A variation of the smooth septate junction in sea spiders (pycnogonida).

A new type of septate junction considered to be a variation of the arthropod smooth septate junction is described in pycnogonid (sea spider) endothermal tissue based on the use of conventional thin-section, lanthanum tracer and freeze-fracture techniques. This new type of septate junction is apparently unique to the Pycnogonida but closely resembles septate junctions previously described in the Merostomata and Collembola. This in conjunction with previous work suggests that the septa of smooth septate junctions may not be as 'smooth' as generally thought and probably have a complex substructure.