Cerviniella bisegmenta, Cho & Kim & Lee, 2023

Cho, Kyuhee, Kim, Jong Guk & Lee, Jimin, 2023, Two new species of Cerviniella Smirnov, 1946 (Copepoda, Harpacticoida, Aegisthidae) from the Yellow Sea, Korea, ZooKeys 1178, pp. 165-189 : 165

publication ID	https://dx.doi.org/10.3897/zookeys.1178.105407
publication LSID	lsid:zoobank.org:pub:49C77DFC-4F09-4786-AFCB-C83F0B745F0C
persistent identifier	https://treatment.plazi.org/id/78650D35-782E-409D-9FE6-4FA038DF9680
taxon LSID	lsid:zoobank.org:act:78650D35-782E-409D-9FE6-4FA038DF9680
treatment provided by	ZooKeys by Pensoft
scientific name	Cerviniella bisegmenta
status	sp. nov.

Treatment

Cerviniella bisegmenta sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4

Type locality.

The Yellow Sea; 34°59'40.14"N, 125°00'2.82"E; 88 m depth.

Type material.

Holotype. One ♀ preserved in a vial with 80% ethanol (MABIK CR00253873); collected from the type locality, 20 April 2019. Paratypes. One ♀ (MABIK CR00253868) dissected on 11 slides, three ♀♀ (MABIK CR00253869-00253871) each dissected on 10 slides, six ♀♀ (MABIK CR00253874) and eight ♀♀ (MInRB-Hr88-L001) preserved in a vial with 80% ethanol, collection data as in holotype; S.L. Kim leg.

Description.

Female (based on the holotype and paratypes). Body length from anterior margin of rostrum to posterior margin of caudal rami (paratype, MABIK CR00253868, in lateral view, telescoping of somites not considered) 797 μm (range: 694-797 μm, n = 11, holotype: 765 μm).

Habitus (Fig. 1A, B View Figure 1 ) subcylindrical, gradually tapering towards posterior caudal rami, with unclear separation between prosome and urosome. Prosome (Fig. 1A, B View Figure 1 ) slightly longer than urosome, comprising cephalothorax with completely fused first pedigerous somite, and three free pedigerous somites; posterior margins finely serrated. Cephalothorax bell-shaped, slightly longer than wide, ~ 28% of body length; integument covered with several sensilla, numerous minute pits and striped pattern (discernible under high resolution); rim with anastomosing patterns. P2-bearing somite longer than following two prosomites, with well-developed pleural area. Pleural areas of P3- and P4-bearing somites with pointed posterolateral corners.

Urosome (Figs 1A, B View Figure 1 , 3D View Figure 3 ) comprising P5-bearing somite, genital double-somite, and three free abdominal somites; integument of tergites covered with minute spinules and posterior margins finely serrated except for anal somite. Genital somite and third urosomite separated dorsally and laterally, but completely fused ventrally, forming genital double-somite (Figs 1A, B View Figure 1 , 3D View Figure 3 ), with one pair of hook-like lateral projections on original genital somite; ventral surface with striations. Genital apertures (Fig. 3D View Figure 3 ) located far anteriorly, closed off by a single plate, on both sides with an outer vestigial seta and an inner bare seta, representing P6 (Fig. 4E View Figure 4 ; based on holotype). Copulatory pore located in median depression at level of gonopores. Anal somite (Figs 1A View Figure 1 , 3D View Figure 3 ) as long as two preceding urosomites combined, ~ 2 × as long as the caudal rami, with one pair of sensilla; semicircular operculum ornamented with minute spinules; anal sinus wide.

