Heterocyathus monileseptatum Filander & Kitahara, 2021

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 monileseptatum Filander & Kitahara sp. nov.

Fig. 4C, D

Type locality.

Off Durban Harbour, South Africa, 99 m.

Type material/.

Holotype. SAM_H1431A: eastern margin, 5 km from Durban/7 km off Umgeni Estuary, (RV 'Pieter Faure’: 29°52'00.00"S, 31°03'00.00"E); 99 m. Paratypes. SAM_H1431B (4 specimens): eastern margin, 5 km from Durban/7 km off Umgeni Estuary, (RV 'Pieter Faure’: 29°52'00.00"S, 31°03'00.00"E); 99 m. SAM_H1246 (8 specimens): Locality data unknown.

Etymology.

The species name Heterocyathus monileseptatum (derived from Latin monile meaning "string of beads" and septum meaning "enclosure, wall, fence") which alludes to the beaded septal margins.

Description.

Corallum unattached and tall, with lateral efferent pores ranging in diameter from 1.00 ≤ 2.00 mm. Base flat, but a prominent basal pore results in an asymmetric corallum with an irregularly shaped base (BD = 1.1-1.6). Calice circular to elliptical (GCD:LCD = 1.0-1.1), with serrate calicular margin. Holotype (SAM_H1431) 11.0 × 9.7 mm in CD, 11.1 × 6.9 mm in BD, and 10.6 mm in H. Paratypes having one or two aboral pores randomly positioned. Costae equidistant and progressively decreasing in width towards base. All costae finely granulated. C4 bears distinctive low spine-like granules. At base each costae become a row of granules. Intercostal striae equal in width and depth. Corallum white, with theca and columella with blackish pigment.

Septa thin, spaced out, delicate, and hexamerally arranged in four complete cycles (which follow a Pourtalès plan) according to the formula: S1 ≥ S2> S4> S3 (48 septa). S1 most exsert and extend to columella with straight and smooth axial margins. S2 only slight less exsert and ca. as wide as S1. S2 axial margins slightly sinuous. S3 least exsert septa and 2/3 the size of S2. In each half-system, a pair of S4 joins common S3 deep in fossa, and extends towards columella as one septum. S3-4 junctions beaded. S4 more exsert than S3, and also with sinuous axial margin. S4 dimorphic in size: those adjacent to S1 being wider and more exsert than those adjacent to S2. At calicular margin, S4 fuses to adjacent S1-2 forming high rectangular lancets. Septal faces granular. No pali. Fossa deep, containing a poorly developed papillose columella composed of ≤ seven sparsely arranged rods.

Distribution.

Regional: Eastern margin of South Africa, off Durban; 99 m.

Remarks.

Amongst the six extant Heterocyathus species ( H. aequicostatus , H. alternatus , H. antoniae Reyes, Santodomingo & Cairns, 2009, H. hemisphaericus Gray 1849, H. japanicus (Verrill, 1866), and H. sulcatus ) ( Hoeksema and Cairns 2021), the specimens reported herein are distinctive in the lack of pali, height of corallum, and by having a beaded axial margin at the S3-4 junctions. However, there are intermediate similarities with each of these species, for example Heterocyathus monileseptatum sp. nov. resembles H. aequicostatus , H. alternatus , and H. hemisphaericus in having septa arranged in four cycles (S1> S2> S4> S3 = 48 septa), but differs from the first two species in having no pali rather than P1-4 (in case of H. aequicostatus ) or P1, 3, 4 (in case of H. alternatus ). On the contrary, the lack of pali in Heterocyathus monileseptatum sp. nov. is a similarity shared with H. hemisphaericus but this species can be distinguished by their septa profile: all septa are thin (max 0.6 mm) and solid in Heterocyathus monileseptatum sp. nov. compared with being thick (max 0.9 mm) and porous in H. hemisphaericus ( Cairns 1998). The maximum height observed in Heterocyathus monileseptatum sp. nov. (10.9 mm) is higher than that reported in the Atlantic H. antoniae (9.0 mm) and both species also have septa arranged in a Pourtalès plan fashion. Nonetheless, differences between Heterocyathus sp. nov. and H. antoniae include (i) septa being arranged according to S1> S2> S4> S3 and S1 = S2 = S4 >> S3, respectively; (ii) lack of pali in Heterocyathus monileseptatum sp. nov.; (iii) columella of Heterocyathus monileseptatum sp. nov. being papillose and composed of sparsely arranged rods versus a spongy columella composed of crispate elements in H. antoniae . Heterocyathus japanicus is also reported to have septa arranged in a Pourtalès plan (Zibrowuis 1997). However, Heterocyathus monileseptatum sp. nov. can be differentiated by beaded S3-4 axial margins, a feature that is unique in relation to all Heterocyathus .

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).