Entogoniopsis morlandii (Grove & Sturt) J. Witkowski, P.A. Sims, N.I. Strelnikova & D.M. Williams, 2015

Witkowski, Jakub, Sims, Patricia A., Strelnikova, Nina I. & Williams, David M., 2015, Entogoniopsis gen. nov. and Trilamina gen. nov. (Bacillariophyta): a survey of multipolar pseudocellate diatoms with internal costae, including comments on the genus Sheshukovia Gleser, Phytotaxa 209 (1), pp. 448-450 : 448-450

1. Entogoniopsis morlandii (Grove & Sturt) J. Witkowski, P.A. Sims, N.I. Strelnikova & D.M. Williams ,

comb. nov.

(SEM: Figs 11–16 ; LM: Figs 17–23 )

BASIONYM: Triceratium morlandii Grove & Sturt (1887a , Journal of the Quekett Microscopical Club Series 2(3): 7, pl. II, fig. 5).

TYPE (here designated):— ‘ Oamaru , Otago, New Zealand’ (BM46565, lectotype! = Fig. 18 ) .

Triceratium morlandii var. subaperta Grunow (1888: 40 , Grunow 1889: 388), nom. nud.

Sheshukovia morlandii (Grove & Sturt) Gleser (1984: 294) .

Frustules subrectangular in girdle view ( Fig. 23 ), valves tripolar with straight or slightly concave sides ( Figs 17–22 ). Valve face centre is conspicuously depressed; the marginal part of the valve face is gently sloping toward the margin and the poles ( Fig. 11 ). At each pole, there is a low elevation terminated in a flat plate that bears a prominent pseudocellus ( Figs 11, 15 ). The pseudocelli continue down the distal faces of the polar elevations onto the mantle ( Fig. 15 ). A hyaline marginal ridge extends between the polar elevations, its crest level with the flat summits of the pseudocelli ( Fig. 11 ). Except for a small hyaline valve centre, whole valve face is perforated ( Figs 11, 13 ). Areolae are poroid, occluded by volae ( Fig. 13 ). In the central part of the valve face areolae are arranged in few irregular rings ( Figs 17–22 ). In most specimens, there are also three conspicuous areas of sparse and scattered areolation adjacent to the proximal sides of the polar elevations ( Figs 11 , 17–22 ). Along the sides, however, the areolae are arranged in rows that are generally perpendicular to the valve face margins ( Figs 11 , 17–22 ). Within the central depression, there is an irregular ring of rimoportulae ( Figs 13–14 ). However, no rimoportulae were observed on some specimens, usually of smaller size ( Figs 20–22 ). The rimoportulae open to the interior as small, slightly raised slits ( Fig. 14 ), and to the outside as inconspicuous, short, buttressed tubes ( Fig. 13 ). Mantle is shallow, steeply downturned ( Figs 11–12, 16 ). Mantle margin is hyaline, smooth, slightly expanded inwardly ( Fig. 16 ). Except for the margin, whole mantle is perforated by poroid areolae, arranged in rows that are generally parallel to the pervalvar axis ( Fig. 16 ). Mantle areolae grade into polar pseudocelli ( Fig. 15 ). On the valve interior, there is a prominent network of robust costae ( Fig. 12 ). Costae are T-shaped in cross-section ( Fig. 16 ), and extend from the marginal part of the central depression to the expanded mantle margin ( Figs 12, 16 ). The areolation pattern on the valve face and the mantle is associated with the sectors formed by the internal costae ( Figs 17–22 ). Measurements (n =42): average side length: 75–231 µm; 2–3 areolae in 10 µm; 2 rows of areolae per sector; 2 costae in 10 µm, measured along the valve face margin; number of rimoportulae: if present, 8–16; pseudocelli: 4–6 porelli in 10 µm.

Typification: Specimens of Triceratium morlandii are found on several slides in the Sturt collection at the BM. A specimen on strewn slide BM46548, annotated with Maltwood Finder (MF) coordinates 36|17.5, is described in the unpublished Sturt catalogue as “perfect” (p. 131). This specimen is considerably tilted, however, and has strongly concave sides, and therefore it is unlikely to have served as the basis for the remarkably detailed illustration in Grove & Sturt (1887a: pl. II, fig. 5). Instead, a straight-sided, selected specimen mounted on slide BM46565 ( Fig. 18 ), also from the Sturt collection, is designated here as lectotype of E. morlandii .

Geographic and stratigraphic distribution ( Fig. 10, sites 12–13, 18–19):

(a) specimens:

Middle Eocene : Falkland Plateau, South Atlantic Ocean: Vema Cruise 17, Core 107: BM stub P.1275 ( Figs 12, 14 ).

Late Eocene-earliest Oligocene: Oamaru , Otago, New Zealand: BM stub P.1277 ( Figs 11, 13, 15–16 ); BM46565 ( Fig. 18 , lectotype), BM46600, BM61155, BM61157, BM63654, BM66534, BM coll. Adams : F1347, G3, G84, G86, G93 ( Fig. 22 ), G133, G142 ( Fig. 20 ), TS270 ( Figs 21, 23 ), TS291, TS315 ( Fig. 17 ). Oamaru Diatomite outcrops at: Allan’s Farm: BM coll. Adams TS 429; Jackson’s Paddock : BM61159, BM63650, BM coll. Adams G 157, G162 ( Fig. 19 ); Totara: BM coll. Adams TS 435; ‘ Railway Cutting’ : BM coll. Adams : G68, G69, G73.

10 • Phytotaxa 209 (1) © 2015 Magnolia Press

WITKOWSKI ET AL.

