(written from a Production point of view)
According to the Star Trek: The Next Generation Companion (3rd ed., p.38), the Ferengi D'Kora-class Marauder design was inspired by a horseshoe crab on Herbert J. Wright's desk. As such it was carried over into the script of "The Last Outpost", where the design was to make its debut, referenced to as "a strange horseshoe crab-like design, a bit smaller than the Enterprise."
Designer Andrew Probert explained his thought processes, when translating the script description into the first new alien ship for the show, "The Ferengi ship I wanted to have, not only an obvious shape difference, but a textural difference as well. The original description of the Ferengi ship ship was a horseshoe crab design with a neck that would extend. The front of the ship I wanted to look fairly dangerous. Something that seems real dangerous-looking to me are the pincers on an earwig insect. I designed the front of the ship to basically have that shape. On the underside of the vessel is a boarding ramp which can be seen when the ship turns around. The back of the ship is basically used for cargo storage seeing how the Ferengi are traders." (Star Trek: The Official Fan Club Magazine issue 60, p. 5) As it so happened, the horseshoe crab design coincided with Gene Roddenberry's dictum of warp engines operating in pairs as Probert reiterated:
"Now, Gene dictated that there are no three-engine starships and no single-engine starships. When I was first designing the new Enterprise he said, "The Federation ship's engines always are co-dependent". It is the same as to say they always worked in twos. So that's why when Sternbach and I came up with the Stargazer, it had two sets of twos. And then I started thinking that, back in World War II, all the nations that had fighter aircraft and airplanes did the same thing: they took off, they flew, they landed, they maneuvered. They usually had one engine, two wings, two tailwings – so they all had the same components, but they all looked different. There was a national design bias to each aircraft, but technically they all did the same thing. So my thinking was in Star Trek – since the Enterprise used to have two engines – I came up with the idea that the engines had to reach out to each other in order to work co-dependently. In other words, there would be no obstructions between the engines to disrupt the energy fields or connecting forces between them. And, well, all the alien ships could look different but still operate in the same principle. So that's why the Ferengi Marauder is curved, is concave, because that allows the two engines to reach each other." wbmFurther clarifying on his design, he commented:
"The Ferengi people were basically space pirates, so I tried to give their ship a threatening look by adding pointed areas at the front, like the back of a pincher bug, and had had it look dirtier and was a little battle-scarred. Then to support the pirate persona, and provide for future episodes, I designed an extendable boarding ramp into the underside of the ship's nose, with a clawed front that would be used on raids. Another feature I designed into the Marauder was a large attack ship nestled into an underside docking cavity. This forward-swept wing "drop ship" could land for planetary raids or maneuver in space. The Marauder's overall length was to have been about 1,200 feet." (Starlog photo guidebook Special Effects, Vol. 5, 1996, pp. 111-112)
Primary studio model Edit
|Construction of the D'Kora-class studio model at Gregory Jein, Inc.|
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As the first new alien starship design for TNG, the intent was faithfully adhered to at Gregory Jein, Inc., when the just founded company constructed the studio model as its first Star Trek commision. Describing the build, model maker and owner of the company, Greg Jein, elaborated, "The Ferengi ship was basically an organic shape, so we chose to carve it out of foam rather than clay. Once the hard foam was vacuformed over it, which gave us a nice removable shell, we detailed those shells with model railroad parts and some pin striping tape. Then the next step to that, was putting the finished pattern into a mold in which we did a fiberglass casting of it which held the armature and the lighting packet." (TNG Season 4 DVD–special feature, "Select Historical Data")
Apart from the below-mentioned articulation, Jein also constructed Probert's drop ship as a detachable piece, so the ship could be filmed with the embedded ship having left, if script requirements ever called for it, which, as it turned out, never would.
The scene where the Ferengi "surrendered" was in the script described as: "The snake head-like prow's pushing out from the ship body," (Scene 21) and (Scene 22): "The Ferengi ship now extends gun-like arms from either side of the prow." Clarifying, Probert put it as follows, "The Marauder's stretching neck...was a locked-in script requirement, to reveal their ship's sensitive areas as their way of surrendering. The writer/producers wanted it to look like a horseshoe crab... [T]he "claws" were a variation of the Klingon disrupter designs from TOS." (remember the metal plates on either side of the "barrel"?"   The "surrender" features were also faithfully translated onto the studio model at Jein's.
