The Incidence and Morphology of Subcuticular Bacteria in the Echinoderm Fauna of New Zealand.

New Zealand echinoderms (33 species drawn from all five extant classes) were examined for the presence of symbiotic bacteria by fluorescence and electron microscopy. Gram-negative, subcuticular bacteria (SCB) were found in 17 species from four classes. The SCB could be classified into two major morphological types. Some species had both types of SCB. The distribution of SCB was not obviously linked to host ecology but did appear to be related to host phylogeny. Related species usually all have SCB or all lack them. The number of SCB in five species was estimated to be between 8.41 x 108 and 4.96 x 109 g-1 ash-free dry weight of host tissue. Significant differences in bacterial load and relative proportions of the different types of bacteria were found among three congeneric echinoids (Pseudechinus huttoni, P. albocinctus and P. novaezealandia). Ophiocoma bollonsi was peculiar in having groups of bacteria enclosed in host cells (bacteriocytes) within the connective tissue of the tube feet.