(b) records:

Middle to late Eocene: Central Tasman Sea, Southwest Pacific Ocean: DSDP Site 283, Cores 283-2 through 283-6: Hajós (1976: 823, pl. 13, figs 7–8).

Late Eocene: South Tasman Rise, Southwest Pacific Ocean: DSDP Site 281, Cores 281-14 through 281-16: Hajós (1976: 822).

Late Eocene-earliest Oligocene: Oamaru , Otago, New Zealand: Laporte & Lefébure (1929: pl. 8, fig. 54), Schmidt (1888: taf. 128, figs 5–6; 1890: taf. 150, fig. 22); Oamaru Diatomite outcrops at: Allan’s Farm: Doig (1991: 112); Bain’s Lower, Bain’s Farm, Cormack’s Top, Forrester’s Hill: Desikachary & Sreelatha (1989: 260); Jackson’s Paddock: Desikachary & Sreelatha (1989: 260), Doig (1991: 114); Cormack’s Siding: Grove & Sturt (1887a: 7, pl. II, fig. 5), De Lautour (1888: 310, pl. XXI, fig. 6), Desikachary & Sreelatha (1989: 260); Totara: Desikachary & Sreelatha (1989: 260); Flume Gully: Doig (1991: 125); Taylor’s Quarry: Doig (1991: 113); William’s Bluff: Desikachary & Sreelatha (1989: 260), Doig (1991: 114); Division Hill: Desikachary & Sreelatha (1989: 260), Doig (1991: 119); Mavor’s Farm: Desikachary & Sreelatha (1989: 260), Doig (1991: 120); Table Top Hill: Doig (1991: 125).

Observations:— Morphological variation in Entogoniopsis morlandii is reflected primarily in the presence or absence of the central of rimoportulae, suggesting that E. morlandii may have formed heterovalvar frustules. Unfortunately, the only frustules available for study were in LM in girdle view ( Fig. 23 ). Therefore, heterovalvy could not be directly investigated. Specimens without rimoportulae, however, tend to be of a relatively small size (e.g., Figs 17 and 19 versus Figs 18, 20–22 ). Thus, it is also possible that at some stages in the vegetative phase of the life cycle, E. morlandii produced valves without rimoportulae.

Entogoniopsis morlandii has a highly variable areolation pattern, associated with the network of internal costae. Next to the midpoint of each side, the pattern of internal costae is usually uninterrupted: costae extend toward the valve face centre over a similar distance, approximately half the distance from the valve face centre to the mid-point of a side, and form sectors , in which there are usually two rows of areolae. However, closer to the poles, the costae on the valve face become shorter, and often bifurcate or intersect at variable angles. As a result, in addition to the central depression, where the areole are larger and arranged more loosely than in the marginal sectors, there are also three areas next to the proximal side of each polar elevation, in which areolae are larger and scattered ( Figs 11 , 17–22 ). These areas appear distinctly thickened in LM, and in some specimens are separated from the central depression by a narrow zone of particularly complex latticework of internal costae (e.g., Fig. 18 ). This is probably what Grunow (1889: 388) meant, when suggesting that forms „in which the ring of meshes round the centre is more or less incomplete in three places” should be grouped in Triceratium morlandii var. subaperta . The degree of separation between the central depression and the areas adjacent to the proximal sides of the polar elevations seems to be size-dependent ( Figs 17–22 ), with none or less separation visible in smaller specimens (e.g., Fig. 21 ). We therefore suggest that the variation with respect to this morphological feature results from purely mechanical reasons. For further comments on the varieties of T. morlandii suggested by Grunow, see discussion under Entogoniopsis grunowii , below.

Figures

FIGURES 11–16. Scanning electron micrographs of Entogoniopsis morlandii from Oamaru, New Zealand (Figs 11, 13, 15–16), and Vema Cruise 17, Core 107, South Atlantic Ocean (Figs 12, 14). Fig. 11: Oblique external view, showing a depressed valve face surrounded by a hyaline marginal ridge level with the summits of the polar pseudocelli. Central ring of rimoportulae indicated by arrowhead. Areas of sparse, scattered areolation next to the proximal sides of polar elevations are indicated with arrows. Fig. 12: Oblique internal view showing the prominent internal costae. Central ring of rimoportulae indicated by arrowhead. Fig. 13: Detail of the specimen in Fig. 11, showing fractured buttressed external tubes of the rimoportulae, and partially dissolved volae. Fig. 14: Detail of the specimen in Fig. 12, showing an irregular central ring of rimoportulae, internal openings in the form of slightly raised slits. Fig. 15: Detail of the specimen in Fig. 11, showing one of the polar pseudocelli. Note the flat summit occupying the whole of the pseudocellus located on the valve face. Fig. 16: Detail of a fractured valve revealing a T-shaped cross-section through a costa (arrowhead), and an inward expansion of the hyaline mantle margin (arrow).

FIGURES 17–23. Light micrographs showing the range of morphological variation in Entogoniopsis morlandii. Fig. 17: BM coll. Adams TS315, Oamaru, New Zealand. Fig. 18: BM46565, Oamaru, New Zealand, lectotype. Fig. 19: BM coll. Adams G162, Jackson’s Paddock, Oamaru, New Zealand. Fig. 20: BM coll. Adams G142, Oamaru, New Zealand. Fig. 21: BM coll. Adams TS270, Oamaru, New Zealand. Fig. 22: BM coll. Adams G93, no locality on slide label, presumably Oamaru, New Zealand. Fig. 23: BM coll. Adams TS270, girdle view of a frustule with attached valvocopula, Oamaru, New Zealand.