Subfamily 1. Zygacanthida, Haeckel
Definition.—Astrolonchida with twenty simple radial spines, without apophyses or lateral transverse processes.
Genus 323. Acanthometron, J. Müller, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 229.
Definition.—Astrolonchida with simple cylindrical or needle-shaped radial spines, without edges and without apophyses; their transverse section is circular.
The genus Acanthometron, with the restricted definition here given, is the most simple form of all Acanthonida, and may be regarded as the common ancestral form not only of this suborder but also of all Acanthophracta, in general of all Icosacantha, or all Acantharia in which twenty radial spines are regularly disposed after the Müllerian law (p. ). In the wider sense, given originally to Acanthometra by Johannes Müller, its discoverer, this genus comprised all Acantharia constituting here our order "Acanthometra" (Radiolaria without lattice-shell, with radial spines united in the centre). In my Monograph (1862, p. 375) I restricted this genus to those "Acanthometrida" in which twenty simple spines of equal size (and without apophyses) are supported one upon another in the centre, and I separated as Astrolithium those forms in which they are grown together in the centre. But this difference now appears not so important, and I restrict here the genus Acanthometron (not Acanthometra) to those most simple forms in which the simple radial spines are cylindrical or conical, without edges.
Subgenus 1. Acanthometrella, Haeckel.
Definition.—Spines at the central base without leaf-cross, united by the opposed triangular faces of their pyramidal bases, resting one upon another.
1. Acanthometron elasticum, Haeckel.
Acanthometra elastica, Haeckel, 1862, Monogr. d. Radiol., p. 376, Taf. xv. fig. 1, Taf. xviii. fig. 1.
Acanthometra elastica, R. Hertwig, 1879, Organismus d. Radiol., Taf. i. figs. 2, 2a, 2b.
Spines cylindrical, very thin and long, needle-shaped, at the central base four-sided pyramidal, without leaf-cross. Distal apex conical. The spines are very elastic, of nearly equal thickness in their whole length. Central capsule quite pellucid, colourless, with a variable number of yellow pigment-bodies (xanthellæ?).
Dimensions.—Length of the spines 0.3 to 0.6, breadth 0.001 to 0.002.
Habitat.—Cosmopolitan, very common in all warmer seas; Mediterranean, Atlantic, Indian, Pacific, surface.
2. Acanthometron cylindricum, n. sp. (Pl. , fig. 2).
Spines cylindrical, thick and long, at the central base thickened with a pear-shaped knob, and with very small central fulcral pyramid, without leaf-cross. Distal apex rounded or truncated. Central capsule opaque, filled with red pigment-bodies.
Dimensions.—Length of the spines 0.4 to 0.8, breadth 0.01 to 0.015.
Habitat.—Central Pacific, Stations 266 to 274, surface.
3. Acanthometron fuscum, J. Müller.
Acanthometra fusca, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. xi. fig. 4.
Acanthometra fusca, Haeckel, 1862, Monogr. d. Radiol, p. 377.
Spines very thin and long, in the proximal half cylindrical, in the distal half conical, gradually thinned towards the simple conical apex. Central base a small four-sided pyramid, without leaf-cross. Central capsule opaque, filled with brown pigment-bodies.
Dimensions.—Length of the spines 0.2 to 0.4, breadth 0.002 to 0.004.
Habitat.—Mediterranean (Cette, Portofino, Messina).
4. Acanthometron bulbosum, Haeckel.
Acanthometra bulbosa, Haeckel, 1862, Monogr. d. Radiol., p. 377, Taf. xv. fig. 2, Taf. xviii fig. 2.
Spines very thin and long, cylindrical, with simple needle-shaped apex; in the basal part conical, towards the centre much thickened, with a short four-sided fulcral pyramid, without leaf-cross. Central capsule opaque, filled with brown pigment-bodies.
Dimensions.—Length of the spines 0.3 to 0.5, breadth in the middle and outer part 0.001, in the basal part 0.008 to 0.012.
