Final answer:
Actinomyces spp. are branching, filamentous microorganisms found in gingival crevices and tonsillar crypts; they can cause periodontitis. They form a mycelium through the interconnection of hyphae and are considered opportunistic pathogens in humans.
Step-by-step explanation:
The branching, filamentous microorganisms that are normal inhabitants of gingival crevices and tonsillar crypts are likely Actinomyces spp., which are part of the Actinobacteria phylum. These microbes form a part of the normal flora of the human mouth but can become opportunistic pathogens, leading to conditions such as periodontitis (gum disease) when the immune system is compromised.
Actinomyces israelii, in particular, is known for its involvement in such infections. These organisms develop a mycelium, a vegetative network of branched, tubular hyphae. This network is capable of fusing with other hyphae, creating an interconnected, anastomosing mass that allows these microorganisms to thrive in their respective environments.
Actinomyces spp. are simple organisms that can either grow as single cells or in filamentous forms. They are important for soil ecology and, in the human mouth, play a role in the decomposition of organic matter. However, if they proliferate excessively or the immune system is weakened, they can cause disease.