Haplognathia asymmetrica Sterrer, 1991

Sterrer, Wolfgang, 2006, Gnathostomulida from the Otago Peninsula, southern New Zealand, Zootaxa 1172, pp. 1-19 : 3-5

Haplognathia asymmetrica Sterrer, 1991

(Figs.1.1–1.13, 2.1–2.3)

Material 10 specimens (one adult, and 9 juveniles or anterior fragments) from samples SI 10 and SI 16.

Distribution Hawaii ( Sterrer 1991b), NE Australia ( Sterrer 2001), and (sub)tropical NW Atlantic ( Sterrer 1998).

Description

Colorless­translucent, often with many refractile granula in the intestine. The only adult (Fig. 1.1) was 1710 µm long and 35 µm wide at U 23.4 (index 48.86), with a pointed rostrum 220 µm long and 35 µm wide at U 8.8 (index 6.29). A single mature egg, 185 µm long and 15 µm wide, extended from U 39 to U 50. This specimen contained a bundle of allosperm at about U 25. The paired testes begin at about U 60; paired vasa deferentia open into a glandular male pore situated ventrally, at U 95, 90 µm anterior to the thin tail end.

The basal plate is asymmetric, triangular, 9.5 µm long and 5.7 µm wide (index 1.74). Its dorsal surface bears two longitudinal ridges. Its posterior corner is usually, and its rostrolateral corners are sometimes knob­shaped. Jaws are 22.20 µm long, toothless, compact, with short, horn­shaped rostral apophyses and a transversely oval symphysis. The jaws of one specimen showed grainy degeneration (Fig. 1.7). The pharynx measures 4 µm behind the symphysis.

Discussion

Most similar to H. simplex ( Sterrer, 1969) , this species is easily identified by its asymmetric basal plate. New Zealand specimens are in agreement with records from other localities (jaw lengths: Hawaii 26.67 µm, Australia 22.67 µm, NW Atlantic 21.93 µm) except by having a considerably narrower basal plate, as expressed in the high basal plate index of 1.74 (Hawaii 1.42, Australia 1.17, NW Atlantic 1.21).