The Sepherim.

Origin: Coreward. System unknown.

Currently, three types of Sepherim have been encountered. The largest of these is the "Daimon". Roughly compariable to our own mid-size cruisers, it is on average three kilometers long, with a shape similar to an irregularly flattened cylinder. It appears to have directed energy weapons similar to our own, but its most feared attack involves several long spikes which can be driven into the hull of our ships, locking them together. The Daimon's hull is capable of highly efficient energy and heat dispersal, rendering our laser and plasma weapons useless against them.

The midrange Sepherim is also the most common, and we call them "Djinn". The Djinn are small domes, 20 meters in diameter and five meters high in the center. However, upon close approach, the underside of a Djinn folds open to reveal a set of grasping claws. These claws appear to have monomolecular edges, allowing them to easily slice into our ships. Once there, the Djinn proceeds to break down the hull of its victim, through a combination of intense heat and certain acids. The swallowed material is shunted into an extendable organ on the back of the Djinn.

The smallest Sepherim are the Boarders. Usually between one and one and a half meters tall, they enter through the spines of a Daimon, and then seek out and kill a ship's crew. Boarders have two pairs of legs, a forward projecting "head" that seems to contain the bulk of their sense organs, two large weapons arms with monomolecular blades similar to the Djinn, and two smaller pairs of manipulator arms. Boarders are equipped with a scaled back version of Sepherim armor, but it is adequate for stopping all but the largest personal weapons.

As near as we are able to determine, the Sepherim are identical in terms of chemical composition. Whether they are an intelligent lifeform or simply organic machines is unknown.

hmmm...
Where have I heard those names before.

I like how you worked it out!

Let's see if more people will do a similar thing

"one of a class of spirits that according to Muslim demonology inhabit the earth, assume various forms, and exercise supernatural power"

Daimon, from the Latin. Adopted into English as demon. I trust no explanation is needed.

I'm surprised no one has asked about Sepherim yet.

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"What is he doing?" "Stop it! No heaving, thrusting, or splaying!"

Sepherim is an ancient Hebrew word for a certain type of demon. It means, IIRC, many, or multitude.