Canthocamptus waldemarschneideri Novikov & Sharafutdinova 2022, sp. nov.

Canthocamptus waldemarschneideri sp. nov.

urn:lsid:zoobank.org:act: 3977FD97-8727-4DEA-BFEF-96DCA66A6BE5

Figs 1–9; Table 2

Canthocamptus sp. 1 – Novikov et al. 2021: 268.

Etymology

The species is named after Mr Waldemar Schneider, who helped us during the eXpedition.

Material examined

Holotype RUSSIA • ♀ (on 2 slides); Lena River Delta, small channel near Mount America-Haia; 72.467560° N, 126.285025° E; depth 1–1.5 m; 21 Aug. 2019; A. Novikov leg.; KFU BP 544/1-a, BP 544/1-b.

Allotype RUSSIA • ♂ (on 2 slides); same collection data as for holotype; KFU BP 544/2-a, BP 544/2-b.

Paratypes RUSSIA • 1 ♂, 1 ♀ (undissected; microtube); same collection data as for holotype; KFU BP 544/4 • 1 ♀; Lena River Delta, Krugloe Lake; 72.468859° N, 126.265658° E; depth 1–1.5 m; 21 Aug. 2019; A. Novikov leg.; KFU.

Other material

RUSSIA • 1 ♂; Lena River Delta, Samoylov Island, Yuzshnoe Lake; 72.369653° N, 126.509606° E; depth 1–1.5 m; 4 Aug. 2019; A. Novikov leg.; KFU • 2 ♂♂, 1 ♀; Lena River Delta, Samoylov Island, Ruiba Lake; 72.373173° N, 126.486302° E; depth 1–1.5 m; 4 Aug. 2019; A. Novikov leg.; KFU.

Description

Female (based on holotype)

BODY. Subcylindrical (as in Fig. 1A). Total body length from anterior margin of rostrum to posterior margin of caudal rami: 904 µm. CephalothoraX (Fig. 2A–B) with blue naupliar eye, wider than remaining somites, largest width 204 µm. Rostrum small, fused with cephalothoraX, with one pair of sensilla and one pore. Posterior margin of cephalothorax and all pedigerous somites slightly serrated.

ABDOMEN (Fig. 3). Consisting of genital double-somite, two free abdominal somites and anal somite with caudal rami. All somites eXcept anal somite serrated on posterior margin, on surface with rows of small spinules. Genital double-somite wider than long; with seven pairs of sensilla, two pairs of lateral pores, paired ventral group of three pores, one unpaired ventral pore and two dorsal unpaired pores; on posterior margin with dorso-lateral row of spinules and small ventral row of spinules. P6 (Fig. 3B) fused with somite with one pinnate and one naked seta. Genital field (Fig. 3B) long, laterally with sieves; copulatory pore in middle of somite, copulatory duct strongly chitinised with two additional tubes, eXtending proXimally to pair of labyrinthic rounded ducts. First free abdominal somite with three pairs of sensilla, one dorsal pore, one pair of lateral pores and five ventral pores; on posterior margin with dorso-lateral row of large spinules and ventral row of small spinules. Second free abdominal somite with one dorsal pore, pair of lateral pores and one ventral pore, on posterior margin with circumsomitic row of spinules. Anal somite with one pair of sensilla, three pairs of pores on ventral, dorsal and lateral sides, and ventral rows of spinules. Anal operculum semilunar, with four long spinules.

CAUDAL RAMI (Fig. 3). Length/width ratio 2, with two ventral pores; with rows of spinules on distal margin and rows of spinules at base of setae II and III. Seta I small, located near seta II. Apical seta IV (Fig. 1B) short, spinulose, with ʻhelle Stelleʼ (sensu Lang 1948). Apical seta V long, spinulose, with bulb at base. Length of apical setae IV and V 92 µm and 556 µm respectively. Seta VII triarticulated (Fig. 1A).

ANTENNULE (Fig. 4A). 8-segmented. Segment 1square, with one pinnate seta and two rows of spinules.Other segments with bare setae. Segment 4 with seta and aesthetasc fused basally. Distal segment with acrothek consisting of aesthetasc and two setae fused basally. Armature formula: 1-[1],2-[9],3-[5],4-[1+(1+ae)],5- [1],6-[3],7-[2],8-[5+acr].

