|Aculeatus / アクレアツス|
|First appearance||Volume 2, Chapter 10|
|Family||Ventricosus (older sister)
Aculeatus was captured by the Lunarians along with his family and comrades. His older sister makes a deal with them in order to free him.
He first appears as a giant slug with an equally large club-shaped spiny shell. In this form, he is enormous, larger than the Lunarians and taking up a lot of space on their sunspot platform to the point that his movement tips the entire platform. He is black with many green eyes dotting the length of his body. His face also has two circular green eyes and a small triangular mouth. Phosphophyllite described him as "cute" in this form.
His "true form" is smaller and takes a more humanoid appearance. Aculeatus' legs branch down into multiple stumped legs. He has multiple long tendrils protruding from this body which are capable of moving and fighting. He has a black motif, his body is composed of a black fleshy material that appears like clothing much like how his sister appears to have a fancy dress.
Aculeatus is described as "a good-for-nothing except for eating and fighting" by his sister. He is loyal to his species and was eager to use Phos as bait without much concern in order to rescue his family and friends. Despite that, he obeyed his sister in the end when she refused to use Phos as bait and agreed to offer pieces of his shell to replace Phos' lost legs.
- Prior to the beginning of the story, Aculeatus and the rest of the Admirabilis were taken by the Lunarians as livestock. They were fed with sweet water and sand, making them giant, mindless creatures.
- Ventricosus lured Phos into the sea in order to trade the Gem for her brother. During negotiations on the Lunarian's sunspot platform, Aculaetus smelled food and woke up. He fell into the sea where he was able to regain his true form. He fought off the Lunarians and commended his older sister for rescuing him. He suggested they continue to use Phos as a trading chip but she declined, saying that they would be no better than the Lunarians. He broke off two pieces of his shell for Phos to serve as the material for their new legs and accompanied the Gem back to their sea home along with Ventricosus.
Ventricosus is his older sister, who he obeys and has a close relationship with. He considers her the key to being freed from the Lunarians since she was the only one among them who retained their mind.
He is loyal to his comrades, even going as far as sacrificing other species just for them to acquire their freedom as well.
- Aculeatus is derived from the Latin word aculeus, meaning prickly, spiked, or barbed.
- Aculeatus is usually used as the species name in the binomial nomenclature, or scientific name, for certain species. Examples include Abdopus acuelatus ( a species of octopus) or Ruscus aculeatus (butcher's broom, a species of shrubby plant). It used in various Kingdoms not limited to sea species.
- Though it was said the Admirabilis were driven mad, Aculeatus remembers clearly what the Lunarians has done and is in a rather sane state similar to his sister.
- His mini slug form resembles a Dumbo octopus.