Kyphocalanus

Kyphocalanus sp. 2.

( Figs 9–10 View FIGURE 9 View FIGURE 10 )

Material examined. Dissected adult female, body length 2.10 mm. Collected in 1998 above the sea bed at abyssal depths ( 4800 m) on Porcupine Abyssal plain ( 48º 58’N 16º 30’W).

Specimen is deposited at the Zoological Museum Hamburg ( ZMH), University of Hamburg.

Description. Female. Prosome 5.3 times as long as urosome.

Rostrum with two strong rami ( Fig. 9 View FIGURE 9 C). Cephalosome and somite 1 and somites 4 and 5 of prosome separate; posterior corners as triangular lobes ( Fig. 9 View FIGURE 9 A–B). Caudal rami with 4 terminal setae, 1 ventral seta, dorsal seta not located ( Fig.9 View FIGURE 9 B).

Antennule entirely lost.

Antenna, attributes of type species.

Mandible ( Fig. 10 View FIGURE 10 A), gnathobase with 4 acutely pointed and 4 very small teeth plus dorsal seta; basis with 2 setae, proximal one larger and with proximal part haft-like; exopod 4(?)-segmented with 5 setae; endopod segment 1 without setae, segment 2 with 9 setae.

Maxillule, shape similar and setation identical to that of type species.

Maxilla ( Fig. 10 View FIGURE 10 C-D), proximal praecoxal endite with 2 setae; distal praecoxal endite with 2 setae; proximal coxal endite with 2 setae; distal coxal endite with 2 setae; proximal basal endite with 1 spine; distal basal endite plus endopod with 8 long and thick worm-like sensory setae.

Maxilliped ( Fig. 9 View FIGURE 9 D), syncoxa with 1 worm-like, comparably thin and short sensory seta on proximal praecoxal lobe, 2 long and thick worm-like setae on middle lobe; distal praecoxal lobe without setae; coxal lobe with 1 seta. Basis with 3 setae. Endopod 6-segmented with 2, 4, 2, 2, 2+1, and 4 setae.

Swimming legs. P1 ( Fig. 9 View FIGURE 9 E), basis with medial distal seta only slightly curved, with setules; endopod 1- segmented without lateral lobe; exopod segments 1, 2 and 3 with lateral spines, proximal spine is the shortest; spine of exopod segment 1 exceeding base of following spine, spine of exopod segment 2 not reaching base of following spine.

Intact segments of P2–P4 as in type species, except for P4 surface not spinulated.

P5 ( Fig. 9 View FIGURE 9 F) 3-segmented, similar to type species, but exopod surface spinules absent.

Remarks. Kyphocalanus sp. 2 differs from K. atlanticus in the shape of rostrum, its rami being more closely spaced ( Figs. 1 View FIGURE 1 C, 9C) and in the presence of 3 setae on inner lobe of antenna endopod segment 2 ( vs 4 setae in K. atlanticus ). From all congeners it is distinct in that spinules are absent on the posterior surface of P5; from Kyphocalanus sp. 1 it can be distinguished by the ratio of the lengths of P5 exopodal spines.

It shares with the type species the following characteristics that differentiate both from Kyphocalanus sp.1: i) its larger size (2.10–2.24 mm vs 1.82 mm in Kyphocalanus sp.1); ii) a longer endopod of antenna (ratio of exopod and endopod lengths as 1.8 vs 2.3 in Kyphocalanus sp.1); iii) presence of 2 setae on maxilla proximal coxal endite ( vs 1 seta); iv) and P1 lateral spine of exopod segment 1 shorter than spines of exopod segments 2 and 3 (this spine is the longest in Kyphocalanus sp.1).