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Tuatara: Volume 1, Issue 3, September 1948

A Key to the Sea Urchins of New Zealand

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A Key to the Sea Urchins of New Zealand

The sea-urchin fauna of New Zealand is rather incompletely known, as the majority of the twenty-odd species recorded are rare or of very local occurrence. The key is constructed to make identification of species as easy as possible to the non-specialist, and consequently some rather unorthodox characters are utilised at certain points. For example, the method of distinguishing Cidaroid and Diademoid* urchins by the length of the spines applies readily in New Zealand species, though certainly not elsewhere. In other respects the arrangement is essentially systematic. An elementary knowledge of echinoderms is assumed (such as for example is given in Thomson's “Outlines of Zoology”), while other technical terms that are unavoidable are explained in the description of the figures. If a sea-urchin is found which does not appear to fit anywhere in the key the chances are that it is either an undescribed species or one of the very rare species; it should in any case be submitted to an appropriate institution for examamination. A collection of sea-urchins should be kept either in formalin or alcohol, or dried; some specimens at least should be kept with the spines intact.

1. Body more or less spherical; the 5 ambulacra all similar, arranged like meridians, traversing the test from apex to peristome. Anus situated at the apex in the centre of the upper surface; mouth situated at the centre of the peristome, the latter occupying the centre of the lower surface. ENDOCYCLICA (or “sea-eggs”) 2
Body ovoid, or flattened into a disc, or heart-shaped. Anus displaced to some position away from the apex (the direction in which the anus is moved being then termed “posterior”). EXOCYLICA (or Sand-dollars and Hearturchins) 9
2. Spines equal in length to, or exceed, the diameter of the test. Each ambulacral plate carries a minute tubercle and only one pair of pores for tube-feet. Each interambulacral plate carries one very large, central tubercle, situated on a bare ovol depression (termed the “scrobicule”). Order CIDAROIDA (Fig. 1) 3
Spines do not exceed in length the diameter of the test. Each ambulacral plate carries 3 or more pairs of pores for tuber-
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feet. Each interambulacral plate carries a number of tubercles of various sizes. Order DIADEMOIDA (Figs. 2-4) 4
3. On the upper surface some of the spines are umbrella-shaped (Fig. 5). On the bare test a vertical zig-zag line is formed by a groove running down the midline of each interambulacrum, while a vertical sinuous line indicates a similar groove along the midline of each ambulacrum. Sub-littoral, rather rare Goniocidaris umbraculum
Serrate spines, none umbrella-shaped (Fig. 18). No grooves along the ambulacra or interambulacra. Sub-littoral, rare. Ogmocidaris benhami
4. Test quite soft and flexible, generally distorted for this reason. Sub-littoral and abyssal. Rare Asthenosoma thetidis
Test rigid 5
5. Test up to 6 inches in diameter. Ambulacra broad, with numerous pores arranged to form horizontal rows of three pore-pairs, and also arranged to form vertical rows, 3 such vertical rows on either side of each ambulacrum. (Fig. 4.) Test and spines bright green, the tubercles lighter, and very numerous. In colonies below low-tide level. Common seaegg or kina Evechinus chloroticus
Test usually less than 2 inches in diameter. Ambulacra narrow, with only one vertical row of pores on either side of each ambulacrum 6
6. Ambulacral plates each have 7-10 pairs of pores, arranged in arcs. Rare (in N.Z.) (Fig. 2.) Heliocidaris tuberculata
Ambulacral plates each have 3 pairs of pores 7
7. Test grey-green. Spines dull green or grey-green. In rock pools below or at low-tide level. In the far south it may have a test up to 3 inches across, but on mainland coasts it is smaller Pseudechinus novaezelandiae
Test purplish, red, or pink (but cream if faded through exposure on beach after death). Spines pink, or red, or pink with white tips 8
8. Test deep purple, very thin and delicate, with buff coloured, sunken ambulacra. Spines very short, forming a dense bristly coat of pink colour. Below low-tide level, or more usually cast up dead on beaches, especially of the north-west coast. Rather rare. Holopneustes inflatus
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Test pink. Each interambulacral plate with up to 14 tubercles, which are arranged in the following manner. Every second plate carries a horizontal row of tubercles, while every alternate plate carries a forked row of tubercles, like a Y lying on its side, with the forks towards the ambulacrum (Fig. 3). Littoral, rather rare, found chiefly south of Cook Strait. Pseudechinus huttoni
Test pink. No horizontal rows of tubercles on interambulacral plates. Spines slender, pink, with white tips. Littoral and sub-littoral. Mainly Cook Strait and southward to Stewart Island. Pseudechinus albocinctus
9. Test very flattened, especially the lower surface, disc-like, the ambulacra forming petal-like areas on the upper surface. Order CLYPEASTROIDA (Sand-dollars) 10
Test ovoid, or heart-shaped; not flattened, or slightly flattened below 12
10. Outline circular, or circular with a slightly wavy edge 11
Outline ellipsoid. Anus on lower surface, near the mouth. Rare, littoral. (Figs. 10 and 11.) Laganum depressum
11. Outline quite circular. Anus below, near mouth. About 1 inch in diameter. Brick-red. Sub-littoral, rare (Figs. 8 and 9.) Peronella hinemoae
Anus above, near posterior margin of disc. Up to about 4 inches in diameter (occasionally larger). Greyish, turning green in alcohol. On sandy bottom below low-tide level. Common sand-dollar. (Figs. 6 and 7.) Arachnoides zelandiae
12. One or more of the ambulacra situated in a groove. Order SPATANGOIDA (Heart-urchins) 14
Ambulacra all flush with surface of test 13
13. Ovoid, concave below. Anus situated in an elongate depression on the upper surface (Figs. 12 and 13). A survivor of Mesozoic faunas, common in locally sandy areas below low-tide level. Purplish but turning green in alcohol, and bleaching white on exposure to weather. Apatopygus recens
Ovoid. Anus on lower surface, behind mouth. Sub-littoral, rare. (Figs. 19 and 20) Echinocyamus polyporus
14. Distinctly heartshaped, owing to the anterior ambulacrum lying in a groove which notches the anterior margin of test. Other ambulacra form petal-like areas on upper surface of test. 15
Ovoid, anterior ambulacrum not in a groove, and therefore no anterior notch. Other ambulacra in deep grooves, petal-like.
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Very large (up to 7 inches in length). Sub-littoral, rare, known only from northern coast (Fig. 17.). Brissus gigas

