Bytholeucon paucidentatis, Mühlenhardt-Siegel, 2025

Bytholeucon paucidentatis sp. nov.

( Figures 1 View FIGURE 1 to 4)

Material

Holotype ovigerous female ( Figure 1 View FIGURE 1 ), ZMH- K 64943 View Materials ; ( 16 July 2009); SW Atlantic, Argentine Basin, FS “Meteor” cruise Me 79/1, station # 534: 36° 00.61'S 49° 01.54'W, 4608 m depth, gear: EBS. GoogleMaps

Paratypes

Argentine Basin

# 532—EBS: 1 cephalothorax ( ZMH K 64965 View Materials ) .

# 533—EBS: 1 non-ovigerous female, 1 ovigerous female (ZMH K 64966 View Materials ), 1 non-ovigerous female, dissected, figured (ZMH K 64944 View Materials ).

#534—EBS: 1 non-ovigerous female (ZMH K 64967 View Materials ).

Brazil Basin

# 554—EBS: 5 non-ovigerous females, 2 mancae ( ZMH K 64968 View Materials ) .

#561—EBS: 1 ovigerous female (uropods missing), 5 non-ovigerous females, 1 manca (ZMH K 64969 View Materials ).

# 604—EBS: 1 juvenile male ( ZMH K 65768 View Materials ) .

#605—EBS: 1 ovigerous female (uropods missing), 1 non-ovigerous female, 1 manca (ZMH K 64970 View Materials ).

Etymology.—The new species is named ” paucidentatis “ referring to the few (lat.: paucus) teeth (lat.: dentis) on the basal article of the exopods on the maxilliped 3 and pereiopod 1.

Diagnosis.—Accessory flagellum of first antenna equal in length to basal article of main flagellum; uropod exopod equal in length to endopod; uropod peduncle shorter than endopod basal article; one tooth on basal article of maxilliped 3 exopod.

Description.—Based on holotype ( Fig. 1 View FIGURE 1 ), ovigerous female ( 3.7 mm long) (ZMH- K 64943 View Materials ).

Carapace slightly longer than free thoracic segments, serrate to hind margin with 12 dorsomedian teeth, with a small gap before last 3 teeth; pseudorostral lobes 0.2 of total carapace length, with 3 teeth below pseudorostrum; siphonal tube little protruding; ocular lobe rudimentary; eye lenses missing.

Antennal notch wide, 47° opening angle between dorsal edge of pseudorostrum and dorsal edge of subrostral tooth; anterolateral tooth strong; ventral margin of carapace serrate; integument smooth, whitish. Five free thoracic segments visible.

Pleon slightly longer than carapace and thoracic segments combined; pleotelson as long as wide.

Appendages: non-ovigerous female, 4.2 mm long ( paratype, ZMH K 64944 View Materials ) .

Antenna 1 ( Fig. 2 View FIGURE 2 , A 1 View FIGURE 1 ): relative length of peduncle articles 1 to 3:41/27/33; basal article with 1 plumose seta, second article with 1 simple and 3 plumose setae; third article with one plumose and 1 simple setae; accessory flagellum as long as basal article of main flagellum with 4 simple setae (1 lateral, 3 distal); main flagellum 3- articulated, with a simple seta distally on articles 1 and 2; article 3 with 4 aesthetascs (not figured).

Maxilliped 2 ( Fig. 2 View FIGURE 2 , Mxp2): B/R ratio 0.6, relative length of articles I to D: 14/29/28/18/11;

basis with long plumose seta; ischium unarmed; merus with fringe of hair-like setae along outer margin, strong plumose seta on distal margin; carpus with 3 barely setulate setae along inner margin; propodus with 4 barely setulate setae along inner margin; one strong plumose seta on outer margin; dactylus with one strong simple terminal seta (unguis) and 4 slender simple setae subterminally.

Maxilliped 3 ( Fig. 2 View FIGURE 2 , Mxp3): B/R ratio 0.8, relative length of articles I to D: 9/22/32/18/18;

basis with 5 plumose setae along inner margin and 3 strong plumose setae on outer distal corner; ischium unarmed; merus with slender plumose seta on inner margin, strong plumose seta on outer distal corner; carpus with tooth distally, 3 simple setae along inner margin, one plumose seta on outer distal corner; propodus with 3 barely setulate setae along inner margin, one plumose seta on outer distal corner; dactylus one simple seta terminally, one plumose seta and 3 simple setae sub terminally, 3 simple setae along inner margin, one simple seta on outer margin; exopod present, basal article with one tooth.

Pereiopod 1 ( Fig. 2 View FIGURE 2 , P 1 View FIGURE 1 ): broken after ischium; basis with 8 plumose setae, no teeth; exopod, basal article with 2 teeth.