Caudal rami (Figs 1A, B View Figure 1 , 3D View Figure 3 ) cylindrical, ~ 1.7 × as long as wide; surface covered with fine spinules; with one pore on ventro-distal surface; with seven setae: ventro-lateral seta I pinnate, short, inserted in proximal third of ramus, dorso-lateral seta II pinnate, twice as long as seta I; seta III pinnate, arising from outer ventro-distal corner, as long as caudal ramus; terminal setae IV and V well-developed, with internal fracture plane proximally, both setae fused basally, of which seta V longest, ~ 4 × as long as seta IV; seta VI shortest, spiniform, located on ventro-posterior margin; tri-articulate seta VII plumose, issuing from dorsal surface subdistally.

Rostrum (Fig. 1A, C View Figure 1 ) completely fused to cephalothorax, triangular, subdistally with paired sensilla and one ventral tube pore; anterior tip slightly concave.

Antennule (Fig. 2A View Figure 2 ) robust, short, five-segmented, covered with diminutive dots (or denticles) as shown in Fig. 2A View Figure 2 . First segment with a blunt conical process on outer distal corner. Second segment longest, with a distal peduncle bearing an aesthetasc fused to a seta. Forth segment shortest. Fifth segment distally with a small aesthetasc fused to a pinnate seta. Armature formula: 1 - [1 pinnate], 2 - [12 pinnate + 2 pinnate spine + (1 pinnate + ae)], 3-[3 pinnate], 4-[3 pinnate], 5-[6 pinnate + (1 pinnate + ae)].

Antenna (Fig. 2B View Figure 2 ) three-segmented, comprising coxa, allobasis, and one-segmented endopod. Coxa small (not figured). Allobasis elongated, covered with various-sized spinules on surface, and with long spinules along abexopodal margin and a patch of denticles near base of exopod as shown in Fig. 2B View Figure 2 ; with one subdistal abexopodal seta. Endopod distinctly shorter than allobasis, with long spinules on inner and outer margins and rows of minute spinules along inner distal margin; lateral armature comprising one plumose and two pinnate elements; distal armature consisting of four serrate spines and three setae, of which outermost spine fused to one seta. Exopod two-segmented, proximal segment longer than distal segment, with two setae; distal segment with two lateral and three apical setae.

Mandible (Fig. 2C View Figure 2 ). Coxa proximally with rows of spinules; gnathobase well-developed, with several multi-cuspidate teeth and one pinnate seta; outermost tooth largest; with two rows of minute spinules proximally and one row of spinules subdistally. Palp biramous, consisting of basis, three-segmented exopod, and one-segmented endopod; basis with four plumose setae distally, covered with spinules on surface, and with one row of setules on lateral margin. Exopod smaller than endopod; exp-1 and exp-2 each with one plumose lateral seta, and exp-3 with three plumose (one lateral and two apical) setae. Endopod with two lateral and five apical plumose setae, of which two apical setae fused at base (indicated by arrowhead in Fig. 2C View Figure 2 ).

Paragnaths (Fig. 3A View Figure 3 ) with well-developed chitinized lobes; distal and lateral margins covered with numerous spinules; posterior face with five strong spinules and one row of tiny spinules.

Maxillule (Fig. 2D View Figure 2 ). Praecoxa ornamented with outer and subdistal spinules; arthrite well-developed, with two juxtaposed anterior setae, ten distal elements, and two pinnate posterior setae; posterior surface with patch of spinules. Coxa ornamented with outer spinules; cylindrical endite with one pinnate and five bare setae. Basis and endopod fused, with spinules on anterior and posterior surface; distal margin with 13 setae. Exopod represented by three pinnate setae.

Maxilla (Fig. 3B View Figure 3 ). Syncoxa (damaged) large, with one row of stout spinules and one row of setules along outer margin, and five groups of spinules on anterior and posterior surfaces; with four endites: proximal praecoxal endite one-segmented, with two pinnate and two bare setae distally; distal praecoxal endite small, incorporated basally into syncoxa, with one pinnate and two bare setae distally; proximal coxal endite large, with one row of spinules subdistally, and one bare and two pinnate setae distally; distal coxal endite cylindrical, with one row of spinules subdistally, and one pinnate spine and two setae (one bare and one pinnate) distally. Allobasis large, with one stout spine and two setae distally; inner part drawn out into a curved strong claw accompanied by one stout pinnate spine and two setae. Endopod small, three-segmented; first segment with two bare setae; second segment with one bare and one geniculate seta; distal segment with one geniculate and three bare setae.

