A new genus and species of Nannopodidae (Crustacea, Copepoda, Harpacticoida) from the Yellow Sea of South Korea

Abstract A new monospecific genus of the family Nannopodidae Brady, 1880 is proposed, based on specimens of both sexes of Concilicoxa hispidagen. et sp. nov. collected from subtidal sandy sediments in the Yellow Sea of South Korea. The presence of a coxal outer projection on the first to fourth legs and reduction of both rami of the second to fourth legs in this new genus show a clear relationship with a clade, which is characterised by the modified thoracopods for burrowing ability, comprising Huntemannia Poppe, 1884, Rosacletodes Wells, 1985, Laophontisochra George, 2002, Acuticoxa Huys & Kihara, 2010 and Talpacoxa Corgosinho, 2012 in Nannopodidae. Within this clade, C. hispidagen. et sp. nov. is most closely related to L. maryamae George, 2002 in having the prehensile endopod in the first leg, broad intercoxal sclerite on the second to fourth legs and the female fifth leg being composed of separate exopod and baseoendopod, but is distinguished by the absence of mandibular exopod, two-segmented mandibular endopod, presence of four setae on the distal exopodal segment of the first leg, and fusion of the intercoxal sclerite to the coxae in the third and fourth legs. These four features are considered as autapomorphies of the new genus. The possible relationship amongst members of the nannopodid clade is further discussed. Additionally, some comments on the taxonomic position of L. terueae Björnberg, 2014 are given, resulting in the transfer of the species to Acuticoxa as A. terueaecomb. nov.


Introduction
In the present study, a new genus, attributed here to the family Nannopodidae, is proposed to accommodate a new harpacticoid collected from subtidal sandy sediments around the Socheongcho Ocean Research Station (SORS), which is a platform-type observation tower in the Yellow Sea of South Korea. SORS plays an important role in monitoring ocean and meteorological changes related to global climate change. Herein, we describe this new taxon and clarify its taxonomic relationship within Nannopodidae. Additionally, we also discuss the taxonomic position of L. terueae Björnberg, 2014.

Materials and methods
Sampling for meiofauna was carried out from off SORS in the Yellow Sea of South Korea (Fig. 1). Sediment sample was taken at a depth of 68 m using a Smith-McIntyre Grab sediment sampler (0.1 m 2 ). To anaesthetise meiofaunal organisms, the sample was immediately bottled with a 7.5% MgCl 2 solution for 1 h and fixed with a 10% formalin solution. In the laboratory, this sample was rinsed and sieved with tap water using a 50 μm sieve. Harpacticoid copepods were sorted out from sediments under a stereomicroscope (M165 C; Leica, Germany) and stored in 95% ethanol. Specimens of a new taxon were cleared in lactic acid. Whole specimens were mounted separately on temporary slides for habitus drawing and measurement of the total body length and the latter was measured from the anterior tip of the rostrum to the posterior end of the caudal rami in lateral view. Specimens were dissected on a reverse slide (Humes and Gooding 1964) using tungsten needles and the dissected parts were examined. All drawings were made with a microscope (DM2500; Leica, Germany) equipped with differential interference contrast (DIC) and a drawing tube. Drawings of the habitus and appendages were prepared at a magnification of 400× and 1000×, respectively. After morphological examination, each dissected part was mounted in lactophenol or fluoromount-G (SouthernBiotech, USA) mounting medium on an H-S slide (Shirayama et al. 1993) and sealed with Hoyer's solution. Scale bars in figures are given in μm.
Prior to scanning electron micrography (SEM), specimens were pre-fixed with 2.5% glutaraldehyde for 4 h, post-fixed with 2% osmium tetroxide for 2 h and then stored in 0.1 M phosphate buffer (pH 7.4) overnight. At each step, the samples were washed with phosphate buffer solution three times for 10 min each. The materials were dehydrated through a graded series of ethanol dilutions (50%, 60%, 70%, 80%, 90%, 100%) for 30 min each, dried in a freeze dryer (Hitachi ES-2030; Japan), coated with gold in an evaporator (Hitachi E-1045; Japan) and then examined via SEM (Hitachi S-4300; Japan).
Type materials were deposited in the Marine Interstitial fauna Resources Bank (MInRB) of the Korea Institute of Ocean Science and Technology (KIOST), Busan, South Korea.
