heart urchin Abatus sp.

Species of Abatus urchins found in McMurdo Sound area are elongatus, ingens, nimrodi, and shackletoni [15].


The genus Abatus is characterized by what's called a peripetalous fasciole in adult urchin tests (shells); this is a different-looking band of fine densely-packed spines circum-navigating the top of the test (see it below this red line) [15].

Heart urchins are deposit feeders, using their oral tube feet to gather up detritus [13]. Heart urchins have a dense coat of spines which keeps sediment away from the urchin's surface, thus maintaining a water-filled surrounding space that the urchin uses for respiration while buried [13].

An Abatus sp. urchin.

A. elongatus has been found in McMurdo Sound and the South Orkney Islands from 11 to 804 meters depth, is typically 4.5 centimeters in length, and rarely up to 6.5 centimeters [15]. A. elongatus has an elongate test (shell) irregularly ovoid, without a frontal notch, and has has a sinuous-looking peripetalous fasciole [15]. A. elongatus is colored dark gray in alcohol [15]. A. shackletoni and A. elongatus are similar; A. shackletoni has a broader fasciole closer to the ambitus at the posterior region and A. elongatus adults are about twice the size of A. shackletoni adults [15].

An Abatus sp. urchin.

A. nimrodi is found in eastern Antarctica from 2 to 716 meters depth [4,5,1,6,9,14]. A. nimrodi can be found partly or completely burrowed into muddy or silty sediment [7,14]. A. nimrodi is common along the western oligotrophic side of McMurdo Sound including New Harbor; it can be found buried just below the surface of fine, silty sediment at New Harbor [1,6,9]. The shell (test) length of A. nimrodi can be up to six centimeters with an average size of 3 - 4 centimeters [15]. The brood pouches of A. nimrodi are widely separated from the apical system at the top of the test (shell) [15]. The color of A. nimrodi is dark brown to nearly black [4,15].

An Abatus sp. urchin.

A. shackletoni is found throughout Antarctica and the Antarctic Peninsula from 8 to 631 meters depth [1,2,3,4,9,10,12,14,15]. Near Cape Evans, A. shackletoni occurs in loose gravel and cobble habitats [1]. At Rocher Jacobsen in the Pointe Géologie Archipelago of Terre Adélie, A. shackletoni individuals live completely buried in the silty sediment [14]. The shell (test) length of A. shackletoni can be up to 6.7 centimeters in length, with a typical size being four centimeters [6,11,15]. The test of A. shackletoni is more or less ovoid, about as long as it is broad, has a regular peripetalous fasciole, and may or may not have a faint notch at the anterior end [4,5,9,10,15]. The color of A. shackletoni is brown to grayish-purple [15].

An Abatus sp. urchin.

A. ingens has been found along the Antarctic coast from 20 to 761 meters depth, and is very large, up to six to seven centimeters in length [15]. A. ingens has a triangular-looking ambitus at its posterior end, has a sinuous-looking peripetalous fasciole, and is very dark, almost black, including its spines [15].

Here's a look at the four brood pouches on an Abatus test (shell).

A. shackletoni broods an average 22 yolk-feeding embryos and juveniles in each of four depressed elongated brood pouches on the urchin's dorsal (aboral) surface; A. nimrodi broods an average of eighteen [1,6].

Here, Abatus embryos and juveniles are pulled out of their brood pouches for illustration. Development of embryos within the brood pouch takes at least eight months [6]. Eggs are released into the brood pouches and fertilized there throughout most or all of the year [6]. From August to January, 71-100% of A. shackletoni females are brooding embryos [6]. From November to January, 60-84% of A. nimrodi females are brooding embryos [6].

Two types of spines form a protective arch over the Abatus brood pouch [1,6]. A. nimrodi juveniles are spine-covered in later stages of development in the brood pouch and are larger in size relative to the juveniles of A. shackletoni [1,6].

The production of large, robust A. nimrodi juveniles may increase their survival for escaping the predatory brittle stars which occur in their environment; these brittle stars are not abundant where A. shackletoni is found [6].


The diversity of Antarctic sea urchins with its prevalence of brooding (thirty-nine of sixty Antarctic and subantarctic species -- 65%) may be a process of species-level selection via extinction and speciation rates related to pelagic or protected development of their young [7,8].

1: Journal of Morphology 216(1):79-93, 1993; 2: Symposium on Antarctic Oceanography. Santiago, Chile 13-16 September 1966. Published by Scott Polar Research Institute for Scientific Committee on Antarctic Research. Cambridge, Printed by W. Heffer, 1966. p.162; 3: R Koehler. Echinodermata Echinoidea. Australasian Antarctic Expedition 1911-1914. Scientific Reports. Series C, Zoology and Botany. Vol 8 Part 3. Sydney : David Harold Paisley, Government Printer, 1926; 4: A Monograph of the Echinoidea. Volume 2, Spatangoida. 2. Amphisternata. 2. Spatangidae, Loveniidae, Pericosmidae, Schizasteridae, Brissidae. T Mortensen. Copenhagen : CA Reitzel, 1951. pp249-263; 5: Hawaiian and Other Pacific Echini. The Spatangina. HL Clark. Memoirs of the Museum of Comparative Zoology at Harvard College. Volume 46 Number 2. Cambridge : Museum of Comparative Zoology at Harvard College, 1917. pp. 174-177; 6: Invertebrate Reproduction and Development 17(3):181-191, 1990; 7: Vie et Milieu 47(4):381-387, 1997; 8: Evolution 50(2):820-830, 1996; 9: Echinoderms Through Time : Proceedings of the Eighth International Echinoderm Conference, Dijon, France, 6-10 September 1993. B David et al, eds. Rotterdam ; Brookfield, Vt. : Balkema, 1994. pp.749-756; 10: Equinodermos Antarticos. I. Equinoideos. 1. Equinoideos de Shetland del Sur y Archipielago Melchior. I Bernasconi. Revista del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" e Instituto Nacional de Investigacion de las Ciencias Naturales. Zoologia 9(9):197-210 and plates, 1969; 11: Biogeografia de la Peninsula Antartica, Archipielagos y Mares Adyacentes. N Bellisio & A Tomo. Buenos Aires : Servicio de Hidrografia Naval, 1974; 12: A Survey of the Marine Fauna in Shallow Coastal Waters of the Vestfold Hills and Rauer Islands, Antarctica. MJ Tucker & HR Burton. ANARE Research Notes 55, 1987; 13: www.nhm.ac.uk/palaeontology/echinoids/; 14: Polar Biology 27(3):177-182, 2004; 15: Antarctic Echinoidea. B David, T Chone, R Mooi & C De Ridder. Ruggell, Liechtenstein: ARG Gantner, 2005

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