Melanocetus eustalus Pietsch & Van Duzer 1980
Female holotype with escal bulb large (length 14.4% SL, width 11.3% SL), slightly compressed, with a low conical distal prolongation, pigment absent; posterior and anterior crests absent; integument as described for M. johnsonii; gill opening exceptionally large, greatest diameter 23.4% SL; vomerine teeth 8; dorsal-fin rays 15; anal-fin rays 4; pectoral-fin rays 16. Tentatively referred specimens similar to holotype, but with a slightly smaller esca, longer illicium and lower-jaw teeth, and a greater number of jaw teeth: least outside width between frontals 16.7–22.6% SL; number of teeth in upper jaw 77–141, in lower jaw 60–85; longest tooth in lower jaw 8.6–13.3% SL; length of illicium 46.2–49.1% SL; width of pectoral-fin lobe 8.6–13.9% SL; length of escal bulb 9.2–15.1% SL; width of escal bulb 8.9–10.9% SL; vomerine teeth 0–6; dorsal-fin rays 14–16; anal-fin rays 4; pectoral-fin rays 18.
Holotype of Melanocetus eustalus: LACM 30037-12, 111 mm.
VELERO IV station 11748, Eastern Pacific off Mazatlan, Sinaloa, Mexico, 21°39'N, 106°58'W, 3-m Isaacs-Kidd Mid-water Trawl, 0–1675 m, bottom depth 2820 m, 1320–2136 h, 11 November 1967.
Data on Catalog of Fishes
View data on Catalog of Fishes here.
Metamorphosed females of Melanocetus eustalus differ from those of all other described members of the genus in having the following combination of characters states (based solely on the holotype): anterior margin of vomer nearly straight; least outside width between frontals 18.0% SL; number of teeth in upper jaw 91, in lower jaw 60; longest tooth in lower jaw 5.9% SL; length of illicium 30.6% SL; width of pectoral-fin lobe 9.9% SL; width of escal bulb 11.3% SL; esca without crests; integument relatively thick.
The body of metamorphosed females is short and deep, globular, the depth 60–75% SL (but often appearing highly compressed due apparently to deformation following capture). The head is short, the mouth large, its opening oblique to nearly vertical and the cleft not extending past the eye. The jaws are equal anteriorly. The oral valves are only weakly developed. There are two nostrils on each side of the snout, situated on the distal surface of a rounded papilla. The eye is small and subcutaneous, appearing through a circular translucent area of the integument, within a shallow orbital pit formed between the sphenotic and frontal bones. The teeth are slender, recurved, and depressible, some slightly hooked distally, those in the lower jaw less numerous (except in some small specimens, less than approximately 20 mm) but slightly longer than those in the upper jaw. There are 29–178 teeth in upper jaw and 32–142 in lower jaw. The longest tooth in the lower jaw measures 6.9–25.0% SL. There are 0–12 vomerine teeth. The first epibranchial and the proximal one-half of the first ceratobranchial are bound to the wall of the pharynx by connective tissue. All four epibranchials are closely bound together. The fourth epibranchial and ceratobranchial are bound to the wall of the pharynx, leaving no opening behind the fourth arch. The proximal one-half of the first ceratobranchial is bound to the wall of the pharynx, while the distal half is free, not bound by connective tissue to the adjacent second ceratobranchial. The proximal one-quarter to one-half of ceratobranchials II–IV are not bound together by connective tissue. Gill filaments are absent on the epibranchials, but present on the proximal tip of ceratobranchial I and the full length of ceratobranchials II–IV. A pseudobranch is absent. The length of illicium is 23.1–60.8% SL. The anterior-most tip of the pterygiophore of the illicium is exposed, emerging on the snout between the eyes, the posterior end concealed under the skin. The escal bulb is simple, usually with a rounded or conical distal prolongation, and often with posterior and anterior crests. Elongate cylindrical escal appendages and filaments are absent. The neuromasts of the acoustico-lateralis system are located at the tips of low cutaneous papillae, the pattern of placement as described for other ceratioids.
Known from four metamorphosed females: the holotype (111 mm) and three tentatively identified specimens (36–93 mm).
Ecology and Distribution
The four known specimens of M. eustales were all collected in the Eastern Pacific Ocean off the coast of Mexico, between 8° and 21°N, all with gear fished open between 0–1675 m.
Meso- to bathypelagic.
Until very recently, the only evidence of sexual parasitism in this family was an anomalous case of a 20-mm male Melanocetus johnsonii attached to the upper lip of a 168-mm female Centrophryne spinulosa (LACM 30843-1). However, the attachment did not involve fusion of male-female tissue and is therefore not considered to be a parasitic association. Two similar couplings in Melanocetus, but between sexes of the same taxon, have recently been discovered. One of these, a 23.5-mm male attached to a 75-mm female Melanocetus johnsonii (BMNH 2004.6.3.2-3), was collected in the eastern North Atlantic off Ireland in 1999 by the RRS Discovery in a cruise partially funded by the British Broadcasting Corporation for the celebrated “Blue Planet” video series. The second example is part of collections made by Hiromitsu Endo, aboard the R/V Tansei-Maru, west of Okinawa, in April 2002: a 15-mm male attached to a 73-mm female Melanocetus murrayi (BSKU 57842). Both males are only loosely attached, with tissue of the female pinched by the tightly closed denticular jaws of the male, the BMNH example hanging from the middle of the belly of the female, the BSKU specimen attached to the right side of the head of the female, just beneath the sphenotic bone. In both cases, it does not appear that any fusion of male and female tissue has taken place. Either the connections of the two were so recent that the tissues did not have time to fuse, or, more likely, these are the first and only known examples of a non-parasitic coupling—male ceratioids caught in the act of temporary attachment.
Pietsch TW. 2009. Oceanic Anglerfishes: Extraordinary Diversity in the Deep Sea. Berkley: University of California Press. 638 p.