Changes in dermal ossicles during somatic growth in the Caribbean littoral sea cucumbers (Echinoidea: Holothurioidea: Aspidochirotida)

Dermal ossicles in holothuroids are important taxonomic characters, but they can change during somatic growth. Ossicles in very young individuals may be so different from those in adults as to indicate separate species. Since juveniles are rarely found, growth changes in ossicles have previously been studied in only a few species worldwide. During 25 years of collecting in Puerto Rico, series of juveniles of many common littoral species of Caribbean holothuroids have been obtained. In this paper, ossicles of 12 of the 17 valid Caribbean species in the Order Aspidochirotida are described. The pattern of changes varies between species. In some it is mainly a change in size, the ossicles becoming gradually either larger, as in Holothuria (Platyperona) parvula (the tables and rods increase in size but the buttons stay about the same length), or smaller and simpler (e.g., the rods in Holothuria (Selenkothuria) glaberrima). In other species, a type of ossicle lacking in small juveniles is added during somatic growth (e.g., buttons in H. (Thymiosycia) arenicola; rosettes in H. (Halodeima) mexicana), or ossicles present in juveniles are absent in adults (e.g., all tables in Astichopus multifidus; tables with quadruped disks in H. (Thymiosycia) impatiens and H. (Theelothuria) princeps; tables with wide, delicate disks and tall spires in H. (H.) mexicana and Isostichopus badionotus). In H. (Cystipus) cubana, the ossicles (tables, rods, buttons) all change almost totally in appearance. The changes in the ossicles are affected by continual dissolution and redeposition of the calcite. Ossicle changes in the species covered in this paper are documented in line drawings and tables of measurements. Changes in external morphology of the species during somatic growth also are noted. There are photographs of some of the juveniles.