Lithacrosiphon cristatus cristatus (Sluiter, 1902)  

The grooved, conical anal shield, sometimes covered with calcareous deposits or algae, is the most notable external characteristic of L. cristatus cristatus. Considered to be a small to medium-sized species, it is commonly 10 – 20 mm in length, but has been reported to reach 38 mm in a few specimens. Found in tropical shallow waters, the species inhabits borings in hard substrata such as coral rubble.