Pereiopod 2 ( Fig. 3 View FIGURE 3 , P 2 View FIGURE 2 ): B/R ratio 0.8, relative length of articles I to D: 5/23/27/13/33;

basis with 4 plumose setae; ischium unarmed; merus with 3 plumose setae; carpus with 2 plumose setae and one simple seta; propodus with one simple seta distally; dactylus with one terminal seta and 3 plumose setae sub terminally, 3 plumose setae along outer margin; exopod present.

Pereiopod 3 ( Fig. 3, P3 View FIGURE 3 ): B/R ratio 1.4, relative length of articles I to D: 19/24/35/17/5;

basis with 7 plumose setae; ischium with 2 plumose setae; merus with 2 plumose setae and one simple seta; carpus with one slender and 2 strong plumose setae, one strong simple seta; propodus with one strong simple seta; dactylus with one strong simple seta terminally one plumose seta sub terminally; exopod present.

Pereiopod 4 ( Fig. 3. P View FIGURE 3 4 View FIGURE 4 ): B/R ratio 1.1, relative length of articles I to D: 18/24/33/16/9;

basis with 6 plumose setae; ischium with one simple seta and 2 plumose setae;

merus with one plumose seta; carpus with 2 plumose setae along inner margin, 3 simple setae on outer distal corner; propodus with one strong simple seta on outer distal corner; dactylus with one strong simple seta terminally and a slender simple seta sub terminally.

Pereiopod 5 ( Fig.4 View FIGURE 4 , P 5 View FIGURE 5 ): B/R ratio 0.9, relative length of articles I to D: 16/24/34/20/6;

basis with 6 plumose setae; ischium with 2 plumose setae; merus with one plumose seta;

carpus with 4 plumose setae; propodus with one simple seta distally; dactylus with one strong simple seta terminally and a slender seta sub terminally.

Uropods ( Fig. 4 View FIGURE 4 , U), peduncle with 3 cuspidate setae along inner margin, 1.5 times longer than pleotelson, 0.9 times shorter than basal article of endopod. Exopod equal in length to endopod; endopod 2 articulated; basal article with 3 cuspidate setae along inner margin, 2.6 times as long as second article which bears 3 cuspidate setae along inner margin and a strong terminal simple seta.

The juvenile male (ZMH K 65768 View Materials ) has no pleopods buds but all 5 pairs of pereiopods.

Distribution: SW Atlantic, Argentine and Brazil Basins, 4484–5188 m.

Remarks: The comparison with the known Bytholeucon species ( Table 2) reveals that the discriminant characters are quite subtle. In fact, the divisions between species are due to the differing combinations of characters rather than to striking morphological features.

According to Table 2 the new species is close to B. kaingo Mühlenhardt-Siegel, 2010 and B. hartmannorum Mühlenhardt-Siegel, 2011 because of the accessory flagellum of the first antenna being equal in length to the basal article of the main flagellum. The uropod exopod is equal in length to the endopod as in B. hartmannorum but in B. kaingo the exopod is longer than the endopod. In the new species the uropod peduncle is shorter than the endopod basal article (as in B. kaingo ) but it is longer in B. hartmannorum .

The number of teeth on the basal article of the maxilliped 3 exopod is one in the B. paucidentatis sp. nov. but more (3 to 6) in the other species. Also the number of teeth on the exopods basal article of pereiopod 2 is lower (2 teeth) in the new species than in the other known species (3 to 6). The number of teeth on the basis of P1 appears to be variable, it is 0 in preadult females but 3 in ovigerous female (ZMH K 64966 View Materials ).

Also variable is the number of teeth along the dorsomediane line. It is 8 to 10 before the gap and 3 to 4 behind the gap in non-ovigerous females, 13 to 17 without a gap in ovigerous females or females with developing oostegites, mancae have less teeth on the dorsomediane line but they do have a gap.

Bishop (1981) recorded Paraleucon? hiscens from the Argentine Basin, 5208–5223 m. This species was transferred to the genus Bytholeucon by Watling (1991). The differences between B. hiscens and the new species are in the length proportion of the accessory flagellum to the basal article of the main flagellum of the antenna 1, it is longer in B. hiscens but equal in length in the new species; the number of teeth on the basal article of the exopods of the maxilliped 3 are 3 to 4 in B. hiscens ( 1 in B. paucidentatus sp. nov.), these teeth on the exopods of pereiopod 1 are 3 to 6 in B. hiscens ( 2 in B. paucidentatus sp. nov.), the number of dorsomedian teeth of the carapace in female are 14 in B. hiscens (variable in B. paucidentatus sp. nov.), the uropods endopod is longer than the exopod in B. hiscens (equal in length in B. paucidentatus sp. nov.) (tab. 2).