Other material for SEM. SOUTH KOREA•2♀♀1♂ on a stub for SEM; same data as for holotype.
Description of holotype female (MInRB-Hr59-S001). Total body length 617 μm (measurement based on holotype and six paratypes: range = 530-626 μm; mean = 588 μm; n = 7); maximum width 86 μm measured at the middle of cephalothorax. Body (Figs 2A, B, 8A) subcylindrical, slightly depressed, without distinct constriction between prosome and urosome; prosome slightly longer than urosome. Rostrum ( Fig. 2C) well-developed, triangular, reaching distal fourth of first antennular segment, defined from cephalothorax basally, with 1 pair of sensilla laterally and 1 median anterior pore ventrally; lateral margins convex proximally. Cephalothorax nearly square in dorsal aspect, slightly wider than long; integument covered with paired sensilla, several round depressions and irregular wrinkles (visible at high magnification, 1,000×; see insert in Fig. 2A); posterior margin ornamented with short and fine setules; arthrodial membrane of first pedigerous somite visible dorsally and laterally. Tergites of somites with surface ornamentation composed of 1-3 transverse furrows, with 1 mid pore (absent in penultimate and anal somites) and 1 pair of lateral pores (absent in penultimate somite); posterior margins with several paired sensilla (absent in penultimate somite); hyaline frills weak, with 1 row of long setules posteriorly except for anal somite. Genital somite and first abdominal somite fused ventrally forming genital double-somite, but original segmentation indicated by internal chitinous rib dorsally and laterally; genital field ( Fig. 3A, D) with 1 large copulatory pore on midventral depression posterior to genital slit; genital slit reverse U-shaped, covered by 1 pair of large opercula derived from P6 on both sides; P6 represented by 1 long and 1 small seta, with 1 row of spinules subdistally; single midventral egg sac carrying 6 large eggs, as long as 1/4 of total body length. Anal somite (Figs 2A, B, 3A, B) with 1 pair of dorsal sensilla near base of operculum, 1 row of long setules on both ventrolateral margins; operculum semicircular, with smooth distal margin; anal opening with lateral row of small posterior spinules on each side; anal opening with 3 fringes of fine setules (Fig. 3B).
Caudal rami (Figs 2A, B, 3A-C) elongate, oval, about 2.4 times as long as largest width, twice as long as anal somite; with a notch in mid-outer margin below caudal setae I and II; anterior half with a row of outer setules ventrolaterally; distal half with non-chitinous lateral margin; with 7 setae: seta I small naked, inserted in mid-length of outer margin ventrolaterally; seta II dorsal to and closely set to seta I, naked, longer than seta I; seta III naked, as long as seta II, arising from subdistal peduncle with  IV, inserted in outer distal corner; dorsal seta VII naked, tri-articulate at base, arising subdistally close to inner margin. Antennule ( Fig. 4A) short, 4-segmented. First segment largest, elongate, as long as distal two segments combined, with 1 small naked seta subdistally; inner margin with short row of spinules subdistally; outer margin convex, with longitudinal row of minute spinules. Second segment smallest, with 3 bi-articulate and 5 naked setae; outer margin with 1 weak protuberance. Third segment about twice as long as second one, gradually widening distally; lateral margin with 3 bi-articulate and 3 naked setae; inner distal corner with 3 peduncles, of which two with 1 apical seta each, and one bearing 1 apical seta fused to basally to 1 ae. Distal segment as long as preceding one, tapering distally; lateral margins with 6 bi-articulate and 3 naked setae; distal margin with 1 naked seta and 1 acrothek composed of 1 ae and 2 bare setae. Setal armature as follows: Antenna ( Fig. 5A) with small, unornamented coxa (not shown). Allobasis elongate, 2.8 times as long as wide, exopod represented by 1 naked seta issuing at proximal third; abexopodal seta absent. Free endopodal segment with 1 short row of spinules subdistally and 1 surface frill distally; lateral armature composed of 2 weakly-serrate setae; distal armature comprising 1 small and 1 stout spine, 3 geniculate setae, innermost one of which fused basally to 1 small naked seta.