Habitat.—Mediterranean; Atlantic, Station 354, surface.
5. Acanthometron dolichoscion, Haeckel (Pl. , figs. 6-8).
Acanthometra dolichoscia, Haeckel, 1862, Monogr. d. Radiol., p. 377, Taf. xviii. figs. 3a, 3b.
Spines very long and thin, cylindrical, in the thickened outer half about twice as thick as in the thin inner half, at the simple apex compressed, two-edged. Central base little thickened, with a small four-sided pyramid, without leaf-cross. Central capsule transparent, whitish or yellowish.
Dimensions.—Length of the spines 0.6 to 0.8, breadth in the proximal part 0.004, in the distal part 0.008.
Habitat.—Mediterranean (Messina, Portofino), surface.
6. Acanthometron conicum, n. sp.
Spines short and thick, conical, gradually thinner from the thick conical base towards the simple apex. Central part of the base with a large fulcral pyramid, but without leaf-cross. Central capsule transparent, colourless (?).
Dimensions.—Length of the spines 0.08 to 0.12, basal breadth 0.02.
Habitat.—North Pacific, Station 244, surface.
7. Acanthometron pellucidum, J. Müller.
Acanthometra pellucida, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. xi. figs. 1-3.
Acanthometra pellucida, Haeckel, 1862, Monogr. d. Radiol., p. 378.
Spines cylindrical, very thin and long, needle-shaped, nearly of equal thickness in their whole length. Central base with a small fulcral pyramid, without leaf-cross. Distal apex bifid or bifurcate, with two thin parallel teeth. Central capsule pellucid, colourless, with yellow pigment-bodies. (Differs from Acanthometron elasticum mainly in the bifid apex.)
Dimensions.—Length of the spine 0.1 to 0.3, breadth 0.002 to 0.004.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.
8. Acanthometron wageneri, Haeckel.
Acanthometra wageneri, Haeckel, 1862, Monogr. d. Radiol., p. 378.
Spines cylindrical, in the thickened outer half about twice as broad as in the thin inner half. Central base a little thickened, with large fulcral pyramid, but without leaf-cross. Distal apex bifid, with two divergent, often denticulated teeth. Central capsule pellucid, with yellow pigment-bodies. (Differs from Acanthometron dolichoscion mainly in the bifid apex.)
Dimensions.—Length of the spines 0.2 to 0.5, breadth in the inner part 0.003, in the outer 0.006.
Habitat.—Adriatic Sea; Triest, Wagner; Corfu, Haeckel, surface.
Subgenus 2. Phyllostaurus, Haeckel, 1862, Monogr. d. Radiol., p. 381.
Definition.—Spines at the central base with a broad leaf-cross, composed of four prominent triangular lamellæ; the meeting edges of the neighbouring lamellæ are propped one upon another in such a manner that there are formed twenty-two hollow pyramidal spaces or compartments (compare p. ).
9. Acanthometron siculum, Haeckel.
Acanthometra sicula, Haeckel, 1862, Monogr. d. Radiol., p. 382, Taf. xvii. figs. 1, 2; Taf. xviii. fig. 8.
Spines elongate, conical, tapering gradually from the thick base towards the simple distal apex. Conical circular base supported by a basal leaf-cross of double the breadth. Central capsule yellowish-brown, opaque.
Dimensions.—Length of the spines 0.3 to 0.4, basal breadth 0.008 to 0.012, leaf-cross 0.024.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.
10. Acanthometron catervatum, Haeckel.
Acanthometra brevispina, Haeckel, 1862, Monogr. d. Radiol., p. 382, Taf. xv. fig. 5, Taf. xviii. fig. 9.
Spines cylindrical, nearly of equal breadth throughout their whole length. Apex either simple, conical, or bifid. Base with a large leaf-cross, four to six times as broad as the spine itself. Central capsule transparent, yellow. The Atlantic specimens have much longer spines than those figured from the Mediterranean, but are otherwise not different. Therefore I have changed the inconvenient name brevispinum into catervatum.
