Arenopontia adriatica, Sak & Karaytuğ & Huys, 2024

Sak, Serdar, Karaytuğ, Süphan & Huys, Rony, 2024, A revision of the genus Arenopontia Kunz, 1937 (Copepoda, Harpacticoida, Arenopontiidae), including the description of five new species, Zootaxa 5433 (1), pp. 1-50 : 23-26

Arenopontia adriatica sp. nov.

Arenopontia daltonae : nomen nudum in Sak (2004: 135) https://zoobank.org/ B4CFEAD7-7582-403E-AC1D-EA4B0BA741EC

( Figs 11–12 )

Type locality. Croatia, Dalmatian coast, Isle of Mljet, Soline; coarse sandy beach .

Material examined. Holotype ♀ (in ethanol) ( NHMUK reg. no 2024.1032) . Paratypes are 3 ♀♀ in alcohol ( NHM reg. nos 2024.1033–1035) ; leg. H. Kunz, 04 May 1986.

Description of female. Total body length from tip of rostrum to posterior margin of caudal rami 180–245 μm (mean = 212 μm; n = 4; holotype = 245 μm). Body slender and cylindrical, without clear distinction between prosome and urosome. Hyaline frills of thoracic somites weakly developed and crenulated, those of genital double-somite and free abdominal somites strongly developed and typically consisting of rectangular digitate lappets ( Fig. 11A, B ). Genital double-somite ( Fig. 11A ) 1.2 times longer than wide; without chitinous ribs marking original segmentation; with two middorsal, two lateral and two ventral pores.Anal somite ( Fig. 11B ) with two dorsal and two ventral pores. Anal operculum pinnate, with minute spinules along free distal margin ( Fig. 11B ). Anus positioned subterminally between caudal rami. Rostrum ( Fig. 11F ) small, broadly subtriangular, tapering distally, with two delicate sensilla and an apical pore.

Caudal rami ( Fig. 11A, B ) approximately 2.25 times longer than wide (measured in dorsal view), tapering posteriorly; outer distal corner produced into posteriorly directed, recurved spinous process, accompanied at base by outer spinular row; dorsal surface without spur-like process but with spinules near inner margin. Armature consisting of seven setae; seta I small; setae II and III long and naked; seta IV short, naked, located between seta V and posterior spinous process; seta V long and with fracture plane; seta VI small, naked and located at inner distal corner; seta VII foliaceous and tri-articulate at base.

Antennule ( Fig. 11C ) slender, six-segmented. Segment 1 with a short seta near anterodistal margin. Segment 2 longest, about three times longer than wide. Segment 4 with long aesthetasc (L: 20 μm) fused at base with seta. Distal segment with seven naked setae (one of which spatulate) and apical acrothek consisting of short aesthetasc (L: 15 μm) and two slender setae, one of which minute. All setae 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-[7 + acrothek].

Antenna ( Fig. 11D, E ). Coxa small (not figured), without ornamentation. Basis and proximal endopodal segment fused, forming elongate allobasis; original segmentation marked by incomplete transverse spinular row. Exopod one-segmented, elongate, with a naked apical seta (about 2.1 times longer than exopod). Distal endopodal segment with spinules on medial surface and at outer distal corner; medial armature consisting of two short spines; apical armature consisting of two spines and three geniculate setae, longest of which with spinules around geniculation and fused basally to naked accessory seta.

Mandible, maxillule, maxilla and maxilliped as in A. anatolica sp. nov.

P1 ( Fig. 12A ). Intercoxal sclerite wide and subrectangular. Praecoxa represented by triangular naked sclerite. Coxa without ornamentation. Basis with spinular row near base of endopod and around outer margin; anterior surface with a small, setiform, naked spine near medial margin, pore not discernible. Exopod three-segmented; exp-1 and -2 with spinules around outer margin; exp-1 1.6 times longer than exp-2, with unipinnate outer spine; exp-2 without outer element; exp-3 with short naked outer spine, a longer curved unipinnate spine and one geniculate seta distally, and one inner, apically penicillate seta subdistally. Endopod two-segmented, prehensile; enp-1 about 8.5 times longer than wide, and 1.7 times longer than exopod; with a serrate inner seta in proximal third, and three groups of two spinules along outer margin; enp-2 slightly longer than wide, with a short unipinnate, curved outer spine and a longer geniculate inner claw, in addition to one spinule.

