Diphasia digitalis (Busk, 1852)

Galea, Horia R., 2013, New additions to the shallow-water hydroids (Cnidaria: Hydrozoa) of the French Lesser Antilles: Martinique, Zootaxa 3686 (1), pp. 1-50 : 21-24

Diphasia digitalis (Busk, 1852)

( Fig. 6A–B )

Material examined. Stn. 8, 25.i.2012, 12– 15 m, M058: numerous sterile stems on sponge (MHNG-INVE-82973). Remarks. For a recent redescription of this species, refer to Schuchert (2003).

Geographical distribution. Circumglobal in tropical and subtropical waters ( Schuchert 2003). In the Caribbean, it was found in Puerto Rico ( Fraser 1944), St. Thomas ( Vervoort 1968), and Martinique (present study).

Sertularella calderi sp. nov. ( Fig. 6 C–G, J–M; Table 3)

Sertularella conica ― Calder, 1983: 11, fig. 4; 1991: 99, fig. 52; 2013: 29, fig. 8I (not S. conica Allman, 1877 ). Sertulariella gayi ― Verrill, 1900: 571 [not S. gayi (Lamouroux, 1821) ; incorrect subsequent spelling]. Sertularella gayi ― Verrill, 1907: 319, fig. 170 [not S. gayi (Lamouroux, 1821) ].

Sertularella tenella ― Bennitt, 1922: 250 (not S. tenella Alder, 1857 ).

Sertularella inconstans ― Calder & Hester, 1978: 91 (not S. inconstans Billard, 1919 ).

Material examined. Stn. 2, 22.ii.2012, 1 m, M244: fertile stems on sponge and limestone (syntype: MHNG- INVE-82937).

Description. Colony comprising both stolonal hydrothecae and erect stems, up to 1.15 cm high, arising from creeping hydrorhiza. Stems monosiphonic, almost straight, unbranched or with an occasional, short side branch; stem composed of a basal part (210–570 µm long) devoid of hydrothecae, and a much longer, distal part, carrying up to 24 successive thecae. Perisarc moderately thick, nodes unnoticeable; equivalents of internodes of uniform length, rather short, bearing a single hydrotheca distally; aperture of a hydrotheca surpassing base of the following one ( Fig. 6 C, D). Side branches, when present, given off from below the base of a stem hydrotheca ( Fig. 6 C); structure similar to stem. Hydrothecae alternate, flask-shaped, adnate for half or slightly less their total length, widest at level where the adaxial wall becomes free; narrowing distally, and provided with a short neck region below the aperture. Abaxial wall provided with 3–4 undulations, free adaxial wall with only 2–3 of these ( Fig. 6 E). Aperture rhomboidal in frontal view ( Fig. 6 F), margin with four triangular cusps separated by shallow embayments; operculum of four triangular valves. Five internal, submarginal teeth (a prominent abaxial one, two smaller latero-abaxial, and two latero adaxial) projecting for 1/3 inside the lumen of hydrotheca. Hydranths greenish, more markedly in their distal halves; 28–30 filiform tentacles. Gonothecae, one per stem, arising from below the base of a hydrotheca through a short pedicel ( Fig. 6 J); male similar to female, elongate-oval, nearly radially symmetrical, though slightly smaller and with fewer transverse annulations (8–9 vs. 8–12); aperture distal, borne on short neck region, surrounded by 2–5 blunt spines. Female gonotheca carrying 20–30 spherical oocytes with large nuclei ( Fig. 6 K); male gonotheca producing a homogenous mass of milky-white sperm cells around the blastostyle ( Fig. 6 J). Aperture of female gonotheca obstructed by thin perisarc in younger stages, changing to an internally-projected, funnel-shaped structure, with simple or fronded margin, in ripe gonothecae ( Fig. 6 M); young male gonothecae closed apically, and provided with a rounded aperture when ripe ( Fig. 6 L).

Remarks. Two Caribbean congeners, S. peculiaris Leloup, 1974 and S. fraseri Galea, 2010a , superficially resemble the present species, and material belonging to them was reexamined in the course of this study. They are immediately distinguished from S. calderi through the more delicate appearance of their colonies, covered by much thinner perisarc, and their slightly smaller hydrothecae, less adnate in the former ( Fig. 6 I) and with many corrugated walls in the latter species ( Fig. 6 H). As to the gonothecae, those of S. peculiaris bear 7–8 more or less distinct, incomplete transverse ridges ( Galea 2008), while those of S. fraseri are comparatively smaller and provided with sharper corrugations ( Galea 2010a). For a morphometrical comparison, see Table 3.

TABLE 3. Comparative measurements of Sertularella calderi sp. nov., S. fraseri Galea, 2010a , and S. peculiaris Leloup, 1974 . *The gonotheca figured by Migotto (1996, fig. 12K) was probably injured, thus explaining its smaller size compared to that of the Caribbean S. peculiaris .

