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Arachnocorallium calvata Petrushevskaya, 1971

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Benson, 1966, p. 359-362; pl. 23, fig. 27; pl. 24, figs. 1-3:

Peridium longispinum J°rgensen

Peridium longispinum J°rgensen, 1905, Bergens Mus. Skrifter, p. 135, Pl. 15, figs. 75-79; Pl. 16, fig. 80.
?Peridium palmipes Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 1154, Pl. 53, fig. 10.

Test consisting of an ovoid cephalis, generally smooth, its upper part in several tests completely smooth, in others completely spiny. Collar ring small, with three or four collar pores dependent upon the absence or presence of the vertical bar; cardinal pores of
type B. Pores of the cephalis generally large, circular, subequal in the lower half and smaller, less regular in the upper half. In a few specimens the upper surface of the cephalis is nearly hyaline. Larger pores along either side of the apical bar in the dorsal face of the cephalis are present in a few specimens. The dorsal and primary lateral bars extend as spines ranging from nearly horizontal to downward divergent. In addition there are spines originating from the apical-lateral arches; these extend either horizontally or downward. All these spines are generally thin, conical, smooth except for numerous branches which originate near their origins and extend upward where they branch, anastomose and join with the cephalis forming an irregular, convex outward, external neck lattice; this lattice is a variable development but is generally present although rudimentary in several specimens. In most specimens there are spines which originate from ribs in the cephalic wall and extend nearly vertically; in most tests at least two lateral ribs are present, one on each side, but as many as seven were observed in one specimen. The apical spine extends from the apical bar of the cephalis and originates from the dorsal cephalic face. Vertical spine thin, conical, of variable length. The apical and accessory lateral spines of the cephalis are generally thin and conical but are three-bladed in a few specimens. A few specimens with only the dorsal and primary lateral spines and without the external neck lattice (Pl. 24, fig. 3) were placed tentatively within this species. The spines are heavy and branched or support an incomplete lattice distally, suggestive of a rudimentary neck lattice. Of these forms one was observed with neck lattice present. Another specimen has a completely smooth ovoid cephalis with the three, heavy, distally branched basal spines, not unlike Peridium palmipes Haeckel.

Measurements; based on 15 specimens from stations 191 and 192: height of cephalis 37-63 Ám, maximum breadth 31-52 Ám; breadth of neck lattice 50-62 Ám; length of apica1 spine 6-31 Ám, of vertical spine 5-25 Ám, of accessory spines extending from cephalic ribs 10-30 Ám, of dorsal and primary lateral spines 18-75 Ám.

Remarks. The distinctly ovoid cephalis with circular pores, the neck lattice, and absence of thorax distinguish this species. Incompletely developed specimens of Lithomelissa hystrix from the Gulf with cephalis and neck lattice but no thorax may be confused with this species if they have an ovoid cephalis.
This species is nearly identical with J°rgensen's illustrations of Peridium longispinum. Specimens from the Gulf that conform to Haeckel's illustration of Peridium palmipes Haeckel were considered tentatively as belonging to P. longispinum. These forms, however, are rare; therefore, whether they should be considered a separate species could not be determined.

Distribution. This species is present as far north as stations 191 and 192 in the Gulf. It is common at stations 192, 151, 133, and 64; absent at stations 27, 71, 90, 95, 99, 130, 184, 194, and all those to the north; and rare at the remaining stations. Its common occurrence at station 64 in the southern Gulf indicates its response to upwelling in this region. Its greater frequency in the northern half of the Gulf indicates its response to upwelling there.
J°rgensen (1905, p. 79) states that Peridium longispinum is rare in Norwegian fjords, occurring at water depths up to 50 meters. It also is present off the west coast of Norway as well as in surface waters of the warmer, more saline, Atlantic Ocean off the Norwegian coast. P. palmipes Haeckel (1887, p. 1154) was reported from the western tropical Pacific at "Challenger" station 224. The Gulf species, therefore, is apparently cosmopolitan, occurring at low as well as at high latitudes.
Benson 1966


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