Leptostyloides quadridentata Gamo 1985

Leptostyloides cf. quadridentata (Gamô, 1985)

(Figs. 10–12)

Material. #7-9: 1 adult female (11.5 mm long; developing oostegites), 1 carapace; ZMH: K 44241; #10-9: 1 preparatory female (6 mm long, developing oostegites, dissected)¸ ZMH: K 44242.

Description. Adult female with developing oostegites, 11.5 mm long (Fig. 10).

Carapace short, 0.22 of total length, twice as long as free thoracic segments combined, globose; a short row of five teeth starting under tip of pseudorostrum, bending ventrally?; carapace with scattered fine spinules; frontal lobe fissure submerged, not visible in lateral view; pseudorostral lobes meeting in front of ocular lobe, 0.16 times of total carapace length, direced slightly upwards, blunt tip; siphonal tube not protruding; ocular lobe small, roundish, no eye lenses. In lateral view of the figured female five oily drops were detectable on the left side (Fig. 10).

Antennal notch and anterolateral tooth missing; anteroventral margin of carapace with long teeth.

Integument whitish, translucent.

Five free thoracic segments visible, the first two narrow. Although the marsupial plates are developing, pereonite 5 has no extremities, the pereiopod 5 is missing.

Pleon much (1.8 times) longer than carapace and free thoracic segments combined, measured without telson.

L. calcar L. secundus L. cf. L. quadridentata quadridentata

distribution Kermadec Trench Argentine Basin Kurile Japan Trench

Kamchatka abyssal plain Row of teeth laterally on pseudorostrum no 7+5 teeth 5 teeth 6 teeth Telsonic segment elongate, 1.3 times longer than telson, 0.7 times as long as pleonite 5.

Telson (Fig. 12, U) with two terminal setae and a pair of lateral setae subterminally.

Appendages: preparatory female (ZMH K 44242), 6 mm long.

Antenna 1 (Fig.11, A1): relative length of peduncle articles 1 to 3: 43/36/31. Article 1 slightly bent, with fringe of hair-like setae along inner and outer margins, two long pappose setae on distal corners, a tooth near outer distal corner; article 2 with simple seta on distal inner corner; accessory flagellum three-articulated, more than half as long as basal article of main flagellum; main flagellum three-articulated, one aesthetasc from penultimate article, one aesthetasc and one annulated seta and three broken setae from terminal article.

Maxilliped 3 (Fig. 11, Mxp3): B/R ratio 1, relative length of articles I to D: 9/15/31 /25/20; basis slightly bent; basis with three pappose setae, two at outer, one at inner distal corner, fringe of setae along inner and outer margin; ischium with one and merus with two pappose setae at inner distal corner; carpus with two pappose setae along inner margin, two at outer distal corner; propodus with one pappose, one simple and two plumose setae, the latter on each distal corner; dactylus with one strong simple seta terminally and three slender setae subterminally; exopod present.

Pereiopod 1 (Fig. 11, P1): B/R ratio 0.5, relative length of articles I to D: 5/ 11/31/42 /11; basis slightly bent and with two small teeth at outer distal corner of basis. Four simple setae at basis, two at merus; two simple setae and two broken at carpus; 11 simple setae at propodus; one simple seta medial, one terminal, and two subterminally at dactylus; exopod present (not figured, lost during dissection).

Pereiopod 2 (Fig. 11, P2): B/R ratio 0.2, relative length of articles I to D: 3/ 8/27/31 /31; one simple seta at basis, one at merus, four at carpus, 11 simple setae at propodus, 11 along dactylus, one terminally and two subterminally. Small tooth at distal corner of ischium; exopod present.

Pereiopod 3 (Fig. 12, P3): B/R ratio 1.7, relative length of articles I to D: 11/18/45 /13/13; basis and ischium each with one simple setae; merus with two simple setae; carpus with one terminally annulated and two simple setae; propodus with one terminally annulated simple seta; dactylus with one strong terminal and one subterminal simple seta; rudimentary exopod present.

Pereiopod 4 (Fig. 12, P4): B/R ratio 0.8, relative length of articles I to D: 12/21/43 /13/11; merus, carpus, propodus and dactylus each with a simple seta, the dactylus terminal seta strong; rudimentary exopod present.

Pereiopod 5: missing.

Uropods (Fig. 12, U), peduncle with eight setae along inner margin in female (7–9). Exopod broken off in both specimens; endopod tri-articulated in female (7–9).

Distribution. Japan Trench and Kurile Kamchatka abyssal plain, 5216–5370 m.

Remarks. Gamô (1985) described Leptostylis quadridentata from the Japan Trench and stated its unique shape in the family Leptostylis due to the dorsal teeth on the pleonite 5. He distinguished his new species from Leptostyloides calcar, described by Jones (1969), by the “different shapes of the carapace and the dorsal projection on the fifth abdominal segment” (Gamô, 1985). Mühlenhardt-Siegel (2014) proposed to transfer Leptostylis quadridentata to the genus Leptostyloides, because of the dorsal ornamentation of the pleonite 5. The absence of the pereiopods 5 in the female from the Japan Trench suggests a young developmental stage of the specimen. Even the larger one of the Kurile Kamchatka females is smaller (11.5 mm) than Gamô’s specimen (12.3 mm) and has developing oostegites; however, there is not even a trace of pereipods on the fifth pedigerous segment. This leads to the conclusion that in L. quadridentata these extremities will not develop.

A comparison of selected characters of all species known so far in the genus Leptostyloides is provided in Table 3.

Gamô (1985) described the first antenna with the main flagellum: two cylindrical and three minute articles. However, in the present specimen the tips of the main flagella are both slightly damaged, it appears to consist of two longer and one short article, but the second and third short articles might be broken off.