Diceratiidae

Introduction

While appearing superficially like himantolophids or basal oneirodids, especially members of the genus Oneirodes, metamorphosed specimens of the deep-sea ceratioid anglerfish family Diceratiidae are unique among all other members of the suborder in having a second light-bearing, dorsal-fin spine emerging from the head directly behind the base of the illicium. On that basis alone they cannot be confused with any other family. Although easily recognized, specimens of diceratiids are rare; the systematics of the family is based almost solely on metamorphosed adolescent females. Only two larvae, one sexually mature female, and one metamorphosed male are known. Differences in illicial length and pterygial insertion and morphology are diagnostic at the generic level, but escal morphology is the only diagnostic character complex at the specific level. Consequently specimens with missing or damaged escae are impossible to identify. Two genera and six species are currently recognized.

Characteristics

Diagnosis 

Metamorphosed females of the family Diceratiidae are distinguished from those of all other ceratioid families by having an externally exposed second cephalic spine, bearing a distal light organ, emerging from the head immediately behind the base of the first dorsal-fin spine (illicium), highly conspicuous in smaller specimens (less than about 30 mm), withdrawn inside a narrow cavity in larger specimens (see Uwate, 1979:134, fig. 11). Metamorphosed females are further differentiated by having the following combination of character states: supraethmoid present; frontals widely separated, each with a prominent ventromedial extension; parietals present; sphenotic spines well developed; pterosphenoid reduced; metapterygoid and mesopterygoid present; hyomandibular with a double head; hypohyals 2; branchiostegal rays 6 (2 + 4); opercle bifurcate; subopercle without posterior notch, anterior margin of ventral part with well-developed spine; quadrate and articular spines present; angular and preopercular spines absent; jaws subequal, lower jaw extending anteriorly slightly beyond upper jaw; lower jaw with well-developed symphysial spine; postmaxillary process of premaxilla absent; anterior-maxillomandibular ligament present; pharyngobranchial I rudimentary; pharyngobranchials II and III well developed and toothed; pharyngobranchial IV absent; epibranchial I well developed; hypobranchials I-III present; a single ossified basibranchial; epibranchial and ceratobranchial teeth absent; epibranchial I free, not bound to wall of pharynx by connective tissue; proximal two-thirds of ceratobranchial I bound to wall of pharynx, distal one-third free; distal end of ceratobranchial I not bound by connective tissue to adjacent ceratobranchial II; proximal one-quarter to one-half of ceratobranchials II-IV not bound together by connective tissue; epurals absent; hypural plate entire, without posterior notch; pterygiophore of illicium bearing two spines, illicium and second cephalic spine; escal bulb and central lumen present, esca without tooth-like denticles; posteroventral process of coracoid absent; pectoral radials 3; pelvic bones slightly expanded distally; dorsal-fin rays 5-7; anal-fin rays 4 (very rarely 5; of 69 specimens counted, only one, the holotype of Diceratias trilobus, had 5 anal rays; see Balushkin and Fedorov, 1986); pectoral-fin rays 13-16; pelvic fins absent; caudal rays 9 (very rarely 8; of 69 specimens counted, only one had 8 caudal rays), 1 simple + 6 bifurcated + 2 simple; skin, including that of illicium and proximal half of escal bulb, covered with small dermal spinules; ovaries paired; pyloric caeca absent.

Metamorphosed males (a single known juvenile specimen, 14 mm SL) differ from those of all other ceratioid families in having the following combination of character states: eyes and nostrils large, directed lateral; parietals, hyomandibular, subopercle, pectoral radials, and pelvic bones as for females; a single pair of denticular teeth on snout; two transverse series of denticular teeth on lower jaw, each containing 4 or 5 separate teeth; fin-ray counts as given for metamorphosed females; skin covered with small dermal spinules (Bertelsen, 1983:310, fig. 1); free-living, apparently never parasitic (see Pietsch, 2005).

Larvae (two known specimens, both females, 7-10.5 mm SL) differ from those of all other ceratioid families in having the following combination of character states: body short, globose, nearly spherical; length of head approximately 60% SL; skin highly inflated; pectoral of normal size, not extending posteriorly to base of dorsal and anal fins; pelvic fins absent; fin-ray counts as given for metamorphosed females (Bertelsen, 1951:67, 69, fig. 28; 1984:330, fig. 169E).