Sertularella calderi sp. nov. S. fraseri Galea , Sertularella peculiaris Leloup, 2010 a 1974

Earlier records of S. calderi appear to be present in the literature. According to the description and illustrations given by Verrill (1907), his Bermudan hydroid assigned to S. gayi (Lamouroux, 1921) corresponds in every respect to the present material. In the absence of formal description and illustrations, I assume that his earlier record ( Verrill 1900) belongs to the present species as well. The same applies also to the hydroid identified as S. tenella Alder, 1857 by Bennitt (1922).

In an earlier paper ( Galea 2008), I considered that the hydroids assigned to S. conica Allman, 1877 by both Calder (1983, 1991) and Migotto (1996) belonged to S. peculiaris Leloup, 1974 . In light of the present material from Martinique, and after comparison with Leloup's species, I now conclude that Migotto's hydroid belongs instead to the latter, given the size of its hydrothecae (see Table 3) and the low degree of fusion (one third) of the adcauline wall with the internode. In contrast, Calder's specimens belong to the new species under discussion here, based on the fact that their hydrothecae are adnate for half their length.

As stated by Calder (1991), the specimens from shallower waters have "smaller and more strongly annulated hydrothecae and shorter internodes", thus perfectly fitting my material. In addition, the dimensions given for his gonothecae fit better those of the males in the specimens in hand.

There is much confusion over the identity of Sertularella conica Allman, 1877 , with almost all the subsequent records apparently belonging to other species, as noted earlier by Calder (1991). According to him, type material of S. conica Allman, 1877 could not be located for reexamination. However, Allman described and figured the internodes of his species as long6, thus appearing radically different from those of S. calderi . The second known record of S. conica is, in my opinion, that by Calder (1991), who identified his material as S. gayi unituba , a new variety of Lamouroux' (1821) species. He stated that the "hydroids of S. gayi unituba resemble those of S. conica Allman, 1877 , in colony form and size, and the hydrothecae of both species bear transverse wrinkles", but I think that he was mislead by the discovery of the gonothecae in what he called S. conica (= S. calderi sp. nov.). According to him, the gonothecae of S. gayi unituba (= S. conica Allman, 1877 ) are "less strongly ridged, especially towards the base" and have "a more slender neck distally with fewer spines around the margin". I suspect that Calder's (1991) account on S. gayi unituba is actually the first redescription of Allman's (1877) species, which further contributes with the discovery of its gonotheca.

The Cape Verde specimens assigned by Medel & Vervoort (1998) to Calder's subspecies, eventually raised to species as S. unituba , is reported to be extremely varied morphologically, and it may or many not, partly or all, belong to S. conica .

Sertularella calderi sp. nov. appears to be related to a group of species including S. africana Stechow, 1919 , S. ellisii (Deshayes & Milne-Edwards, 1836) , S. fusiformis (Hincks, 1861) , S. mixta Galea & Schories, 2012 , S. lagenoides Stechow, 1919 , S. mediterranea Hartlaub, 1901 , S. simplex (Hutton, 1873) , and S. uruguayensis Mañé- Garzón & Milstein, 1973, whose common features were summarized by Galea & Schories (2012). Unlike them, S. calderi has equally developed hydrothecal cusps (the abcauline one is not conspicuously tilted outwards), five (instead of only three) submarginal perisarc projections, and its female gonotheca is provided with a peculiar, funnel-shaped, interal structure with simple or fronded margin. In addition, its geographical distribution sets it apart from its congeners listed above.

Etymology. It is my pleasure to dedicate this species to my colleague Dale R. Calder of the Royal Ontario Museum, Toronto, Canada, for his valuable contribution to the sudy of hydroids during more than four decades.

Geographical distribution. South Carolina ( Calder 1983, as S. conica ), Bermuda ( Verrill 1907, as S. gayi ; Calder 1991, as S. conica ), Florida ( Calder 2013, as S. conica ), Martinique (present study).

Figures

FIGURE 6. A, B: Diphasia digitalis (Busk, 1852) ― stem internode in frontal (left) and lateral (right) views (A); optical cross section through internode at level of hydrothecal apertures (B). C – G, J – M: Sertularella calderi sp. nov. ― fragments of stem (C, D); hydrothecae (E) and aperture viewed from above (F); comparison of the hydrotheca (G) with those of S. fraseri Galea, 2010 a (H) and S. peculiaris Leloup, 1974 (I); male (J) and female (K) gonothecae; apertures of male (L) and female (M) gonothecae viewed laterally (below) and apically (above). N – P: Sertularelloides cylindritheca (Allman, 1888) ― internodes (N); lateral view of hydrotheca (O) with thickened internal ring of perisarc at base of apophysis (right), and frontal view of the latter (left); apical view of hydrotheca (P). Q – T: Thyroscyphus longicaulis Splettstösser, 1929 ― fragment of stem (Q); internode and hydrotheca (R); aperture (S); male (left) and female (right) gonothecae (T). U – Z: Hincksella formosa (Fewkes, 1881) ― hydrotheca (U); gonotheca seen laterally (V), and in optical cross section (X); aperture (Y). Scale bars: 10 µm (Z), 200 µm (F, L, M), 300 µm (P), 500 µm (A, B, E, G – I, O, S, U, Y), 1 mm (C, D, J, K, N, R, T, V, X), 4 mm (Q).