Porifera, more commonly known as sponges, are animals that make up a phylum of the Kingdom, Animalia (Animal). This phylum contains the most of the main/major characters and all of the other animals on the show.
This is the most common look of sponges in the series. The sponges that are square are SpongeBob, Grandpa SquarePants, Primitive Sponge, SpongeBob's Grandson, Stanley, Sherm, the Drifter, Girly Teengirl, SpongeTron, SpongeGar, SpongeBuck, Todd, and the sponge on the New Sponge billboard. All but Sherm have a long nose.
This is the most common look of the square sponges in the series. The sponges that are square are SpongeBob, Grandpa SquarePants, Primitive Sponge, SpongeBob's Grandson, Sherm, the Drifter, Girly Teengirl, SpongeTron, and SpongeGar, SpongeBuck, Todd, and the sponge on the New Sponge billboard.
They are all vertical rectangular shaped.
This is the most common color of the short square sponges. The sponges that are yellow are SpongeBob, Grandpa SquarePants, Primitive Sponge, SpongeBob's Grandson, Sherm, the Drifter, Girly Teengirl, SpongeTron, and SpongeGar, SpongeBuck, and Todd.
The only sponge that is green is the sponge on the New Sponge billboard.
The only sponge that is tall is Stanley S. SquarePants. Unlike the short square sponges, he has a vertical rectangular head and a skinny body. He is yellow with olive green holes.
The sponges that are round are Blue SquarePants, Harold SquarePants, Grandma SquarePants, Margaret SquarePants, and BlackJack.
The only sponge that is brown is Harold SquarePants.
The sponges that are tan are Blue SquarePants, Grandma SquarePants, Margaret SquarePants, and BlackJack.
The first known SpongeBob family member was Primitive Sponge. He was the first known family member to be friends with a member of the Star family, Primitive Star.
Several generations later, there was a member known as SpongeGar. He was the first known family member to be friends with a Tentacles Family member, Squog. He is also the first known family member to own a member of Gary's family as a pet.
Sometime between SpongeGar and SpongeBuck, a member left the place now known as Bikini Bottom.
SpongeBuck arrived by train to a town called Dead Eye Gulch, one of Bikini Bottom's former names. He soon met Pecos Patrick, Mr. Krabs, Polene Puff, Hopalong Tentacles, and Dead Eye Plankton, the "mayor" of the town. Dead Eye was a cruel creature who drove out of town or killed all the sheriffs in the town. SpongeBuck, looking for the fry cook position, was given the sheriff position because the advertisement that SpongeBuck had shown Mr. Krabs, the creature who bestows the position of fry cook and sheriff, had a large advertisement for the sheriff's position. At first, SpongeBuck was driven out of town by Dead Eye, but after Pecos Patrick gave SpongeBuck a pep talk, SpongeBuck saved the town from Dead Eye by accidentally stepping on him, which none of the citizens had thought of. The town was then renamed back to Bikini Gulch, the former name of Dead Eye Gulch before Dead Eye took over. SpongeBuck was given a statue, made out of Dead Eye's gold, and the fry cook position.
Several Generations later, there was a member known as "Grandpa SquarePants". The only thing that is known about him is that he gave out good advice. The two most notable pieces are "If we were meant to fly, we'd have propellers on our heads and jet engines on our backs." and "Never run for a bus, especially one that's going up at a 90-degree angle." He married a female sponge now known as "Grandma SquarePants". With her, he had at least 6 children.
Grandma SquarePants is the oldest living SquarePants family member. She lives alone in a cottage. She is most known for baking, in SpongeBob's words, "the best cookies in the deep blue sea.,
Sherm is a son of Grandma and Grandpa SquarePants. The only known things about him are that he can stick a watermelon up his nose and he has a son named "Stanley S. SquarePants".
Stanley S. SquarePants, the son of Sherm, is a sponge that cannot do anything right.
Blue SquarePants, son of Grandma and Grandpa SquarePants, is a former police chief that lives next to his nephew, BlackJack.
BlackJack is a sponge that was arrested and eventually released, for littering. When he and SpongeBob were children, BlackJack would beat up SpongeBob.
Todd is a sponge that came to live with his cousin, SpongeBob, for a few weeks.
Larry is one of SpongeBob's cousins.
Harold, son of Grandma and Grandpa SquarePants is a father and husband. According to SpongeBob's thoughts, he works or at least used to work at an office. He married Margaret and had SpongeBob with her.
Margaret SquarePants, formerly Margaret BubbleBottom, is the wife of Harold SquarePants and the mother of SpongeBob SquarePants.
SpongeBob SquarePants, the son of Harold and Margaret SquarePants, is the fry cook at the Krusty Krab and the main character of the series.
SpongeBob will have a grandson without a known name. He will listen to at least one of SpongeBob's stories but will be bored of it and more involved in his video games.
Several generations later, about 2000 years after SpongeBob's time, there will be a new robotic member known as SpongeTron who is an employee at the Krusty Krab in a Chrome Bikini Bottom.
The first known family member, Primitive Sponge, had an arched back, two saber teeth, wore a brown cloth, his mouth was wide, he had a chin, a prominent forehead, and flat cheeks with three freckles on each. He also had an almost straight nose which was yellow with light olive holes, had skinny appendages, and two eyes.