ANTENNA (Fig. 4B). With allobasis. Coxa with three spinular rows. Allobasis with two pinnate setae and one spinular row. Free endopodal segment with two lateral rows of big spinules, with two spinulose spines and slender seta; distally with two rows of spinules; apically with three geniculate setae, two long spines and one small accessory seta; outermost geniculate seta fused basally with small seta. Exopod 2-segmented; first segment with one unipinnate seta; second segment with three bipinnate setae.

LABRUM (FIG. 1C). Typical for Canthocamptidae. On outer side with row of thin setulles and a pore. On inner side with lateral rows of big spinules and rows of spinules fused into comb; with distal spinules and proximal groups of very thin setulles.

MANDIBLE (FIG. 1D). Coxa with spinules proximally. Gnathobase with few multicuspidate teeth and spinulose seta; pars incisiva with one process; lacinia mobilis with two blunt teeth. Pars molaris sharply-

edged. Palp consisting of free basis and 1-segmented endopod. Basis with row of spinules; endopod with two spinular rows, one pinnate proXimal seta and four naked distal setae.

MAXILLULE (Fig. 4C–D). Praecoxa with two rows of slender spinules on outer edge and one row of spinules on posterior side. Praecoxal arthrite medially with row of spinules; with seven strong distal spines, distal seta with long spinules and two proXimal setae. CoXa with row of slender spinules, coXal endite with one pinnate and spinulose setae. Basis with two groups of spinules, two subdistal setae and three distal setae. Endopod and eXopod incorporated into basis, each represented by protuberance with two pinnate setae.

MAXILLA (Fig. 5A). Basis with several rows of spinules on outer and inner edge as figured, with two endites. ProXimal endite with one strong bipinnate seta, two pinnate setae and spinular row, distal endite with three pinnate setae. ProXimal endopodal segment with two setae, small process near one of setae and massive distal claw. Distal endopodal segment with three naked setae.

MAXILLIPED (Fig. 2C). Subchelate. SyncoXa elongated with several rows of spinules as figured, distally with one unipinnate seta. Basis with two rows of large spinules on anterior and posterior sides and three outer rows of small spinules. Endopod on posterior side with one seta. Endopodal claw elongated, with five small spinules.

P1 (Fig. 5B). With 3-segmented rami. PraecoXa with row of spinules. CoXa rectangular, with eight spinular rows. IntercoXal sclerite wide, with one pair of spinular rows. Basis with proXimal pore, medial row of spinules, rows of spinules at base of endopod and eXopod, row of spinules at base of inner seta and two inner rows of spinules; with strong inner and outer spines. All endopodal and exopodal segments with outer spinules. First eXopodal segment with one outer spine; second segment with inner spinular row, inner seta and outer spine; third exopodal segment with two outer spines and two slender apical geniculate setae. Endopod longer than eXopod. First endopodal segment reaching middle of third eXopodal segment,

with inner seta and inner spinular row; second endopodal segments with one inner seta, third segment with outer spine, long apical geniculate seta and small inner seta.

P2 (Fig. 6A). Praecoxa with row of spinules. Coxa with one lateral row of spinules and six rows of spinules on anterior side. IntercoXal sclerite with two paired spinular rows. Basis with proXimal pore, medial row of spinules, two rows of slender spinules on inner edge and rows of spinules at base of endopod and exopod; with outer spine.All endopodal and exopodal segments with outer spinules. Exopod 3-segmented; first eXopodal segment with outer spine, inner row of slender spinules and apically with frill; second segment with outer spine, inner seta, inner spinules and apical frill; third segment with three outer spines, two apical setae and one inner seta. Endopod 3-segmented; first and second segments with inner setae and inner spinular rows; third segment with inner spinular row, small outer spine, two apical setae and one inner seta.

P3 (Fig. 6B). Similar to P2. PraecoXa, coXa, basis, first and second eXopodal segments and first and second endopodal segments as in P2. Intercoxal sclerite with only one paired spinular row. Third exopodal segment with three outer spines, two apical setae and two inner setae. Third eXopodal segment with outer spine, two long apical setae and two inner setae with pectinate tip.