Description

Metamorphosed females with body short, globular, depth approximately 50% SL; mouth large, cleft extending past eye, opening oblique; oral valve well developed, lining inside of both upper and lower jaws; two nostrils on each side at end of a single short tube; jaw teeth slender, recurved, and depressible, arranged in overlapping sets (as described for other ceratioids; see Pietsch, 1972b); number of teeth in lower jaw 14-65, in upper jaw 12-99; vomerine teeth 4-15; epibranchial I free from wall of pharynx; epibranchial I free from wall of pharynx; epibranchials I-IV closely bound together; proximal two-thirds of ceratobranchial I bound to wall of pharynx, distal one-third free; epibranchial IV and ceratobranchial IV bound to wall of pharynx, no opening behind fourth arch; gill filaments absent on epibranchials, present on proximal tip of ceratobranchial I, full length of ceratobranchials II and III, and distal three-quarters of ceratobranchial IV; pseudobranch absent; length of illicium of females highly variable, 26-47% SL in Diceratias, 83-225% SL in Bufoceratias; anterior end of pterygiophore of illicium exposed, emerging on snout (Diceratias), or concealed beneath skin of head, illicium emerging on back at rear of skull (Bufoceratias); posterior end of pterygiophore of illicium concealed beneath skin of head; second cephalic spine (second dorsal-fin spine) with a distal light organ, emerging from dorsal surface of head just behind base of illicium, tending to sink beneath skin of the head with age, but remaining connected to the surface through a small pore; lumen of escal bulb connected to outside by a pore located on posterior margin of base of terminal escal papilla; internal pigment of escal lumen visible in lateral view; basal half of escal bulb usually covered with dark pigment; numerous, small, rounded, darkly pigmented papillae on head and body associated with acoustico-lateralis system, each with an unpigmented distal tip (Regan and Trewavas, 1932:23), pattern of placement as described for other ceratioids (Pietsch, 1969, 1972, 1974a, 1974b).

Metamorphosed males (a single known specimen, 14 mm SL) with eyes 1.2 mm (8.6% SL) in diameter, a narrow aphakic space surrounding lens; olfactory organs well separated from eye, vertical diameter of posterior nostrils about 0.5 mm, larger than anterior nostrils; number of olfactory lamellae less than 10 (no exact count possible); frontals broad, meeting on midline; parietals present, relatively small, crescent shaped, anterior tips touching posterior edge of frontals; opercle bifurcate, dorsal fork nearly as long (95%) as ventral fork; dorsal part of subopercle slender tapering to a fine point, ventral part elongate rounded, with well-developed spine on anterior margin; dorsal-fin rays 6; anal-fin rays 4; pectoral-fin rays 15; caudal-fin rays 9, 9th caudal ray well developed, nearly one-half length of longest medial rays; all caudal rays simple; testes oval in shape, about 2 mm in length and 0.9 mm in greatest width (see Bertelsen, 1983:312, fig. 1). Premaxilla and dentary of male with irregularly resorbed edges; larval teeth few, 2-4 on each premaxilla, 1-2 on each side of dentary; a pair of curved pointed denticular teeth on snout lying slightly posterior to symphysis of upper jaw, 0.25 mm in length; 9 curved pointed denticular teeth lying slightly behind tip of lower jaw, 8 of which arranged in a regular symmetrical pattern consisting of an anterior and posterior transverse series of 4 teeth in each series; 9th denticular tooth smallest, placed asymmetrically to right of lower series; slender distal part of each of four largest denticular teeth 0.25-0.30 mm in length (lying medial to anterior series and lateral to posterior series), emerging in an obtuse angle from a stout, nearly cylindrical base; all denticular teeth mutually free without expanded connecting bases (see Bertelsen, 1983, fig. 1). Pterygiophore of illicium of male subdermal, length 2.5 mm or 18% SL, anterior end lying near tip of snout, posterior end connected to anterior edge of frontals by relatively strong extrinsic muscles (supracarinales anterior); an irregularly shaped rudiment of second cephalic spine lying slightly posterior to middle of pterygiophore, connected with anterior edge of parietals by retractor muscles (posterior inclinatores dorsalis).

Skin of male everywhere covered with tiny conical dermal spinules, those on tip of snout and chin slightly larger, more sharply pointed, and more closely spaced, rounded basal plates of largest spinules 0.15-0.2 mm in diameter. Larvae (two known specimens, 7.0-10.5 mm SL) extremely similar despite difference in size; eye diameter 1.1-1.2 mm, relatively larger in smaller specimen; skin inflated, forming an almost perfect sphere; head very large, length more than 50% SL; mouth comparatively small; both specimens female with relatively large rudiments of two cephalic spines on head; illicium arising just in front of eyes, length almost equal to diameter of eye; second cephalic spine arising just behind first, about one-half as large; color light gray-brown; skin with tiny melanophores of almost uniform density over entire body; only illicium and distal part of fins unpigmented; second cephalic spine pigmented with same density as rest of skin; inner pigmentation of body visible through skin, consisting of very small branched melanophores, arranged without distinct groups; dorsal surface slightly darker than belly; melanophores grouped slightly more densely along margins between myomeres; dorsal-fin rays 5-6; anal-fin rays 4; pectoral-fin rays 14-15; caudal-fin rays 9 (Bertelsen, 1951:67, 69, fig. 28; 1984:327, fig. 169E).

Color dark brown to black over entire surface of head, body, and oral cavity; dorsal, anal, and caudal fins, as well as distal portion of escal bulb, white in smaller females. Male with skin brownish black, except for that associated with olfactory organs and tip of snout; subdermal pigmentation light without distinct concentrations of melanophores.

