Stichopathes cf. diversa ( Brook, 1889 )

Terrana, Lucas, Bo, Marzia, Opresko, Dennis M. & Eeckhaut, Igor, 2020, Shallow-water black corals (Cnidaria: Anthozoa: Hexacorallia: Antipatharia) from SW Madagascar, Zootaxa 4826 (1), pp. 1-62 : 38-40

Stichopathes cf. diversa ( Brook, 1889)

Fig. 22

Cirrhipathes diversa Brook 1889, p.87 , pl.12, fig. 12

Stichopathes diversa Summers 1910, p.275 –276

Material examined. Distal parts of two colonies, Toliara 27 m specimen INV.131377, 52 m specimen INV.131375 .

Depth range. 30–52 m.

Description. The colony is tightly coiled with dextral helicospirals that are more or less regularly spaced with a pitch of 1–1.9 cm ( Fig. 22 , a, b). Breaking events can lead to the restart of the coiling process in a different direction ( Fig. 22 , a). The spirals start to coil at about 3 to 4 cm from the base and have an average diameter of about 1.5 cm. The entire corallum measures 35 to 57 cm in height with a basal diameter of 4–4.4 mm. It slightly tapers towards the apex. The colony appears bright white or brown and the polyps are found in a single row on the outer side of the coils ( Fig. 22 , c). Smaller polyps are inserted between bigger ones irregularly ( Fig. 22 , c). Polyps are crowded (5–8 polyps per cm) and sagittally elongated, with no interpolypar spaces since the lateral tentacles of each polyp are touching the adjacent ones ( Fig. 22 , c). They measure 0.6-1.2 mm in transverse diameter, have a prominent oral cone, and their sagittal tentacles are longer than the lateral ones.

Two kinds of spines are visible, primary and secondary spines ( Fig. 22 , d–f). The primary spines are taller on the outer side of the coils and disposed at a right angle to the corallum ( Fig. 22 , e). These spines are either blunt, papillose and knobbed at the apex ( Fig. 22 , e), or blunt and tuberculated ( Fig. 22 , f). They correspond to the polypar spines and measure up to 0.4 mm high. The primary spines on the abpolypar side are triangular to conical ( Fig. 22 , g) or tall and cylindrical ( Fig. 22 , h) and have large papillae, but no tubercles. They measure up to 0.2 mm high. Secondary spines are interspersed among the primary ones on the entire skeleton ( Fig. 22 , d–h). They are generally small, smooth and triangular. Up to nine longitudinal rows of primary spines are visible in frontal view in a coiled section 2.1 mm in diameter.

Taxonomic remarks. The description of the present specimens shares some similarities with two species described in the literature for the area as having a coiled corallum, secondary spines and a clear distinction of polypar and abpolypar primary spines. Cirrhipathes diversa Brook, 1889 , was described from Sri Lanka and successively reported by Forster Cooper (1903) for the Maldives and by Summers (1910) for Mozambique (at 44 m depth). This species, originally described as Cirrhipathes due to the lack of polyps, was later synonymized by Summers (1910) as Stichopathes diversa . Brook’s (1889) type is a 30 cm-tall spiral colony, 1.5 mm in diameter at base and overall quite slender. Usually polyps of thin, coiled Stichopathes are not as large, compressed and crowded as in thick coiled Stichopathes (or thick straight ones as S. maldivensis ), but polyps are not available in Brook’s type. Examples of thin coiled colonies are given in “Clade A” of Bo et al. (2009). In Brook’s specimen, the primary spines are stout, cylindrical and with a blunt apex, and are up to 0.35 mm high. Small knobs and a distinctly papillose surface are visible in the type material (pers. obs. DMO). In the drawing, a difference between polypar and abpolypar spines is visible. Forster Cooper (1903) described a specimen 25 cm-tall with a 3 mm basal diameter, tight coils and an overall thick appearance of the stem with a comparable pattern of spines given by the drawings. No information on polyps was given. Summers (1910) described a specimen 15 cm-tall characterized by a tight spiral and compressed, flat polyps; similar to Forster Cooper (1903), she reported a similar pattern of spines but no measures.

Stichopathes alcocki Forster Cooper, 1909 is another species sharing similarities with the specimens considered here. It was originally described from Sri Lanka at 62 m depth, but the type specimen is lost. The 30-cm long fragment described by Forster Cooper (1909) was depicted as a close spiral covered by crowded, flat polyps of 1 mm in diameter, which are consistent with a thick stem (probably 2–3 mm in diameter from the drawing). The spines located on the outer side of the spirals were reported to be blunt, conical and 0.3 mm high, while the inner ones were triangular, hooked upwards and 0.2 mm. No clear tuberculation of the primary spines is obvious from the drawing, but secondary spines are evident. These primary spines seen in the drawing recall those in Fig. 22 , e as tuberculation cannot be always so distinct, and little knobs appear only at high magnification under SEM. Summers (1910) suggested synonymizing S. alcocki with Ci. diversa based on the characteristic pattern of spines in coils.

A few other species can be taken into consideration for comparision as they show secondary spines and a difference in polypar and abpolypar primary spines: Stichopathes bispinosa Summers, 1910 from East Africa redescribed on Brook’s Cirrhipathes (?) flagellum from Sri Lanka, and Stichopathes papillosa Thomson & Simpson, 1905 . Summers (1910) described S. bispinosa , as having similar flat polyps, but it is a very tall, thick colony with large spirals and very crowded, distinctly papillose and elongated, inclined spines (0.5 mm high polypar, 0.1 mm high abpolypar). Its synonymy with Cirrhipathes (?) flagellum is uncertain, given the straight colony and the poor preservation status of polyps of the latter. Stichopathes papillosa is described as having a stout, spiral corallum (up to 30 cm high) with tight coils and large, flat polyps 1 mm in diameter. Spines are depicted as very cylindrical, crowded and not particulary different between the two sides (0.3 mm and 0.2 mm, respectively), however knobs are reported (pers. com. DMO). The species variant described by Cooper (1909) from Indonesia is reported has having secondary spines.

In consideration of the fact that a high chance of synonymy is possible between S. diversa (at least some of the described specimens), S. alcocki and possibly S. papillosa (at least the variant), and that the present specimens do show a distinctly tall colony not reported for the discussed taxa, no definitive identification can be made. Pending a revision of the coiled species of Stichopathes , the name S. cf. diversa is used, based on its early Description. The present species recalls the “Clade C” of Stichopathes species as described by Bo et al. 2012a from Indonesia.

Distribution. Sri Lanka (type locality, Brook, 1889), Maldives ( Cooper, 1903), Mozambique ( Summers, 1910), Indonesia ( Bo et al., 2012a), Madagascar (present study).

Figures

FIGURE 22. Stichopathes cf. diversa (Brook, 1889). (a–b) In situ pictures of the white (INV.131375) and brown (INV.131377) phenotypes. (c) Close-up view of the sagittally compressed polyps, which are found on the outer side of the coils. (d) SEM view of a 2.1 mm in diameter skeleton of an apical coil (INV.131375). The size difference between polypar spines (the outer ones) and abpolypar spines (the inner ones) is clear. (e–f) Blunt, conical polypar spines showing the variability between papillose and tuberculated surfaces and small tubercles at the tip. Small triangular, secondary spines can be seen all around. (g–h) Variability in abpolypar spines that can be sub-triangular or cylindrical, always showing a papillose surface. Small secondary, triangular spines are seen all around as well.