diff --git a/Sources/FirebladeECS/Entity.swift b/Sources/FirebladeECS/Entity.swift
index 4f217f5..43c1817 100644
--- a/Sources/FirebladeECS/Entity.swift
+++ b/Sources/FirebladeECS/Entity.swift
@@ -17,19 +17,6 @@ public final class Entity: UniqueEntityIdentifiable {
 	}
 }
 
-// MARK: - Invalidate
-extension Entity {
-
-	public var isValid: Bool {
-		return nexus.isValid(entity: self)
-	}
-
-	func invalidate() {
-		identifier = EntityIdentifier.invalid
-		name = nil
-	}
-}
-
 // MARK: - Equatable
 public func == (lhs: Entity, rhs: Entity) -> Bool {
 	return lhs.identifier == rhs.identifier
diff --git a/Sources/FirebladeECS/ManagedContiguousArray.swift b/Sources/FirebladeECS/ManagedContiguousArray.swift
index ddc8b3a..54a918b 100644
--- a/Sources/FirebladeECS/ManagedContiguousArray.swift
+++ b/Sources/FirebladeECS/ManagedContiguousArray.swift
@@ -14,7 +14,8 @@ public protocol UniformStorage: class {
 	func add(_ element: Element, at index: Index)
 	func has(_ index: Index) -> Bool
 	func get(at index: Index) -> Element?
-	func remove(at index: Index)
+	@discardableResult
+	func remove(at index: Index) -> Bool
 	func clear(keepingCapacity: Bool)
 }
 
@@ -56,7 +57,8 @@ public class ManagedContiguousArray: UniformStorage {
 		return store[index]
 	}
 
-	public func remove(at index: Index) {
+	@discardableResult
+	public func remove(at index: Index) -> Bool {
 		if store[index] != nil {
 			size -= 1
 		}
@@ -64,6 +66,7 @@ public class ManagedContiguousArray: UniformStorage {
 		if size == 0 {
 			clear()
 		}
+		return true
 	}
 
 	public func clear(keepingCapacity: Bool = false) {
diff --git a/Sources/FirebladeECS/Nexus+Component.swift b/Sources/FirebladeECS/Nexus+Component.swift
index 2065c64..0363848 100644
--- a/Sources/FirebladeECS/Nexus+Component.swift
+++ b/Sources/FirebladeECS/Nexus+Component.swift
@@ -30,6 +30,8 @@ extension Nexus {
 	public func assign(component: Component, to entity: Entity) {
 		let componentId = component.identifier
 		let entityIdx = entity.identifier.index
+		let entityId: EntityIdentifier = entity.identifier
+
 		/// test if component is already assigned
 		guard !has(componentId: componentId, entityIdx: entityIdx) else {
 			// FIXME: this is still open to debate
@@ -53,7 +55,6 @@ extension Nexus {
 		componentIdsByEntity[entityIdx]?.add(componentId, at: componentId.hashValue)
 
 		// FIXME: iterating all families is costly for many families
-		let entityId: EntityIdentifier = entity.identifier
 		for (_, family) in familiesByTraitHash {
 			update(membership: family, for: entityId)
 		}
diff --git a/Sources/FirebladeECS/Nexus+Entity.swift b/Sources/FirebladeECS/Nexus+Entity.swift
index e226aa3..79a6219 100644
--- a/Sources/FirebladeECS/Nexus+Entity.swift
+++ b/Sources/FirebladeECS/Nexus+Entity.swift
@@ -7,11 +7,6 @@
 