Etymology. The species epithet "hispida" is derived from the Latin adjective híspĭdus, which means 'hairy' and refers to the setulose lateral ornamentation of the anal somite and caudal rami in the female. It is a noun in the feminine singular.
Variability and abnormality. The investigated individuals of Concilicoxa hispida gen. et sp. nov. show intraspecific differences in appendage ornamentation. Dense spinular ornamentation was observed on the mandibular basis in one female paratype (MInRB-Hr-59-S003). This paratype also displays fusion of the coxa and basis of the P2 symmetrically (Fig. 6C).
Remarks. George (2002) established the genus Laophontisochra to accommodate L. maryamae from the Patagonian continental slope (Chile) and Laophontisochra sp. from the Magellan Straits (Chile). He allocated this genus into the family Cristacoxidae Huys, 1990, based on the presence of an outward growth on the coxa of P1, an enlarged maxilliped and atrophy of the antennary exopod and abexopodal seta despite the discrepancies with the following characters of the family Cristacoxidae, which were defined by Huys (1990): the first antennular segment with an outer spinous process, the absence of the exopod and an abexopodal seta in the antenna, the presence of modified seta on the middle endite of maxillary syncoxa and the single plate P5 with the same setae/spines in both sexes, which is considered as a neotenous origin. George (2002) suggested that the Cristacoxidae could be divided into two lineages: a plesiomorphic group comprising only Laophontisochra and a derived group composed of Noodtorthopsyllus Lang, 1965, Cubanocleta Petkovski, 1977and Cristacoxa Huys, 1990 [the latter was considered as a junior synonym of Noodtorthopsyllus by Huys and Kihara (2010)]. However, Huys and Kihara (2010) transferred the genus Laophontisochra to the family Nannopodidae, based on a re-evaluation of the three fundamental morphological differences between the two groups suggested by George, with their newly-erected genus Acuticoxa within the family Nannopodidae for Laophontisochra sp. sensu George, 2002(= A. biarticulata Huys & Kihara, 2010 and A. ubatubaensis Huys & Kihara, 2010 from the Brazilian coast. They assumed that both genera differ from the Cristacoxidae with the following evidence: (1) P1 coxa with a pair of serrated cristae (outer projections) in Noodtorthopsyllus and Cubanocleta vs. a single non-serrate, lobate or spinulose outgrowth in Laophontisochra and Acuticoxa; (2) maxillipedal endopod represented by a geniculated claw in Laophontisochra and Acuticoxa vs. nongeniculated in Noodtorthopsyllus and Cubanocleta; (3) antennary exopod consistently absent in Noodtorthopsyllus and Cubanocleta vs. atrophied in Laophontisochra and Acuticoxa (see Huys and Kihara 2010: 34). In addition, Huys and Kihara (2010) suggested that Laophontisochra and Acuticoxa are more closely related to both Huntemannia and Rosacletodes than to the cristacoxid genera, in that they share the presence of a coxal projection on the P1 -P4 (vs. the plesiomorphic state of this character expressed in Laophontisochra, which lacks the coxal processes in the P2-P4). Corgosinho (2012) created the genus Talpacoxa, which was first mentioned as "Genus X" by Huys and Kihara (2010) and revealed close relationships amongst the genera of the nannopodid clade-Huntemannia, Rosacletodes, Laophontisochra, Acuticoxa and Talpacoxa-supported by three synapomorphies that are likely morphological adaptations to a burrowing lifestyle: (1) P1 coxa with an outer projection; (2) the P2-P4 exopods one-or twosegmented; and (3) the P2-P4 endopods one-segmented or vestigial.
The new genus Concilicoxa gen. nov. is assigned to the Nannopodidae because, as a member of the nannopodid clade, it exhibits the burrowing adaptation of the thoracopods. Concilicoxa gen. nov. appears to be closely related to both Laophontisochra and Acuticoxa in that they share four-segmented female antennules with elongate first segments, the prehensile P1 endopod, the presence of coxal outer projection on the P1, large and broad intercoxal sclerites on the P2-P4, the general shape of the female geni-tal field (with a large copulatory pore and a well-developed operculum derived from P6) and elongate caudal rami. However, the novel genus is easily distinguishable from Laophontisochra by the distal armature of the antennary endopod with three geniculate and three non-geniculate elements (vs. four geniculate and two non-geniculate elements in Laophontisochra), the presence of coxal outer projections in the P2-P4 (vs. absent in Laophontisochra) and one-segmented exopods in the P2-P4 (vs. two-segmented in Laophontisochra). The new genus is also different from Acuticoxa in the absence of the P2 endopod (vs. one-segmented in Acuticoxa), a serrate coxal outer projection in the P1-P4 (vs. acute in Acuticoxa) and the female P5 exopod and baseoendopod separate (vs. fused into a single plate in Acuticoxa).
