The image is actually from a set of muster rolls, for which one part of this batch of returns is subtitled, "Discharged." The graphic below is from the same image page listed above, it shows the subheading. (Your man FEITLER was the fourth listed corporal.)

See Ancestry's "Source Description" for "About U.S. Marine Corps Muster Rolls, 1798-1958." Citing James C. Neagles, U.S. Military Records: A Guide to Federal and State Sources, (Provo, UT, USA: Ancestry, 1994)
Muster rolls are lists ... of the names of soldiers assigned to any military unit ... The rolls were made at the time a unit was created (muster-in rolls), when a unit was reorganized, when two or more units were merged, and when a unit was disbanded (muster-out rolls). Names appearing on a muster roll indicate those who were present or accounted for on a given date ...This roll was used as the basis for pay due the soldiers ... Remarks might include information about any individuals absent or deceased ...
I suspect there are separate discharge papers about your marine.
Sadly, it would seem US Marine Corps officials have chosen to move relevant personnel manuals off-line. See, for example, "Marine Corps Personnel Manual (MCPM) (1949)." Note the foia ("Freedom of Information Act") in the URL; then click the link for the big "404 - Page not found." Links like "United States Marine Corps (USMC) Orders and Directives," "USMC Chronologies," and "USMC in WWII" on the "USMC FOIA Reading Room" also returned 404 errors for me.
While the Marines likely had different procedures, the discharge papers in my father's US Army 201 file are quite different than these "muster rolls." Dad was actually honorably discharged twice; the back side of each "discharge" paper includes a summary of service.
Blush, blush, blush. I just realized that in my personal files I have the final discharge papers of two men--my father (1946) and his ancestor, Rev. War patriot, William Preston (1780). Wow. What an honor.
You inquired about "Footnote K"; it can be found in the same batch of images. The image you reference is actually 626; there are footnotes that seem relative to that batch on 629 of 995.

(I was working on a better graphic, may yet pop it up here.)
You inquired about "Spec No"; it is likely aka Specialist Number, which would identify a functional position/job. See "Marine Corps Officer Job Descriptions" (About.com), "Marine Corps unrestricted line officer, limited duty officer, and warrant officer jobs have specific designators, called "Military Occupational Specialties," or MOS. Similar MOS's are grouped together into occupational fields.". This article goes on to list/link to present day Marine Corp "Office Jobs."
While the classifications likely changed, for time relevant usage of the term "specialist number," see the article, "Marine is one of 26 from
company to survive Iwo Jima" (Sauk Valley Media, November 14, 2011)
Oliver Taylor stormed Japan’s Iwo Jima with 284 Marines at his side.
With barely a scratch, the machine gunner sailed back to Hawaii’s
Pearl Harbor with just 25 men, only to be redeployed for a planned
invasion of Japan ... “I was an especially big target, because everyone wants to lick a machine gun man,” Taylor said. “I got that specialist number, and I
couldn’t get rid of it.”
Only somewhat related, in my dad's Army 201 file, the document that served as the authority for his final discharge was called a "Separate Qualification Record," it contains his "Army Serial No" and a list of his assignments, each of which is associated with a "Military Occupational Specialty" that was identified by a title such as "Supply and Evacuation Officer Staff" and a number, like "2100."
You inquired about "sat ser." The reference "U.S. Navy Abbreviations of World War II" didn't include the combined abbreviation. According to that reference "Sat" means "saturated"; in this context, "Ser" would mean "service." (Perhaps someone will find a reference to the combined abbreviation.)
Additional references:
"U.S. Navy Abbreviations of World War II," by asisbiz (asisbiz.com), reportedly "The text of the [Glossary of U.S. Naval Abbreviations which] was prepared shortly after the close of World War II. Transcriber/site owner reports it is "exactly as in the original, except that fifty-nine words which originally appeared in an addenda page have been integrated in the main text of the document." [Wow!]
Julius Augustus Furer, Rear Admiral, USN, Administration of the Navy Department in World War II (1959); electronic typescript version, The Public Library and Digital Archive. Includes the chapter"The United States Marine Corp."
Division of Public Inquiries, Office of War Information, "Department of the Navy," United States Government Manual, 1945; electronic typescript version, The Public Library and Digital Archive.
Patrick Clancy (deceased), "HyperWar: A HyperText history of the Second World War, especially for Links and additional resources, "US Marine Corps in World War II."
According to the Ancestry.com description, the database and digital images that make up, "U.S. Marine Corps Muster Rolls, 1798-1958," come from two National Archives (NARA) collections:
- Muster Rolls of the U.S. Marine Corps, 1798-1892; (National Archives Microfilm Publication T1118, 123 rolls); Records of the U.S. Marine Corps, Record Group 127; National Archives, Washington, D.C.
- U.S. Marine Corps Muster Rolls, 1893-1958; (National Archives Microfilm Publication T977, 460 rolls); Records of the U.S. Marine Corps, Record Group 127; National Archives, Washington, D.C.
See also, Trevor K. Plante, "An Overview of the Records at the National Archives Relating to Military Service" (Prologue: Selected Articles).