15. Other ambulacra flush with surface of test. Dull violet in colour. Sub-littoral, rare; Cook Strait only known locality as yet. (Fig. 14.) Spatangus multispinus
Other ambulacra also in grooves 16
16. Ambulacral groves not separately distinguishable owing to confluence of their pore zones. Grey, with a bristly coating of flexible spines. Common on sandy bottom below low-tide level. (Fig. 15.) Echinocardium australe
Ambulacral grooves rather shallow, but not confluent at the apex, and not extending beyond the central region of the upper surface. Sub-littoral, rare. (Fig. 16.) Brissopsis zelandiae


The literature is extremely scattered, and there is no single volume containing descriptions of New Zealand sea-urchins. For general information on echinoderms, Mortensen's “Echinoderms of the British Isles” will be found helpful. Some of the New Zealand species are illustrated and described in Mortensen (1921); Echinoidea of New Zealand and Auckland-Campbell Islands, Medd, Dansk, naturh. Foren., 73, p. 139. The Trans. Roy. Soc. N.Z. may also be consulted, and publications of the United States National Museum deal with Pacific sea-urchins.


The editorial committee has much pleasure in acknowledging the financial assistance given by the following organisations for the publication of plates: The Royal Society of New Zealand for the plates accompanying Dr. Allan's article, the Wellington Branch of the Federation of University Women for one of the plates accompanying Dr. H. B. Fell's article. Assistance in the cost of printing this number of “Tuatara” was given from the Publications Fund of Victoria University College.

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Explanation Of Plates

Plate 1

Fig. 1.—Cidaroid type of plates. Ambulacral plates lie to the left, each bearing a small tubercle and a pair of pores for tube-feet. Interambulacral plates to the right, each bearing one very large tubercle, lying in the centre of an extensive ovoid bare, depressed area (the scrobicule). Magnification X 4.

Fig. 2.—Multiporous ambulacral plates of Heliocidaris tuberculata. Magnification X 4.

Fig. 3.—Diademoid structure of plates as in Pseudechinus huttoni. Ambulacral plates to the left, each carrying 3 large, and several smaller tubercles, and 3 pairs of pores. Interambulacral plates to the right, showing the alternating arrangement of plates with a horizontal row of large tubercles and those with tubercles arranged to form a Y-shape. Magnification X 4.

Fig. 4.—Evechinus chloroticus. Ambulacral plates to the left, showing broad poriferous portion, with pores arranged to form both both vertical and horizontal rows. Part of interambulacra to the right. Magnification X 2.

Fig. 5.—Umbrella-shaped spine of Goniocidaris umbraculum. Magnification X 2.

Fig. 6.—Arachnoides zelandiae, seen from upper (aboral) side, showing anus above near posterior border. Half natural size.

Fig. 7.—Arachnoides zelandiae, posterior view, showing flattened under-surface, domed above. Half natural size.

Fig. 8.—Peronella hinemoae, seen from upper surface. Anus not visible as it lies below. Half natural size.

Fig. 9.—Peronella hinemoae, posterior view, showing conical upper surface, and flattened lower surface. Half natural size.

Fig. 10.—Laganum depressum, seen from upper surface. Anus not visible as it lies below. Half natural size.

Fig. 11.—Laganum depressum, posterior view, showing convexoconcave upper surface, and flattened; lower surface. Half natural size.

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Plate 1

Plate 1

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Plate 2

Fig. 12.—Apatopygus recens, seen from above, showing anus lying in elongate depression on posterior part of upper surface. Natural size.

Fig. 13.—Apatopygus recens, posterior view, showing convex upper surface and concave lower surface. Natural size.

Fig. 14.—Spatangus multispinus, seen from above, showing anterior ambulacrum in a groove which notches the anterior margin, while the other ambulacra form petals flush with the surface of the test. Half natural size.

Fig. 15.—Echinocardium australe, seen from above, showing anterior ambulacrum in a groove, while the other four ambulacra have become confluent. Half natural size.

Fig. 16.—Brissopsis zelandiae, seen from above, showing anterior groove, while other ambulacra remain as distinct, sunken petals, not confluent. The petals are surrounded by a sinuous line of microscopic tubercles called a “fasciole”. Natural size.

Fig. 17.—Brissus gigas, seen from above, showing absence of an anterior notch, while the other ambulacra form long slender petals lying in deep grooves. A fasciole is also present. One quarter natural size.

Fig. 18.—Spine of Ogmocidaris benhami, showing serrated borders. Magnification X 5.

Fig. 19.—Echinocyamus polyporus, seen from below, showing centrally placed peristome and anus lying midway between peristome and posterior border. Natural size.

Fig. 20.—Echinocyamus polyporus, seen from above. Natural size.


The above figures show no more detail than is actually required for identification purposes. In the case of Figs. 6-17, 19 and 20, the tests are shown with the spines removed.

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Plate 2

Plate 2

* The recent decision of the International Zoological Congress to codify Diadema (in place of Centrechinus) requires the use of the ordinal name Diademoida instead of Centrechinoida as formerly.