Truncatoflabellum zuluense Cairns in Cairns & Keller, 1993

Truncatoflabellum zuluense Cairns in Cairns & Keller, 1993

Fig. 13C, D View Figure 13

Truncatoflabellum zuluense Cairns in Cairns & Keller, 1993: 267-268, figs 11F, G. - Cairns 2016: 16, fig. 3A.

Flabellum inconstans . - Boshoff 1981: 34.

Type locality.

Off Zululand, South Africa (RV 'Meiring Naude’ stn. ZK21: 27°47'00"S, 32°39'10"E); 62-84 m ( Cairns and Keller 1993).

Type material.

The holotype and most paratypes are deposited at NMNH, whilst one paratype being deposited at SAM ( Cairns and Keller 1993).

Material examined.

SAMC_A073113 (1 specimen): Eastern margin, 47 km from Cape Vidal / 21 km from Mgobezeleni Estuary, 27°43'14.88"S, 32°40'36.11"E; 110 m. GoogleMaps SAMC_A073182 (1 specimen): Southern margin, 26 km from East London / 24 km off Buffalo Estuary, 33°11'48.11"S, 28°03'11.88"E; 90 m. GoogleMaps SAMC_A090095 (1 specimen): Eastern margin, 16 km from Scottburgh / 12 km off Mkomazi Estuary, 30°15'00.00"S, 30°54'18.00"E; 100 m. GoogleMaps SAMC_A090096 (1 specimen): Eastern margin, 66 km from Cape Vidal / 7 km off Mgobezeleni Estuary, 27°33'11.99"S, 32°43'00.00"E; 85 m. GoogleMaps SAM_H1398 (12 specimens): Southern margin, 32 km from Cintsa / 11 km off Cwili Estuary, 32°45'45.00"S, 28°26'15.00"E; 66 m. GoogleMaps SAM_H3156 (12 specimens): Southern margin, 18 km from Gonubie /off Gqunube Estuary, 33°04'35.99"S, 28°06'35.99"E; 90 m. GoogleMaps SAM_H4581 (1 specimen: paratype): Eastern margin, 25 km south of Ponta Do Ouro / 17 km from Kosi Bay Estuary, 27°04'47.99"S, 32°53'30.00"E; 65 m. GoogleMaps USNM 91747 (Holotype): Eastern margin, 39 km from Cape Vidal / 29 km off Mgobezeleni Estuary, 27°47'21.59"S, 32°39'03.60"E; 62- 84 m. GoogleMaps

Description.

Corallum small to medium-sized (GCD ~ 10.0-18.0 mm), with thecal edge diverging in an angle between 28 and 38°. Calice compressed (GCD:LCD = 1.1-1.8), with a slightly serrated calicular margin. Basal scar 6.8 × 4.8 mm in diameter, with 24 septa originating from scar. Largest specimen examined (SAMC_A073182) 19.0 × 10.6 mm in CD, and 18.7 mm in H. Theca smooth, sometimes bearing a pair of basal spines. Thecal faces diverge in an angle ~ 18-23° and thecal edge ~ 35-48°. Anthocyathi and anthocauli remain attached, but fracture zone is demarcated by a thin line. Corallum white, with costae a darker tint of reddish or greenish brown.

Septa hexamerally arranged in five cycles, the last cycle incomplete, according to the formula: S1-2 > S3 >> S4 > S5 (≤ 80 septa). S1-2 bear vertical and sinuous axial margins. S3 ~ ¾ the width of S1-2, also with sinuous axial margin. S4 small, ~ 1/3 the width of S3, and bearing dentate axial margin. S5 rudimentary. Septal faces granular. Fossa deep, with a rudimentary columella formed by the fusion of S1-2 lower axial margins.

Distribution.

Regional: Southern and eastern margin of South Africa, from off Gonubie extending towards Cape Vidal; 62-110 m. Elsewhere: Only known from South Africa.

Remarks.

Truncatoflabellum zuluense is known to occur in the KwaZulu-Natal region and is distinctive in the anthocaulus often remains attached to the anthocyathus throughout development. Amongst the 38 Recent species of the genus, T. zuluense and T. dens (Alcock, 1902a) are the only two species known to usually maintain such an attachment long into ontogenesis. However, the two species may be distinguished by thecal face (14-18° in T. dens vs. 18-22° in T. zuluense ) and thecal edge angles (bimodal in T. dens vs. 35 to 48° in T. zuluense ), and GCD:LCD ratio (1.7-2.3 in T. dens vs. 1.4-2.0 in T. zuluense ). Among South African congeners, T. zuluense may be mistaken with T. gardineri , whereby the resemblance and morphological differences between them are detailed by Cairns and Keller (1993) in their account of the species and keyed by Cairns (2016).