 extension Nexus {
 
-	public var entities: [Entity] {
-		// FIXME: we do not want this kind of access to the underlying entity store
-		return entityStorage.filter { isValid(entity: $0.identifier) }
-	}
-
 	private func nextEntityIdx() -> EntityIndex {
 		guard let nextReused: EntityIdentifier = freeEntities.popLast() else {
 			return entityStorage.count
@@ -22,49 +17,32 @@ extension Nexus {
 	public func create(entity name: String? = nil) -> Entity {
 		let newEntityIndex: EntityIndex = nextEntityIdx()
 		let newEntityIdentifier: EntityIdentifier = newEntityIndex.identifier
-		if entityStorage.count > newEntityIndex {
-			let reusedEntity: Entity = entityStorage[newEntityIndex]
-			assert(reusedEntity.identifier == EntityIdentifier.invalid, "Stil valid entity \(reusedEntity)")
-			reusedEntity.identifier = newEntityIdentifier
-			reusedEntity.name = name
-			notify(EntityCreated(entityId: newEntityIdentifier))
-			return reusedEntity
-		} else {
-			let newEntity = Entity(nexus: self, id: newEntityIdentifier, name: name)
-			entityStorage.insert(newEntity, at: newEntityIndex)
-			notify(EntityCreated(entityId: newEntityIdentifier))
-			return newEntity
-		}
+
+		let newEntity = Entity(nexus: self, id: newEntityIdentifier, name: name)
+		entityStorage.add(newEntity, at: newEntityIndex)
+		notify(EntityCreated(entityId: newEntityIdentifier))
+		return newEntity
 	}
 
 	/// Number of entities in nexus.
 	public var numEntities: Int {
-		return entityStorage.count - freeEntities.count
-	}
-
-	func isValid(entity: Entity) -> Bool {
-		return isValid(entity: entity.identifier)
-	}
-
-	func isValid(entity entitiyId: EntityIdentifier) -> Bool {
-		return entitiyId != EntityIdentifier.invalid &&
-			entitiyId.index >= 0 &&
-			entitiyId.index < entityStorage.count
+		return entityStorage.count
 	}
 
 	public func has(entity entityId: EntityIdentifier) -> Bool {
-		return isValid(entity: entityId)
+		return entityStorage.has(entityId.index)
 	}
 
-	public func get(entity entityId: EntityIdentifier) -> Entity {
-		return entityStorage[entityId.index]
+	public func get(entity entityId: EntityIdentifier) -> Entity? {
+		return entityStorage.get(at: entityId.index)
 	}
 
 	@discardableResult
 	public func destroy(entity: Entity) -> Bool {
 		let entityId: EntityIdentifier = entity.identifier
-		// FIXME: we can make this cheaper by eliminating the need to ask if entity is present
-		guard has(entity: entityId) else {
+		let entityIdx: EntityIndex = entityId.index
+
+		guard entityStorage.remove(at: entityIdx) else {
 			report("EntityRemove failure: no entity \(entityId) to remove")
 			return false
 		}
@@ -72,12 +50,6 @@ extension Nexus {
 		let cleared: Bool = clear(componentes: entityId)
 		assert(cleared, "Could not clear all components form entity \(entityId)")
 
-		entity.invalidate()
-
-		// replace with "new" invalid entity to keep capacity of array
-		let invalidEntity = Entity(nexus: self, id: EntityIdentifier.invalid)
-		entityStorage[entityId.index] = invalidEntity
-
 		freeEntities.append(entityId)
 
 		// FIXME: iterating all families is costly for many families
diff --git a/Sources/FirebladeECS/Nexus+Family.swift b/Sources/FirebladeECS/Nexus+Family.swift
index 1688188..65a62a5 100644
--- a/Sources/FirebladeECS/Nexus+Family.swift
+++ b/Sources/FirebladeECS/Nexus+Family.swift
@@ -66,7 +66,6 @@ extension Nexus {
 	/// will be called on family init defer
 	func onFamilyInit(family: Family) {
 		// FIXME: this is costly for many entities
-		// FIXME: we iterate invalid entities here
 		for entity: Entity in entityStorage {
 			update(membership: family, for: entity.identifier)
 		}
@@ -87,7 +86,7 @@ extension Nexus {
 		}
 