P2–P4 ( Fig. 12B–D ) intercoxal sclerites naked, with concave distal margin. Praecoxae small and naked, represented by triangular sclerite. Coxae rectangular and without ornamentation. Bases slightly smaller than coxae, with a spinular row near base of endopod and at outer distal corner; anterior surface with a pore near articulation with coxa; outer basal seta absent (P2), plumose (P3) or naked (P4). Exopods three-segmented; segments with spinular ornamentation as figured; all elements uni- or bipinnate (inner apical spine of exp-3); hyaline frills of exp-1 and -2 well developed; exp-2 with lateral pore halfway down inner margin length; P3–P4 exp-3 with anterior surface pore. Endopods two-segmented, with enp-1 longer than enp-2; P2–P4 enp-1 about 1.5, 2.4 and 1.8 times longer than their respective distal segments, with few coarse spinules as figured. P2 enp-2 with a long, apically serrate, posteriorly directed inner seta. P2–P3 enp-2 with a long bipinnate seta terminally. P4 enp-2 minute, with a basally fused, apically serrate seta, and a long unipinnate seta at outer distal corner. Spine and seta formula as follows:

Fifth legs ( Fig. 11A ) closely set together but not touching medially. Baseoendopod and exopod fused forming a rectangular plate with anterior surface pore near outer margin; distal margin with three pinnate setae, middle one markedly shorter than others, outer marginal seta longest; outer basal seta long and plumose.

Genital field as in A. anatolica sp. nov.

Male. Unknown.

Etymology. The species name (a noun in the genitive case) is named after the Adriatic Sea where the Croatian type locality is situated.

Remarks. Arenopontia adriatica sp. nov. belongs to a close-knit species group defined by the absence of a dorsal spur on the caudal ramus, presence of only four elements on the female P5, ornamentation of P1 enp-1 (with three groups of spinules along outer margin) and an anal operculum that is either pinnate (with fine spinules) or smooth. Other members of this group include A. subterranea , A. problematica and A. anatolica sp. nov., all of which display a P1 endopod ( Fig. 12A ) that is less slender than in A. adriatica sp. nov. In the latter species and A. problematica , enp-1 is about 1.7 times the length of the exopod, compared to 1.5 and 1.3 times in A. subterranea and A. anatolica sp. nov., respectively. However, in A. adriatica sp. nov. enp-1 is 8.5 times as long as its maximum width vs 6.9 times in A. problematica . Additional differences can be found in the relative proportions of some of the segments of P2–P4 (e.g. compare Figs 1B and 12B , and Figs 1D and 12D , respectively). Masry’s (1970: Fig. 65) illustration of the female P5 shows differences in proportional lengths of the marginal elements compared to those of A. adriatica sp. nov. However, given the deficiencies observed in other aspects of his morphological description (see above), additional material of A. problematica needs to be re-examined before these discrepancies can be corroborated.

Figures

FIGURE 1. Arenopontia problematica Masry, 1970 (♀): (A) P1, anterior [coxa omitted]; (B) P2, anterior [protopod omitted]; (C) P3, anterior [protopod omitted]; (D) P4, anterior [protopod largely omitted]; (E) antennule, dorsal; (F) right caudal ramus, lateral; (G) antenna [coxa omitted].

FIGURE 11. Arenopontia adriatica sp. nov. (♀): (A) urosome, ventral [genital field not figured]; (B) anal somite and caudal rami, dorsal; (C) antennule, dorsal; (D) antenna, lateral; (E) free antennary endopod, medial; (F) rostrum and first antennulary segment, dorsal.

FIGURE 12. Arenopontia adriatica sp. nov. (♀): (A) P1, anterior; (B) P2, anterior; (C) P3, anterior; (D) P4, anterior.