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Plannapus mauricei O'Connor, 1999

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Plannapus mauricei
Description: Cephalis internally spheroidal, externally hemispheroidal to inflated truncate-conical because lower part enveloped by upper thorax; surface smooth to dimpled: bearing anteriorly offset, very short, three-bladed apical horn; pores eparse, circular to subcircular, irregular in size and distribution; generally unobtrusive vertical tube posteriorly located at base of cephalis, relatively large and generally circular in transverse section, may be expressed externally as very short, truncate cone (pl. 1, figs. II, 12); collar stricture generally externally expressed as slight change in shell contour.
Thorax truncate-ovoid; approximately same width distally as proximally; widest part at or slightly below mid thorax; pores large, circular to subcircular. countersunk, hexagonally framed, generally quincuncially arranged, with generally slight size increase to widest part of thorax then slight decrease to peristome; low longitudinal ridges separating longitudinal pore rows begin just below collar stricture and terminate at peristome, zigzag slightly due to their origin as pore bars; distal-most pore row downward directed and pore bars join to peristome; three internally distinct, externally indistinct ribs corresponding to D, Ll and Lr may extend outside as tiny wings on upper thorax (pl. 5. fig. 15); no external contour change between thorax and peristome; peristome short, smooth, poreless, externally inverted truncate-conical, internally cylindrical; aperture constricted; termination smooth.
Internal skeletal structure as for P. hornibrooki except that arches Ll-Vbl, Lr-Vbr, ll-Ll, lr-Lr, D-ll and D-lr are not fused to cephalic wall, but arc joined to it by short accessory bars and the extensions of bars Ll and Lr: bars ll and lr extend to arches, rather than to cephalic wall.
Dimensions: Range of 40 specimens (Holotype measurement given in parentheses): length of apical horn: 5-12Ám (8Ám); length of cephalis: 14-18Ám (17Ám); maximum width of cephalis: 28-35Ám (30Ám); length of thorax: 60-85Ám (70Ám); maximum width of thorax: 63-80Ám (72Ám); maximum num- ber of pores on half equator of thorax: 11-15 (12); maximum number of pores in longitudinal pore row on thorax: 7-10 (8).
Etymology: In honour of my father, Maurice O'Connor.
Holotype and Type Locality: R409. Flume Gully (J41/f8005), Oamaru.
Discussion: Plannapus mauricei is placed in Plannapus because it is a two-segmented artostrobiid (see O'Connor 1997a). It differs from other members of the genus in the following ways (see Plannapus for synonymies): from P. hornihrooki O'Connor by having more and hexagonally framed thoracic pores that are not flush with the surface of the thorax (ie. countersunk), longitudinal ridges separating pore rows, and a downwardly directed pore row just before the peristome; from P. australis (Haeckel) by being more inflated, and by having more thoracic pores, longitudinal ridges separating pore rows, a less prominent vertical tube that is larger in transverse section, no contour change between thorax and peristome, and a shorter peristome; from P. mediterraneus (Haeckel) by having more and hexagonally framed and countersunk thoracic pores, longitudinal ridges separating pore rows, no contour change between thorax and peristome, and a shorter peristome; from P. microcephalus (Haeckel) by not being laterally compressed in the sagittal plane and by having a shorter apical horn, more and larger and hexagonally framed and countersunk thoracic pores, longitudinal ridges separating pore rows, and a row of downwardly directed pores whose pore bars join to the peristome; from P. papillosus (Ehrenberg) by having more and regularly arranged thoracic pores, longitudinal ridges separating pore rows, and a shorter peristome that is not distinguished from the thorax by a contour change; from Plannapus sp. (Nishimura) by having a less prominent vertical tube that is larger in transverse section, more thoracic pores in a longitudinal pore row, more longitudinal pore rows, and a shorter peristome that is not distinguished from the thorax by a contour change; from Plannapus sp. (Petrushevskaya) by having a less prominent vertical tube, more thoracic pores, longitudinal ridges separating pore rows, a shorter peristome, and a smooth termination.
O'Connor 1999


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