O 'Connor, 1997
Description - Add description
|Siphocampe grantmackiei n.sp. O'Connor 1997 p. 106, Pl. I, fig. 5-8; pl. 4. fig. 7-12|
Description: Shell of three segments, hyaline, pupoid, abdomen divided into "sub-segments".
Cephalis ovoid, smooth-surfaced, lower 1/3 sunk into upper thorax. Pores few, circular to subcircular, irregularly distributed. Well developed vertical tube (approx. 8-10μm long) projects upward at 24°-34° angle, generally circular in cross-section (approx. 8µm diameter), tapers distally, may have slight distal flare. Lateral lobes externally delineated by furrows (see below). Vertical spine well developed (1/3 to 1/2 length of vertical tube), protrudes freely into vertical tube (see below). Small, conical to bladed apical horn anteriorly offset on cephalis (see below). Collar stricture externally indistinct.
Thorax inflated truncate-conical, bears three to four transverse rows of circular to subcircular pores. Occasionally small wings present: one corresponding to D (see below) protrudes anteriorly from upper thorax (pl.l, fig.6, pi.4, fig.9); another corresponding to Vbd (see below) protrudes posteriorly from upper thorax just below vertical tube (pl.l, figs.7, 8, pl.4, figs.9, 10). Lumbar stricture externally distinct as smooth, rounded constriction, seen internally as ledge or ring.
Abdomen pupoid, divided into series of six "sub-segments" by smooth, shallow, rounded, external constrictions (not defined by ledge or ring internally): two transverse rows of circular to subcircular pores on first "sub-segment", two to three rows on second and one row on each of following four. Maximum width of shell attained by third or fourth "sub-segment". Aperture slightly constricted, termination ragged as though broken along a transverse pore row. On some specimens an incipient peristome present, smooth-surfaced, with slightly ragged termination.
Surface of thorax and abdomen covered in wavy longitudinal ridges that gradually become less pronounced distally and disappear before termination so last "sub-segment" of abdomen smooth-surfaced.
Internal skeleton consists of bars M, D, V, A, LI, Lr, 11, Ir, Vbl, Vbr, Vbd, spines Vs. seven Ax and arches A-Vbl, A-Vbr, Vbl-Vbd. Vbr-Vbd, LI-Vbl, Lr-Vbr, 11-L1, Ir-Lr, D-Il and D-lr (text-fig.4; pl.4, fig.l 1, 12). A extends freely upward from M to top of cephalis protruding as tiny apical horn (see above); small antecephalic lobe anterior to A. D extends downward at an angle to collar stricture, may protrude outside as small dorsal wing (see above). V extends upward at an angle, branches to form Vbl, Vbr and Vbd. Vbl and Vbr extend laterally to join cephalic wall at either side of base of vertical tube. Vbd extends downward at an angle to join cephalic wall at lower base of vertical tube, may protrude outside as small wing (see above). Rest of bars extend to cephalic wall and do not penetrate. Vs continues from V extending freely into vertical tube. Seven Ax extend straight downward - one from junction of V and M, shorter than others; two each from bars M, LI and Lr near their junction with each other. Ax may be hollow. Arches A-Vbl and A-Vbr mostly incorporated in cephalic wall so internally indistinct, curve downward from point where A joins cephalic wall to join Vbl and Vbr at cephalic wall; define lateral lobes (see above). Arches Vbl-Vbd and Vbr-Vbd form partial ring at lower part of base of vertical tube and together with rest of arches form ring at base of cephalis.
Dimensions: Holotype (range of 20 specimens): length of apical horn: 3μm (3-5); length of cephalis: 20μm (17-21); maximum width of cephalis: 30μm (23-30); length of thorax: 25μm (21-27); maximum width of thorax: 43μm (37-43); length of abdomen: 120μm (98-131); maximum width of abdomen: 70μm (60-70).
Etymology: This species is named in honour of Associate-Professor J. A. Grant-Mackic, paleontologist at the University of Auckland, who has provided invaluable advice through the course of this and previous studies.
Holotype: R253 (Plate 1, figures 5, 6).
Type Locality: Te Kopua Point, Q08/254532
Discussion: Siphocampe grantmackiei differs from other members of Siphocampe in the following ways: from S. acephala (in Nigrini 1977, p.254, pl.3, fig.5), S. elizabethae (in Nigrini 1977, p.256, pl.3, fig.6), S. pachyderma (in Caulet 1991, p.539, pl.3, fig. 12), S. (?) quadrata (in Nigrini 1977, p.257, pl.3, fig. 12) and S. missilis O'Connor (1994, p.340, pl.l, figs.7, 9-12, pl.3. figs.8-12) by having well developed abdominal constrictions: from S. arachnea (in Nigrini 1977, p.255, pl.3, figs.7, 8: Petrushevskaya 1967, p. 145, figs.83.IV-VII as Lithomitra arachnea (?)), S. imbricata (in Nigrini 1977, p.255; Caulet 1991, p.539, pl.3, fig. 13: Petrushevskaya and Kozlova 1972, p.539, pi.24, figs.2-5 as Lithomitra imbricata group), S. lineata (in Nigrini 1977, p.256, pl.3, figs.9, 10; Petrushcvskaya 1967, figs.83.I-III as Lithomitra lineata: Nakaseko and Nishimura 1982, p. 100, pl.49, fig.7, pl,65, figs.5. 6 as Lithomitra lineata group), and S. nodosaria (in Nigrini 1977, p.256, pl.3, fig. 11; O'Connor 1993, p.52, pl.4, figs.23, 24; Petrushevskaya 1967, figs.83.VIll, IX as Lithomitra nodosaria), which also have definite abdominal constrictions, by the constrictions being much more marked. It also differs from other Siphocampe by having an apical horn and a vertical tube that is more well developed than that of other similar forms.
Forms illustrated in Riedel and Sanfilippo (1971, p. 1600. pi. II, figs 4, 9; pi.21, fig. 14 partim) as Lithomitra lineata) and Petrushevskaya and Kozlova (1972, p.539, pl.24, figs2-4, table 10B (partim) as Lithomitra imbricata group) appear similar to S. grantmackiei in having well developed abdominal constrictions, but they do not appear to have an apical horn (though on some of the illustrations it is hard to see any detail) and the vertical tube is not as developed as that of S. grantmackiei (except for that on Riedel and Sanfilippo's pi.21, fig. 14).
Abundance and Range: Siphocampe grantmackiei is rare in sample Q08/1569 and very rare in sample Q08/I570. It has been observed in the upper Stichocorys delmontensis Zone / lower Stichocorys wolfii Zone (early Miocene (mid-Otaian)).