Amoeboid gliding on mucous tracks: Organisms with cells that glide within a mucus network belong to which protozoan group?

Introduction:
Some marine/estuarine protists move by a distinctive gliding mechanism along self-secreted mucous tracks. Classical protozoology grouped these as Labyrinthomorpha (labyrinthulids), now often placed among stramenopiles but retained in many teaching keys.

Given Data / Assumptions:

• Amoeboid cells travel within a network of mucous tracks.
• Movement is smooth “gliding,” not flagellar beating or ciliary stroke.
• Question follows older but still instructional phylum names.

Concept / Approach:
Labyrinthomorpha (labyrinthulids) form ectoplasmic nets or mucous tracks in which spindle-shaped or amoeboid cells glide. This separates them from Apicomplexa (gliding motility without external mucous tracks and parasitic lifestyle), Microspora (spore-forming intracellular parasites), and Myxozoa (metazoan parasites).

Step-by-Step Solution:
Identify the key phrase “gliding within a mucous network.” Recall that labyrinthulids produce ectoplasmic nets (“slime nets”). Match this signature behavior to Labyrinthomorpha. Exclude parasitic phyla lacking such external track networks.

Verification / Alternative check:
Descriptions of Labyrinthula/Thraustochytrium emphasize ectoplasmic networks and gliding cells; microscopy shows cells shuttling inside tubular nets, confirming the trait.

Why Other Options Are Wrong:
Microspora – defined by polar tube spores, not mucous tracks.

Apicomplexa – gliding occurs but without an extracellular slime net; they are obligate parasites.

Myxozoa – multicellular endoparasites with spores; not free-gliding protists.

Sarcomastigophora – broad group; does not specifically denote slime-net gliding.

Common Pitfalls:
Equating any “gliding” with apicomplexans; the mucous network is the diagnostic clue for labyrinthulids.

Final Answer:
Labyrinthomorpha.