COMPARATIVE-STUDY OF SUB-CUTICULAR BACTERIA IN BRITTLESTARS (ECHINODERMATA, OPHIUROIDEA)

Arm tissues from species of brittlestars from the British Isles and No rth America were examined by light and electron microscopy for the pre sence of sub-cuticular bacteria (SCB) which were recorded in 17 of the 19 species studied. Three major groups of SCB could be distinguished on the basis of their morphology. The bacterial morphology was not cor related with the host ecology but did appear to be related to the phyl ogeny of the hosts. Ophiuroids of the same genera had morphologically similar SCB and this was also generally true of species from the same family. This indicates the possibility of co-evolution between the SCB and their hosts. Estimates of SCB load were made for 9 of the species by direct counting and by quantifying the amount of bacterial endotox in present in the host tissues. SCB numbers varied interspecifically f rom 3.7x10(8) to 4.6x10(9) SCB per gram of ash-free brittlestar arm ti ssue. Endotoxin values ranged from 5.97 to 285 mu g g(-1) ash-free arm tissue. Calculations suggest that SCB form at least 0.1 to 1% of the total biomass of the arm tissues. There was considerable intraspecific variation in SCB load. The possible role and significance of SCB is d iscussed.