Bytholeucon hartmannorum, Mühlenhardt-Siegel, 2011

Mühlenhardt-Siegel, Ute, 2011, New and known species of the family Leuconidae (Cumacea, Peracarida) from Antarctic deep-sea basins 3117, Zootaxa 3117 (1), pp. 1-68 : 62-66

Bytholeucon hartmannorum sp. n.

( Figures 45–47 )

Material. Holotype female with developed oostegites, ZMH: K 42959 ; 27 February 2005.

Type locality. Antarctica, eastern Weddell Sea , 68° 03.84’ S 20° 31.39’ W, depth: 3488 m, ANDEEP III, # 88- E, epibenthic sledge .

Paratypes: Peninsula: ANT XIX #42 : 6 females with developing oostegites (1 dissected), 1 female with developed oostegites; ANT XIX #43 : 1 non-ovigerous female; ANT XIX #129 : 1 subadult male (figured paratype); W Weddell Sea: ANT XIX #131 : 1 female (dissected), 1 male; ANT XIX #136 : 1 female (dissected), 3 non-ovigerous females, 3 mancas; ANT XIX #138 : 3 non-ovigerous females, 1 male manca; E Weddell Sea: ANDEEP III #80: 2 subadult females (damaged), 1 male manca; ANDEEP III #88: 1 female (dissected), 1 ovigerous female (figured paratype); S Sandwich Trench: ANT XIX #139 : 1 male manca; ANT XIX #140 : 1 non-ovigerous female (dissected). ZMH: K 42960 .

Etymology. The new species is dedicated to Prof. emer. Dr. Gerd Hartmann, who sadly passed away in 2010, and his wife Dr. Gesa Hartmann-Schröder to honor their contribution (among others) on Antarctic research.

Diagnosis. Accessory flagellum of first antenna equal in length to basal article of main flagellum; ischium of pereiopod 2 fused to basis; uropod peduncle longer than basal article of endopod; uropod exopod equal in length to endopod.

Description. Holotype, 3.6 mm long ( Fig. 45 ).

Carapace dorsomedian line serrate with 14 teeth reaching up to the end; pseudorostral lobes projecting anteriorly, short, slightly upturned, on ventral part with two shallow teeth; siphonal tube short; ocular lobe reduced; eyes missing. Antennal notch distinct, wide open; anterolateral tooth acute; anteroventral margin of carapace serrate; integument shiny smooth, slightly calcified. Five free thoracic segments visible, slightly shorter than carapace. Pleon longer than carapace and free thoracic segments combined. Pleotelson wider than long, 0.8 times as long as uropod peduncle.

Appendages: female (paratype, ANT XIX #131 ) .

Antenna 1 ( Fig. 46 , A 1 ): relative length of peduncle articles 1 to 3 not given, article 1 broken; geniculate between article 1 and 2; accessory flagellum with three long simple setae terminally, as long as basal article of main flagellum; main flagellum tri-articulated, with two aesthetascs inserting at penultimate and terminal article.

Maxilliped 2 ( Fig. 46 , Mxp2): B/R ratio 0.6, relative length of articles I to D: 9/30/29/20/13; strong setulate seta distally at basis; carpus with five shorter setulate setae; propodus with three shorter setulate setae; dactylus with terminal seta longer than dactylus, two hair-like setae subterminally.

Maxilliped 3 ( Fig. 46 , Mxp3): B/R ratio 1.1, relative length of articles I to D: 16/16/30/17/22; basis distally broadened with three long setulate setae (the innermost broken); merus with one long setulate seta; propodus with one long and one shorter simple seta; dactylus with three fine simple setae; exopod broken off.

Pereiopod 1 ( Fig. 46 , P 1 ): B/R ratio 0.6, relative length of articles I to D: 5/18/31/26/19; basis with four setulate setae at distal end; ischium with one setulate seta distally; merus with two setulate setae distally; carpus with two setulate setae along margins and two setulate setae at distal end; propodus with one setulate seta distally; dactylus with terminal seta slightly longer than dactylus, three simple and two hair-like setae subterminally; exopod with four teeth along outer margin.

Pereiopod 2 ( Fig. 46 , P 2 ): B/R ratio 0.8, relative length of articles I to D: 0/22/27/15/36; basis with one setulate seta at distal end; ischium fused with basis; merus with one simple and one setulate seta distally; carpus with one simple seta distally; dactylus with terminal seta longer than dactylus, three simple setae subterminally, one simple seta on inner margin; exopod present.

Pereiopod 3 ( Fig. 47 , P 3 ): B/R ratio 1.5, relative length of articles I to D: 11/23/36/21/9; basis with one simple and two setulate setae along inner margin; merus with one simple and one setulate seta at distal inner corner; carpus with two setulate setae at outer distal corner; propodus with one simple seta at outer distal corner; dactylus minute with long terminal seta and one hair-like seta subterminally; exopod present.

Pereiopod 4 ( Fig. 47 , P 4 ): B/R ratio not given, basis broken, relative length of articles I to D: 8/24/35/22/10; basis with two setulate setae along margins, at distal inner corner three hair-like setae; ischium with one setulate seta; carpus with two setulate setae along outer margin and two simple setae along inner margin; propodus with one setulate seta distally, dactylus small, with long terminal seta and one hair-like seta subterminally.

Pereiopod 5 ( Fig. 47 , P 5 ): B/R ratio 0.7, relative length of articles I to D: 18/19/31/23/8; basis with one simple and one setulate seta; merus with one simple seta distally; carpus and propodus with one long simple seta distally, propodus with short simple seta distally; dactylus with terminal seta broken off.

