While working on the Serpulidae two new species of Hydroides were found in the shallow depths of the South China Sea. The description of the two new species are given below. Hydroides rhombobulus sp. nov. (Fig. 1: 1-9)
Holotype 9 mm long by 0.4 mm wide in the region of the thorax. Body consists of thoracic and abdominal setigers. Branchial plume made up of about 12 pinnate filaments. The distal part of the operculum with 20 teeth. Corona consisting of 5-6 large rhomboid valves. The collar setae of two types. The first type is bayonetshaped, with a pair of large conical processes at the base of the blade. The second type of collar setae is hairlike. Thoracic uncini with 7 teeth. Abdominal uncini with a single row oL6 teeth. Abdominal neurosetae trumpet-shaped. The tube is white, sub-trapezoidrul in cross-section with two raised ridges and small growth rings. The tube, together with Bryozoa, is adherent to shell of Pinctada chemnitzi (Philippi).
Remarks Hydroides rhombobulus resembles Hydroides xishaensis Chen et Wu, 1976, in the shape of the operculum. However, H. rhombobulus has rhomboid valves in the corona, and bayonet-shaped setae with a pair of large conical processes, while H. xishaensis has triangular valves, and besides having bayonet-shaped setae with a pair o.f large conical processes there are three small processes at the base of the blade. Hydroides longistylaris sp. nov. (Fig. 2: 1-8)
Holotype 12 mm long by 0.7mm wide in the region of the thorax, Branchial plume with about 15 pinnate filaments. Proximal and distal parts of the operculum are differentiated into the infundibulum and the corona respectively. The infundibulum possesses 21-27 teeth. Corona consisting of 6-9 spines; the wall of the spine is smooth. The collar setae are of two types. The first type is bayonet-shaped setae with 2 conical processes at the base of the blade. The second type is very slender and covered with very fine hair-like processes. Thoracic uncini with 7 teeth. Abdominal setae are trumpet-shaped. Abdominal uncini with 6 teeth, smaller than those of the thorax. The tube is white, with two longitudinal ridges and smaller wavy markings on the dorsal side. The tube is adherent to the shell of Pinctada chemnitzi (Philippi) or Haliotis diversicolor Reeve.
Remarks Hydroides longistylaris is characterized by its short opercular crown and the long opercular stalk.