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Didymocyrtis tetrathalamus (Haeckel, 1887)

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Panartus tetrathalamus:
All four chambers of the cortical shell of the same form, size, and structure, kidney-shaped, twice as broad as long. Pores irregular, roundish, twice to three times as broad as the bars; a circle of larger pores at the base of both distal chambers; five to six pores on the half meridian, ten to twelve on the half equator of each chamber. Surface of the cortical shell smooth; its main axis two and a half times as long as the equatorial axis. Both medullary shells spheroidal, compressed, the outer one-third as broad as the constriction. (In the specimen figured spines begin to arise from both distal chambers; this forms a transition to Panartus quadrijugus.)

Dimensions.-Main axis of the cortical shell 0.18, equatorial axis 0.07; breadth of every chamber 0.09; meshes 0.003 to 0.01, bars 0.002 to 0.004.
Habitat.-Comopolitan; Mediterranean, Atlantic, Pacific, in various depths.
Haeckel 1887
Benson, 1966, p. 193-199; pl. 8, figs. 8-13; pl. 9, figs 1-2; text-fig. 10:

Zygocampe chrysalidium Haeckel

Zygocampe chrysalidium Haeckel, 1887, p. 400; pl. 40, fig. 13

Basic shell consisting of two concentric medullary shells joined to the equatorial constriction of the figure-8 cortical shell (cylindrical to ellipsoidal latticed shell divided into two approximately equal halves by an equatorial constriction) by 15-20 or more cylindrical radial beams arising from the surface of the outer medullary shell and confined to the equatorial region. Inner medullary shell spherical with subequal, polygonal pores, 3-5 on the half circumference; joined to the outer medullary shell by numerous radial beams. Outer medullary shell ellipsoidal, compressed in the polar axis, with subequal, circular to subcircular pores, 7-9 on half the major circumference. Pores of the cortical shell variable, relatively large, polygonal, subpolygonal, subcircular, or with irregular shapes, with or without polygonal frames, nearly equal with subregular arrangement in some specimens to unequal with less regular arrangement in others, slightly smaller in the region of the equatorial constriction, 7-12 on half the circumference of the broadest part of the shell. Surface of cortical shell with numerous thorns or cylindrical spines, some or all of which are branched distally in most specimens, representing rudimentary structures of the secondary shell; surface rarely devoid of spines, always with relatively stout thorns if spines lacking.
Secondary shell consists of the latticed polar caps and one or two outer latticed mantles; represented in various states of development (P1. 8, figs. 8-13; P1. 9, figs. 1-2) from absent but generally rudimentary to the form illustrated in figure 10 with three polar caps at each pole and two outer mantles; the latter form is not complete because there are spines on each of the third caps (indicating a fourth cap) as well as a few spines on the outer mantle. No specimen was observed without some structure indicating either additional polar caps, an outer mantle, or both. First polar caps supported by numerous radial beams whose points of origin define an approximate polar circle on the cortical shell; second and third polar caps supported by similar beams which are less constant in their position on the preceding cap but generally define a polar circle. Caps of variable shape from subhemispherical, to subconical, to irregular in outline; with pores similar in shape and arrangement to those of the cortical shell but slightly smaller. First outer mantle developed between the distally branched spines of the cortical shell, generally cylindrical but with irregular surface, relatively thin-walled, with unequal, generally very small, irregularly arranged pores of all shapes; it tapers at each pole, merging with the lattice of the first polar cap; if a second cap is present the mantle is double-layered at each pole, the outer layer merging with the lattice of the second cap (fig. 10). Second outer mantle with lattice similar to that of the first, joined to the first mantle by numerous cylindrical beams, tapers at each pole merging with the third latticed polar cap if present.

Measurements; based on 38 specimens from stations 46, 81, and 92: length of specimens with one cap at each pole (16 specimens) 172-252 Ám, with two caps at each pole (9 specimens) 232-317 Ám; maximum breadth of first outer mantle (18 specimens) 135-178 Ám, of second outer mantle (5 specimens) 178-196 Ám, of polar caps (14 specimens) 68-105 Ám; length of cortical shell 102-141 Ám, maximum breadth 74-104 Ám; diameter of inner medullary shell 11-16 Ám; polar diameter of outer medullary shell 26-31 Ám, equatorial diameter 3l-37 Ám.