 		let is_Member: Bool = isMember(entityId, in: family)
-		if !isValid(entity: entityId) && is_Member {
+		if !has(entity: entityId) && is_Member {
 			remove(from: traitHash, entityId: entityId, entityIdx: entityIdx)
 			return
 		}
diff --git a/Sources/FirebladeECS/Nexus.swift b/Sources/FirebladeECS/Nexus.swift
index f26a200..9ad924d 100644
--- a/Sources/FirebladeECS/Nexus.swift
+++ b/Sources/FirebladeECS/Nexus.swift
@@ -13,7 +13,7 @@ public typealias UniformComponents = ContiguousComponentArray
 public typealias UniformEntityIdentifiers = SparseEntityIdentifierSet
 public typealias ComponentIdentifiers = ContiguousArray<ComponentIdentifier>
 public typealias ComponentSet = Set<ComponentIdentifier>
-public typealias Entities = ContiguousArray<Entity>
+public typealias Entities = SparseEntitySet
 public typealias EntityIdSet = Set<EntityIdentifier>
 public typealias FamilyTraitSetHash = Int
 public typealias TraitEntityIdHash = Int
@@ -31,7 +31,6 @@ public class Nexus {
 
 	/// - Index: index value matching entity identifier shifted to Int
 	/// - Value: each element is a entity instance
-	// FIXME: sparse set my be valuable
 	var entityStorage: Entities
 
 	/// - Key: component type identifier
@@ -40,7 +39,6 @@ public class Nexus {
 
 	/// - Key: entity id as index
 	/// - Value: each element is a component identifier associated with this entity
-	// FIXME: this may be refactored to a uniform sparse set
 	var componentIdsByEntity: [EntityIndex: SparseComponentIdentifierSet]
 
 	/// - Values: entity ids that are currently not used
@@ -61,11 +59,12 @@ public class Nexus {
 	}
 
 	deinit {
-		for e in entities {
+
+		for e: Entity in entityStorage {
 			destroy(entity: e)
 		}
 
-		entityStorage.removeAll()
+		entityStorage.clear()
 		freeEntities.removeAll()
 
 		assert(entityStorage.isEmpty)
diff --git a/Sources/FirebladeECS/SparseSet.swift b/Sources/FirebladeECS/SparseSet.swift
index 7c1fcee..3e763ec 100644
--- a/Sources/FirebladeECS/SparseSet.swift
+++ b/Sources/FirebladeECS/SparseSet.swift
@@ -24,6 +24,7 @@ public class SparseSet<Element>: UniformStorage, Sequence {
 	}
 
 	public var count: Int { return size }
+	var isEmpty: Bool { return size == 0 }
 	var capacitySparse: Int { return sparse.capacity }
 	var capacityDense: Int { return dense.capacity }
 
@@ -52,18 +53,19 @@ public class SparseSet<Element>: UniformStorage, Sequence {
 		return dense[sIdx]?.value
 	}
 
-	public func remove(at index: Index) {
+	@discardableResult
+	public func remove(at index: Index) -> Bool {
 		guard has(index) else {
-			return
+			return false
 		}
 		guard let removeIdx: DenseIndex = sparse[index] else {
-			return
+			return false
 		}
 		let lastIdx: DenseIndex = count - 1
 		dense.swapAt(removeIdx, lastIdx)
 		sparse[index] = nil
 		guard let swapped: Pair = dense[removeIdx] else {
-			return
+			return false
 		}
 		sparse[swapped.key] = removeIdx
 		dense.removeLast()
@@ -71,6 +73,7 @@ public class SparseSet<Element>: UniformStorage, Sequence {
 		if size == 0 {
 			clear(keepingCapacity: false)
 		}
+		return true
 	}
 
 	public func clear(keepingCapacity: Bool = false) {
@@ -105,6 +108,10 @@ public class SparseSet<Element>: UniformStorage, Sequence {
 
