Photostomias guernei Collett 1889

Photostomias guernei is an asynchronous vertical migrator, erratically moving from the mesopelagic during the day to the epipelagic at night (Sutton and Hopkins, 1996a; Kenaley, 2008). Like other species of the genus, P. guernei specializes in consuming sergestid shrimps (Sutton and Hopkins, 1996b)

Ultimostomias mirabilis Beebe, 1933: 174-175, Fig. 1.8 (original description; holotype USNM 170932, 12 mi. south of Nonsuch I., Bermuda, 900 fm, 24 June 1929); Morrow, 1964: 529-531 (description).

Photostomias mirabilis: Harold, 2003: 903 (new combination; synonymy; distribution).

Data for P. guernei in the Catalog of Fishes

Body elongate, depth tapering slightly from cleithrum (5.5–12.3% SL) to anal-fin origin (3.3–7.6% SL), and more abruptly toward peduncle (1.3–2.3% SL). Soft keel along ventral midline from last IP photophore to anus. Caudal peduncle short (2.0–4.0% SL) and shallow (1.3–2.3% SL). Head small (5.2–9.8% SL). Jaws elongate (12.1–24.6% SL) extending far behind fleshy orbit. Fleshy orbit large (11.1–29.7% JL). Snout blunt and short (11.4–22.5% JL). Opercular flap long and sloping posteroventrally to posterior tip of jaw. Soft fleshy ridge present along posterior portion of isthmus, terminating on body as a small tab where posterior end of lower jaws rests when closed. Nostril facing forward on snout; a round anteroventral opening about one–third width of ovular upper dorsolateral opening. Tip of basihyal with a white, fleshy, nautilus-shaped tab. Branchiostegal rays 10-13.

All teeth fixed and curved posteriorly. Dentary teeth numerous (17–94) and variable in size, most anterior pair slender and barbed, enormous (9.6–28.8% JL) and negatively allometric; posterior teeth moderate and smaller, unbarbed. Premaxillary teeth small to moderate, less numerous (5–11) and variable in size; second anteriormost tooth, or that positioned under fleshy orbit, longest and barbed (4.4–15.2% JL). Maxillary teeth small, numerous (3–31), positively allometric; anterior maxillary teeth smaller, posterior teeth larger. Palatine teeth in one group on each side with 1–10 teeth per group. Basibranchial teeth placed dorsolaterally in two or three groups on each side, depending on species, with 1–7 teeth per group; developed by 27 mm. The more common condition being three groups, a group positioned at posterior end of basibranchials of first, second, and third arches. Those with two groups have a group positioned at posterior end of basibranchials of second and third arches. Pharyngobranchial teeth in two groups on each side; anterior group with 2–11, posterior with 2–13. Gill rakers 4–13, as patches of small tack-like teeth or as a single tooth.

Pectoral fin absent in transformed specimens larger than about 27 mm; present in larvae up to 30 mm as large, paddle-shaped, stalked fin, gradually lost during transformation. Pelvic fins elongate (36.8–52.3% SL); pelvic-fin rays 6, proximal ray flattened and separate from remaining five elongate rays, placed at about mid-body; prepelvic length 37.2–47.0% SL. Dorsal and anal fins placed far back on body and nearly opposite, predorsal length 72.0–85.8% SL, preanal length 71.1–83.5% SL. Dorsal-fin base 1.01–1.25 times in anal-fin base. Dorsal-fin rays 22–26, anal-fin rays 27–30. Anteriormost rays of dorsal and anal fins small and tightly spaced, often obscured by a thin layer of skin. Caudal fin small and forked. Total vertebrae 54–57, precaudal vertebrae 35–38.

