Heterogenys microphthalma

Heterogenys microphthalma (Smith, 1885)

Acanthephyra microphthalma Smith, 1885:502 [type-locality: northwestern Sargasso Sea, east of North Carolina: 36°16′30″N, 68°21′00″W, 4707 m]; 1886b:668, pl. 13: fig. 3.

Acanthephyra longidens Bate, 1888:735, pl. 124: fig. 4 [type-locality: the two Challenger specimens were taken at two widely distant stations: eastern Celebes Sea: 2°55′N, 124°53′E, 3932 m, and South Pacific south of Tuamotu Archipelago: 32°36′S, 137°43′W, 4344 m].

DIAGNOSIS.—Rostrum directed anterodorsad, about as long as carapace, overreaching antennal scale, armed with 3 small dorsal teeth above orbit and 8 or 9 ventral teeth on anterior of length; carapace rounded in dorsal midline, postcervical groove distinct laterally, not mesially, branchiostegal spine without buttress; abdomen with 3rd somite bearing long, slender posterodorsal spine overreaching 4th somite and preventing full extension of abdomen, 4th and 5th somites posteriorly unarmed, 6th with inconspicuous posterodorsal tooth; telson overreaching both branches of uropod, sulcate in anterior part of dorsal midline and armed with 7 or 8 dorsolateral spines; maximum carapace length 23 mm.

RANGE.—Although the number of published records of H. microphthalmia is relatively low, they represent such remote localities (see generic “Range”) as to suggest a nearly worldwide distribution in tropical and temperate seas. Most of the records are based on specimens taken in bottom trawls between 2000 and 4792 m, but two (Coutière, 1911, and Aizawa, 1974) refer to open midwater nets, and Wasmer (1972b:261) concluded, from an analysis of the foregut contents of a specimen taken in a beam trawl that the species “is probably not confined to the immediate neighborhood of the bottom.” It seems to me, however, that a nektonic species would be seriously hampered by the unusual posteromesial spine on the third abdominal somite, which effectively prevents extension of the abdomen.

Hymenodora G.O. Sars, 1877

Hymenodora G.O. Sars, 1877:340. [Type-species, by monotypy: Pasiphaë glacialis Buchholz, 1874:279; gender: feminine.]

DIAGNOSIS.—Integument thin, sometimes membranous; rostrum dentate on dorsal margin only; carapace not denticulate dorsally, without uninterrupted lateral carina extending from near orbit to near posterior margin, without hepatic spine, posterior slope of hepatic furrow not abruptly delimited by oblique carina; abdomen without carina or posteromesial teeth in dorsal midline on any somites, 6th somite longer than 5th; telson superficially blunt, not tapering regularly to sharply acute posterior end, rarely with spinose endpiece; eye with cornea narrower than eyestalk; antennal scale without lateral teeth proximal to distolateral spine; mandibles dissimilar, molar process with transverse distal surface triangular on right member of pair, compressed, sub-bilinear on left, incisor process toothed along entire opposable margin; 2nd maxilla with proximal endite lacking papilla and submarginal lamina; 1st maxilliped with slender central lobe subdivided by only 1 transverse suture; 2nd maxilliped with distal segment somewhat ovoid, attached diagonally to preceding segment; 3rd maxilliped and 1st pereopod with exopods not unusually broad or rigid; pereopods with neither ischium nor merus broadly compressed, 4th pair with epipod vestigial or absent; appendix masculina present on 2nd pleopod of males; eggs large and few (less than 50).

RANGE.—South Africa, Indian Ocean, Australian Basin, Philippine Sea, northern and eastern Pacific and western and eastern North and South Atlantic; mesopelagic and bathypelagic. I am unaware of any records of Hymenodora from either the Philippines or Indonesia, proper.

CLASSIFICATION.—In some respects, Hymenodora seems to bridge the gap between some of the species of the possibly polyphyletic genus Acanthephyra and other oplophorid genera, even sharing some characters with the very different appearing large-eyed genera Janicella and Oplophorus. The only other genus without a semblance of a dorsal carina on any of the abdominal somites is Ephyrina, which has very different mouthparts, especially mandibles. The sharply sulcate telson is similar to that found in Meningodora and Notostomus but a similar form is noticed in Systellaspis cristata and the surprising occurrence of an endpiece in Hymenodora acanthitelsonis is certainly reminiscent of the similar structure in Janicella and Systellaspis. The rather unusual molar process on the left mandible may be intermediate between the form characteristic of Acanthephyra and the very different one found in Systellaspis. The second maxilla seems to lack both a papilla and a submarginal lamina on the proximal endite, an extreme condition that seems to be approached only in Janicella and, of course, Hymenodora and Janicella are the only oplophorid genera in which there is only a single transverse suture subdividing the slender central lobe of the first maxilliped. The terminal segment of the second maxilliped is similar in shape to the one in Ephyrina and both of them are intermediate between the triangular outline in Acanthephyra and Notostomus and the almost regularly ovoid segment in Janicella, Oplophorus and Systellaspis. Finally, the large eggs produced by the species of Hymenodora are like those found otherwise in Ephyrina, Janicella, Oplophorus and Systellaspis whereas small eggs are characteristic of Acanthephyra, Notostomus and the other genera.