Dimensions.—Length of the spines 0.1 to 0.3, breadth 0.005 to 0.008; basal leaf-cross 0.02 to 0.032.
Habitat.—Mediterranean (Messina); North Atlantic, Station 354, Gulf Stream (Færöe Channel) in great abundance, John Murray, surface.
Subgenus 3. Astrolithium, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 810.
Definition.—Spines in the basal part grown perfectly together, so that the whole skeleton forms a single piece of acanthin; a star with twenty equal rays.
11. Acanthometron bulbiferum, n. sp. (Pl. , fig. 1).
Astrolithium bulbiferum, Haeckel, 1881, Prodromus, p. 466.
Spines needle-shaped, cylindrical, very thin and long, with simple apex; suddenly thickened and forming a broad regular cone at the central base; all twenty conical bulbs have their broad bases grown together and forming a central icosahedron of acanthin; from its twenty faces arise the circular bases of the cones in regular disposition.
Dimensions.—Length of the spines 0.2 to 0.5, breadth 0.001 to 0.003; height of the basal cones 0.06, basal breadth of them 0.02.
Habitat.—Central Pacific, Stations 265 to 274, surface.
12. Acanthometron bifidum, Haeckel.
Astrolithium bifidum, Haeckel, 1862, Monogr. d. Radiol., p. 400, Taf. xx. fig. 5.
Spines needle-shaped, cylindrical, of equal breadth in their whole length. Distal apex bifid, with two parallel straight teeth. Central bases of all twenty spines grown perfectly together and forming a central sphere of acanthin. Central capsule brown opaque.
Dimensions.—Length of the spines 0.2, breadth 0.003.
Habitat.—Mediterranean (Messina), Haeckel, surface.
Genus 324. Zygacantha, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 51.
Definition.—Astrolonchida with simple, compressed, and two-edged radial spines, without apophyses; their transverse section is elliptical or rhomboidal.
The genus Zygacantha comprised in the original definition of J. Müller only a single species, Zygacantha furcata, distinguished from the other Acanthometra by forked spines with two long parallel teeth. It seems now advisable to unite in this genus all those Astrolonchida in which the simple spines are two-edged, compressed, or leaf-shaped. The term Zygacantha may be conceived as the general expression of the important fact, that in all Icosacantha the twenty spines are opposite in pairs.
Subgenus 1. Zygacantharium, Haeckel.
Definition.—Spines at the central base without leaf-cross and without hollow pyramidal compartments, united by the opposed triangular faces of their pyramidal bases, resting one upon another.
1. Zygacantha lanceolata, Haeckel.
Acanthometra lanceolata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 48, Taf. xi. fig. 12.
Acanthometra lanceolata, Haeckel, 1862, Monogr. d. Radiol., p. 380.
Spines lanceolate, from the broader middle part equally thinned towards the two ends. Apex simple. Base pyramidal, without leaf-cross. Each flat lamellar spine exhibits an elevated middle rib (like a lanceolate leaf), and is therefore compressed quadrangular.
Dimensions.—Length of the spines 0.1 to 0.15, greatest breadth (in the width) 0.03 to 0.04.
Habitat.—Mediterranean (Saint Tropez, French shore), J. Müller; North Atlantic (Canary Islands), Haeckel, surface.
2. Zygacantha costata, n. sp.
Spines compressed, two-edged, linear, of nearly equal breadth in their whole length. Apex truncate. Base pyramidal, without leaf-cross. Each flat lamellar spine exhibits an elevated middle rib, which in the distal half is cleft into two divergent rods ending in the corners of the truncated apex. (Similar to Zygacantha dicopa, but with broader free spines, which are not grown together in the centre.)
Dimensions.—Length of the spines 0.1 to 0.15, breadth 0.02.
Habitat.—Central Pacific, Stations 265 to 274, surface.