P4 (Fig. 6C). Similar to P2. PraecoXa, coXa and basis as in P2. IntercoXal sclerite with only one paired spinular row. EXopod as in P2, but third eXopodal segment with two inner setae with strong spinules. Endopod small; first segment with inner seta; second segment with outer spine, two apical setae and two inner pectinate setae; outer apical seta short, about as long as outer spine.

P5 (Fig. 5C). With separate right and left baseoendopods. Baseoendopod reaching about proximal third of eXopodal segment; with three pores, spinular row at base of outer seta; outer seta of basis naked. Endopodal lobe with five long bipinnate setae and one minute seta between fourth and siXth normal setae. EXopod with three equal outer setae, one long apical seta and minute inner seta.

Male

Total body length from tip of rostrum to posterior margin of caudal rami: 765 µm. Sexual dimorphism eXpressed in the antennule, P2–P6, genital segmentation and ornamentation. CephalothoraX and thoracic somites as in female. P6 (Fig. 7B) two asymmetric flaps fused to somite, with two slender setae and pinnate inner spine. Anal somite and caudal rami as in female, but seta V without bulb at base. Anal operculum with five spinules.

ANTENNULE (Fig. 8A–B). 10-segmented, haplocer with geniculation between segments 7 and 8. Segment 5 with large aestetasc fused at base with long seta. Segment 7 with articular plate, with one filiform seta, one pinnate seta and with two modified laminar setae. Segment 8 with 3 similar modified laminar setae. Segment 10 with acrothek consisting of slender aesthetasc and two setae. Armature formula: 1-[1],2- [9],3-[8],4-[2],5-[7+(1+ae)],6-[2],7-[2+2 modified],8-[3 modified],9-[1],10-[7+acr].

P2 (Figs 9A, 10A–B). PraecoXa, coXa, intercoXal sclerite and basis as in female. EXopod as in female, but segments broader and shorter. Endopod 2-segmented. First segment as in female. Second segment long, with well-defined border between original segments evidenced by proXimal inner seta and outer cuticular process; with two apical setae and two inner setae.

P3 (Figs 9B, 10C–D). PraecoXa, coXa, intercoXal sclerite and basis as in female. EXopod as in female, but segments broader and shorter. Endopod 3-segmented. First endopodal segment with slender seta and cuticular process on posterior side. Second endopodal segment with one small posterior seta and long apophysis with tip. Third segment with two small inner setae and one apical pinnate seta and one apical naked seta.

P4 (Fig. 9C). PraecoXa, coXa, intercoXal sclerite and basis as in female. EXopod as in female, but segments broader and shorter, and outer spines of third eXopodal segment curved. Endopod 2-segmented; first segment with inner seta; second segment with outer spinules, outer seta modified into finger-like process, two long apical setae and two pectinate inner setae.

P5 (Fig. 8C). Asymmetric; right and left P5 fused medially. Baseoendopod with four pairs of pores, outer spinular row and long outer naked seta; endopodal lobe with strong apical spine and small inner seta; left lobe with spinule near distal margin. EXopod with three equal in length outer setae, long apical seta, one minute inner seta and one long inner pectinate seta. Difference between left and right eXopods is that left one has much longer inner seta and shorter proximal outer spine.

Ecology

The species was found in four water-bodies of the Lena River Delta. The type locality at the collection site is a small channel without macrophytes with a silty bottom. The other three reservoirs are typical old thermokarst lakes with a large number of macrophytes and a silty bottom. At the type locality, the species was found with the following Copepoda species: Attheyella nordenskioldii (Lilljeborg, 1902), Bryocamptus nivalis (Willey, 1925), Moraria duthiei (Scott T. & Scott A., 1896), Cyclops kikuchi Smirnov, 1932, Diacyclops bicuspidatus (Claus, 1857), Eucyclops serrulatus (Fischer, 1851), Macrocyclops albidus (Jurine, 1820), Megacyclops gigas (Claus, 1857), Megacyclops viridis (Jurine, 1820), Metacyclops planus (Gurney, 1909), Paracyclops fimbriatus (Fischer, 1853) and Eurytemora gracilicauda Akatova, 1949.

