Diphasia delagei Billard, 1912

Gil, Marta & Ramil, Fran, 2017, The genus Diphasia L. Agassiz, 1862 (Cnidaria, Hydrozoa) in Northwest Africa, Zootaxa 4363 (3), pp. 301-349 : 335-339

Diphasia delagei Billard, 1912

( Fig. 17 , 18 ; Table 10, 11)

Diphasia delagei Billard, 1912: 466 –467, figs. 3–4.

Diphasia delagei: Cornelius, 1979: 259 –260, fig. 10; Medel & Vervoort, 1998: 14 –15, fig. 2. Not Diphasia delagei: Ramil & Vervoort, 1992: 200 –201, fig. 56A (= Diphasia anaramosae n. sp.).

Material examined. Cape Verde Islands. CCLME 2011–406 , stn SL–6, 23º06´06"N, 15º51´88"W, 107 m, 11-VI- 2011: one hydrocladia 12 mm high, no gonothecae.

Additional material. Pourquoi-Pas. MNHN.L459, Dr.27, 28-VIII-1927: one slide with three hydrocladia of 5, 7 and 8 mm high, no gonothecae, neotype.

RMNH.COEL.26859, slide 1958, CANCAP VI, stn 6069, 15º53´N, 23º00´W, 76–79 m, 13-VI-1982: one hydrocladia 7 mm high without gonothecae.

RMNH.COEL.26861, slide 1960, CANCAP VII, stn 7058, 15º07´N, 23º14´W, 69 m, 26-VIII-1986: one hydrocladia 12 mm high with gonothecae.

Biology. Recorded growing mainly on other hydroids: A. tubulifera ( Billard 1912) ; D. rosacea ( Cornelius 1979) ; D. margareta (Billard 1931 as D. pinaster ; Medel 1996; Medel & Vervoort 1998); Diphasia sp. and Sertularella gayi gayi (Lamouroux, 1821) ( Ramil & Vervoort 1992); Hydrallmania falcata ( Linnaeus, 1758) ( Medel 1996) and Streptocaulus pulcherrimus ( Medel & Vervoort 1998) as well as on pebbles, gravel and shell fragments ( Teissier 1965; Cornelius 1979, 1995).

Fertile material was recorded in August in Cape Verde ( Medel & Vervoort 1998) and in September in Roscoff, France ( Teissier 1965; Cornelius 1979, 1995). The scarcity of reproductive data was interpreted as a possible indicator of a predominance of asexual reproduction in this species by Cornelius (1979) and a short reproductive period by Medel & Vervoort (1998). In any case, the global records for D. delagei in the literature are currently very scarce.

Distribution. This species has been reported in Bretagne, Northwest France ( Billard 1912, 1931; Teissier 1965; Cornelius 1979, 1995), the Strait of Gibraltar ( Medel 1996) and Cape Verde ( Medel & Vervoort 1998). Diphasia delagei seems to be a circalittoral species with a bathymetrical distribution of 39 ( Medel 1996) to 90 m ( Teissier 1965; Medel & Vervoort 1998). The records of Ramil & Vervoort (1992) from 150 to 1250 m are here included in Diphasia anaramosae n. sp.

MNHN.L459 CCLME-2011-406

Stn SL-06 Description. Colonies erect, unbranched. Basal part without hydrothecae, separated from the thecate region by an oblique node.

Hydrothecae opposite, tubular, with well-developed transverse ridges along the abcauline side. Hydrothecal aperture semicircular, closed by an operculum attached to the adcauline side, slightly tilted in the abcauline direction.

Neotype material shows the hydrothecae adnate along 2/3 to 3/4 of their length, hydrothecae pairs are vertically separated, and the adcauline walls are touching frontally but remain separate along the abfrontal side; the most distal part of the hydrothecae are devoid of transverse ridges (fig. 18A–B). Moreover, the hydrothecae are provided with intrathecal adcauline laminae, similar to those described in D. attenuata .

In the Cape Verde material, the hydrothecae are almost completely adnate, each pair of hydrothecae overlaps the base of the next pair, the adcauline walls remain separate in both frontal and abfrontal sides, and the transverse ridges reach the hydrothecal border; intrathecal adcauline laminae were also observed (fig. 17E).

Male gonothecae inserted under a pair of hydrothecae, large, S-shaped, with a short pedicel in the basal part, and a terminal aperture at the end of a short and laterally tilted neck. Gonothecal walls with well-developed transverse ridges throughout, similar to those described in the hydrothecae (fig. 17C–D). Female gonothecae remain unknown.

Remarks. Diphasia delagei is a very uncommon species and only known off Britanny ( France) and Cape Verde Islands. The species was described by Billard (1912) from Roscoff ( France), and the original description includes two different morphotypes collected at the same station (Stn 3) and growing on A. tubulifera . In the first morphotype, the hydrothecae pairs are vertically separated, and the hydrothecae of the same pair are touching laterally in the frontal side but are separate abfrontally. In the second morphotype the hydrothecae of successive pairs are vertically overlapped, the hydrothecae of the same pair remain separated on both frontal and abfrontal sides, and the free part of the adcauline wall only represents around one-tenth. Cornelius (1979, 1995) has also reported both morphotypes growing on D. rosacea in the Roscoff area.

The type material for D. delagei was lost ( Cornelius 1979; Van Praët 1979), and a neotype was designated by Van Praët (1979) after material sampled by the R/V Pourquoi-Pas in 1927, probably off Camaret ( France) (see Billard 1931). The neotype (fig. 18), collected growing on D. pinaster (= D. margareta ), was sterile and only included colonies with hydrothecal pairs vertically separated (see Billard 1931).

Comparison of the neotype with the material collected from Cape Verde showed identical development of the transverse ridges on the hydrothecal walls, which seems to support Billard’s and Cornelius’s opinion that the two morphotypes belong to a single species.

The gonosome was described by Cornelius (1979) using an empty gonotheca; consequently, it was not possible to establish the sex. Nevertheless, gonothecae with identical morphology and filled with developing spermatocytes were reported by Medel & Vervoort (1998) in Cape Verde; in both cases, the gonothecae were found in colonies with overlapping hydrothecae. The female gonothecae remain undescribed.

The material described by Ramil & Vervoort (1992) as D. delagei is considered here as a different species (see below).

The differences with Diphasia tropica Nutting, 1904 , another species with transverse striations on the hydrothecal wall that has also been reported in this region, have been discussed below.

Figures

FIGURE 18. Diphasia delagei Billard, 1912. A–B, MNHN.L459. A, part of hydrocladium; B, basal part of hydrocladium. Scales: a–b, 0.5 mm.

FIGURE17. Diphasia delageiBillard, 1912.A–B, RMNH.COEL.26859, slide 1958; A, part of hydrocladium; B,basal part of hydrocladium.C–D, RMNH.COEL.26861, slide 1960, gonothecae.E, stn SL–6, part of hydrocladium.Scales:a–e, 0.5 mm.