Corallium johnsoni Gray 1860

Corallium johnsoni Gray, 1860

(Figures 8, 9, tables 2, 3)

Corallium johnsoni Gray, 1860: 394, pl. 18.

Corallium Johnsoni: Gray 1861: 214.— Stephens 1909: 7.— Thomson 1927: 19, pl. 1, fig. 13, pl. 3, fig. 27 (partim).

Hemicorallium johnsoni: Gray 1867: 127 (partim).

Hemicorallium (Pleurocorallium) johnsoni: Schmitz 1898: 269, fig. 2.

Pleurocorallium johnsoni: Wright & Studer 1889: 186, 293.— Johnson 1899: 61, pl. 6, pl.7, fig. 2, 5.

Corallium johnsoni: Kükenthal 1924: 49.— Carpine & Grasshoff 1985: 13.— Bayer & Cairns 2003: 222.— Watling & Auster 2005: 292 (app. 1).—? Fuller et al. 2008: 9 (tab. 1.4.2.1).— Sampaio et al. 2009: 74, fig. 1a-c.—Simpson & Watling 2011: 370.—Watling et al. 2011: 55 (tab. 2.1).

Material examined. NHM 1889.4.10.1, slide with sclerites labeled “ Pleurocorallium (Corallium) johnsoni Gray, Madeira, from type ”, depth unknown; NHM 1960.12.1.175, slide with sclerites labeled “ Corallium johnsoni Gray, Madeira, schizoholotype, J.A. Thomson collection, Gray P.Z.S. 1860 p. 393”; NHM 1933.3.13.55 (Fig. 8 A, 9), CAM Stn. 2743, 40º05N – 009º54’W, 1241 m, off Portugal, one small colony; SMF 2426 (Fig. 8 B), off Madeira, depth unknown, one small colony 9 mm in height.

Description. The specimen 1933.3.13.55 is composed of a flexuous main stem with a first-order branch that irregularly branches in one plane to the third degree, forming an open and simple system of ramification (Fig. 8 A). The main stem (13.58 mm in height) is ramified into two first-order branches, from which only one, ca. 43.14 mm long, remains. The tip of the first-order branch is bifurcated into two second-order branches, which are 3.62 mm and 7.76 mm long, respectively. The tips of the third-order branches are lacking. There are four short branches 5.0 mm to 9.0 mm in length that arise from the main stem and the first-order branch.

The cortex is thick and has been frayed at the third-order branches. When closely examined, the surface of the cortex exhibits reticular veins (Fig. 8 A) without bumps or protuberances. The axis is compact and longitudinally grooved, lack pits, and has an elliptical transverse section.

Autozooids can fully retract into wart-like and subhemispherical cortical mounds that are 1.06–1.32 mm tall and 1.33–1.89 mm wide (Fig. 8 A). The cortical mounds are scattered mainly on one side of the colony but there are some cortical mounds on the flank and the opposite side. Most cortical mounds are 1.0 to 5.0 mm apart from each other, but sometimes they are in contact, especially at the tips of the branches forming a blunt end. Siphonozooids are usually distributed at the base of the cortical mounds (Fig. 8 A).

Sclerome (Fig. 9): Cortex: the main types of sclerites include double clubs, 6- and 8-radiates, in addition with 7-radiates in low frequency (Fig. 9 A). Some of the 6-radiates are crosses, 0.055 mm tall, and others are asymmetrical ranging from 0.049 mm to 0.070 mm in height. Seven-radiates range from 0.060 mm to 0.065 mm in height. Eight-radiates include both asymmetrical and symmetrical forms, ranging from 0.049 mm to 0.076 mm in height. Furthermore, some 8-radiates are elongated and reach 0.106 mm in height (Fig. 9 Ae). Both 8-radiates and 6-radiates are the predominant types of sclerites, accounting for 32% and 37% of sclerites in the cortex, respectively. Doubles clubs are ca. 0.048 mm wide, sometimes having a transition shape between asymmetrical 6- radiates and double clubs.

Autozooids and cortical mounds: most common types are 8-radiates and 6-radiates (Fig. 9 B). In general, the relative abundance, size and forms of the sclerites are similar to those of the cortex (Fig. 9 A). The elongated 8- radiates are also present in the cortical mounds (Fig. 9 Be).

The cortex of the colony and the cortical mounds are cream in color. The axis is white and almost translucent at the tip of the branches. Sclerites are transparent when examined with a microscope under transmitted light.

Distribution. Corallium johnsoni is known from the northeast Atlantic Ocean (Watling & Auster 2005; Watling et al. 2011), although there is a record (name in species list) from northeastern Canada (Fuller et al. 2008; NAFO 2008) that should be verified. The holotype was harvested off Madeira at an unknown depth (Gray 1860; Johnson 1899), and the species was later reported from the Azores, Portugal, and off Ireland between 919–1241 m depth (Stephens 1909; Thomson 1927; Carpine & Grasshoff 1985; Sampaio et al. 2009).

Remarks. Corallium johnsoni was first described by Gray (1860), but he disregarded the sclerites. The complete description of the species including colony form, cortex, and sclerome is from Johnson (1899). According to this author (p. 61–62), this species has only ‘three forms of spicula.’ One type is the double-club, and the other two are more or less elongated 8-radiates. Thomson (1927, p. 19–20) also mentioned these three types of sclerites in agreement with Johnson (1899). Kükenthal (1924) and Bayer (1964) used the exclusive presence of 8- radiates (absence of 6- and 7-radiates) in the cortex to differentiate C. johnsoni from other species in the genus. Corallium johnsoni has not been thoroughly redescribed since Johnson (1899), and a detailed study of the sclerites of this species has been never undertaken.

Sample 1933.3.13.55 from NHM described herein (Fig. 8 A) was collected from CAM Stn. 2743 (as inferred by the coordinates written in the Zoology Accessions Register of NHM p. 239). Material from this station was listed by Thomson (1927, p. 19) and by Carpine & Grasshoff (1985) as C. johnsoni, and presumably the sample was identified by the former author. Sclerites from this material are more varied in form than previously described by Johnson (1899), Thomson (1927), and others. Similar variation in sclerite form was also found in the type material (NHM 1889.4.10.1) and in a specimen of C. johnsoni deposited in SMF and examined herein (Fig. 8 B).

Cortical mounds of C. johnsoni shown by Gray (1860, but not 1867 p. 126 as Hemicorallium johnsoni = Corallium tricolor, see below remarks on this species) are similar to those from the material examined herein. In both slides with sclerites from the type (1889.4.10.1 and 1960.12.1.175) there are also four main types of sclerites, namely, 6-radiates, 7-radiates, 8-radiates, and double clubs. Most 6-radiates are symmetrical, ranging from 0.045 mm to 0.063 mm in height. Symmetrical 8-radiates are more abundant than asymmetrical ones, ranging from 0.054 mm to 0.081 mm in height. The width of double clubs range from 0.043 mm to 0.052 mm, and of height from 0.036 mm to 0.043 mm. Seven-radiates are very scarce, ranging from 0.058 mm to 0.062 mm in height. Long spindles were not seen. Previous authors have overlooked the presence of both 6- and 7-radiates in this species.