Neoleptastacus emendatus, Sak & Karaytuğ & Huys, 2024

Sak, Serdar, Karaytuğ, Süphan & Huys, Rony, 2024, Review of Neoleptastacus Nicholls, 1945 (Harpacticoida, Arenopontiidae), including an updated key to species and proposal of Phreatipontia gen. nov., Zootaxa 5525 (1), pp. 1-66 : 31-36

Neoleptastacus emendatus sp. nov.

( Figs 6–8 )

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Arenopontia (Neoleptastacus) acantha accraensis Lang, 1965 sensu Kunz (1971: 354)

Neoleptastacus emendatus —nomen nudum by Sak (2004: 211)

Original description. Kunz (1971 —as Arenopontia (N.) acantha accraensis ): 354–356; Abb. 25–32 (♀ only). Abb. 33 is probably based on a different species.

Type locality. Angola, Luanda Province, south of Fastaleza (near Luanda); coarse sandy beach, 8 m from lowtide mark, salinity 35‰.

Type material. Undissected holotype ♀ in alcohol (reg. no NHMUK 2024.1062 ) .

Body length. Not given in Kunz (1971); 390 μm (♀) [present account].

Description of female. Total body length from tip of rostrum to posterior margin of caudal rami 390 μm (n = 1). Maximum body width 34 μm, measured near posterior margin of cephalothorax. Body ( Fig. 6A, B ) slender and cylindrical, without clear distinction between prosome and urosome. Sensillar pattern on body as figured. Hyaline frills of thoracic somites weakly developed and crenulated; those of genital double-somite and free abdominal somites strongly developed and consisting of rectangular lappets with weakly incised free margin ( Figs 6A, B ; 7A ). Integument of cephalothorax and pedigerous somites with internal pattern of ridges. Somites connected by well-developed intersomitic membranes. Cephalothorax and somites bearing P2–P4 with midventral, backwardly directed, spinous process located anterior to intercoxal sclerites of swimming legs 1–4 ( Fig. 7F, G ).

Genital double-somite about 1.5 times longer than wide (measured in dorsal aspect); with two conspicuous ventrolateral pores ( Figs 6A, B ; 7A ). Anal somite ( Figs 6C, D ; 7A ) with paired, posteriorly directed, spinous processes near posterior border either side of anal opening. Anal frill triradiate, minutely incised.

Caudal rami ( Figs 6C, D ; 7A ) about 3.5 times longer than maximum width (measured in dorsal view from anterior margin to apex of spinous process), only slightly tapering in anterior two-thirds; inner margin expanded medially in anterior third; with a pore near ventral proximal margin ( Fig. 7A ); outer distal corner produced into posteriorly directed, dorsally recurved spinous process; no spinular ornamentation discernible. Armature consisting of seven setae; seta I small; setae II and III (displaced to dorsal surface) long and naked; seta IV short, naked, located between seta V and posterior spinous process; seta V long, naked, with proximal fracture plane and few long setules at around 1/3 its length ( Fig. 6B ); seta VI small, naked and located at inner distal corner; seta VII weakly foliaceous and tri-articulate at base.

Rostrum ( Fig. 7E ) small, subtriangular, tapering distally and rounded apically; with two delicate sensillae and one midventral pore.

Antennule ( Fig. 7B ) long and slender, 6-segmented. Segment 1 with well developed seta near anterodistal margin. Segment 2 longest, about 3.2 times longer than wide. Segment 4 with long aesthetasc (L: 29 μm) fused at base with seta. Distal segment with eight setae (none of them noticeably spatulate) and apical acrothek consisting of short aesthetasc (L: 10 μm) and two setae. All setal elements naked except for plumose seta on dorsal surface of segment 2. Armature formula: 1-[1], 2-[7 + 1 plumose], 3-[4], 4-[(1 + ae)], 5-[1], 6-[8 + acrothek].

Antenna ( Fig. 7C, D ). Coxa small, without ornamentation (not figured). Basis and proximal endopodal segment forming incompletely fused allobasis, about 3.4 times as long as maximum width; original basis-endopod boundary marked by transverse surface suture at level of exopodal articulation; proximal part representing original basis with few small spinules at distal exopodal corner. Exopod one-segmented, unornamented and elongate, with a long naked apical seta (about twice longer than exopod). Free endopodal segment with few lateral spinules proximally and transverse spinular row distally; medial armature consisting of two short spines (indicated by arrows in Fig. 7C, D ); apical armature consisting of two naked spines and three geniculate setae, longest of which with spinule around geniculation and fused basally to naked accessory seta.

Mandible, maxillule, maxilla and maxilliped as in N. spinicaudatus (see Sak et al. 2008: Figs 16D, E ; 17E, F ).

P1 ( Fig. 8A ). Praecoxa, coxa, basis and intercoxal sclerite not observed. Exopod three-segmented; all segments with several spinules around outer margin; exp-1 with outer spine; exp-2 without outer element; exp-3 with unipinnate outer spine, a long naked spine and two geniculate setae distally; distal margin of exp-3 with spinules. Endopod two-segmented, about as long as exopod; enp-1 about 1.6 times longer than enp-2, with a serrate seta arising from halfway down inner margin and two sets of two coarse spinules along outer margin; enp-2 without spinules, distal margin with naked outer spine and geniculate inner seta.

