed of a basal stolon that supports an erect and monosiphonic axis loosely pinnate, with hydrocladia disposed left and right in the same plane. Axis and hydrocladia divided into internodes by strong oblique nodes, with a pair of hydrothecae at each internode (fig. 20C).

Hydrothecae opposite, tubular, adnate for 1/2 to 2/3 of the total length and rather abruptly curved outwards. Free part of the adcauline wall almost straight; abcauline wall with basal and distal parts almost straight and separated by the flexure point. Hydrothecal rim smooth with an adcauline sinus; aperture circular, tilted in the abcauline direction and closed by a single operculum attached to the adcauline sinus. External wall of the hydrotheca with three longitudinal ridges: two lateral, one on each side, and one abcauline.

Female gonothecae pear-shaped, tapering basally, with eight longitudinal ridges that end distally in eight angular projections, performing a brood chamber; two of these projections located at opposite sides are a little longer than the other six (fig. 20A–B).

Male gonothecae smaller than the female gonothecae, tubular and slowly tapering towards the base; lateral walls with eight longitudinal ridges, each one ending distally in a short and blunt spine disposed around a tubular aperture (fig. 20D–E).

Remarks. Cornelius (1979, 1995) suggested the synonym of D. attenuata with D. rosacea , but we agree with Ramil (1988), Ramil & Vervoort (1992) and Schuchert (2001) in considering it as a separate species. Diphasia rosacea differs from D. attenuata on the basis of the morphology of the gonothecae, presence of three longitudinal ridges or carinae on the hydrothecal walls, and division of the axis and hydrocladia at the internodes by strongly oblique nodes.

MAROC-0411 BERGEN MUSEUM Stn MO14 Nr.3755

Figures

FIGURE 20. Diphasia rosacea (Linnaeus, 1758). A–C, stn MO14. A–B, female gonothecae; C, part of hydrocladium. D–E, Nr.3755 (Bergen Museum), male gonothecae. Scales: a–e, 0.5 mm.