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Actinomma delicatulum (Dogiel and Reschetnjak, 1952)

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Heliosoma delicatulum
The skeleton has the form of a regular double sphere. Diameter of the outer sphere 0.09 mm, of the inner sphere 0.03 mm. The sphere wall is perforated by numerous pores 6µ - 7µ in diameter. The pores are surrounded by regular hexagonal frames which turn inward in the form of a funnel; since the frames of the pores are contiguous, the surface of the sphere seems as if it were polyhedral. From the corners of the facets extend numerous thin, rather short (25µ) secondary spines; in addition there are 12 main spines of approximately 0.09 mm length. These spines extend into the inside of the inner sphere. The interval between the pores is greater than the diameter of pores. This species was encountered from the surface of the sea to a depth of 1000 m. Actually it apparently occurs even deeper but does not reach the depth of the next sample, i.e., 4000 m, since this species has not been encountered there. In total we found 76 specimens.
Remark: It is interesting to note that out of 6 Heliosoma species 3 were encountered so far only in the central part of the Pacific Ocean at depths from the surface of 4000 m.

Dogiel and Reshetnyak 1952
Benson, 1966, p. 162-166; pl. 5, figs. 3-4:

Actinomma cf. hystrix Müller

?Haliomma hystrix Müller, 1856, Akad. Berlin, Monatsb. (1856), p. 489; 1859b, Akad. Berlin, Abhandl. p. 37, Pl. 5, figs. 1, 2.

Test consisting of three concentric lattice shells joined by numerous (8-20, generally 10-15) three-bladed to cylindrical radial beams that arise from the surface of the first shell and extend beyond the third (cortical) shell as generally conical, (in several specimens three-bladed, completely or only proximally) radial spines of nearly equal length. Cortical shell generally spherical to subspherical but subpolyhedral in a few specimens, with shell wall of variable thickness (up to 22 µm), with equal, circular to subpolygonal, hexagonally arranged pores, with or without polygonal frames, 10-18 (generally 10-14) on the half circumference; surface of cortical shell generally thorny, in a few specimens nearly smooth, in others with short thin conical spines at the nodes of the intervening bars, in one specimen with a thin, delicate, spherical outer veil developed between distal branches of the by-spines. Second shell subspherical to spherical, generally smooth, with nearly equal polygonal to subpolygonal pores, hexagonally arranged, 7-10 on the half circumference, smaller than those of the cortical shell. First shell subspherical to subpolyhedral or globular, with 2-3 relatively large polygonal pores on the half circumference. A few tests were observed with the inner two shells missing but with each main spine continuing inward as a centripetal spine (rudimentary beam).

Measurements; based on 30 specimens from stations 27, 34, 46, 56, 60, 64, and 71: diameter of cortical shell 90-119 µm, of second shell 37-47 µm,, of first shell 15-21 µm; length of main spines 6-62 µm.

Remarks. This species differs from Actinomma sp. from the Gulf in the presence of smaller, more nearly equal, regularly arranged pores of the cortical shell and in the presence of conical, instead of three-bladed, main spines in most specimens. The cortical shell of this species and the nature of its pores are nearly identical with Thecosphaera sp. and Amphisphaera cf. uranus Haeckel from the Gulf, but the former has no radial spines and the latter has only two polar spines.
Haliomma hystrix Müller (1859a, p. 37, P1. 5, figs. 1,2) agrees well with the Gulf species except for the lack of the inner shell, a structure which in many specimens is not easily observed. Müller states that there are 20 symmetrically arranged radial beams continuous as spines; a few of the Gulf forms have as many as 20 spines, and the spines of a few approach a symmetrical distribution. The conical shape of the radial spines and the arrangement, number, and size of the pores of the cortical shell of Müller’s species agrees with the Gulf species. If Müller had observed the first shell, there would be no doubt that his species and the Gulf species are the same. Haliomma octacantha Ehrenberg (1873a, p. 313; l873b, P1.8, fig. 11) is similar to the Gulf species but lacks the innermost shell and has eight symmetrically disposed beams continuous as spines.

Distribution. This species is rare at all Gulf stations except at 194 where it is common (2.7%) which may reflect its tolerance of waters with slightly higher than average salinity and temperature but also may be due to the reduction of number of species at this station. It is absent only at stations 151, 203, 206, and 21/4. Its frequency at other stations in the Gulf does not undergo any significant fluctuations, but at stations 90 and 91, located in a region of upwelling, it has a slightly greater frequency which may reflect only the reduction in its dilution by other species but may also indicate its response to upwelling.
Haliomma hystrix Müller was reported from the Mediterranean Sea, and H. octacantha Ehrenberg was reported from the Philippine Sea. This species, therefore, may be confined to the tropical parts of the world’s oceans.

Benson 1966
Echinomma delicatulum:
Skeleton constructed of three concentric spheres: innermost of somewhat irregular form (Figure 11, I), often poorly marked. Second sphere (Figure 11, II) with approximately 10 round pores in half equator, connected by 9-14 radial needle to outer. These needles extending beyond shell as powerful processes, always smooth, cylindrical, their ends usually broken off.

Outer shell thick-walled, with hexagonally framed regular round pores, 11-12 pores on half equator of sphere. Slender supplementary spicules arising from wall of shell at points of junction of margins of pores; these spicules often broken off, even in specimens from plankton.

Dimensions:
Diameter of innermost sphere 10-15µm, diameter of intermediate sphere 30-40µm, diameter of outer sphere 90-120µm, length of accessory spines 20-25µm, thickness of main radial needles at base 5-8µm.
Petrushevskaya 1967


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