In contrast to a close resemblance with both genera in habitus and thoracopod morphology, Concilicoxa gen. nov. displays unambiguous autapomorphies that require the formation of a new genus: (1) the loss of the mandibular exopod, as observed in Huntemannia, is more derived than the exopod represented by a single seta; (2) the mandibular endopod is two-segmented, which seems to be secondarily divided, comparing to other related genera with only one-segmented endopod; (3) the P1 exp-2 comprises a total of only four elements, but five or six setae in Laophontisochra and Acuticoxa, respectively (in the original description of L. terueae, this segment was described as having one lateral and three terminal setae, but was depicted as having three outer and three terminal elements; see Björnberg 2014: fig. 11A); and (4) the intercoxal sclerites of P3 and P4 are laterally fused with the coxae in Concilicoxa gen. nov. (Figs 6D, 7C, E, 8B-D), but this fusion has rarely been reported in harpacticoid copepods (i.e. Orthopsyllus sp. of the family Orthopsyllidae Huys, 1990;cf. Huys and Boxshall 1991). By contrast, the presence of the maxillular exopod, as observed in Talpacoxa demonstrates a more plesiomorphic state than the lack of endopod.
The males of Concilicoxa gen. nov. exhibit distinctive potential autapomorphies for the genus as follows: (1) the P3 endopod has a sexual dimorphic distal element that is a robust spine; (2) the shape of P5 is nearly similar to that of the female; and (3) the caudal rami show sexual dimorphisms in the length of caudal seta V, the issuing position of setae I and II and the number of tube pores. However, we could not compare these characters with other related genera, because males of L. maryamae and A. ubatubaensis remain unknown. The sexual dimorphism of thoracopods is one of the most robust characters used to assess the phylogenic relationships between genera and between families because it facilitates comparison of the positions of homologue elements (such as setae or apophyses) of rami in females and males (Huys 1990;Huys and Kihara 2010). In this nannopodid clade, the known males tend to exhibit differences in morphology of the P3 endopod: (1) the male of Rosacletodes has a two-segmented P3 endopod with an elongate inner apophysis on enp-2, instead of a single seta as in the female (Pallares 1982); (2) all known males of the species of Huntemannia have an additional armature element on the P3 endopod, with no differences in segmentation as in Nannopus and Pontopolites (Song et al. 2007;Karanovic and Cho 2018); (3) the male of T. brandini exhibits a distal small apophysis on the one-segmented P3 endopod; and (4) although the male of L. maryamae has yet to be discovered, there is no sexual dimorphism on the P3 in L. terueae, whose taxonomic position seems to be problematic (see below). The male P3 endopod of the new genus presented herein is one-segmented with a stout spine (Figs 6D, 8D), whereas the female P3 endopod is represented by an unarmed protrusion. Such diverse sexual dimorphism of the P3 endopod prevents deeper insight into the systematic position of this clade within the Nannopodidae. We hypothesise that the lack of original outer element on the female P3 endopod in L. maryamae and C. hispida gen. et sp. nov. leads to the absence of the sexual dimorphic apophysis in the male. In contrast, the presence of a small apophysis on the corresponding ramus in T. brandini seems to be derived from a rudimental apical seta in the female.
