Corallium medea Bayer 1964

Corallium medea Bayer, 1964

(Figs. 1–4)

Corallium medea Bayer 1964: 468 –473, figs. 1–3; Messing et al. 1990: 32, fig. 7a.

Diagnosis. Branches nearly round in cross section. Coenenchymal surface smooth or with extremely small granulations. Axis without pits beneath autozooids. Autozooids predominantly facing one side of the colony and retracted within hemispherical coenenchymal mounds. Coenenchyme with 6­, 7­, and 8­radiates, and double clubs. Double clubs with small protuberances on their heads.

Material examined. MNRJ 4263 (intertwined with a colony of the scleractinian coral Lophelia pertusa — only a small area with tissue), MNRJ 4265 (fragment), MNRJ 4887 (colony with base), Almirante Saldanha Bank (22 22.35” S, 0 37 39.32” W), 380–500 m, collected by REVIZEE project, research vessel Astro Garoupa, 6 November 1997.

Description. Arborescent planar colonies (Fig. 1 A). Studied specimens include an almost complete colony (MNRJ 4887) and a fragment (MNRJ 4265), 15.5 and 28.6 cm high, 18.0 and 14.0 cm wide, and 6.1 and 5.3 cm deep, respectively. Branching irregular, up to the fourth order. Terminal branches may anastomose. Colony base (MNRJ 4887) spreads irregularly, as a thin calcareous holdfast, over an area 63 x 39 mm in its maximum dimensions. Branches taper from base to tip — example of thickness of consecutive branch axes (just after branching): near base 20 mm; trunk 17.2 mm; secondary branch 11.7 mm; tertiary branch 8.4 mm; terminal (lateral) twigs 1.8–2.9 mm; distal branch tips 2.0– 3.4 mm. Branches round in cross section. Axis with several narrow longitudinal grooves: surface almost smooth under light microscope, with minute scattered “spines” on the surface; surface finely tuberculated/spinous under SEM (Fig. 2). Coenenchymal surface smooth or with extremely small granulations. Polyps scattered on one side of the colony (front), up to seven per centimetre of branch, absent on proximal regions of trunk and main branches, retracted within low, hemispherical, coenenchymal mounds, up to 1.2 mm high and 2.5 mm wide (Fig. 1 B). Polyp aperture present as a small depression on mounds, sometimes not visible; marginal lobes or furrows absent on coenenchymal mound or aperture margins. Siphonozooids as small depressions with minute pores (circa 0.1 mm in diameter) around the base of autozooid mounds and sparse on the general coenenchyme. Coenenchyme with two layers of sclerites: outer mainly with double clubs (0.05 x 0.05– 0.06 x 0.07 mm), with small protuberances on their heads (Fig. 3 A); inner with double clubs (size equal to outer layer), 8­radiate (0.07–0.09 mm long), 7­radiate (0.05–0.08 mm long), and 6­radiate capstans (0.05–0.08 mm long) (Fig. 3 B). Polyp sclerites as multiple rows of small radiates along bases and proximal parts of tentacles (0.03–0.06 mm long) (Fig. 3 C), which are absent from distal areas of tentacles, and slender, spinous rods (0.04– 0.06 mm long) (Fig. 3 D) in the pharynx. Calcareous axis white; coenenchyme yellowish white; polyps yellow.

Discussion. The specimens here reported are very close to the C. medea specimens recorded from the Straits of Florida (Bayer 1964). There are only minor differences, most probably of no taxonomic significance.

Specimen MNRJ 4265 (Fig. 1) is much larger (28.6 cm long) than the broken terminal branches described by Bayer (1964: figured types circa 4 and 7 cm long). Messing et al. (1990: 32) reports colonies of C. medea up to 25 cm high, which is roughly the size of our largest specimen. However, they describe the full colonies as “flabellate, sparsely branched colonies” (see Messing et al. 1990: 32, fig. 7a). Their figure suggests colonies without a trunk, differently from our largest specimen (Fig. 1). The original description indicates that polyp aperture margins form 8 lobes; these lobes are absent in our specimens. Bayer’s (1964: fig. 3f) drawings show somewhat stouter pharyngeal rods (0.04 mm long); our specimens show mostly longer (0.04–0.06 mm), slender rods, with spines chiefly on their extremities. However, a few stouter rods were also seen in our preparations.

Bayer (1964) described two forms of branches in C. medea. The form associated with his “ type fragments” (see Bayer, 1964: fig. 1 legend) has stout terminal branches and few lateral twigs. Their coenenchymal mounds are prominent and grouped in clusters. Bayer did not mention branch diameters, but his figure 2a shows a fragment with branch diameters, coenenchymal mounds excluded, of 1.8–2.2 mm, with terminal branch tips conspicuously clavate due to the clustering of autozooids. Bayer also described a “variation with irregular branching” (see Bayer, 1964: 471, figs.1 right, 2b), which presented more slender branches (diameters, without coenenchymal mounds, 1.5–2.2 mm) with several rather short lateral twigs. The autozooids of this form have less prominent mounds, not so obviously grouped in clusters, and the branch tips are not so conspicuously clavate. Our specimens have intermediate characteristics, with some stouter terminal (lateral) twigs like the “ type fragments”, but also several rather short lateral twigs like in the “variation”. Also, coenenchymal mound size is closer to that of the “ type fragments”, but their distribution seems to be closer to the “variation”. Bayer (1964: 471) suggested these forms could represent individual variation within one species or two species differing morphologically in only minor details. Our specimens indicate Bayer’s forms belong to a single species or even to different branches of the same colony.

Part of the studied material (MNRJ 4263) was found associated (intermingled) with the deep water, reef forming, scleractinian coral Lophelia pertusa. According to Messing et al. (1990), Corallium medea is a quite common species in open sediment and low hardground environments in deep­water coral banks in the Straits of Florida (a trough between peninsular Florida and the Bahamas Islands), which are partly dominated by Lophelia prolifera (Pallas, 1766) (= L. pertusa acc. Cairns, 2000). C. medea was observed in 21.1% of the “low hardground/pavement” frames of 867 photographs taken in these habitats (Messing et al. 1990). Deep­water coral banks have also been described off south­eastern Brazil, attaining up to hundreds of meters in length, 10–15 m in height, and developing a 40­kmlong coral field (Viana et al. 1997). These coral fields also have live L. pertusa (D. O. Pires, pers. comm.) and they are just 300 km away from the oceanic bank where C. medea was found in Brazil. The size of these fields and their proximity suggest C. medea may be found there in the future. The known distribution of C. medea is shown in Fig. 4.