Richardson, who nearly came to blows with Marshall last season after a Week 3 loss to the Kansas City Chiefs, took a belated parting shot Tuesday on the first day of OTA practices.
"The locker room is a whole lot easier to get along with now," Richardson told reporters. Asked to elaborate, he smiled and said, "Man oh man, y'all are thirsty. Let's just say I've got 15 reasons why it's better."
That was a reference to Marshall, who wore No. 15.
Marshall requested his release after the season and signed with the New York Giants. He didn't return a message seeking comment.
Marshall did, however, say that the 2016 season was "extremely difficult" in a text message sent to Newsday.
"Last year was an extremely difficult season for all of us," Marshall told the newspaper. "Players and coaches fought their tails off trying to get our season turned around and it didn't happen for us. It was disappointing, but now it's a fresh year for Sheldon, for myself, for the Jets, and now I'm a Giant and I'm so excited for this opportunity.
"I'm working my butt off to learn the plays. It's like I'm starting all over again from scratch. I feel like a rookie, and I kind of like that feeling. And hopefully, I can do my job this year to the best of my ability to bring that Lombardi Trophy back where it belongs. That's my only focus right now and I'm excited to be a New York Football Giant."
The heated altercation between Marshall and Richardson became a turning point in the season, players said. The feud continued throughout the season and might have fractured the locker room.
In December, Marshall publicly chided Richardson for posting a profane Snapchat video from the locker room before a game, and Richardson responded by ripping Marshall to reporters after a Christmas Eve loss to the New England Patriots.
Coach Todd Bowles said he had no reaction to Richardson's comment on Tuesday. Asked whether the locker room chemistry will be better without the outspoken Marshall, Bowles said, "Our chemistry is still developing. We'll see how it goes."
Asked whether Marshall hurt last season's chemistry, Bowles said simply, "No."
The Jets tried to trade Richardson before the draft and still could look to deal him before the midseason deadline. He's coming off a down year (1.5 sacks) and is due to make a guaranteed $8.1 million in the final year of his contract.
Richardson, addressing the trade speculation for the first time, shrugged it off. He said he'd like to remain with the Jets, the team that made him a first-round pick in 2013.
Defensive coordinator Kacy Rodgers said Richardson has "something to prove" this season, expressing hope that using him more in his natural position -- the 3-technique defensive tackle -- will lead to more production.
Richardson didn't exactly agree with his coach's sentiment.
"I'm proven, honestly," he said. "I just have to get more stats. It's my contract year."
Also on Tuesday, Jets safety and former No. 1 pick Calvin Pryor did not show up to the first day of OTAs. Bowles wouldn't comment, saying, "It's voluntary." The Jets drafted two safeties in the first two rounds of this year's draft.