Organism that structurally resembles another organism

Wiktionary Word definitions in Wiktionary
n. Anything that exhibits isomorphism

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Isomorph \I"so*morph\, n. [See Isomorphous .] A substance which is similar to another in crystalline form and composition. (Biol.) An animal, plant, or group having superficial similarity to another, although phylogenetically different.

Wikipedia Word definitions in Wikipedia
An isomorph is an organism that does not change in shape during growth. The implication is that its volume is proportional to its cubed length, and its surface area to its squared length. This holds for any shape it might have; the actual shape determines ...