Sea Stars, Sea Urchins, and Sea Cucumbers (Phylum Echinodermata)
Dennis Gordon, Franz Smith and Taoho Patuawa
General Description
The phylum Echinodermata includes sea stars, sea urchins, sea cucumbers, sea lilies, and relatives. They are exclusively marine organisms characterised by five-radial symmetry, an internal water-vascular system, and skeletal elements of calcium carbonate that can be fused into a test or are imbedded or protruding from the body wall, giving the phylum its name "spiny skin". The water-vascular system forms a network of canals throughout the body and ends in structures called tube feet. The tube feet are used for respiration, feeding, locomotion, and adhering to the substratum. Echinoderms are widely distributed in the world's seas, from the intertidal to abyssal depths, and occur in rocky and soft-sediment habitats. They occupy a variety of trophic and ecological roles in marine systems. Within the phylum, there are six classes, all of them with representatives in the New Zealand region.
Class Crinoidea, the feather stars and sea lilies, represents a group of exclusively suspension-feeding echinoderms with elongated arms and pinnules. Tube feet along each arm's length are used to capture food particles, such as detritus, invertebrate larvae, and other zooplankton. Crinoids occupy a broad range of depths and can be found in many shallow subtidal areas around New Zealand. Sea lilies are commoner in water depths greater than 200 m, and are anchored to the sea floor by a stalk. The fossil record of Crinoidea is extensive, with over 5000 fossil species, which is now reduced to about 540 living species. In the New Zealand region, there are some 69 species distributed in three orders and eleven families. Almost 30% of New Zealand's feather-star species are endemic to the region.
Class Asteroidea, commonly known as sea stars, represents a group of largely carnivorous and omnivorous species, with some species known to rely on detritus as a source of nutrition while others are suspension-feeders. Larger species, such as members of the genus Luidia, with an arm radius of 20 cm, can be important predators of bivalves and other echinoderms, while smaller species, such as members of the genus Patiriella, with an arm radius of 2 cm, are omnivorous, feeding mainly on algae and detritus. In the New Zealand region, there are at least 184 species in 31 families and 7 orders, with at least 57% of the species endemic to the exclusive economic zone.
A small but intriguing class of echinoderms is the Concentricycloidea, or sea daisies, with just two named species (New Zealand and Bahamas) and one unnamed species (North Pacific). First discovered in New Zealand, these creatures resemble small medusae surrounded by spines. One species lacks a mouth and none have arms. Their biology is poorly known, but they live in shipworm borings in sunken wood and are believed to absorb nutrients derived from the digestion of wood cellulose by bacteria. Endemic New Zealand Xyloplax medusiformis has been found at depths of 1100 m in canyons off Hokitika and Castle Point.
Members of the class Ophiuroidea, comprising brittlestars, snakestars, and basket-stars, have a central disc and five elongated arms. In some species of brittlestar, these arms are ornamented with spines or hooks, and, in the basket-stars, arms split repeatedly to form a feeding net. Ophiuroids inhabit both rocky and soft-sediment areas, with some species living cryptically under rocks or amongst other sessile organisms. Other species of ophiuroid are more conspicuous, living in open sedimentary habitats or are suspension feeders, like the basket-stars, requiring them to live in exposed areas. There are about 2000 species of ophiuroid described worldwide, comprising 244 genera in 18 families. The Ophiuroidea fauna of New Zealand has at least 176 species in 72 genera and 16 families. An additional 21 species have not been formally described. (This diversity is comparable to that found in Australia, where 124 species are found in 95 genera with representatives of 15 families). At least 28% of the brittlestars in New Zealand are endemic to the region.
Class Echinoidea, containing sea urchins or sea eggs, is a group of echinoderms with no arms, having a spherical or flattened-disc shape. Skeletal plates are fused to form a test, which is commonly covered with spines. Sea urchins can be important consumers of rocky and soft-sediment habitats, and have been renowned for their capacity to alter habitat structure through their feeding activities. The best-known sea urchin in New Zealand is the endemic kina, Evechinus chloroticus, which can attain a large test size. Worldwide, there are about 800 species of echinoids. In the New Zealand region, there are at least 90 species in 56 genera and 27 families, which contrasts with Australia's echinoid fauna of 207 species in 95 genera and 32 families. Overall, at least 33% of the sea urchin species in New Zealand's exclusive economic zone are endemic.
Class Holothuroidea, the sea cucumbers, comprises a group of roughly cylindrical echinoderms with reduced skeletons, occurring at a wide range of depths in rocky and soft-sediment habitats. Sea cucumbers feed with a set of tentacles - modified tube feet -surrounding the mouth, mostly by suspension-feeding, in which particles are captured from the water column, or detritus-feeding, in which tentacles pick up organic matter and particles found in sediment. Several kinds of sea cucumber are commercially fished in other regions of the world, including species of Stichopus, which occurs in the New Zealand region and is the conspicuous sea cucumber of rocky intertidal and shallow subtidal reefs. Of the Holothuroidea, the sea cucumbers, there are at least 98 species in 6 orders with 19 families. The New Zealand holothurian fauna comprises 98 species in 19 families and 6 orders. There is a relatively high proportion (60%) of dactylochirotid and dendrochirotid species compared to Australia where they comprise about 30%. Almost one-third (27 species) of the New Zealand fauna is endemic.
Status
No species is threatened, or formally protected, other than in marine reserves.
Key Locations
Echinoderm diversity is generally correlated with diversity of other invertebrates in the same environment, hence they are common in reefal environments at Raoul Island and at offshore islands where key indicators of high biodiversity hold for other taxa.