Three head photophores near orbit: AO, SO, and PO. AO small to large in specimens greater than 60 mm (4.5–21.7% fleshy orbit), oblong, and positioned at anteroventral edge of fleshy orbit; sexually dimorphic, obvious in males, smaller and subcutaneous in females. SO small, round and situated on mid-orbital ventral margin in an elongate pocket with both a lateral and larger dorsomedial opening, color deep red in fresh specimens. PO moderate to large in specimens greater than 60 mm (45.5–144.5% fleshy orbit), an elongate triangle pointing posteriorly, placed posterior to fleshy orbit with lower edge aligned with ventral margin of fleshy orbit; size varying with sex and between species. Color of PO pinkish-purple in fresh specimens. Small photophores and unorganized areas of accessory white luminous tissue scattered over head and body, often arranged around lateral photophores or along dark vertical lines composed of minute photophore-like structures. One patch of luminous tissue below each ventral nostril.

IP 7, last two close together; PV 12–17, separated from IP by a space equal to width of 3–5 photophores; VAV 20–25, separated from PV by a space equal to width of 4–6 photophores, last 2–3 photophores over anal base; AC 12-–16, elevated at level of VAL and separated from them by a space equal to width of 4–7 photophores, first AC directly over last VAV. OV 13–17, arched anteroventrally, ventralmost (first) photophore becoming obscured in larger specimens; VAL 19–23, separated from OV by a space equal to width of 4–6 photophores. A single small photophore placed approximately at mid-point of opercular flap on margin of operculum.

Skin thin, scaleless; color in alcohol black, fading to dark brown after lengthy preservation.

Photostomias guernei is distinguished from all other species of the genus based on the following: two pairs of basibranchial tooth patches; dorsal-fin rays 23–26, anal-fin rays 27–30, sum of dorsal- and anal-fin rays [50]51–55[56]. Male PO moderate, in specimens greater than 60 mm, 45.5–144.5% fleshy orbit, 7.8-28.1% JL. Male AO moderate, in specimens greater than 60 mm, 4.5–21.7% fleshy orbit, 0.8–4.9% JL.

Temperate and northern subtropical waters of the North Atlantic, including the Gulf of Mexico, south to 03^˚58'N in the eastern Atlantic

Sequences on GenBank for P. guernei.

Mesopelagic during the day, epipelagic at night.

Kenaley C, Hartel K. 2005. A revision of Atlantic species of Photostomias (Teleostei: Stomiidae: Malacosteinae), with a description of a new species. Ichthyological Research 52(3):251–263.

Perhaps the most conspicuous aspect of this species morphology is the lack of a floor to the mouth (i.e., the "loosejaw" condition). This character, which is shared with all other species of Photostomias and species of the genera Malacosteus and Aristostomias, would seem to inhibit the ability to capture prey. It is possible, however, that the lack of an intermandibular membrane affords these species some hydrodynamic advantage important in capturing their prey (see Günther and Deckert, 1959).

Günther K, Deckert K. 1959. Morphologie und Funktion des Keifer- und Kiemenapparates von Tiefseefishcen der Gattungen Malacosteus und Photostomias (Teleostei, Isospondyli, Stomiatoidea, Malacosteidae). Dana Report 49:1–54.

Kenaley CP. 2008. Diel vertical migration of the loosejaw dragonfishes (Stomiiformes: Stomiidae: Malacosteinae): a new analysis for rare pelagic taxa. Journal of Fish Biology 73(4):888–901.

Sutton TT, Hopkins TL. 1996a. Species composition, abundance, and vertical distribution of the stomiid (Pisces: Stomiiformes) fish assemblage of the Gulf of Mexico. Bulletin of Marine Science 59(3):530–542.

Sutton TT, Hopkins TL. 1996b. Trophic ecology of the stomiid (Pisces: Stomiidae) fish assemblage of the eastern Gulf of Mexico: strategies, selectivity and impact of a top mesopelagic predator group. Marine Biology 127(2):179–192.

The sexual dimporphism of the AO and PO suggest that these organs function is intraspecific sexual communication.

To 125 mm SL.

This species consumes species of sergestid shrimps almost exclusively (Sutton and Hopkins, 1996b).

Azores, 38°34'N, 30°43'W, Hirundelle Sta. 111, 0-1138 m, 30 June 1887.

Holotype: MOM 0091-005.