Remarks

C. waldemarschneideri sp. nov. is closely related to the North American species with four setae on P2 endopod. This is an apparent synapomorphy of this group of species, which also includes C. assimilis Kiefer, 1931, C. robertcockeri M.S. Wilson, 1958 and C. vagus Coker & Morgan, 1940. The new species is closely related to C. assimilis based on similar caudal rami and the shape and length of the setae of P5. The differences between these two species are as follows: 1) the new species has a closed row of spinules on the posterior edge of the third abdominal somite, whereas C. assimilis has a gap on the dorsal side; 2) the caudal seta V of C. waldemarschneideri sp. nov. has a clearly visible thickening at the base, directed upwards; 3) the setal lengths of the male P5 vary more markedly in C. waldemarschneideri sp. nov., especially in the basoendopod, where inner seta/outer seta length = 4.8, whereas in C. assimilis inner seta/outer seta length = 3.1 (Kiefer 1931).

Cladistic analysis

The result of the cladistic analysis is the puzzled tree shown in Fig. 11A. The length of the tree is 216, and the consistency indeX (CI) and retention indeX (RI) are 0.468 and 0.703, respectively.

The most interesting feature was the division of the genus into two groups, one of which (C. mirabilis species group) is closely related to the genera Attheyella and Bryocamptus Chappuis, 1929. Such a division was previously assumed, and this group of species was considered intermediate between the genera Canthocamptus and Attheyella (Ito & Takashio 1980). The most significant characteristic connecting the C. mirabilis species group and the genus Attheyella is the form of the male P2 endopod, with the third segment without an outer seta and with a notch on the distal outer margin (ʻAttheyella-likeʼ endopod, Fig. 11B, character 36). Other synapomorphies of this group include dumbbell-shaped dorsal window (character 4), basis of mandible without setae (character 15), long first endopodal segment of P1 (character 30) and anal operculum with smooth margin (character 69). Based on this and some other differences (Table 7), we propose a new genus, Kikuchicamptus gen. nov., for this monophyletic group.

One species, C. gibba, is most closely related to A. nordenskioldii. According to the characteristics described and depicted by Okuneva (1983), this species is completely identical to the studied individuals of the species A. nordenskioldii from the Lena River Delta; therefore, it should be its junior synonym.

The Canthocamptus clade is supported by two reliable characters in the structure of the male P2 and P4 endopods: the endopod P2 with fused second and third segment, the third ancestral segment without outer seta, and with a posterio-lateral cuticular process on the border between the second and the third segment (ʻCanthocamptus-likeʼ endopod, character 37); the P4 endopod with modified ʻfinger-likeʼ outer spine (character 50). The division within Canthocamptus s. str. is rather controversial. The entire genus is divided into three large but poorly supported clades.

One of the clades includes C. staphilinus and all Baikal species. They were brought together by the similarity in the structure of the male P3 endopod, with a powerful second segment (character 44) and different degrees of reduction in the apical setae (character 43). If this hypothesis is correct, then the simple spine on the male P4 endopod (character 50) of the Baikal species is an apomorphy, not a plesiomorphy. In addition, the placement of the Baikal species C. verestschagini (Borutzky, 1931) and C. longifurcatus Borutzky, 1947 into a separate subgenus, C. (Baikalocamptus) Borutzky, 1931, is also incorrect in this case, since the subgenus Canthocamptus (Canthocamptus), in which Borutzky (1952) proposed to include all other species of the genus, becomes non-monophyletic. Moreover, our own material from Baikal shows that the spine on the male P4 endopod is modified in all the studied males of Canthocamptus sp. However, further research is needed here.

Another interesting clade is the C. glacialis species group, which includes C. glacialis, C. sinuus Coker, 1934, C. staphylinoides Pearse, 1905, C. assimilis, C. robertcokeri M.S. Wilson, 1958, C. vagus and C. waldemarschneideri sp. nov. Most species of this group live in North America. The relationship of C. glacialis to the American species was pointed out by M.S. Wilson (1956), though without naming specific common characters. Representatives of the group as a whole are characterized by the primitive structure of the male P2, P3 and P4 endopods (all endopods are slender, with unmodified, normally developed setae). They also lack the characteristic unguiform processes on the anal somite. However, the synapomorphies that combine these species are not sufficiently reliable. These are the loss of outer spinules on the P5 eXopod (character 56) and a large difference between the length of the spines on the P5 baseoendopod of males (character 60). Thus, the monophyly of the clade remains in question.

Based on the results of the cladistic analysis, we carry out the following taXonomic changes.