Summary of Threats
Bottom trawling and consequent habitat modification pose the greatest threat to echinoderm diversity. In parts of continental shelves and the deep sea, echinoderms can dominate fisheries bycatch and many tonnes can be captured. In shallow waters, over-harvesting of kina for roe and Stichopus mollis for trepang (bêche-de-mer) is possible.
Typical Habitats
Echinoderms are found in all benthic environments, from the intertidal zone to abyssal depths. Feather stars are encountered in unpolluted reefal environments where diversity of other suspension feeders is high, as at Raoul Island and on rock walls of offshore islands. The stalked sea lilies are found only in deep water, on hard bottoms where other fixed suspension-feeding benthos, like corals, occur. Sea-stars, brittlestars, sea urchins, and sea cucumbers are fairly ubiquitous and their diversity and density depend on the the type of sea floor (hard rock or soft sediment) in relation to behaviour and method of feeding.
State of Information
Several monographs have been published over the years and chapters on echinoderms are in press in major volumes to be published in the next two years, on New Zealand's biota and coastal invertebrates respectively.
Significance for Maori
The roe of kina, the endemic sea urchin Evechinus chloroticus, is a well-known delicacy to Maori. The fourth edition of Powell's Native Animals of New Zealand (David Bateman, 1998) gives the Maori name "kiri taratara" for echinoderms in general. Starfish are referred to as "papatangaroa" or "pekapeka", and were sometimes used as bait in crayfish pots if more desirable bait could not be found.
Key References
Clark, H E S and McKnight, D G. 2001a. The marine fauna of New Zealand: Echinodermata: Asteroidea (sea-stars) Order Paxillosida, Order Notomyotida. NIWA Biodiversity Memoir 116: 1-269.
--.2001b. The marine fauna of New Zealand: Echinodermata: Asteroidea (sea-stars) Order Valvatida. NIWA Biodiversity Memoir 117: 1-269.
McKnight, D G. 1969. An outline distribution of the New Zealand shelf fauna. Benthos survey, station list, and distribution of the Echinoidea. New Zealand Oceanographic Institute Memoir 47: 1-89.
--.2000. The marine fauna of New Zealand: Basket-stars and snake-stars (Echinodermata: Ophiuroidea: Euryalina). NIWA Biodiversity Memoir 115: 1-79.
McKnight, D G, Eagle, M K, Pawson, D L, Améziane, N, Clark, H E S, Alcock, N and D J Vance. In revision. Phylum Echinodermata: Sea-stars, brittle stars, sea urchins, sea cucumbers, sea lilies, and kin. In Gordon, D P (ed). In press: The New Zealand Inventory of Biodiversity Volume 1. Kingdom Animalia: Radiata, Lophotrochozoa, and Deuterostomia. Canterbury University Press, Christchurch.
Pawson, D L. 1970. The marine fauna of New Zealand: Sea cucumbers (Echinodermata: Holothuroidea). New Zealand Oceanographic Institute Memoir 52: 1-69.
Tracey, D M, Anderson, O F, Clark, M R and M D Oliver. 2005. A guide to common deepsea invertebrates in New Zealand waters. New Zealand Aquatic Environment and Biodiversity Report No. 1: 1-160.
Table 26: Sea Stars, Feather Stars, Sea Urchins, and Sea Cucumbers (Phylum Echinodermata) in New Zealand
| Class | Order | Families | Endemicspecies | Total species |
|---|---|---|---|---|
| ASTEROIDEA | Brisingida | 4 | 6 | 12 |
| Forcipulatida | 4 | 16 | 27 | |
| Notomyotida | 1 | 6 | 9 | |
| PAXILLOSIDA | 4 | 16 | 32 | |
| Spinulosida | 2 | 5 | 9 | |
| Valvatida | 11 | 47 | 76 | |
| Velatida | 5 | 9 | 19 | |
| Total | 31 | 105 | 184 | |
| CONCENTRICYCLOIDEA | PERIPODIDA | 1 | 1 | 1 |
| Total | 1 | 1 | 1 | |
| CRINOIDEA | ARTICULATA | 7 | 14 | 49 |
| ISOCRINIDA | 1 | 9 | ||
| MILLERICRINIDA | 3 | 3 | 11 | |
| Total | 11 | 17 | 69 | |
| ECHINOIDEA | Cassiduloida | 2 | 2 | 3 |
| CIDAROIDA | 1 | 6 | 21 | |
| Clypeasteroida | 4 | 1 | 7 | |
| Diadematoida | 2 | 3 | ||
| Echinoida | 2 | 1 | 5 | |
| Echinothurioida | 2 | 6 | ||
| Holasteroida | 2 | 3 | 8 | |
| Holectypoida | 1 | 1 | ||
| Pedinoida | 1 | 1 | 2 | |
| Salenioida | 1 | 1 | ||
| Spatangoida | 7 | 10 | 22 | |
| Temnopleuroida | 2 | 6 | 11 | |
| Total | 27 | 30 | 90 | |
| HOLOTHUROIDEA | APODIDA | 3 | 12 | |
| ASPIDOCHIROTIDA | 3 | 1 | 12 | |
| DACTYLOCHIROTIDA | 1 | 3 | ||
| DENDROCHIROTIDA | 5 | 14 | 25 | |
| ELASIPODIDA | 5 | 3 | 33 | |
| MOLPADIIDA | 2 | 2 | 13 | |
| Total | 19 | 27 | 98 | |
| OPHIUROIDEA | Euryalinida | 4 | 8 | 32 |
| Ophiurida | 12 | 41 | 144 | |
| Total | 16 | 49 | 176 | |
| Grand Total | 105 | 229 | 618 |
Figure 73: Kier's echinoid Porterpygus kieri annual distribution.
Figure 74: Sea daisy Xyloplax medusiformis annual distribution.