P2–P4 ( Fig. 8B–D ). Intercoxal sclerite of P2 rectangular with concave ventral margin; not observed in P3–P4. Praecoxae triangular, small and naked (not figured). Coxae broadly rectangular and without ornamentation. Bases smaller than coxae, with few spinules near base of P3 endopod and around outer corner in P2 and P4; anterior surface pore not discerned; outer basal seta absent in P2, long and either plumose (P3) or naked (P4) in remaining legs. Exopods three-segmented; exp-1 and -2 with coarse spinular ornamentation as illustrated; outer spine of exp-1 and -2 naked; exp-3 with an outer unipinnate (P3) or naked (P2, P4) spine, and two unipinnate (P2–P3) or bipinnate (P4) setae apically; P4 exp-2 elongate, distinctly longer than exp-1; inner seta of P4 exp-3 serrate in distal half and originating near distal margin from posterior surface. Endopods two-segmented; P2–P4 enp-1 unarmed, about 1.0, 1.3, and 4.0 times longer than their respective distal segments, with few coarse spinules along outer margin in P2–P3, but without ornamentation along inner margin; P2 enp-2 with long, apically serrate, backwardly directed seta near proximal margin and two unequal unipinnate setae around distal margin; apical margin of P3 enp-2 with long, sparsely bipinnate seta; apical margin of P4 enp-2 with long, distally serrate and basally fused, inner seta, and long, naked outer seta. Spine and seta formula as follows:

	Exopod	Endopod
P2	0.0.021	0.120
P3	0.0.021	0.010
P4	0.0.121	0.020

Fifth legs ( Fig. 7A ) closely set together, but not touching in ventral midline. Baseoendopod and exopod fused, forming elongate plate (about 2.3 times as long as maximim width); anterior surface with one pore; inner distal corner with long and straight, unornamented spinous process (homologous to inner spine); distal margin with one naked seta, and two short, equally long, bipinnate spines; outer basal seta plumose.

Male. Unknown.

Etymology. The specific epithet is derived from the Latin emendatus , past participle of emendare, meaning to correct or improve, and refers to the present redescription which amends Kunz’s (1971) original description, leading to the proposal of the new species.

Remarks. Kunz(1971) reported several females fromAngola which he attributed to Arenopontia (Neoleptastacus) acantha accraensis Lang, 1965 . Our re-examination of the only extant female of Kunz’s (1971) original material revealed several differences with Chappuis & Rouch’s (1961) type population of N. accraensis , warranting the proposal of a new species for the former in the acanthus -group. Neoleptastacus emendatus sp. nov. is so far the only species of the genus that displays strongly developed, median sternal processes on the posterior part of the cephalothorax and on the pedigerous somites bearing P2–P4. The midventral chitinous projections are typically hook-shaped and originate anterior to the intercoxal sclerites of the first four pairs of swimming legs. The function of the processes is unknown but it is conceivable that they enhance the wriggling ability of these tiny copepods in the interstitial habitat. Kunz (1971) observed some variability in the degree of their development and claimed that in some specimens they are replaced altogether by chitinous nodular outgrowths. The significance of the latter observation is difficult to assess because his reported variability in caudal ramus structure and presence/absence of anal processes (compare his Abb. 32–33) almost certainly reflects an amalgam of two species in his sample. The second form illustrated by Kunz (1971) in his Abb. 33 (and underrepresented in his sample) that displays a straight spinous terminal process on the caudal ramus and lacks the paired anal processes does not belong to the acanthus - group. Note that Kunz (1971) did not list the inner seta on P1 enp- 1 in his setal formula table. The species is so far known from the type locality only.

Figures

FIGURE 6. Neoleptastacus emendatus sp. nov. (♀): (A) habitus, dorsal; (B) habitus, lateral; (C) anal somite and caudal rami, dorsal; (D) anal somite and right caudal ramus, lateral.

FIGURE 7. Neoleptastacus emendatus sp. nov. (♀): (A) urosome, ventral; (B) antennule, dorsal; (C) antenna, outer; (D) antennary endopod, medial; (E) rostrum, dorsal; (F) midventral hook-like processes [indicated by arrows] on pedigerous somites; (G) hook-like process, lateral. [lateral endopodal spines indicated by arrows in C–D]

FIGURE 8. Neoleptastacus emendatus sp. nov. (♀): (A) P1, anterior; (B) P2, anterior; (C) P3, anterior; (D) P4, anterior.

FIGURE 16. Phreatipontia speluncae (Cottarelli, Bruno & Venanzetti, 1994) comb. nov. (♀): (A) habitus, dorsal; (B) habitus, lateral; (C) anal somite and caudal rami, dorsal [arrow indicating modified seta IV]; (D) anal somite and right caudal ramus, lateral.

FIGURE 17. Phreatipontia speluncae (Cottarelli, Bruno & Venanzetti, 1994) comb. nov.: (A) habitus (♂), dorsal; (B) antennule (♂), ventral; (C) antennule (♀), ventral; (D) antenna (♀), medial [lateral endopodal spines indicated by arrows].