The Echinoid Directory

Lanthonia Coppard, 2016, p. 160

Diagnostic Features
  • Test flat with sharp and thin margins; usually slightly wider than long.
  • Apical disc monobasal with four gonopores.
  • Test with four ambulacral lunules and an anal lunule in the type.
  • Paired interambulacra disjunct on oral surface, but posterior interambulacrum continuous.
  • Basicoronal circlet pentastellate with interambulacral plates strongly projecting.
  • Periproct opening on inner margin of first pair of post-basicoronal plates and at inner edge of anal lunule.
  • Internal butressing well developed; composed of dense mesh. Pillers separate the buccal cavity from the intestinal space.
  • Food grooves bifurcating at edge of basicoronals and highly branched distally. Passing the ambulacral lunules very close to the lunule margin.
Distribution Early Pliocene to Recent, Tropical and subtropical Pacific coast of the Americas (Mexico to Colombia).
Name gender feminine
Type Mellita longifissa Michelin, 1858, by original designation.
Species Included
  • L. longifissa (Michelin, 1858); Recent, eastern seaboard of central America from central Mexico to Ecuador; Galapagos Islands.
  • L. grantii (Mortensen, 1948); Recent, northern Gulf of California to Panama.
Classification and/or Status Clypeasteroida; Scutellina; Scutelliformes; Scutellidea; Mellitidae.
Remarks It differs from Leodia in having no lunule in the anterior ambulacrum (see Mooi & Peterson 2000 for discussion) and from Mellita in having bidentate pedicellariae with simple valves and small peripheral teeth present along the edge of the blade (no enlarged terminal teeth) and food grooves passing close to the ambulacral lunule edges (widely spaced in Mellita). While highly similar to Mellita in morphology, the two genera form two very distinct groups in genetical analyses (based both on mtDNA and nDNA, see Coppard et al. 2013).

See Harold & Telford (1990) for an excellent review of the genus Mellita together with a key to the species.

Coppard, S. E., Zigler, K. S. & Lessios, H. A. 2013. Phylogeography of the sand dollar genus Mellita: Cryptic speciation along the coasts of the Americas. Molecular Phylogenetics and Evolution, 69, 1033-1042.

Harold, A. S. & Telford, M. 1990. Systematics, phylogeny and biogeography of the genus Mellita (Echinoidea: Clypeasteroida). Journal of Natural History 24, 987-1026. -