3. Zygacantha compressa, Haeckel.
Acanthometra compressa, Haeckel, 1862, Monogr. d. Radiol., p. 378, Taf. xviii. figs. 4a, 4b.
Spines in the proximal half compressed, broad lanceolate, four to six times as broad as in the thin cylindrical distal half. Apex simple or short bifid. Base pyramidal, thickened, without leaf-cross. No middle rib. Central capsule opaque, yellowish or reddish-brown.
Dimensions.—Length of the spines 0.3 to 0.5, breadth of the inner half 0.015 to 0.02, of the outer half 0.002 to 0.003.
Habitat.—Mediterranean (Messina); Atlantic (Canary Islands), Station 352, surface.
4. Zygacantha furcata, J. Müller.
Zygacantha furcata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 51, Taf. ix. fig. 6.
Acanthometra furcata, J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 499.
Acanthometra furcata, Haeckel, 1862, Monogr. d. Radiol., p. 380.
Spines compressed, fork-shaped, divided by two thickened knots into three sections of nearly equal length; middle section broader than the proximal, but smaller than the distal section, which is cleft by a deep fissure into two long parallel straight branches. Base pyramidal, without leaf-cross. Central capsule purple, with yellow bodies.
Dimensions.—Length of the spines 0.1 to 0.15, basal breadth 0.003 to 0.005, distal breadth 0.02 to 0.03.
Habitat.—Mediterranean (Cette). J. Müller, surface.
Subgenus 2. Zygacanthidium, Haeckel.
Definition.—Spines at the central base with a cross of four prominent leaves; the meeting edges of the neighbouring lamellæ so rest one upon another that twenty-two hollow pyramidal compartments are formed (compare p. ).
5. Zygacantha dichotoma, Haeckel.
Zygacantha dichotoma, Haeckel, 1862, Monogr. d. Radiol., p. 381.
Acanthometra dichotoma, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 50, Taf. ix. fig. 5.
Spines compressed, pincer-shaped, cleft nearly throughout their whole length into two thin parallel straight rods or fork branches, which are united only in their middle by a narrow bridge, and at their central base by the pyramidal small central apex; above this pyramid each rod is divided into two broad triangular leaves, forming a large basal leaf-cross. Central capsule purple, with yellow bodies.
Dimensions.—Length of the spines 0.1 to 0.15, breadth 0.01 to 0.02.
Habitat.—Mediterranean (Nice), J. Müller, surface.
6. Zygacantha complanata, n. sp.
Spines compressed, two-edged, linear, of equal breadth throughout their whole length. Apex bifid. Base thickened, with a large leaf-cross. (Similar to Amphilonche complanata, but different in the equal size of all twenty spines, which are somewhat broader.)
Dimensions.—Length of the spines 0.12 to 0.18, breadth 0.002.
Habitat.—North Pacific, Station 244, surface.
7. Zygacantha semicompressa, Haeckel.
Acanthometra hemicompressa, Car, 1884, Zool. Anzeiger, p. 94, with woodcut.
Spines in the proximal half compressed, two-edged, linear, three to four times as broad as in the needle-shaped cylindrical distal half. Apex simple. Base pyramidal, with a small leaf-cross. Central capsule transparent.
Dimensions.—Length of the spines 0.1 to 0.2, breadth in the proximal half 0.02, in the distal half 0.006.
Habitat.—Mediterranean (Genoa), Haeckel; Adriatic Sea (Trieste), Car, surface.
8. Zygacantha foliacea, n. sp.
Spines lanceolate, tapering from the broader middle part towards the two ends, with two dentated or serrated edges and a prominent middle rib. Apex simple. Base with a small leaf-cross. The spines like the leaves of Agave americana.
Dimensions.—Length of the spines 0.15 to 0.2, middle breadth 0.02 to 0.03.
Habitat.—Indian Ocean, near the Island of Socotra, Haeckel.
Subgenus 3. Zygacanthonium, Haeckel.