Several generations later, SpongeGar had a straighter back, the teeth of Primitive Sponge were replaced by a single tooth in the middle of SpongeGar's face, he wore cloths more like clothing, he had a smaller chin, his forehead was not as prominent, and a unibrow was present. Everything else remained the same.
Several generations later, the tooth of SpongeGar was replaced by two buckteeth, he wore clothing, he had an even smaller chin, his forehead was even less prominent, the unibrow of SpongeGar was no longer there, SpongeBuck had three eyelashes on each eye, his cheeks were much more prominent, and his nose was more arched. Everything else remained the same.
A few generations later, not much is known about the teeth of Grandpa SquarePants as he has only appeared old, the only thing we know is that he had at least one bottom tooth, nothing is known about his chin, forehead, or cheeks. Unlike SpongeBuck, he has eyebrows, which are thick and cloud-shaped. Everything else remained the same or almost the same.
Every known generation, up to Grandpa SquarePants appears to have been purely square Sponge, but some time before Grandma SquarePants, a common ancestor of her and Margaret SquarePants, was brown and round.
Grandma SquarePants is round and tan with brown holes. She has a triangle of puffy hair, her nose is somewhat arched, she does not have eyebrows and might not have eyelashes either, and, like her husband's family, she has skinny appendages. Her eye color could either be green or brown as two of her children, Sherm, has brown eyes, and Blue has green eyes. She does not have cheeks or at least has flat cheeks without freckles.
There are three known children of Grandma and Grandpa SquarePants:
Harold SquarePants: Like his mother he is round, however, he is darker brown than her. Unlike both of his parent, he has a large nose that appears to be on his face, instead of protruding outward. He also has lighter holes than his mother, but still darker than his "skin". His eye color could either be green or brown as two of his brother, Sherm, has brown eyes, and Blue has green eyes. Unlike his father, he has a mustache. Like his mother, he does not eyebrows. Like his mother, he does not have cheeks or at least has flat cheeks without freckles Everything else is the same. However, in later seasons, he has long feet.
Sherm SquarePants: Like his father, he is square, yellow with olive green holes, has three eyelashes, possibly unlike his father, has at least six prominent teeth, on or above his nose, are some holes. Not much is known about his nose because it was seen with a watermelon in it, all that is known is that he can stick a watermelon up it. Unlike his father and possibly his mother, he has brown eyes. Everything else is the same. Possibly like his father, he has prominent cheeks with freckles.
Blue SquarePants: Like his mother, he is round and tan, however, his holes are lighter than her holes. Possibly like his father, he has prominent cheeks with freckles. Like his father, he has eyebrows, however, they are a lot thinner. Unlike his father and possibly like his mother, he has green eyes. Possibly like his father, he has prominent cheeks with freckles.
Margaret SquarePants, wife of Harold SquarePants, is tan and round with dark tan holes. Unlike her husband's family (except Stanley, BlackJack, and Grandma SquarePants), she has a full head of hair. She has three eyelashes one each eye, blue eyes, a small nose that sort of arches, and prominent cheeks with three freckles. She also has skinny appendages.
SpongeBob, son of Harold and Margaret SquarePants, is square and yellow with olive green holes. Like his mother, he has three eyelashes on each eye, prominent cheeks with three freckles, and his eyes are blue. He has a somewhat straight nose, but also droops down on his face when he is sad, like his father's nose is normally. He has a wide mouth with two buck teeth.
Stanley S. SquarePants, son of Sherm SquarePants, is yellow and has a square head with olive green holes like his father. Like his father, he has skinny appendages and prominent cheeks with three freckles. Unlike his father and most likely his mother, he has blue eyes, eyebrows, a full head of hair, does not have eyelashes, and is tall.
Todd, grandson of Grandma and Grandpa SquarePants, is square and yellow with olive green holes. His nose is protruding and is fairly straight. He has blue eyes, slightly curling upwards, a pointy beard, and thick black eyebrows. He also wears glasses similar to the ones that SpongeBob wears when Jellyfishing, but with round lenses instead of squarish ones.
The Drifter's family
Not much is known about this family. The only known member is the Drifter, a sponge who appeared at The Salty Spitoon and was thought to be SpongeBob by its bouncer, Reg.
Not much is known about this family. The only known family member is Girly TeenGirl, a sponge who appeared at Mr. Krabs' House during Pearl's sleepover. Pearl thought that Girly was SpongeBob in disguise, working for Mr. Krabs, who was kicked out to avoid trouble. 
SpongeGar lived in a primitive pineapple. He lived with his snail Gary.
Grandma SquarePants lives alone in a cottage.
Blue and Harold and Margaret live in metal houses.
BlackJack lives in a wooden house with his pet worm.
SpongeBob lives in a pineapple at the address 124 Conch Street. He lives with his pet snail, Gary.
Although it has not been confirmed, SpongeBob's grandson might also live in the pineapple with or instead of SpongeBob in the future.
As SpongeBob once said, in real life, sponges do filter-feed. However, in the show, they are able to consume many things.
SpongeGar was able to eat a large amount of plants and non-living things, such as sand once he and his friends discovered fire.
SpongeBuck was known to have made chili that tasted bad to at least Mr. Krabs.
Grandma SquarePants is best known for her cookies. She has also appeared with a cake. Her kitchen also contains a bowl of what might be food balls.
Blue was seen with a fruit juice.
Harold, Margaret, and SpongeBob have all appeared eating Krabby Patties.