Harpacticoids generally display sexual dimorphism in the size, shape and setae of the male P5. However, no sexual dimorphism has been observed in the male P5 of Arenopontiidae Martínez Arbizu &Moura, 1994 (Martínez Arbizu andMoura 1994). Additionally, both sexes bear the same number of setae/spines on the P5 of some taxa, such as Metidae Boeck, 1873, Rotundiclipeidae Huys, 1988, Ectinosomatidae Sars, 1903and Cristacoxidae Huys, 1990(Huys 1988Fiers 1992;Clément and Moore 1995;Huys and Kihara 2010). Except for Ectinosomatidae, the P5 of these families is remarkably reduced or represented by a single plate in both sexes. Although this sexual dimorphism is observed in other nannopodid genera, the structure of this leg in our new taxon is very similar in both sexes, except for micro-ornamentation, such as cuticular spinules and pores (Fig. 6B, E). In addition, the male of Concilicoxa gen. nov. expresses rare sexual dimorphisms in the shape of the caudal rami (oval in the female, but rectangular in the male), the length of caudal seta V (slightly longer than the caudal ramus in the female, but slightly shorter than the urosome in the male), the number of pores on the surface (one pore in the female vs. two pores in the male) and the lateral ornamentation (the presence of a row of long setules proximally in the female vs. absent in the male). These sexual dimorphisms could support the erection of a new genus Concilicoxa gen. nov.

Discussion
Taxonomic position of Laophontisochra terueae Björnberg, 2014Björnberg (2014 described the second species of Laophontisochra (L. terueae) from the south-eastern coast of Brazil, but provided insufficient description and illustrations. She argued that L. terueae fits the generic diagnosis of the genus as amended by Huys and Kihara (2010), despite obvious differences in the presence of endopods in P2 and P3 and in the structure of the female P5. Huys and Kihara (2010) suggested that two species of Acuticoxa, A. biarticulata and A. ubatubaensis, share five synapomorphies: (1) body somites with dense setular surface ornamentation; (2) distal armature of antennary endopod composed of three geniculate and three non-geniculate elements; (3) P2-P4 coxae with outer spinous process; (4) P4 exopod one-segmented; and (5) female P5 exopod and baseoendopod fused into a single plate, with eight elements in total. Laophontisochra terueae expresses these characters except for character 3, i.e. the outer spinous process on the coxae of P2-P4 is absent in L. terueae. Based on the absence of this character alone, Björnberg (2014) assigned this species, not to Acuticoxa, but to Laophontisochra. This species also shares the biarticulated condition of the caudal seta V comprising swollen proximal part and setular distal part with all Acuticoxa species (cf. Huys and Kihara 2010), indicating a probable close affinity between these taxa. Thus, we propose to tentatively re-allocate L. terueae into Acuticoxa as A. terueae (Björnberg, 2014) comb. nov.

Relationships amongst clade members with coxal outer projections on the thoracopods
The monophyly of the family Nannopodidae has been questioned by several researchers (e.g. Boxshall and Halsey 2004;Kihara and Huys 2009;Huys and Kihara 2010;Karanovic and Cho 2018). Por (1986) proposed the family Huntemanniidae and presented a brief diagnosis combining Metahuntemannia, Huntemannia, Beckeria, Nannopus, Pontopolites and Pseudocletodes, being unaware of the previous composition of Nannopodidae, which included Nannopus. Huys (2009) thereafter synonymised Huntemanniidae with Nannopodidae. Although the taxonomy, conceptualised by Por's (1986), remains available for nannopodid copepods (Huys and Kihara 2010), this old familial diagnosis cannot satisfactorily accommodate the morphological range of nannopodid copepods because it is neither specific nor accurate. Since Por's (1986) proposal, some nannopodid genera have been included and some excluded (see Dahms and Pottek 1992;Huys et al. 1996;Kihara and Huys 2009;Huys and Kihara 2010;Corgosinho 2012). Only three genera, Huntemannia, Nannopus and Pontopolites have remained in the family Nannopodidae, amongst which the genus Pontopolites remains questionable in that it differs from the familial diagnosis in having two-segmented antennary exopods and a natatorial P1 exopod. Based on its affinity with Huntemannia, which shares the presence of coxal processes on the P1, Huys and Kihara (2010) and Corgosinho (2012) included four genera, Rosacletodes, Laophontisochra, Acuticoxa and Talpacoxa in this family; however, both Laophontisochra and Acuticoxa show significant deviations from Por's (1986) diagnosis, including female antennules with four segments, prehensile P1 and elongate caudal rami. These deviations imply that either the familial diagnosis should be