Sternoptychidae

Marranzino, Ashley N & Webb, Jacqueline F, 2018, Flow sensing in the deep sea: the lateral line system of stomiiform fishes, Zoological Journal of the Linnean Society 183 (4), pp. 945-965 : 955-956

Family Sternoptychidae

Hundreds of small, round, white, domed structures (~50–100 µm in diameter) were found on the head and body of four species of Argyropelecus ( Table 2; Fig. 6). These are densely placed, with six to eight per millimetre in linear series. They were also found on the caudal fin ( A. hemigymnus ; Fig. 6C) and pectoral fins ( A. aculeatus ). Histology ( A. aculeatus ; Fig. 7C, D ) and SEM (in A. hemigymnus ; Fig. 7F, G ) confirmed that these structures are SNs ( Fig. 7 ). SEM revealed linear series of oval neuromasts with a longer axis parallel to the line in which they are situated. The sensory hair cells have very long kinocilia and are restricted to an area in the centre of each neuromast ( Fig. 7G ). Hair cell orientation is defined by the location of the kinocilium relative to the multiple stereocilia on the surface of each hair cell. Hair cell orientation determines the axis of best physiological sensitivity of the neuromast, which in this case is perpendicular to the line of neuromasts (parallel with the rosto-caudal axis of the fish). Histological analysis of a portion of the head

Neuromast counts in stomiiforms are conservative estimates for one side of head and body in whole preserved specimens. * Sumi et al. (2015).

† Hirota et al. (2015).

‡ Sato et al. (2017).

§ Asaoka, Nakae & Sasaki (2010).

|| Asaoka, Nakae & Sasaki (2012).

¶ Asaoka, Nakae & Sasaki (2014).

( A. aculeatus ; 39-mm standard length, SL) revealed hundreds of SNs (Fig. 6B, 7C, D). An examination of whole preserved specimens revealed that all four species of Argyropelecus demonstrated a similar proliferation and distribution of SNs, with ~220 SNs in one A. lychnus , and ~420 SNs in one A. affinis (Fig. 6A). Variability in specimen condition resulted in notable variation in the number of SNs observed. Comparison of SN number and distributions in multiple specimens of the same species revealed as many as ~356 SNs on one side of the head and body of A. aculeatus (Fig. 6B) and as many as ~521 SNs on one side of the head and body of A. hemigymnus (Fig. 6C; Table 2).

Figures

Figure 7. Superficial neuromasts (SNs) in Argyropelecus spp. A, SNs (arrowheads) rostral to the eye of A. affinis (49-mm SL), see also Figure 6A. B, close-up of SNs (arrowheads) from box in (A), rostral to the eye. C, histological section showing closely placed SNs with nerve innervation (nv) in A. aculeatus on dorsal midline of head. D, close-up of an SN in same general location as (C), showing nerve (nv) innervating SN. E, area rostral to eye in A. hemigymnus (MCZ 150985, 30-mm SL) with lines of closely placed SNs (arrowheads); see also Figure 6C. F, SEM of the same portion of the specimen as in (H) indicating the same SNs (arrowheads). G, close-up of a representative SN (from F) reveals an oval outline with the population of hair cells (with long kinocilia) located in a central, circular area; axis of best physiological sensitivity of the neuromast is rostro-caudal (perpendicular to the line of neuromasts; double-headed arrow). C–G, © President and Fellows of Harvard College.