Eobathynella gwangjuensis, Ji & Min, 2022

Ji, Su-Jung & Min, Gi-Sik, 2022, Eobathynella gwangjuensis sp. nov., a new species of Parabathynellidae (Crustacea, Bathynellacea) from South Korea, Zootaxa 5138 (5), pp. 549-562 : 552-557

Eobathynella gwangjuensis sp. nov.

Figures 2–6

Type locality. Gwangju-si (35°7'19.16"N, 126°47'1.28"E), South Korea. Collected by Su-Jung Ji , Geon-Hyuk Lee and Yong-Uk Ahn (4 June 2021) .

Type material. Holotype: female (NNIBRIV90869), dissected on seven slides. Allotype: male ( NNIBRIV 90870 ), dissected on six slides . Paratypes: five females (NNIBRIV90871–90875) and four males ( NNIBRIV 90876–90879 ) .

Diagnosis. Antennule six segmented with one lateral seta on the third segment. Antenna six segmented without setae on the penultimate segment. Labrum with 12 teeth. Mandible incisor process with four teeth, a seta-like proximal tooth; molar process with five spines. Maxillule distal segment with six spines and one tiny spine. Maxilla four segmented with setal formula 1-3-6-5. Thoracopod III-VII each with an epipod. Protopod of male thoracopod VIII having hand-like inner lobe. Female thoracopod VIII forming a pair of small round protrusions. Uropod sympod with six spines decreasing in length distally. Anal operculum protruded. Furcal ramus with four spines.

Description of adult female

Body ( Fig. 2A ) length 1.25 mm, approximately nine times as long as wide. Head as long as anterior three thoracic segments combined.

Antennule ( Fig. 2B ) six segmented, first segment with one small seta on inner distal margin, one simple dorsal seta and with one dorsal, one lateral and one ventral plumose seta on outer margin; second segment with one simple seta on inner distal margin, one group of four plumose setae on outer margin; third segment with one simple inner seta ventro-laterally and one outer lateral seta; inner flagellum of third segment with three simple setae; fourth segment with one stub seta and one plumose seta on dorsal margin, two stub setae and two plumose setae on outer distal apophysis being protruded; fifth segment with three inner simple setae, dorsally with two aesthetascs and one simple and one aesthetascs on outer margin; sixth segment with three subterminal aesthetascs and four simple setae.

Antenna ( Fig. 2C ) six segmented; setal formula 0 + 0/0 + 0/0 + 1/1 + 1/0 + 0/4(1).

Labrum ( Fig. 2D ) with 10 median teeth of similar size flanked by a small acute tooth on both sides; inner surface with two pairs of nipple-like lateral protrusion and with ctenidia.

Mandible ( Fig. 2E ) with incisor process of four teeth; tooth of ventral edge seta-like; spine row consisting of five spines; palp one segmented with an apical seta exceeding incisor process in length.

Maxillule ( Fig. 3A ) two segmented, proximal segment with four setae on distal margin; distal segment with six spines and one tiny spine near proximal segment; three subterminal smooth setae on outer distal margin.

Maxilla ( Fig. 3B ) four segmented, setal formula 1-3-6-5.

Thoracopods I–VII ( Figs. 3C–E , 4A–D ) slightly increasing in size up to thoracopod IV, thoracopods IV–VII similar in size; thoracopods III–VII each bearing one epipod on protopod; basis of thoracopod I–VII with 1 seta each on inner distal margin; exopod of thoracopods I–VII two segmented; endopods of thoracopods I–VII four segmented, setal formulae:

Thoracopod I 1 + 0/0 + 1/0 + 0/2(1)

Thoracopods II–VII 0 + 0/0 + 1/0 + 0/2(1)

Thoracopod VIII ( Fig. 6C ) forming a pair of small round protrusions in the hollow in the shape of a rectangle at the middle of the abdomen; without setae.

First pleopod absent ( Fig. 2A ).

Uropod ( Fig. 5B ) with cylindrical sympod bearing six spines decreasing in length distally on inner margin; endopod 46 % as long as sympod length, with one large spur and with a small inner spine; terminally with two plumose setae and one plumose and one simple seta on dorsal surface; with a spines row consisting 14 tiny spines on inner side; exopod similar in length with endopod, with two terminal plumose setae and an outer subterminal plumose seta and a basiventral simple seta.

Pleotelson ( Fig. 5A ) with one lateral seta on both sides.

Anal operculum ( Fig. 5A ) protruded.

Furcal rami ( Fig. 5A ) slightly longer than wide, with four spines and with two setae, of which longer one is plumose.

Description of adult male

The male differs from the female in thoracopod VIII. Thoracopod VIII massive in relation to body size; protopod massive occupying almost two thirds of whole in ventral view, inner lobe dentate distally, hand-like; basipod with numerous spinules partially (yellow arrows in Fig. 6A, B ); epipod absent; exopod with two distal setae and one medial seta, finger-like; endopod with two terminal setae, fused with basipod.

Remarks. Eobathynella gwangjuensis sp. nov. is morphologically most similar to E. yeojuensis in that: 1) the mandible has a seta-like tooth of the ventral edge, 2) the uropod sympod bears six setae, 3) the endopod of the uropod has a terminal spine and additionally smaller spines on the inner margin, 4) the exopod of male thoracopod VIII has two distal lobes, and the lower dentated lobe resembles a hand, and 5) the anal operculum protrudes. However, the new species differs from E. yeojuensis by the following features (characters of E. yeojuensis in parentheses): 1) the third segment of the antennule bears one lateral seta (two different size lateral setae), 2) the proximal segment of the maxilla bears one seta (two setae), 3) the endopod of thoracopod bears two claws (two claws and one seta) on the last segment, 4) the female thoracopod VIII displays two small round protrusions (round flattened protrusion), 5) the terminal spine on the endopod of uropod is unfused (fused) with the endopod and 6) the furcal ramus bears four (three) spines. The new species also shares characteristics with E. gracillima in female thoracopod VIII, forming a pair of small protrusions and having one seta on the proximal segment of the maxilla. However, the new species has four teeth instead of three on the mandibular incisor process and six spines instead of seven or eight spines on the uropod sympod.

Etymology. The species name is derived from Gwangju City, where the material was collected.

Figures

FIGURE 2. Eobathynella gwangjuensis sp. nov., (A) paratype female, (B–E) holotype female. (A) habitus (lateral); (B) antennule (dorsal); (C) antenna (dorsal); (D) labrum (ventral); (E) mandible. Scale bars: 0.5 mm (A); 0.05 mm (B–E).

FIGURE 3. Eobathynella gwangjuensis sp. nov., holotype female. (A) maxillule; (B) maxilla; (C–D) thoracopod I–III. Scale bar: 0.05 mm.

FIGURE 4. Eobathynella gwangjuensis sp. nov., holotype female. (A–D) thoracopod IV–VII.

FIGURE 5. Eobathynella gwangjuensis sp. nov., holotype female. (A) pleotelson and furcal rami (dorsal); (B) uropod (lateral). Scale bar: 0.05 mm.

FIGURE 6. Eobathynella gwangjuensis sp. nov., yellow arrows pointing numerous spinules on basipod of male thoracopod VIII. (A, B) paratype male (NNIBRIV90878, NNIBRIV90879), (C) paratype female (NNIBRIV90875). (A) thoracopod VIII (ventral); (B) thoracopod VIII (dorso-lateral); (C) thoracopod VIII (ventral). Scale bars: 0.02 mm.