Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† hŏlŏthūrĭa, ōrum, n., = ὁλοθούρια, τά, a sort of water-polype, Holothuria priapus, Linn.; Plin. 9, 47, 71, § 154.