|
|
|
Nephrospyris knutheieri
Goll and Bjørklund, 1985
|
Description - Add description
Nephrospyris knutheieri sp.n.:
Tiaspyris pervia Haeckel, 1887 Haeckel 1887: 1082, pl. 87, fig. 7 (questionable synonym).
Diagnosis: A species of Nephrospyris characterized by a densely trellised cephalis with numerous thread like lattice bars interjoining chaotically disposed lattice spines.
Name: In honor of Professor Dr. Knut Heier, Director of the Norwegian Geological Survey, Trondheim, Norway.
Description: Sagittal ring short, about one half total lattice shell height; shape approximates an irregular trapezoid with longest side formed by A M bar (Figs 6D, 8E, 9D), 69 85 µm high, 50 77 µm thick. External longitudinal rib on A M bar (Figs 6C and 8C). Slender A spine 18 27 µm long, trifurcates distally to join apex of lattice shell (Fig. 6C). Small but prominent V spine arises from basal third of V side of sagittal ring in some species (Fig. 6A), but most commonly arises from approximate midpoint of sagittal ring height (Figs 7F, SA, 9D). Micronodular Ax process occurs on M bar at point of juncture with L bars (Figs 6E, 7D E). This structure is represented by an asymmetrical bulbous protrusion in some specimens (Fig. 6F) and in other by a dispersed micronodular field on a smooth ring surface (Fig. 7C). D bar and two L bars are the only basal sagittal ring bars; no sternal bar, secondary or tertiary lateral bars.
Sagittal ring joined directly to D and V sides of lattice shell. Three to five single or paired lattice bars are fused to the A M and A V bars of the sagittal ring. One such pair of lattice bars invariably joins the sagittal ring at the base of the A spine (Fig. 6Q. Lattice bars joined near the midpoints of sagittal ring on both the D and V sides (Figs 613 C, 8C, 9J) are unpaired on many specimens and result in enlarged sagittal lattice pores (gates according to the terminology of HAECKEL 1887). On other specimens, enlarged sagittal lattice pores are produced by elevation of the attachment points of lattice bars to sagittal ring (Figs 8A, 9C).
Basal ring of lattice shell subpolygonal; 87 102 µm wide, 68 92 µm thick; joined directly to D and V sides of sagittal ring; strongly constricted by sagittal ring and L bars; encloses two pairs of large basal pores (Figs 6E, 7D E, 9M). Major lattice bars 2.5 6.0 µm in diameter arise from basal and sagittal rings and branch chaotically distally to form densely trellised lattice shell. Inflated, D V compressed lattice shell 85 132 µm high, 73 135 µm thick; extends 25 32 µm above apex of sagittal ring without horizontal constriction (Figs 6C D, 913). Numerous small lattice spines arise randomly from the major lattice bars; very fine lattice bars approximately 1.0 µm in diameter arch between these spines to form a loose secondary meshwork (Figs 6B 6D), 9I) that partially covers the sagittal lattice pores of some specimens (Fig. 8B).
Incompletely formed specimens have 8 13 short spines projecting from the basal ring (Fig. 7E F). These spines include a D spine and one or two pairs of spines projecting from the juncture with the L bars (Fig. 6G). Other basal lattice spines are randomly distributed. Complete specimens have an imperfectly formed thorax composed of a sparce trellis of lattice bars joined to the basal lattice spines (Fig. 7A B). Composition of thoracic lattice similar to that of cephalis. Thorax 35 56 µm high; terminates in a broad, loosely framed basal aperture. A strong horizontal constriction separates the cephalis and thorax of some specimens (Fig. 8A), but this constriction is not well developed on other specimens (Fig. 6A).
Holotype: Norwegian-Greenland Sea; RIV Håkon Mosby cruise 57, Stn 11 (67°07.04' N, 08°17.62'W); Figs 9J K, 9M O; Zoological Museum of the University of Bergen (ZMUB) Cat. No. 64137; England Finder coordinator P27/3.
Remarks: Nephrospyris knutheieri sp.n. differs from its North, Pacific homeomorph, Tiaraspyris pervia HAECKEL, by the presence of a profusion of short lattice spines and a secondary meshwork of fine lattice bars. T. pervia must be transferred to Nephrospyris according to our generic emendation. The Antarctic analog, Phormospyris stabilis antarctica (HAECKER), has a small lattice shell densely perforated by circular lattice pores and bears a pronounced sagittal constriction. Two trissocyclids occupied the Norwegian Sea in the Late Miocene and might be regarded as potential precursors to N. knutheieri: Clathrospyris sandellae GOLL and Eucoronis fridtjofnanseni GOLL & BJØRKLUND. The large sagittal lattice pores described for N. knutheieri are well developed on specimens of E. fridtjofnanseni, but the massive skeleton of the latter species does not bear Nephrospyris morphology, and the species appears to have undergone an abrupt extinction in the Late Miocene. C. sandellae is easily distinguished from N. knutheieri by its massive, tuberculate lattice shell. The extinction level of this latter species appears to be coincident with that of E. fridtjofnanseni (GOLL & BJØRKLUND 1980).
The extremely fine microspicules that cover the external surface of all lattice bars and spines of one specimen of N. knutheieri (Fig. 6B, G) may be an unique occurrence. Similar microspicular development has not been observed on other specimens of this species or on any other trissocyclid.
The broad range of skeletal size of N. knutheieri is illustrated in Fig. 7. The specimen represented in Fig. 7E F is approximately one half the height of the specimen in Fig. 7B.
Lateral contortion of the sagittal ring, which has been observed on approximately half the specimens of this species, has been described in the 'Discussion'.
Occurrence: N. knutheieri has been observed only in the plankton and Holocene sediments of the Norwegian Sea. The stratigraphic position of its first appearance is unknown, but it is assumed to have occurred during the Pleistocene based on the absence of N. knutheieri in Late Miocene and Pliocene sediments of this region. Its known zoogeographic distribution is restricted to the Icelandic Current, and the species occurs most frequently at depths between 500 and 1000 m. | | Goll and Bjørklund 1985 |
|
|
 |
|
