The Echinoid Directory



Scutelliforms include all of the common sand dollars and are the best studied of all clypeasteroids. They are mainly shallow water forms inhabiting sandy substrata and living immediately underneath the sediment-water interface often in beach-face or shallow shoal settings. Most seive the sediment for its fine organic particles, but one, Dendraster, inclines its test to the sea-floor and suspension feeds under appropriate conditions (Timko 1976). The lunules act as pressure drainage channels to help prevent sand dollars from being washed out of the sediment by wave surge (Telford 1983). General accounts of the biology of echinarachniid sand dollars can be found in Mooi & Telford (1982) and Ghiold (1983) and of mellitids in Ghiold (1984) and Telford et al. (1985).

Ghiold, J. 1983. The role of external appendages in the distribution and life habits of the sand dollar Echinarachnius parma (Echinodermata: Echinoidea). Journal of Zoology, London 200, 405-419.

Mooi, R. & Telford, M. 1982. The feeding mechanism of the sand dollar Echinarachnius parma (Lamarck). Pp. 51-57 in J. M. Lawrence (ed.) International Echinoderms Conference, Tampa Bay. A. A. Balkema, Rotterdam.

Ghiold, J. 1984. Adaptive shifts in clypeasteroid evolution - feeding strategies in the soft-bottom realm. Neues Jahrbuch fur Geologie und Palaontologie Abhandlungen 169, 41-73.

Telford, M. 1983. An experimental analysis of lunule function in the sand dollar Mellita quinquesperforata (Leske). Marine Biology 76, 125-134.

Telford, M., Mooi, R. & Ellers, O. 1985. A new model of podial deposit feeding in the sand dollar Mellita quinquesperforata (Leske): the seive hypothesis challanged. Biological Bulletins 169, 431-448.

Timlo, P. L. 1976. Sand dollars as suspension feeders: a new description of feeding in Dendraster excentricus. Biological Bulletin 151, 247-259.

Geological history
True scutelliforms first appear in the Middle Eocene of the Pacific coast of America (Eoscutella), the Gulf coast of America (Protoscutellidae) and western Europe (Scutulum), implying divergence of the group somewhat earlier in the Palaeocene or early Eocene. They are locally abundant in the right facies from the Late Eocene onwards, and can form shell coquinas in beach deposits.