Uropod ( Fig. 47 , U): Peduncle shorter than rami; exopod equal in length to endopod; endopod bi-articulated; basal article with three short cuspidate setae along inner margin, slightly longer than distal article, which bears two short cuspidate setae at inner margin, distally three long setae, one terminally and two subterminally.

Males: similar to female, with one pair of (developing?) pleopods.

Remarks. Watling (1991) erected the new genus Bytholeucon . The main differences from the genus Paraleucon Calman, 1907 , to which the two species B. ultraabyssalis ( Gamô, 1987) and B. hiscens ( Bishop, 1981) were assigned earlier, besides the great geographic and depth differences from Paraleucon suteri Calman, 1907b ( New Zealand, shallow water), are the long flagellum of the antenna 2 in males and the short ischium of the pereiopod 2. Unfortunately adult males are extremely rare in the samples, making determination of the flagellum length on the antenna 2 and the pleopods impossible.

There are only four species known in the genus Bytholeucon : B. hiscens ( Bishop, 1981) , B. ultraabyssalis ( Gamô, 1987) , B. angolensis Mühlenhardt-Siegel, 2005 and B. kaingo Mühlenhardt-Siegel, 2010 .

The main differences between the known species are the length proportion of the carapace to the free thoracic segments (less than two times longer than the free thoracic segments in B. hiscens , B. angolensis and B. kaingo as well as in the new species, but more than two times longer in B. ultaabyssalis ), the length proportion of the uropod peduncle to the basal article of the uropod endopod (shorter in B. hiscens and B. kaingo , equal in angolensis , but longer in the new species), the number of spines at the basal article of the exopod of pereiopod 1 (two in B. hiscens , four in B. ultraabyssalis and five in B. angolensis ) and the number of spines at the basal article of the exopod of maxilliped 3 (three in B. hiscens , six in B. ultraabyssalis and four in B. angolensis ).

Although the new species resembles Bytholeucon angolensis , it differs from the latter mainly in the length of the serration and number of teeth at the dorsomedian line being shorter and with less teeth (10 in females) in the Angola Basin. The ischium of the pereiopod 2 in the new species is fused to the basis, a character obviously typical for the genus.

Specimens from the western (ANT XIX #136-S) and the eastern Weddell Sea (ovigerous female, ANDEEP III #88-S) as well as the South Sandwich Trench (ANT XIX #140-S) were dissected. Unfortunately in most of the specimens the uropods were broken off.

● The extremities of all specimens resemble each other very much, however, there is a difference in the number of teeth:

- along the basal article of the exopod of pereiopod 1: three teeth in ovigerous females, four to five in non-ovigerous or subadult females and four teeth in young males;

- at the basal article of the exopod of maxilliped 3: one tooth in ovigerous females, four teeth in subadult females and males.

● There is also a difference in the number of teeth along the dorsomedian line in females from the

- western Weddell Sea: 11–12 teeth,

- eastern Weddell Sea: 11–14 teeth,

- Peninsula: 13 teeth,

- South Sandwich Trench: 13 teeth;

in males (mostly young males with not developed pleopods) from the

- South Sandwich Trench: 10 teeth,

- Peninsula and western Weddell Sea: 12 teeth,

- eastern Weddell Sea: 13 teeth.

● The number of teeth below the pseudorostral lobes is two or three, only a juvenile male from the South Sandwich Trench has five teeth.

The length proportion of the carapace to the free thoracic segments is <2 in most females and males, but> 2 in some female specimens from the Weddell Sea and one juvenile male from the South Sandwich Trench.

The question remains: is Bytholeucon hartmannorum sp. n. a complex species or a cryptic species complex? I regard the difference in the number of teeth as variability within one species.

Figures

FIGURE 1. Leucon (A.) polarsterni Ledoyer, 1993, subadult female habitus, 5.5 mm long.

FIGURE 2. Leucon (A.) polarsterni Ledoyer, 1993, A1: antenna 1, Mxp2: maxilliped 2, Mxp3: maxilliped 3, P1: pereiopod 1, P2: pereiopod 2; scale bars 100 µm (A1, Mxp2, Mxp3) and 200 µm (P1, P2).

FIGURE 3. Leucon (A.) polarsterni Ledoyer, 1993, P3: pereiopod 3, P4: pereiopod 4, P5: pereiopod 5, U: pleotelson and uropods; scale bars 100 µm (P3, P4, P5) and 200 µm (U).

FIGURE 4. Leucon (A.) polarsterni Ledoyer, 1993, SEM photos, habitus female (above left), carapace (above right, middle left), uropods (middle right), endopod’s terminal seta (below).

FIGURE 5. Leucon (C.) antarcticus Zimmer, 1907, non-ovigerous female habitus, 3.5 mm long.

FIGURE 45. Bytholeucon hartmannorum sp. n., habitus holotype, adult female (above), scale bar: 0.5 mm; subadult male, ANT XIX#129 (below).

FIGURE 46. Bytholeucon hartmannorum sp. n., A1: antenna 1, Mxp2: maxilliped 2, Mxp3: maxilliped 3, P1: pereiopod 1, P2: pereiopod 2; scale bars: 50 µm (Mxp2), 100 µm (Mxp3, P2) and 200 µm (A1, P1).

FIGURE 47. Bytholeucon hartmannorum sp. n., P3: pereiopod 3, P4: pereiopod 4, P5: pereiopod 5, U: pleotelson and uropods; scale bars: 50 µm (P4), 100 µm (P5, U) and 200 µm (P3).