(covers information from several alternate timelines)
Archer IV wildlife
Klingon food animal
Loracus Prime termites
Mirror universe animal
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A bipedal species, from an unknown star system.
This species and their technology were unknown even to the Vulcan database. They chased Enterprise NX-01 in September 2151, and did not respond to hails. Then they returned several other times, causing significant damage. During one attack, this species activated a dampening field, while two of its crew boarded Enterprise. They were fired at by Captain Archer, but a phase pistol he carried had no effect and they soon left. (ENT: "Silent Enemy")
This species was physically designed by Dan Curry. John Teska, who built the CGI models of the aliens for "Silent Enemy", referred to them as "Shroomies" after their mushroom-shaped heads. Other members of the art department, such as Doug Drexler, also used this name. Teska commented, "Some fans out there must know the name of the mysterious aliens from 'Silent Enemy', but I'll only know them as ‘the Shroomies'." (Star Trek: The Magazine Volume 3, Issue 7, p. 52)
"Silent Enemy" writer André Bormanis devised these aliens as highly enigmatic to portray his belief that, in reality, humans would most likely encounter extreme difficulty in establishing communication with extraterrestrials and understanding their motives. ("Silent Enemy" audio commentary, ENT Season 1 Blu-ray) Bormanis revealed, "I wondered whether they might be Romulans until we decided to do a CGI alien effect." He considered that they were not established as Romulans mainly because their technology seemed too advanced for that of 22nd-century Romulans.  The idea that the newly devised aliens would spy on the crew of Enterprise was, said Bormanis, "included to make it clear that, you know, these aliens are really, really insidious." ("Silent Enemy" audio commentary, ENT Season 1 Blu-ray)
The visual effects artists of Star Trek: Enterprise first learned about the species from the script for "Silent Enemy". "Following the lead in André's script," said Dan Curry, "we [...] talked about the alien." The decision that the aliens would be depicted with CGI impacted on considerations such as time and budgetary restrictions. Bormanis recalled that "with respect to the CGI aliens," thought had to be given to questions such as, "How much time can we actually spend with these guys? How many scenes can we have them in?" The answer was, Bormanis stated, "Probably not more than, I don't know, twenty-five or thirty seconds, which, in a way, is a good thing. It's an advantage because it keeps the suspense, I think, at a higher level when you can't see the monster, you know, as often or as soon, so we can hold it back and build some dramatic tension that way." ("Silent Enemy" audio commentary, ENT Season 1 Blu-ray)
Dan Curry began generating concept artwork for the aliens. The availability of CGI allowed the team freedom to avoid designing them as human actors in suits. "We wanted to do something that couldn't possibly be a person in a suit, to enhance its alienness," Dan Curry explained. "And so, when I decided to sit down and sketch out the creatures, it certainly needed humanoid means of conveying itself." Thus, the creatures were made bipedal. "To make it look strange," Curry further elucidated, "we wanted to give it a vertical mouth and with kind of crenelated ribbing ridges around it and wanted to give it a different technology [....] We wanted them to have proper, high-tech-looking clothes that are higher tech than ours, and that they wouldn't necessarily conveniently breath our atmosphere. So, I thought it would be cool to give them space helmets [...] [that] were forcefields rather than physical space helmets [....] I think I was inspired by the roof of the mouth of a hippopotamus for the surface texture of these creatures." ("Silent Enemy" audio commentary, ENT Season 1 Blu-ray) Curry also said of the aliens, "I wanted their skin to be somewhat transparent, like those fish where you can see their internal organs." (Star Trek: The Magazine Volume 3, Issue 7, p. 52)
Devising the appearance of the aliens meanwhile remained a collaborative effort. Dan Curry continued, "Of course, we would show the sketches to Rick Berman and Peter Lauritson and the other producers and André, and see how our designs were working with their vision, and they would of course have feedback. And so, it was a collective project to shape it into what the final version would be." ("Silent Enemy" audio commentary, ENT Season 1 Blu-ray)
Recalling another collaborator, Dan Curry noted, "I worked with John Teska up at Foundation Imaging." (Star Trek: The Magazine Volume 3, Issue 7, p. 52) Teska himself remembered, "I recall Dan Curry brought these sketches and we discussed ways to make their appearance and actions non-human – there should be no mistaking them for actors in costume. I had fun fleshing them out in 3D from the pencil drawings. The skin surface had layers of organic texture as if their heads were filled with organs. You probably would not enjoy eating dinner with one if you were invited… which is very rare indeed." wbm Teska took notice of Curry's concept that the aliens would have transparent skin. "John did a great job in creating a creature like that," Curry remarked, "where it's almost like a jellyfish on the outside and you can see the nerves under the skin." (Star Trek: The Magazine Volume 3, Issue 7, p. 52)
When it came to animating the aliens, it was decided that they should be shown to walk in a different way from how Humans walk. The CGI aliens also had to seem as if they fit naturally into their environments. Remembered Dan Curry, "We made sure that they would cast shadows on the physical set, so that you buy that they're there." ("Silent Enemy" audio commentary, ENT Season 1 Blu-ray)
Dan Curry thought the aliens were a success in general, relating, "I was very happy with those." (Star Trek: The Magazine Volume 3, Issue 7, p. 52) He regarded the aliens as "a testament to the wonderful artistry of" John Teska and his colleagues at Foundation. Curry was particularly pleased with the lighting of the aliens, saying, "If you look at how beautifully the creatures are lit, [...] they feel like they are in that environment." ("Silent Enemy" audio commentary, ENT Season 1 Blu-ray) Similarly, John Teska appreciatively described the aliens as "lovely bulbous-headed beauties." (Star Trek: The Magazine Volume 3, Issue 7, p. 52) André Bormanis said, "I couldn't have been more thrilled with the creatures." He especially approved of how realistic they were. "That's what's great about these guys, is they're creepy and mysterious but they are believable," he observed. "You can believe that this is something that evolution could produce." ("Silent Enemy" audio commentary, ENT Season 1 Blu-ray)
- See also: "Shroomie" starship
In Star Trek Online, this species – called the "Elachi" – play a large role in the Romulan Republic storyline. They are also shown to use identical dimension-gate effects as the solanogen-based lifeforms encountered in TNG: "Schisms", however, they are not implied to be related.
Skagaran colony creatures
Apart from the trophies pictured, there were also at least two hides, a horn, and several more hard-to-see trophies.
Spiked pig-like animal
Xindi Biorifle lifeform
Typically, eel-like engineered lifeforms formed the power sources of such technologies as Xindi-Reptilian biorifles and seekers. Such creatures were capable of reproducing, and thrived when exposed to omicron radiation. However, a sustained burst of delta radiation could kill this type of creature. (ENT: "The Shipment")