The largest known specimen of the family is a 275-mm female of Diceratias pileatus found floating on the surface off Kona, Hawaii. The only known metamorphosed male measures 14 mm SL.

Distribution

The Diceratiidae is widely distributed in the Atlantic, Indian, and western Pacific oceans. Diceratias pileatus and B. wedli occur sympatrically on both side of the Atlantic; the latter is represented in addition by a single specimen collected in the East China Sea. Diceratias bispinosus and B. thele are sympatric in the western Pacific; the former is found as well in the central Indian Ocean and the later is also represented by a single female collected off Kona, Hawaii. Diceratias trilobus is known only from the holotype collected in the western North Pacific off the east coast of Honshu, Japan.  Bufoceratias wedli is restricted to the Atlantic Ocean, while B. thele is found only in the Western Pacific.  Bufoceratias shaoi is known from three specimens, two collected from off Taiwan and a third in the Mozambique Channel, Western Indian Ocean.

Key to the Genera of the Diceratiidae

The following key will differentiate metamorphosed female specimens only. Metamorphosis occurs between 10 and 15 mm SL, after which all subtaxa of the family can be readily determined.

1A. Pterygiophore of illicium emerging from snout, distance between point of emergence and symphysis of upper jaw less than 15% SL (Diceratias Günther, 1887)

1B. Pterygiophore of illicium embedded beneath skin of head, illicium emerging from dorsal surface of head at rear of skull, distance between point of emergence and symphysis of upper jaw greater than 30% SL (Bufoceratias Whitley, 1931)

Other Names for Diceratiidae

• Doublespine Seadevils

References

Balushkin, A. V., and V. V. Fedorov. 1986. A new species of diceratiid deepsea anglerfish, Diceratias trilobus sp. n. (Fam. Diceratiidae, Ceratioidei), from the coast of Japan. Vopr. Ikhtiol., 26(5): 855-856. [In Russian, English translation in J. Ichthy., 27(1): 136-138, 1987.]

Bertelsen, E. 1951. The ceratioid fishes. Ontogeny, taxonomy, distribution and biology. Dana Rept., 39, 276 pp.

Bertelsen, E. 1983. First records of metamorphosed males of the families Diceratiidae and Centrophrynidae (Pisces, Ceratioidei). Steenstrupia, 8(16): 309-315.

Bertelsen, E. 1984. Ceratioidei: Development and relationships. pp. 325-334, In: Moser, H. G., W. J. Richards, D. M. Cohen, M. P. Fahay, A. W. Kendall, Jr., and S. L. Richardson (editors), Ontogeny and Systematics of Fishes, Spec. Publ. No. 1, Amer. Soc. Ichthy. Herpet., ix + 760 pp.

Günther, A. 1887. Report on the deep-sea fishes collected by H. M. S. Challenger during the years 1873-76. Rep. Sci. Res. Voy. H.M.S. Challenger, 22 (57): i-lxv + 1-268, Pls. 1-66.

Pietsch, T. W. 1969. A remarkable new genus and species of deep-sea anglerfish (family Oneirodidae) from off Guadalupe Island, Mexico. Copeia, 1969(2): 365-369.

Pietsch, T. W. 1972. A second specimen of the deep-sea anglerfish, Phyllorhinichthys micractis (family Oneirodidae), with a histological description of the snout flaps. Copeia, 1972(2): 335-340.

Pietsch, T. W. 1974a. Osteology and relationships of ceratioid anglerfishes of the family Oneirodidae, with a review of the genus Oneirodes Lütken. Nat. Hist. Mus. L. A. Co., Sci. Bull., 18, 113 pp.

Pietsch, T. W. 1974b. Systematics and distribution of ceratioid anglerfishes of the genus Lophodolos (family Oneirodidae). Breviora, 425: 1-19.

Pietsch, T. W. 2005. Dimorphism, parasitism, and sex revisited: modes of reproduction among deep-sea ceratioid anglerfishes (Teleostei: Lophiiformes). Ichthyol. Res., 52: 207-236.

Pietsch, T. W., H.-C. Ho, and H.-M. Hong. 2004. Revision of the deep-sea anglerfish genus Bufoceratias Whitley (Lophiiformes: Ceratioidei: Diceratiidae), with description of a new species from the Indo-West Pacific Ocean. Copeia, 2004(1): 98-107.

Pietschmann, V. 1926. Ein neuer Tiefseefisch aus der Ordnung der Pediculati. Anz. Akad. Wiss. Wien, 63(11): 88-89.

Regan, C. T., and E. Trewavas. 1932. Deep-sea anglerfish (Ceratioidea). Dana Rept., 2, 113 pp.

Uwate, K. R. 1979. Revision of the anglerfish Diceratiidae with descriptions of two new species. Copeia, 1979(1): 129-144.