Definition.—Spines in the centre grown perfectly together and forming a single star-shaped piece of acanthin.
9. Zygacantha dicopa, Haeckel.
Astrolithium dicopum, Haeckel, 1862, Monogr. d. Radiol., p. 400, Taf. xx. figs. 3, 4.
Spines compressed, two-edged, linear, of nearly equal breadth throughout their whole length, with a prominent middle rib, which in the distal third is cleft into two divergent teeth, ending in the two corners of the broad, obliquely truncated apex. All twenty spines with their central bases grown together and forming one single piece of acanthin—a star with twenty rays.
Dimensions.—Length of the spines 0.12 to 0.2, breadth 0.01 to 0.02.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, many Stations, surface.
Genus 325. Acanthonia, Haeckel, 1881, Prodromus, p. 465.
Definition.—Astrolonchida with simple, four-edged, prismatic or pyramidal radial spines, without apophyses; their transverse section is square.
The genus Acanthonia comprises all those Astrolonchida (formerly united with Acanthometron) in which the simple spines either in their whole length or in the greatest part of it are four-edged, with square transverse section. They are sometimes more prismatic (with equal breadth), at other times more pyramidal (with decreasing breadth towards the distal apex). If Acanthometron be the common simple ancestral form of the Acanthonida, then the two-edged Zygacantha, and the four-edged Acanthonia may be regarded as two divergent main lines arising from it; the former leading to the Phractacanthida and Diporaspida, the latter leading to the Stauracanthida and Tessaraspida.
Subgenus 1. Acanthonarium, Haeckel.
Definition.—Spines at the central base, without leaf-cross and without hollow pyramidal compartments, united by the triangular faces of their pyramidal bases, resting one upon another.
1. Acanthonia tetracopa, Haeckel (Pl. , figs. 9-11).
Acanthometra tetracopa, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. vii. figs. 3 to 5, Taf. xi. fig. 5.
Acanthometra tetracopa, Haeckel, 1862, Monogr. d. Radiol., p. 379, Taf. xviii. fig. 5.
Spines quadrangular prismatic, with prominent lamellar edges, of equal breadth in their whole length. Base pyramidal, without leaf-cross. Apex truncated, or with four short teeth (sometimes only two teeth). Central capsule opaque, brown or yellow.
Dimensions.—Length of the spines 0.15 to 0.2, breadth 0.01 to 0.012.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, many Stations, surface.
2. Acanthonia prismatica, n. sp.
Spines quadrangular prismatic, without prominent edges, with four plane lateral faces, of equal breadth throughout their whole length. Base pyramidal, without leaf-cross. Apex truncate, with square apical face.
Dimensions.—Length of the spines 0.1 to 0.16, breadth 0.005 to 0.008.
Habitat.—Antarctic Ocean, Station 154, surface.
3. Acanthonia denticulata, n. sp.
Spines quadrangular prismatic, with prominent elegantly denticulated edges, of equal breadth throughout their whole length. Both ends pyramidal, without leaf-cross. (Similar to Amphilonche denticulata, but with the twenty spines all equal, and with spherical central capsule.)
Dimensions.—Length of the spines 0.12 to 0.16, breadth 0.008.
Habitat.—Central Pacific, Stations 266 to 274, surface.
4. Acanthonia mülleri, Haeckel.
Acanthometra mülleri, Haeckel, 1862, Monogr. d. Radiol., p. 379, Taf. xv. fig. 3, Taf. xviii. fig. 6.
Spines quadrangular, nearly prismatic, but tapering gradually from the pyramidal base towards the distal bifid apex, which bears two thin, parallel, or little divergent teeth; four edges elegantly denticulated; base without leaf-cross. Central capsule yellowish or reddish.
Dimensions.—Length of the spines 0.12 to 0.18, basal breadth 0.005.
Habitat.—Mediterranean (Messina); Atlantic, Stations 348 to 352, surface.