Maxilliped (Fig. 3C View Figure 3 ) three-segmented, composed of protopod, and two-segmented endopod. Protopod elongate, with two rows of long outer setules, one row of posterior spinules; with four endites ornamented with inner and anterior spinules: three syncoxal endites represented proximal to distal by one pinnate spine and one pinnate seta, one pinnate spine and two plumose setae, and one pinnate spine and one plumose seta; basal endite represented by one pinnate spine and one plumose seta. Endopod small; first segment with one row of outer spinules and one plumose subdistal seta; second segment with two pinnate distal spines and two pinnate lateral setae, of which proximal one plumose proximally.

P1 (Fig. 4A View Figure 4 ). Intercoxal sclerite transversely elongated and narrow, with surface reticulation distally. Praecoxa with spinules on anterior surface. Coxa with various-sized spinules and setules on anterior surface. Basis larger than coxa, with one anterior pore and several rows of anterior spinules; with one long plumose outer and one pinnate inner seta; rami set far away from each other. Exopod one-segmented, with a row of setules on inner margin, and rows of spinules on outer proximal margin and around bases of outer setae; with three inner, two apical, and five outer setae. Endopod one-segmented, with one anterior pore medially, setules along inner and outer margins, and anterior spinules around distal margin; with one inner, one outer, and two apical setae.

P2 (Fig. 4B View Figure 4 ) larger than other thoracic legs. Intercoxal sclerite well-developed, cordiform; anterior surface with conspicuous reticulation, distally with one pair of rows of long setules; distal margin concave. Praecoxa small, with minute spinules along distal margin. Coxa with several rows of various-sized anterior spinules and three rows of long outer spinules. Basis with one anterior pore and numerous rows of various-sized anterior spinules; distal margin with one small acute process between rami; plumose outer seta shorter than those of P1 and P3. Exopod one-segmented, with one anterior pore distally and several rows of setules along inner and outer margins; with five serrate outer spines, increasing in size distally, one serrate apical spines, one plumose apical seta, and four plumose inner setae; outer and distal margins with four acute and three small processes near base of spines. Endopod two-segmented, shorter than exopod; enp-1 with three outer rows of setules and two distal rows of minute spinules, outer margin drawn out into a chitinous process bearing weakly concave tip and inner margin with one plumose seta; enp-2 longer than preceding one, ~ 1.6 × as long as wide, with one outer, two apical, and four inner pinnate setae, outer and distal margins with two acute processes.

P3 (Fig. 4C View Figure 4 ) smaller than P2. Intercoxal sclerite well-developed, subrectangular, with surface reticulation; distal margin concave, with long setules. Praecoxa small, with two distal rows of minute spinules. Coxa with numerous rows of various-sized anterior spinules. Basis with numerous minute anterior spinules and row of inner setules, and one small acute process between rami; anterior pore larger than that of P2; outer seta plumose and ~ 3 × as long as outer margin of basis. Exopod one-segmented, with one row of outer spinules and several rows of outer and inner setules; outer margin with two blunt and five acute processes; with five serrate outer spines, increasing in size distally, one serrate apical spine and one pinnate apical seta, and three plumose inner setae. Endopod two-segmented, distinctly shorter than exopod; enp-1 with three groups of outer spinules and one plumose inner seta, outer corner drawn out into a chitinous blunt process; enp-2 oval, ~ 2.3 × as long as wide, with one plumose apical seta, outer and inner margins with row of setules.

P4 (Fig. 4D View Figure 4 ) rudimentary, uniramous, comprising outer setophore and exopod, fused basally to fourth pedigerous somite, covered with various-sized spinules; outer setophore cylindrical, longer than exopod, with long plumose seta. Exopod one-segmented, with one apical and one outer setae. Endopod absent.

