Hyachelia lowryi Serejo and Sittrop, 2009

Yabut, Mia G., Lazo-Wasem, Eric A., Sterling, Eleanor J. & Gómez, Andrés, 2014, New Records of Hyachelia tortugae Barnard, 1967, and H. lowryi Serejo and Sittrop, 2009 (Amphipoda: Gammaridea: Hyalidae), from Palmyra Atoll National Wildlife Refuge: Cooccurrence on Pacific Green Turtles (Chelonia mydas)., American Museum Novitates 2014 (3809), pp. 1-12 : 5-6

Hyachelia lowryi Serejo and Sittrop, 2009

Figures 5B , 6 , and 7

The presence of a whiplike seta on the distal segment of the maxilliped palp (males only) immediately distinguishes the specimen as H. lowryi (figs. 5B and 6). This whiplike seta on the maxilliped can be seen in lateral view of the head without dissection (figs. 1B and 5B). In many of the male specimens examined the large second gnathopods were seen “reversed,” or upside down, reflecting an essentially prehensile condition. Males and females of H. lowryi can be identified by their strongly oblique anterodistal margin of pereopods 6 and 7. These anterior distal margins are covered by seven falcate, robust setae. The morphology of the uropods in H. lowryi is consistent among males and females: both rami are lanceolate and their posterior margins are armed with robust setae (figs. 6D and 6E). Another notable feature limited to males is the broadly convex palm of the gnathopod 1; the anterodistal corner is weakly produced and covered with fine scales. The dactyl length equals that of the palm. In male gnathopod 2 the palm exceeds the length of the dactyl and the proximoposterior corner lacks robust setate.

When encountered together, adults of H. tortugae are generally much larger than H. lowryi . For example, males of H. tortugae are typically 7–8 mm and females are approximately 6–7 mm. Males of H. lowryi are smaller at about 4.5–5.0 mm in length, while females are typically around 4 mm. Although many of the aforementioned characteristics are useful in recognizing both species, the strong sexual dimorphism displayed in H. tortugae and H. lowryi limit several of these characteristics to the males. Females of H. lowryi do not possess the whiplike seta of the maxilliped and neither female Hyachelia species exhibit distinctive gnathopods. However, the diagnostic characters of the pereopods are observable in all adult specimens. Furthermore, the robust setae in the anterodistal corner of the pereopods are not fully developed in very small juveniles of H. tortugae , and their distal margin may appear oblique.

Figures

FIGURE 5. A. Hyachelia tortugae. AMNH 12533–10008–451, male 7.52 mm. B. H. lowryi. AMNH 12533- 11008-002, male 4.86 mm. Scale bars = 0.5 mm.

FIGURE 6. Hyachelia lowryi. AMNH 12533-11008-033, male 5.03 mm. A. Pereopod 6. B. Pereopod 7. AMNH 12533-11008-111, male 5.23 mm. C. Maxilliped. D. Uropod 1. E. Uropod 2.