The articulated D'Kora-class model (measuring 36"×32") was listed as Lot 710 in the 40 Years of Star Trek: The Collection auction with an estimated sale price of US$4,000 to $6,000. It sold on 7 October 2006 for US$15,000 (US$18,000 with buyer's premium).
After acquirement, the owner sought out professional modeler Richard Long of Sovereign Replicas, in order to have restoration work done on the model. Long had to repair a crack on the ventral side of the model, repair a flaw in the casting and reconstruct the drop ship, as the model came to him without it.  In return for his services, the owner allowed Long to take molds from the model and construct a limited number of non-articulating models from them as payment.  
Other physical studio models Edit
"The only person we could find who was willing to try to build it on our timeline was Greg Jein, who had been working on Star Trek forever. But on top of everything there was supposed to be this articulation – the arms were going to extend out into a threatening posture. Well, of course, we were trying to knock this stuff out in an incredibly short period of time. We're literally talking about a situation where hours made the difference. The Art Department came up with drawings, and Greg did exactly what was required; it was a motion control, articulated ship that had these arms that extended out, but, because of the timeline, that articulation was never really seen on the show. The model worked but it was too time-consuming to shoot it. I remember it had internal lighting, but when we went to articulate the arms it crushed the neon, so the lights all got knocked out right away! Because of the problem with the articulated ship, Greg knocked out an additional version that was literally just a casting that he did in a day. We slapped it on a stick, and that's what we used in the show more than anything else. We did end up with a shot where the arms moved a little bit. Then, when they finally cut the show together and put it on the air, there was almost none of that left either. Then, when they decided the show ran a little bit long, they cut another second; then, if there were any extra commercials, that cuts out the rest of the shot. From then on, we used this shell, and we never used the articulated one again." (Star Trek: The Magazine Volume 3, Issue 1, pp. 61-62)
All the footage taken from the physical studio model(s) were shot at Image G, footage of the faulty model also used in later episodes as stock footage.
A smaller, simplified studio model, cast in resin, painted in a base color with additional weathering, showed up in the Profiles in History Hollywood Auction 40 as Lot 1483. Incorrectly described as a "Screen-used Ferengi ship from Star Trek: Deep Space Nine", measuring 12"×10", and with a mounting rod attached to it. At a first cursory glance it fitted the description Barron gave of the second model. However, one of the above shown behind-the-scene photos, showed a smaller model under construction at Jein's model shop at approximately one-third scale, nicely conforming to the model offered up for auction. Furthermore, the auction description notwithstanding, the apparent lack of detail and lighting made it almost certain that the model was constructed to function as a camera test model, something the description itself hinted at, "It has the attached puppeteer rod and handle that allowed an off-screen handler to manipulate the miniature during flight sequences." (In motion control photography, it is the camera that moves, not the model). Estimated at US$1,000-$1,500, it sold on 12 June 2010 for US$1,400.
CGI model Edit
Making its last appearance in TNG Season 7 episode "Force of Nature", the design was not seen again in the Star Trek franchise for nearly seven years. Its non-appearance in Star Trek: Deep Space Nine is somewhat ironic, as the Ferengi were one of the more regularly-featured species in the series. It was not until the VOY Season 7 episode "Inside Man" that the design was called upon to make another appearance as a protagonist. By that time however motion control photography, using physical studio models, was no longer employed by the franchise as a filming technique, and a CGI model had to be constructed. Visual Effects Supervisor for the episode, Ronald B. Moore, had the studio model shipped over to newly-formed Eden FX as reference for the CGI build, being one of their very first projects as a new company. The studio appeared not to be in a hurry to get the model back, as it resided crated-up in the kitchen of Eden FX for weeks after the episode had finished. (Star Trek: The Magazine Volume 1, Issue 24, p. 54) As the next-to-last existing physical studio model to be translated into a CGI version for a running Star trek television production, the CGI model was built and rendered by Brandon MacDougall, who had moved over from Foundation Imaging, to join the new company.