Stephanocyathus (Acinocyathus) explanans (von Marenzeller, 1904)

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

Stephanocyathus (Acinocyathus) explanans (von Marenzeller, 1904)

Fig. 5A-F

Stephanotrochus explanans von Marenzeller, 1940a: 304-307, pl. 8, fig. 19A, B. -Gardiner and Waugh 1938: 192.

Stephanocyathus nobilis . - Boshoff 1981: 39.

Stephanocyathus (Acinocyathus) spiniger . - Cairns and Keller 1993: 243-244.

Stephanocyathus (Acinocyathus) explanans . - Cairns and Zibrowius 1997: 119, fig. 14E. - Cairns 1998: 38. -Cairns 2004a: 285.

Type locality.

Off Sumatra, Zanzibar Island and Pemba (SS ' Valdivia ' stns. 194, 243 and 245: 0°15'02"N, 98°08'08"E, 6°39'01"S, 39°30'08"E, and 05°27'09"S, 39°18'08"E, respectively); 245-614 m (von Marenzeller 1904a).

Type material.

Ten syntypes are deposited at the ZMB (Cairns 2004a).

Material examined.

SAMC_A090144 (2 specimens): Eastern margin, 8 km from Port St. Johns / 11 km off Bulolo Estuary, 31°39'43.19"S, 29°36'38.16"E; 96-98 m. ORI_DIIIk2 (I specimen): Eastern margin, 33 km from Durban / 31 km off Beachwood Mangroves, 29°55'00.00"S, 31°19'59.99"E; 442 m. USNM 62500 (4 specimens): Eastern margin, 11 km from Durban / 4 km off Beachwood Mangroves, 29°46'29.16"S, 31°04'18.42"E; 183-220 m.

Imagery data.

RV ‘Galathea’ stn. 202 (1 specimen): Eastern margin, Natal.

Description.

Corallum bowl-shaped, free, with a slightly rounded base. BD smaller than CD; base has a basal attachment scar. All specimens bear short, straight, and slender C1 costal spines, and are usually longer (in relation to CD) in juveniles. Calice circular to slightly elliptical (GCD:LCD = 1.0-1.1), with a serrated calicular margin. Largest specimen examined (USNM 62500) 30.4 × 27.6 mm in CD, 26.6 in BD, and 11.2 mm in H. Costae slightly convex and granular, extending from calicular margin and disappearing towards base. Costae absent at base epicentre, which is usually eroded. Corallum white.

Septa hexamerally arranged in five cycles, the last cycle being incomplete, according to the formula: S1 ≥ S2 > S3 > S4 > S5 (≤ 72 septa). S1 highly exsert and extend to columella with straight axial margin. A deep notch separates P1 from S1. P1 fuse to columella. S2 as exsert and as large to only slightly smaller than S1. P2 also fuse to columella, but is slightly smaller than P1. S3 ~ 1 mm less exsert and ¾ the width of S1-2. P3 broad and separated from S3 by a narrow notch. S4 flanked by S5 as wide and exsert as S3, but those unflanked S4 are the least exsert septa, and only ½ the width of S3. S4 become rudimentary deeper in fossa. P4 fuse to P3. S5 closely resembling unflanked S4. All septal margins straight. Paliform lobes also straight, and appear to be arranged in a single palar crown. Fossa relatively shallow, containing a papillose columella, composed of ≤ 20 granular and closely-packed rods.

Distribution.

Regional: Eastern margin of South Africa, off Port St. Johns extending towards Durban; 96-695 m. Elsewhere: Indonesia ( Cairns and Zibrowius 1997); Tanzania; Madagascar ( Cairns and Keller 1993); 180-1016 m.

Remarks.

Stephanocyathus (A.) explanans differs from the only other subgeneric extant species [ S. spiniger (von Marenzeller, 1888)], in its calicular margin, number of septa, and costal spines. Cairns and Zibrowius (1997) elaborated on these taxonomic differences, highlighting that S. explanans may be distinguished in having a serrated calicular margin (lanceted in S. spiniger ), 48-72 septa (instead of 96 septa), and 6-11 marginal circular spines (consistently 6 elongated and basally compressed in S. spiniger ). Stephanocyathus explanans was first reported from South Africa by Gardiner and Waugh (1938), however no further locality information apart from noting that specimens were collected "off South Africa" was provided. Subsequently, Boshoff (1981) incorrectly identified the species as Stephanocyathus (O.) nobilis (von Marenzeller, 1904a) (ORI _ D111k2), a record later corrected as S. explanans by Cairns and Keller (1993). The South African representatives add no new morphological information apart from S1 being slightly wider than S2 in some of the examined specimens.

Figures

Figure 5. A, F Stephanocyathus (Acinocyathus) explanans: A, C (USNM 62500, off Durban, 183 - 220 m) Calicular view B basal view C lateral view D, F (SAMC _ A 090144, off Port St Johns, 96 - 98 m) D calicular view E basal view F lateral view G, I Stephanocyathus (Odontocyathus) campaniformis (SAM _ H 3178, off Coffee Bay, 1420 m) G calicular view H basal view I lateral view J, L Stephanocyathus (Odontocyathus) nobilis (SAM _ H 1697, off Groot Berg Estuary, 1050 m) J calicular view K basal view L lateral view M, N Tethocyathus virgatus (SAMC _ A 073180, off Mazeppa Bay, 240 - 250 m) M calicular view N lateral view O, P Trochocyathus (Trochocyathus) sp. 1 (SAM _ H 1244, off East London, 59 m) O calicular view P lateral view. Scale bars: 10 mm.