Gnathophausia affinis G.O. Sars, 1883

Meland, Kenneth & Aas, Pål Øyvind, 2013, A taxonomical review of the Gnathophausia (Crustacea, Lophogastrida), with new records from the northern mid-Atlantic ridge, Zootaxa 3664 (2), pp. 199-225 : 206-207

Gnathophausia affinis G.O. Sars, 1883

( Fig. 4 )

Gnathophausia affinis G.O. Sars, 1883: 7 .—G.O. Sars 1885: 41–42.—Hansen 1927: 19.—Nouvel 1943: 19–20. Gnathophausia zoea —Willemoes-Suhm 1875: 32–33 (in part).

Material examined. In formaldehyde (transferred to ethanol). Stn 24-352-1095, 1 specimen (3 6.0cm) (ZMBN 81177); Stn 30-358-1117, 2 specimens (ZMBN 86544); Stn 30-358-1118, 2 specimens (ZMBN 86618); Stn 30- 358-1119, 1 specimen (ZMBN 86543); Stn 30-359-1122, 7 specimens (immature 4.5 cm, immature 5.5cm, Ƥ 5.0cm, Ƥ 6.5cm, Ƥ 7.0cm, 3 7.0cm, 1 damaged) (ZMBN 81178); Stn 32-361-1126, 3 specimens (immature 5.0cm, Ƥ 6.0cm, Ƥ 6.5cm) (ZMBN 81180); Stn 32-362-1128, 4 specimens (ZMBN 86547); Stn 32-362-1129, 5 specimens (ZMBN 86546); Stn 32-362-1130, 3 specimens (ZMBN 86545); Stn 32-362-1131, 1 specimen (ZMBN 86619); Stn 36-365-1142, 1 specimen (ZMBN 86548); Stn 42-368-1150, 1 specimen (Ƥ 7.0cm) (ZMBN 81181); Stn 44-369- 1151, 1 specimen (Ƥ 7.0 cm) (ZMBN 81182).

In ethanol. Stn 30-359-1123, 2 specimens (Ƥ 6.5cm, 1 damaged) (ZMBN 81179, ZMBN 86620).

Diagnosis. Body slender. Integument bright red. Carapace does not extend beyond last thorax somite; rostrum shorter than carapace, dorsal edge with marked denticles extending posteriorly to base; dorsal keel interrupted in region of cervical groove, forms raised keel proximal to rostrum and extends posteriorly to posterodorsal end. Posterolateral spine short, barely extending past first abdominal somite. Upper lateral keels distinct, anterior portion curves down towards antroventral corner, connecting to ventral keels. Lower lateral keels distinct, stopping abruptly before reaching posterior margin of carapace. Supra-orbital spines small, barely extending beyond eyes; antennal spines barely visible; branchiostegal lobes somewhat angular. Antennal scale about twice as long as broad, outer margin entire terminating in a strong spine, terminal lobe extending past outer spine. Abdominal somites bearing no dorsal keels nor spines, ventrolateral margins rounded. Telson linguiform, extending past the uropods. Obtains lengths up to 80 mm.

Distribution. Gnathophausia affinis was first described by G.O. Sars (1883, 1885) on a misidentified G. z o e a from "Challenger" station 107, between Africa and Brazil at a depth of 2744 m (see Willemoes-Suhm 1875: p. 32). Additional specimens have later been retrieved off Morocco at a depth of 2600 m (Hansen 1927), and in the northern region of the Azores Islands at a depth of 2102 m (Nouvel 1943). With the Mar-Eco material 20 additional specimens of G. affinis are now recorded north of the Azore Islands at depths down to 2383 m.

Remarks. G. affinis is morphologically most similar to the Pacific species, G. childressi Casanova, 1996 b, but is distinguished from G. childressi by the presence of upper lateral keels. Also in G. affinis the pleura of the sixth abdominal somite is not rounded, but ends in a spine. Based on a presumed close relationship between G. childressi and G. affinis , a similar vertical distribution to G. childressi , exclusively found associated to deep benthic water masses (0–50 m of the bottom), has been suggested for G. affinis (Casanova 1996b) . However, as most of the Mar- Eco specimens were caught with a midwater trawl at depth ranges between 1500 and 2400 m, more than 400 m from the ocean floor, G. affinis is shown not to be limited to benthic water masses.

Gnathophausia childressi Casanova, 1996 ( Fig. 5 )

Gnathophausia childressi Casanova, 1996b: 192 –199.

Diagnosis. Body robust. Carapace large, more or less covering first abdominal somite; rostrum of moderate size, denticulate dorsally, denticles present, but less visible ventrally; posterodorsal spine short; median dorsal keel interrupted in region of cervical groove, forms raised keel proximal to rostrum and extends posteriorly to posterodorsal end; upper lateral keels absent; lower lateral keels continuous, stopping abruptly before the posterolateral margin of carapace; supra-orbital spines present; branchiostegal expansions shaped like collars, antennal spines absent. Apex of antennal scale extending past the outer lateral spine in older specimens. Abdominal somites without dorsal spines; pleura consisting of anterior and posterior rounded lappets, anterior lappets almost as pronounced as posterior lappets in 1–3 abdominal somites; pleura of sixth abdominal somite rounded. Telson as long as uropods, linguiform; apex armed with small spiniform setae. Obtains lengths from 25–102 mm (Casanova 1996b).

Distribution. G. childressi is a Pacific species collected from the San Clemente Basin and East Cortes Basin (off California). It has been collected at 2000 m in the San Clemente Basin and 1800 m in the East Cortes Basin (Casanova 1996b).

Remarks. Specimens of G. childressi were first collected, and sorted as Gnathophausia sp. by J.J. Childress, and later identified and described as a new species by Casanova (1996b).

G. childressi is morphologically similar to the Atlantic Ocean distributed species G. affinis , but is most easily distinguished from its Atlantic relative by the absence of upper lateral keels and the pleura of sixth somite that is not drawn out into a spine, but rounded posteriorly.

Based on observations where G. childressi has only been reported from near bottom trawl samples in close vicinity to the deep sea benthos, it is suggested that unlike other Gnathophausia species, G. childressi is not pelagic, but has a more hyperbenthic habitat preference, associated to the deep sea benthic boundary layer.

Figures

FIGURE 4. Gnathophausia affinis G. O. Sars 1883. Adult female: A, lateral view; B, dorsal view; C, antenna (ventral view); D, telson and right uropod (dorsal view) (from G. O. Sars 1885: pl. V, figs 7 – 10).

FIGURE 5. Gnathophausia childressi Casanova, 1996. A, lateral view; B, antennal scale (dorsal view); C, telson (dorsal view).