- Test ovate with modest anterior sulcus; rather depressed in profile.
- Apical disc ethmolytic, with 3 (rarely 2) gonopores (no gonopore in plate G2); subcentral.
- Anterior ambulacrum narrow and sunken from apex to peristome; pore-pairs and tube-feet specialized; uniserially arranged.
- Other ambulacra petaloid and obviously sunken, anterior petals longer than posterior petals; petals cruciform and not particularly strongly flexed. Perradial zone wider than pore-pairs. Petals deeply sunken and enlarged in females for brood protection.
- Periproct longitudinal, on vertically truncate face; bound orally by Iamb plates 5.a.5/5.b.5; 3-4 plates each side form opening.
- Peristome large and kidney-shaped; facing forwards; labral plate projecting.
- Labral plate short and wide, not usually extending beyond the first ambulacral plate; in broad contact with sternal plates. Sternal plates symmetrical, forming the entire plastron. Rear of sternal plates coincident with 6th or 7th ambulacral plate.
- Aboral tuberculation fine, uniform and dense. Oral tubercles also dense and uniform.
- Well-developed peripetalous fasciole passing around the distal end of the petals. Crossing amb III plates 7 or 8. Latero-anal band present only in juveniles; lost in adults.
- Sexual dimorphism in gonopore size and petal development (females brood juveniles in petals).
Eocene and Recent, circum Antarctic
Spatangus (Tripylus) cavernosus Philippi, 1845, p. 435, by original designation.
- A. cavernosus (Philippi, 1845); Recent, Southern South America and Antarctic region
- A. curvidens Mortensen, 1936; Recent, circum-Antarctic
- A. cordatus (Verrill, 1876); Recent, Kerguelen Islands
- A. agassizii (Pfeffer, 1889); Recent, South Georgia and Falklands
- A. philippi Loven; Recent, Antarctic and southern Atlantic
- A. elongatus (Koehler, 1908); Recent, South Orkneys
- A. kieri McKinney et al. 1988; Eocene, Seymour Island
|Classification and/or Status
Spatangoida, Paleopneustina, Schizasteridae
Differs from Pseudabatus in having the petals sunken along their entire length; in Pseudabatus the petals become sunken only at some distance from the apex. Abatus has the labrum extending no further than the first ambulacral plate, whereas in Pseudabatus the labrum extends to at least the third ambulacral plate.
Mortensen, T. 1951. A monograph of the Echinoidea V Spatangoida 2. C. A. Reitzel, Copenhagen.
McKinney, M. L., McNamara, K. J. & Wiedman, L. A. 1988. Echinoids from the La Mesta Formation (Eocene), Seymour Island, Antarctica. Memoir of the Geological Society of America 169, 499-503.
Troschel, F. 1851. Arch. Naturges. 17(1), p. 72.