Stomiidae

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 : 957

Family Stomiidae

Well-preserved specimens of representative stomiids had SNs appearing as numerous small, white, domed structures (30–40 µm in diameter) arranged in lines that stand out against the darkly pigmented skin of the head and trunk ( Fig. 8G ).

Acknowledging the damage to the epidermis on the head and body, it was determined that ~214 SNs are present on the head and more than 2000 SNs are present on the elongated trunk ( Fig. 8C, G ) of a specimen of I. antrostomus . An assessment of the number and distribution of SNs and small depressions on the skin (see above) provides a conservative estimate of well over 2000 SNs on one side of the head and trunk. A similar number and distribution of SNs was found in a specimen of T. macropus , with ~450 SNs on the head and over 1840 SNs in discrete vertical lines running around the circumference of the trunk, with one line of neuromasts per body segment. Additional SNs were found on the dorsal and ventral surfaces of the trunk and SNs form horizontal lines between the vertical lines found on each body segment (not counted). Thus, a conservative estimate suggests that this specimen of T. macropus has ~2286 SNs on one side of the head and trunk ( Table 2).

Specimens of other stomiids ( A. niger , B. filifer , E. barbatum , E. hulleyi , F. boureei and O. micripnus ) had a damaged epidermis with no evidence of the small, white, domed structures seen in other taxa. However, numerous small depressions were observed on the head and in discrete vertical lines around the circumference of their body (one per body segment, between serial photophores; Fig. 8F ) as in Gonostoma , Idiacanthus and Tactostoma . Histological analysis of one A. niger confirmed the presence of numerous, closely placed SNs in vertical lines on the head ( Fig. 8H, I ). These SNs are smaller than canal neuromasts and morphologically distinct from photophores, which are convex and rise above the surrounding epithelium ( Fig. 8F ). They are densely placed in vertical lines (with as many as 13 in a single vertical row) in the same locations as depressions observed in whole preserved specimens of A. niger (and in other stomiids). This confirms the interpretation that the small depressions in the skin are the locations of SNs that were damaged and lost.

Figures

Figure 8. Superficial neuromasts (SNs) in representative gonostomatids and stomiids. SN distribution in (A) Cyclothone spp. (based on whole preserved specimens of C.acclinidens, C.braueri, C. microdon, C.signata, body outline from Mukhacheva, 1966), (B) Gonostoma elongatum (50-mm SL; canals based on several whole preserved specimens, 50- to 100-mm SL), (C) Idiacanthus antrostomus (79-mm SL; canals based on two whole preserved specimens, 41 and 79-mm SL). Blue – SNs, black – small, complex photophores, open circles – pores and dotted lines – canals. Grey – location of simple photophores. D, Gonostoma elongatum (50-mm SL; rostral to left) with small, white, domed structures (SNs, arrowheads) densely placed in vertical lines that contrast with pigmented epithelium. Small arrows – photophores. E, several body segments [lateral view; boundary defined by vertical line of depressions (arrowheads)] on trunk of G. elongatum (50-mm SL) showing discrete vertical lines of small depressions (locations of damaged SNs) between lines of photophores (small arrows).F, several body segments in lateral view [body segment boundaries defined by vertical lines of depressions, the locations of damaged SNs (arrowheads)] on the trunk of Bathophilus filifer (46-mm SL) between lines of comparably sized photophores. G, several body segments (in latero-ventral view), bounded by vertical lines of small SNs (arrowheads) on trunk of I. antrostomus (79-mm SL; rostral to left) between lines of photophores (small arrows). H, histological section of head of Astronesthes niger (MCZ 52847, 52-mm SL; haematoxylin and eosin stained) showing multiple SNs (arrowheads) over pigment layer.I, close-up of SN in A.niger showing apical sensory hair cell nuclei, more basal support cell nuclei and underlying pigment layer. H, I, © President and Fellows of Harvard College.