 // MARK: - specialized sparse sets
 
+public class SparseEntitySet: SparseSet<Entity> {
+	public typealias Index = EntityIndex
+}
+
 public class SparseEntityIdentifierSet: SparseSet<EntityIdentifier> {
 	public typealias Index = EntityIndex
 
diff --git a/Tests/FirebladeECSTests/FamilyTests.swift b/Tests/FirebladeECSTests/FamilyTests.swift
index 57ca96d..38da168 100644
--- a/Tests/FirebladeECSTests/FamilyTests.swift
+++ b/Tests/FirebladeECSTests/FamilyTests.swift
@@ -144,7 +144,7 @@ class FamilyTests: XCTestCase {
 
 		var countA: Int = 0
 		familyA.iterate(components: Position.self) { (entityId, _) in
-			let e = nexus.get(entity: entityId)
+			let e = nexus.get(entity: entityId)!
 			e.assign(Velocity(a: 3.14))
 			e.remove(Position.self)
 			countA += 1
@@ -153,7 +153,7 @@ class FamilyTests: XCTestCase {
 
 		var countB: Int = 0
 		familyB.iterate(components: Velocity.self) { eId, velocity in
-			let e = nexus.get(entity: eId)
+			let e = nexus.get(entity: eId)!
 			e.assign(Position(x: 1, y: 2))
 			e.remove(velocity!)
 			countB += 1
diff --git a/Tests/FirebladeECSTests/NexusTests.swift b/Tests/FirebladeECSTests/NexusTests.swift
index 8917230..cb0d498 100644
--- a/Tests/FirebladeECSTests/NexusTests.swift
+++ b/Tests/FirebladeECSTests/NexusTests.swift
@@ -24,51 +24,20 @@ class NexusTests: XCTestCase {
 
 		let e0 = nexus.create()
 		XCTAssert(e0.identifier.index == 0)
-		XCTAssert(e0.isValid)
 		XCTAssert(nexus.numEntities == 1)
 
 		let e1 = nexus.create(entity: "Named e1")
 		XCTAssert(e1.identifier.index == 1)
-		XCTAssert(e1.isValid)
 		XCTAssert(nexus.numEntities == 2)
 
 		XCTAssert(e0.name == nil)
 		XCTAssert(e1.name == "Named e1")
 
-		let rE0 = nexus.get(entity: e0.identifier)
+		let rE0 = nexus.get(entity: e0.identifier)!
 		XCTAssert(rE0.name == e0.name)
 		XCTAssert(rE0.identifier == e0.identifier)
 	}
 
-	func testDestroyAndReuseEntity() {
-		let nexus: Nexus = Nexus()
-		XCTAssert(nexus.numEntities == 0)
-
-		let e0 = nexus.create(entity: "e0")
-		XCTAssert(e0.isValid)
-		XCTAssert(nexus.numEntities == 1)
-
-		let e1 = nexus.create(entity: "e1")
-		XCTAssert(e1.isValid)
-		XCTAssert(nexus.numEntities == 2)
-
-		e0.destroy()
-
-		XCTAssert(!e0.isValid)
-		XCTAssert(e1.isValid)
-		XCTAssert(nexus.numEntities == 1)
-
-		let e2 = nexus.create(entity: "e2")
-		XCTAssert(!e0.isValid)
-		XCTAssert(e1.isValid)
-		XCTAssert(e2.isValid)
-
-		XCTAssert(nexus.numEntities == 2)
-
-		XCTAssert(!(e0 == e2))
-		XCTAssert(!(e0 === e2))
-	}
-
 	func testComponentCreation() {
 		let nexus: Nexus = Nexus()
 		XCTAssert(nexus.numEntities == 0)
@@ -80,7 +49,6 @@ class NexusTests: XCTestCase {
 		e0.assign(p0)
 		e0.assign(p0)
 
-		XCTAssert(e0.isValid)
 		XCTAssert(e0.hasComponents)
 		XCTAssert(e0.numComponents == 1)
 
@@ -93,7 +61,7 @@ class NexusTests: XCTestCase {
 		let nexus = Nexus()
 		let identifier: EntityIdentifier = nexus.create(entity: "e0").identifier
 
-		let e0 = nexus.get(entity: identifier)
+		let e0 = nexus.get(entity: identifier)!
 
 		XCTAssert(e0.numComponents == 0)
 		e0.remove(Position.self)
@@ -134,7 +102,6 @@ class NexusTests: XCTestCase {
 		e0.destroy()
 
 		XCTAssert(e0.numComponents == 0)
-		XCTAssert(!e0.isValid)
 
 	}