5. Acanthonia fragilis, Haeckel.
Acanthometra fragilis, Haeckel, 1862, Monogr. d. Radiol., p. 380, Taf. xv. fig. 4, Taf. xviii. fig. 7.
Spines quadrangular, nearly prismatic, but gradually thickened from the pyramidal base towards the distal truncated end; four edges regularly denticulated; base without leaf-cross. Central capsule opaque.
Dimensions.—Length of the spines 0.5 and more, basal breadth 0.002 to 0.003, distal breadth 0.008 to 0.016 or more.
Habitat.—Mediterranean (Messina); North Atlantic, Station 354, surface.
6. Acanthonia convexa, n. sp.
Spines quadrangular, with four broad lamellar, convex, prominent edges, which from the broader middle part are thinned towards the two emarginated ends; each end with a small quadrangular pyramid, without leaf-cross. All the twenty spines of this species exhibit nearly the same form, which is seen in the caudal or posterior (geotomical) spine of Amphilonche anomala (Monogr. d. Radiol., Taf. xviii. fig. 23, b).
Dimensions.—Length of the spines 0.12 to 0.16, breadth in the middle part 0.02 to 0.025.
Habitat.—North Pacific, Station 244, surface.
7. Acanthonia concava, n. sp.
Spines quadrangular, with four broad lamellar, concave, prominent edges, which from the smaller middle part are broadened towards the two emarginated ends; each end with a small quadrangular pyramid, without leaf-cross. All the twenty spines of this species exhibit nearly the same form, which is seen in the frontal or anterior (hydrotomical) spine of Amphilonche anomala (Monogr. d. Radiol., Taf. xviii. fig. 23, a).
Dimensions.—Length of the spines 0.15, breadth in the middle part 0.012, on both ends 0.025.
Habitat.—South Pacific, Station 288, surface.
8. Acanthonia quadrangula, n. sp.
Spines quadrangular prismatic, with smooth prominent straight edges, but of very different breadth in both halves; the inner or proximal half (inside the central capsule) twice to four times as broad as the outer or distal half (outside the central capsule); both ends suddenly separated by a constriction, in which is inserted the membrane of the capsule. The latter is pellucid, with a number of yellow bodies. Apex of the spines simple, base pyramidal, without leaf-cross.
Dimensions.—Length of the spines 0.2 to 0.4, breadth of the basal half 0.01, of the distal half 0.002 to 0.004.
Habitat.—Atlantic, Canary Islands, Azores, Station 354, surface.
Subgenus 2. Acanthonidium, Haeckel.
Definition.—Spines at the central base with a broad leaf-cross, composed of four prominent triangular lamellæ; the meeting edges of these crossed lamellæ between every three or four neighbouring spines so rest one upon another that twenty-two hollow pyramidal compartments are formed (compare p. ).
9. Acanthonia echinoides, Haeckel.
Acanthometra echinoides, Claparède et Lachmann, 1858, Études sur les Infusoires et les Rhizopodes, &c., p. 459, pl. xxiii. figs. 1-5.
Acanthometra echinoides, Haeckel, 1862, Monogr. d. Radiol., p. 383.
Spines quadrangular prismatic without prominent edges, with four plane lateral faces, of equal breadth throughout their whole length. Central base three to four times as broad, with large leaf-cross. Apex truncated or bifid (sometimes with four short teeth).
Dimensions.—Length of the spines 0.3 to 0.5, breadth 0.004 to 0.008; leaf-cross 0.02 to 0.03.
Habitat.—North Atlantic, west coast of Norway (Claparède et Lachmann); Færöe Channel (Gulf Stream), John Murray, surface.
10. Acanthonia claparedei, Haeckel.
Acanthometra claparedei, Haeckel, 1862, Monogr. d. Radiol., p. 383, Taf. xviii. fig. 12.
Spines quadrangular prismatic, with four prominent lamellar edges, of equal breadth throughout their whole length. Apex bifid. Central base twice as broad, with large leaf-cross. Central capsule opaque, reddish-brown.