Remarks. The earlier-defined genus Zygartus Haeckel (1882, p. 463) differs from Zygocampe Haeckel only in the presence of hollow fenestrated tubes, opposite on both poles of the main axis. No specimens of Zygocampe chrysa1idium Haeckel from the Gulf were observed with these tubes; however, none were observed with more than three polar caps at each pole (text-fig. 10), whereas Haeckel's illustration (1887, P1. 40, fig. 13) shows 7-8 caps. The Gulf forms apparently are not fully-developed; therefore, the presence or absence of polar tubes could not be determined. Study of Haeckel's type material of Zygartus chrysalis Haeckel (1887, pp.40l-402) may reveal that the fenestrated polar tubes are subject to intraspecific variation; if this be the case, Zygocampe chrysalidium would be placed in the genus Zygartus but would retain the trivial name because it has page priority over Zygartus chrysalis. Another problem associated with these two species is that Haeckel referred both to the same illustration (op. cit., P1. 40, fig. 13), but in the plate explanation he stated that figure 13 is "Zygartus chrysalis, n. sp. (vel Zygocampe chrysalis)". The Latin word "vel" is defined by E.A. Andrews (A Copius and Critical Latin-English Lexicon, Harper and Brothers, New York, 1851, p. 1610) as follows:

....specifies, in connection with something previously mentioned, another or a different thing, and leaves the preference between the two to be decided by subjective opinion or choice..

Apparently the trivial name of Zygocampe chrysalis is a typographical error and should read Z. chrysalidium. Haeckel' s illustration shows 8 polar caps at one pole of the figure-8 shell with the eighth cap surmounted by a fenestrated three-bladed spine or tube; at the other pole there are only 7 caps, the seventh cap being without a fenestrated spine or tube but, instead, with spines which appear to represent a rudimentary eighth cap. Haeckel's illustration, however, is subject to various interpretations. First, because it was first referred to in his text as Zygocampe chrysalidium it can be interpreted as representing that species. Secondly, because Haeckel's figure explanation apparently offers the choice between Zygartus chrysalis or Zygocampe chrysalidium, the figure may represent a combination drawing, i.e., half representing the former, half representing the latter. Thirdly, and most likely, the drawing is an illustration of a specimen of Zygartus chrysalis with one pole having an incomplete eighth cap. Because the presence or absence of the fenestrated polar spine or tube cannot be determined in the Gulf
specimens, page priority requires assignment of the Gulf species to Zygocampe chrysalidium.
The illustrations of several species and genera of earlier workers conform to several of the ontogenetic stages of the Gulf species. Without study of the type material of these apparently "ontogenetic" species and genera, however, they were not placed in synonymy with Zygocampe chrysa1idium because they may represent ontogenetic stages of other valid taxa. In the writer's opinion, study and revision of this group of forms with figure-8 cortical shells will reduce the number of genera and species to only a few.

Distribution. In the Gulf this species is cosmopolitan, being present at all stations except 203, and 214. It is rare at all stations except 90 (7.4%), 92 (2.4%), 184 (2.2%), 194 (7.5%), and 206 (3.0%) where it is common. At stations 90 and 194 it is the fifth most abundant species. In general, its frequency in the southern Gulf is slightly greater than that in the northern Gulf, but its frequency at stations 90 and 194 is much greater than its average throughout the Gulf. Its increase at station 90 may be explained by upwelling in this region. The increase in its abundance at stations 194 and 184 may be explained by its tolerance for higher than average salinity and temperature, although upwelling may be important in this region except that there is no direct evidence that it occurs. It is of almost common occurrence in the southern Gulf; therefore, it is an important member of the tropical Pacific fauna.
Because the taxonomy of this species as well as of forms similar to it is poorly known, little can be said about its world wide distribution. The basic shell with or without polar caps has been reported by numerous workers from the tropical parts of the world's oceans. The writer could find no reference to its occurrence in high latitudes; therefore, it may be confined to tropical seas.
Benson 1966


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