Armature formulae of P1-P4 as follows:

P5 (Fig. 3D View Figure 3 ) bilobate as in P4, fused to somite, covered with minute spinules; outer setophore cylindrical, with one plumose seta. Exopod slightly exceeding setophore, with one plumose outer and one plumose apical seta, the latter ~ 2.5 × longer than outer seta.

Male. Unknown.

Variability.

The morphological variation in Cerviniella bisegmenta sp. nov. appears in the armature formula of thoracopods. P2enp-2 presumably has four inner setae in the normal condition, but the P2enp-2 of some specimens (four of 18 specimens) has two or three inner setae.

Abnormality.

Abnormal exopod and endopod of P2 were observed in one specimen (paratype, MABIK CR00253869) (Fig. 4F, G View Figure 4 ). In comparison with the normal condition of P2 (Fig. 4B View Figure 4 ), the abnormal exopod has a seta in place of the proximal fourth outer spine and a spine in place of the proximal third inner seta (Fig. 4F View Figure 4 , indicated by arrowheads), and the enp-2 lacks a small pointed protrusion on either side of the two apical setae (Fig. 4G View Figure 4 , indicated by arrowheads). In addition, paratype (MABIK CR00253868) displayed two setae (the normal condition) on one of the exopods of P4 (Fig. 4D View Figure 4 ) and three setae on the other exopod (Fig. 4D View Figure 4 ').

Etymology.

The specific name Cerviniella bisegmenta is derived from a combination of the Latin prefix bi -, meaning 'having two parts’ and the Latin noun segmentum, meaning ‘cutting’ or ‘piece’, and refers to the two-segmented antennary exopod, which is an autapomorphy of this species. It is a noun in the nominative plural.

Remarks.

Based on the presence or absence of the P4 endopod, Apostolov (2011) subdivided the genus Cerviniella into the Cerviniella brodskayae and Cerviniella mirabilipes groups. Cerviniella bisegmenta sp. nov. lacks the ramus and can be classified within the Cerviniella mirabilipes group, which includes C. danae , C. lagarderei , C. langi , C. mirabilipes , and C. talpa .

The segmentation of the female antennule is useful for differentiating among species of Cerviniella . Cerviniella bisegmenta sp. nov. has an advanced five-segmented antennule, shared in C. danae and C. hitoshii , but the latter species is in the Cerviniella brodskayae group. The other 11 Cerviniella species have a six- or seven-segmented antennule (see discussion below).

Cerviniella bisegmenta sp. nov. can be easily distinguished differs in several characters from the same group, C. danae . First, the antenna of C. bisegmenta sp. nov. has a two-segmented exopod, compared with the four-segmented antennary exopod of C. danae . Second, the mandibular endopod of C. bisegmenta sp. nov. has two lateral setae, whereas the mandibular endopod of C. danae has three lateral setae. Third, the basis and endopod of the maxillule of C. bisegmenta sp. nov. have a total of 13 setae, compared with 14 setae in C. danae . Fourth, the syncoxa of the maxilliped of C. bisegmenta sp. nov. has nine setae and spines, compared with the seven elements of C. danae . Fifth, the P1 endopod of C. bisegmenta sp. nov. has four setae, compared with six setae in C. danae . Sixth, the P3 exopod of C. bisegmenta sp. nov. has three inner setae, compared with two inner setae in C. danae . Finally, the caudal ramus of C. bisegmenta sp. nov. is short with a 1.7-fold length relative to width, compared with a 3.5-fold length for C. danae . The first and seventh aforementioned characteristics provide conclusive evidence for the identification of C. bisegmenta sp. nov. In all species of Cerviniella , except C. bisegmenta sp. nov., the antennary exopod is four-segmented, and the length of the caudal rami is> 3-fold to width and longer than the length of the anal somite.