Dimensions.—Length of the spines 0.6, breadth 0.016; leaf-cross 0.032.
Habitat.—Mediterranean (Messina); Atlantic, Station 347, surface.
11. Acanthonia cuspidata, Haeckel.
Acanthometra cuspidata, Haeckel, 1862, Monogr. d. Radiol., p. 383, Taf. xviii. fig. 11.
Spines quadrangular pyramidal, with four prominent lamellar edges, tapering gradually from the broad base towards the simple distal apex. Basal leaf-cross as broad, with a small central pyramid.
Dimensions.—Length of the spines 0.5, basal breadth 0.012; leaf-cross 0.025.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.
12. Acanthonia quadrifolia, Haeckel.
Acanthometra quadrifolia, Haeckel, 1862, Monogr. d. Radiol., p. 382, Taf. xviii. fig. 10.
Spines in the basal part quadrangular pyramidal, with four prominent lamellar edges and a large basal leaf-cross; in the distal part three to six times as long, cylindrical, of equal breadth. Apex simple, conical, or bifid. Central capsule yellow or whitish. This common species differs from the nearly allied Acanthometron catervatum mainly by the strong development of the large basal leaves or wings.
Dimensions.—Length of the spines 0.3 to 0.5, breadth in the distal half 0.002, in the basal part 0.02.
Habitat.—Mediterranean; North Atlantic, Stations 252 to 254; Færöe Channel, Gulf Stream, in enormous numbers, John Murray, surface and at various depths.
13. Acanthonia diplopyramis, n. sp.
Spines formed like a quadrangular double pyramid or an irregular octahedron; the basal leaf-cross being extremely developed, with four very large and thin lamellar leaves; the basal halves of the twenty double pyramids are united by the meeting edges of those leaves, while their distal halves are free, with simple apices. Therefore the four triangular leaves of each spine are equally thinned from the middle towards the two ends.
Dimensions.—Length of the spines 0.1 to 0.2, greatest breadth 0.04 to 0.08.
Habitat.—Central Pacific, Stations 266 to 274, surface.
14. Acanthonia multispina, Haeckel.
Acanthometra multispina, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. vii. figs. 6-9.
Acanthometra multispina, Haeckel, 1862, Monogr. d. Radiol., p. 384.
Spines quadrangular, with four lamellar prominent edges, in the proximal half nearly prismatic, in the distal half pyramidal; both halves separated by a prominent short tooth on each edge. Here in the middle part the breadth (including the four teeth) is equal to the basal leaf-cross. Central capsule opaque, brown.
Dimensions.—Length of the spines 0.2 to 0.3, greatest breadth 0.01 to 0.02.
Habitat.—Mediterranean (Messina); Tropical Atlantic, Station 348.
15. Acanthonia serrulata, n. sp.
Spines quadrangular pyramidal, with simple apex; the large basal leaf-cross nearly half as long as the prolonged distal part. The four prominent triangular edges of the latter are very thin and broad lamellæ, finely dentate or serrate.
Dimensions.—Length of the spines 0.2 to 0.3, greatest breadth 0.05 to 0.06.
Habitat.—Central Pacific, Station 272, surface.
Subgenus 3. Acantholithium, Haeckel.
Definition.—Spines in the basal part grown together, so that the whole skeleton is not composed of twenty separated pieces, but represents a single piece of acanthin—a star with twenty equal rays.
16. Acanthonia stellata, n. sp.
Spines quadrangular pyramidal, with simple distal apex, in the basal part grown perfectly together, so that the whole skeleton forms a single piece of acanthin—a starlet with twenty equal rays. The free pyramidal part of each spine is twice to four times as long as the basal part.
Dimensions.—Length of the spines 0.1 to 0.15, greatest breadth (on the surface of the central solid sphere) 0.02 to 0.04.
Habitat.—Central Pacific, Station 271, surface.