Heterocyathus alternatus Verrill, 1865

Filander, Zoleka N., Kitahara, Marcelo V., Cairns, Stephen D., Sink, Kerry J. & Lombard, Amanda T., 2021, Azooxanthellate Scleractinia (Cnidaria, Anthozoa) from South Africa, ZooKeys 1066, pp. 1-198 : 1

Heterocyathus alternatus Verrill, 1865

Fig. 4A, B

Heterocyathus alternata Verrill, 1865: 149

Heterocyathus alternatus . -Folkeson 1919: 10-11, pl. 1, figs 10-11. -Hoeksema and Best 1991: 230-231, figs 12-18. - Cairns 1998: 384, fig. 3D-E. - Cairns 1999a: 99-100, fig. 14E-F. -Cairns 2004a: 281.

Heterocyathus aequicostatus . - Boshoff 1981: 37 (in part).

Type locality.

Gaspar Straits, between the Bangka and Belitung Islands, Sumatra, (Indonesia); depth unknown (Hoeksema and Best 1991).

Type material.

The holotype is deposited at the YPM (Hoeksema and Best 1991).

Material examined.

SAMC_A073105 (1 specimen): Eastern margin, 36 km from Cape Vidal / 32 km off Mgobezeleni Estuary, 27°48'54.00"S, 32°38'24.00"E ; 52 m. SAMC_A073126 (5 specimens): Eastern margin, 25 km from Cape Vidal / 23 km off St Lucia Estuary, 27°54'42.11"S, 32°36'42.11"E ; 42- 50 m. SAMC_A073214 (1 specimen): Eastern margin, 37 km from Cape Vidal / 32 km off Mgobezeleni Estuary, 27°48'47.88"S, 32°38'53.87"E ; 50 m. SAM_H2808 (10 specimens): Eastern margin, 20 km from Cape Vidal / 22 km off St Lucia Estuary, 27°59'04.99"S, 32°40'08.00"E ; 550 m. SAM_H3118 (19 specimens): Eastern margin, 2 km from Durban / 8 km off Umgeni Estuary, 29°52'00.00"S, 31°00'00.00"E ; 99 m. SAM_H3119 (1 specimen): Southern margin, 3 km from Plettenberg Bay / 2 km off Piesang Estuary, 34°03'06.80"S, 23°22'48.65"E ; 30- 35 m. ORI_DIIIe1_1 (1 specimen): Locality data unknown .

Description.

Corallum squat, free, and with aboral or lateral efferent pores smaller than 1.5 mm in diameter. Base flat, but a prominent pore result in an asymmetric corallum. Calice circular to elliptical (GCD:LCD = 1.0-1.1). Largest specimen examined (SAMC_A073126) 9.5 × 8.6 mm in CD, and 6.4 mm in H. Costae well-defined, finely granulated, and usually unequal in width. C1-2 sometimes slightly narrower than other costae. Intercostal striae relatively deep but disappear towards base. Base finely granulated. Central part of corallum darker than costae and associated septa.

Septa loosely packed and having a star-like appearance, hexamerally arranged in four complete cycles according to the formula: S1> S2> S4> S3 (48 septa). S1 highly exsert, each bearing two or three paliform lobes. S2 slightly less exsert than S1. S3 smallest septa, not as exsert as S1-2, and bearing one or two paliform lobes. S4 wider than S3 and bears four or five paliform lobes, which are distinguishable from columellar elements. At calicular margin, S4 fuses to adjacent S1-2 forming prominent lancets. All septa appear to have straight axial margins, with granules arranged perpendicular to septal faces. All paliform lobes cylindrical, rising slightly above columellar elements, with traces of small and sparsely arranged granules. Fossa relatively deep, containing a papillose columella composed of 5-20 cylindrical elements.

Distribution.

Regional: Southern to eastern margin of South Africa, from Plettenberg Bay extending towards Cape Vidal; 30-150 m. Elsewhere: Off Indonesia (Hoeksema and Best 1991; Cairns 2004a); Vanuatu; and Wallis and Futuna Islands ( Cairns 1999a); 0-319 m.

Remarks.

Examined specimens closely resemble specimens reported by Hoeksema and Best (1991) as Heterocyathus alternatus . However, some of the examined specimens (e.g., SAMC_A073126) have a darker centre and costal pigmentation, characters which Hoeksema and Best (1991) suggested to be representative of H. sulcatus (see key from Hoeksema and Best 1991 [page 222]). Cairns (1999) also noted specimens of Heterocyathus that are conspecific to H. sulcatus , but lacked pigmentation, and other specimens of Heterocyathus that display colouration but are distinctively different from H. sulcatus . Based on this, we suggest that colouration is of low taxonomic importance. Nonetheless, H. alternatus closely resembles H. aequicostatus among the South African congers. Apart from the differences in septa and costae profile highlighted in the H. aequicostatus account (see remarks section), the less crowded septa and star-like appearance (a result of S4 inclination towards S3) of H. alternatus distinguishes it from H. aequicostatus . Furthermore, the pali of H. alternatus are distinguishable from columellar elements in comparison to that of H. aequicostatus , which are indistinguishable. Heterocyathus alternatus was first reported in South Africa by Boshoff (1991), who identified it as H. aequicostatus (ORI_DIIIe1). Additionally, specimens examined include zooxanthellate representatives (> 40 m) (Hoeksema and Best 2015) and should therefore not be considered in biodiversity assessments focusing on azooxanthellate forms.

Figures

Figure 4. A, B Heterocyathus alternatus (ORI _ DIIIe 1 _ 1, locality data unknown) A calicular view B lateral view C, D Heterocyathus monileseptatum sp. nov. (SAM _ H 1431, off Durban Harbour, 99 m) C calicular view D lateral view E, F Heterocyathus sulcatus (SAMC _ A 073123, off Shaka's Rock, 100 - 105 m) E calicular view F lateral view G, H Labyrinthocyathus delicatus (SAM _ H 2836, off East London, 146 - 238 m) G calicular view H lateral view I, K Monohedotrochus capensis comb. nov. I, J (SAMC _ A 088924, off Kidds Beach, 247 - 147 m) I calicular view J lateral view K (SAM _ H 3210, off Scottburgh, 690 m) calicular view L, M Polycyathus sp. (USNM 91677, off Port Dunford, 69 m) L calicular view M full view N, O Rhizosmilia robusta (USNM 91689, off Kosi Bay Estuary, 74 m) N calicular view O lateral view P Solenosmilia variabilis (SAM _ H 3158, off Cintsa, 630 m) P full view. Scale bars: 10 mm (A-G, I-O); 100 mm (H, P).