Heterochondria similis (Yü and Wu, 1932)

Heterochondria similis (Yü and Wu, 1932)

( figure 11 View FIG )

Material examined. Eleven adult ♀♀ (eight with attached ♂) from gill fi laments of Crossorhombus azureus (Alcock) : four collected on 11 March 1994, four on 20 July 1994 and three on 29 April 1994.

Female. Body ( figure 11A View FIG ) elongated, with pinball-shaped trunk and measuring 4.98-6.89 mm long. Head longer than wide, 1.20✕ 1.09 mm (not including inflated antennule), with lateral protrusion in front and large, swollen, oral region in rear. Neck region (first pediger) not marked off from trunk. Trunk region posterior to second pediger enlarged laterally (1.87 mm) and becoming wider than head. Both genital double somite and abdomen ( figure 11B View FIG ) distinctly wider than long. Caudal ramus ( figure 11C View FIG ) a spiniform, pointed process bearing three setae. Egg sac about as long as body.

Antennule ( figure 11D View FIG ) fl eshy, sausage-shaped, and tipped with seven setae. Antenna broken in all specimens examined. Labrum ( figure 11E View FIG ) with smooth posterior margin. Terminal blade of mandible ( figure 11F View FIG ) with a row of 45 teeth on convex (inner) side and a row of 15 teeth on concave (outer) side. Paragnath ( figure 11G View FIG ) a small, spinulose lobe. Maxillule ( figure 11E View FIG ) tipped with two setae. Second segment of maxilla ( figure 11H View FIG ) bearing in basal region a small, simple seta and one large seta with hyaline tip, and a row of about 20 teeth on terminal process. Maxilliped ( figure 11I View FIG ) three-segmented; first segment largest but unarmed; second segment with a large, basal swelling and a spinulose distal lobe; and third segment ( figure 11J View FIG ) a short, stout claw. Leg 1 ( figure 11K View FIG ) and leg 2 ( figure 11L View FIG ) alike and about equal in size; appearing as a large, blunt process covered with fi ne spinules and armed with a long outer seta and a small terminal seta.

Male. Body ( figure 11M View FIG ) 642 μ m long, with swollen cephalosome and cylindrical metasome and urosome. Details of body parts as in H. pillaii . Antennule reduced to a simple seta as in Acanthochondria zebriae . Antenna and mouth parts as in H. pillaii . Leg 1 reduced to a spiniform seta (see figure 11M View FIG ) and leg 2 missing.

Remarks. This is the first record of H. similis since its discovery at Hainan (in the South China Sea) more than half a century ago by Yü and Wu (1932). Of the 21 species of flatfishes examined in our survey, H. similis was found parasitic only on the bluespotted fl ounder ( Crossorhombus azureus ) and it is also the only host from its type locality. Therefore, it is very likely that H. similis is host speci fi c to C. azureus .

In their original description of the present species, the maxilliped of H. similis was stated and illustrated to be`of two joints’ and the`terminal joint’ was`much smaller and divided at tip into two equal lobes.’ Apparently, Yü and Wu (1932) observed the maxilliped in a view as shown here in figure 11I View FIG and did not examine it in a view shown here in figure 11J View FIG . Thus, they stated that the terminal claw was`not seen in the ventral lobe.’

The most outstanding characteristic of the present species is in the general appearance of the body. It is the only species of Heterochondria without a long head and cylindrical trunk. As noted above in the description, it has a pinball-shaped body. Another remarkable distinction is in the shape of the antennule. Its terminal, setae-bearing portion is large, not constricted into a small process protruding at the tip of the tremendously enlarged, basal portion.