extended or the phylogenetic relationship of the family members should be re-assessed. Corgosinho (2012) suggested that Huntemannia, Rosacletodes, Laophontisochra, Acuticoxa and Talpacoxa form a clade within the family Nannopodidae; this relationship is supported by the presence of an outer coxal projection on the P1 and reduced P2-P4. However, there are morphological differences in the rostrum, male antennules, antennary endopod and exopod, both rami of the P1 and sexual dimorphism in the P3. It raises questions about the validity of this relationship amongst the five genera. George (2002) suggested that L. maryamae and A. biarticulata belong to a plesiomor-phic lineage of the family Cristacoxidae. This argument was subsequently rejected by Huys and Kihara (2010) who provided contrary evidence showing a close relationship between L. maryamae and A. biarticulata and the nannopodid genus Huntemannia, rather than between those two species and any cristacoxid genera. These authors suggested that the presence of coxal projections on the P1-P4 is a significant synapomorphy between Huntemannia and Laophontisochra. However, a closer relationship between Huntemannia and Nannopus is evident. These two genera share the presence of anterior setules on the rostrum, the absence of geniculate distal elements on the antennary endopod, the uniramous mandibular palp, the non-prehensile P1 endopod, the short caudal rami and the shape of the sexually-dimorphic male P3. Karanovic and Cho (2018) noted that some species of both genera show different endopodal complements on the P3 between females and males, without any differences in segmentation. By contrast, the species of Nannopus display certain primitive characters, such as the presence of two abexopodal setae on the antennary allobasis (e.g. Fiers and Kotwicki 2013;Kim et al. 2017;Vakati and Lee 2017).
As reported by Huys and Kihara (2010), the prehensile P1 endopod is a significant synapomorphy for Laophontisochra and Acuticoxa. The new nannopodid genus, Concilicoxa gen. nov., described from the Yellow Sea of South Korea, also shares this character, as well as additional synapomorphies that provide evidence of affinity amongst these three genera: (1) the four-segmented female antennule and its elongate first segment (vs. five-segmented in other congeners); (2) antennary exopod and abexopodal seta rudimentary or missing (vs. a one-segmented exopod and presence of a developed abexopodal seta in other congeners); (3) the enlarged maxilliped with a geniculate claw-like endopod (vs. non-geniculate endopod in other congeners); (4) both coxae of the P2-P4 are connected by a large, broad intercoxal sclerite (vs. a small and narrow plate in other congeners); and (5) the female genital complex with a typical structure comprising a large copulatory pore and reverse 'V'-or 'U'-shaped genital slit (vs. small copulatory pore and transverse genital slit in other congeners).
Although the male of Laophontisochra remains unknown, a derived condition may be expressed in the male antennules-with a single compound segment distal to geniculation in A. terueae comb. nov. and C. hispida gen. et sp. nov. The male antennule of T. brandini possesses two segments distal to geniculation and the male antennule of R. kuehnemanni (Pallares, 1982) remains undescribed. Huys and Kihara (2010) assumed that the P1 endopods in Rosacletodes and Talpacoxa are structurally identical with those of Laophontisochra and Acuticoxa in the segmentation and setal armature, even though there is a remarkable difference in the length of the first endopodal segment. However, a fundamental difference in exopods of Rosacletodes and Talpacoxa from those of Laophontisochra and Acuticoxa, as well as Concilicoxa gen. nov., is also readily recognised: the exopodal elements on the P1 are strong and enlarged in Rosacletodes and Talpacoxa, except for a single delicate one, but Laophontisochra, Acuticoxa and Concilicoxa gen. nov. have setiform or geniculate elements instead. Except for A. ubatubaensis, the setal pattern of the P1 exp-2 is identical in Laophontisochra, Acuticoxa and Concilicoxa gen. nov., with one to three small outer setae, one stout and uniplumose outer seta, one delicate distal seta and one geniculate distal seta.
Given these characteristics, the clade with outer coxal projections on the P1-P4 can be subdivided into three groups: (1) Huntemannia, which is characterised by the presence of a setular group on the rostrum, a five-segmented female antennule, the absence of geniculate setae on the distal armature of the antennary endopod, a onesegmented antennary exopod with four setae, a one-segmented mandibular palp, nonprehensile P1 endopod, sexual dimorphism expressed in the number of elements on the distal segment of the male P3 endopod; (2) Rosacletodes and Talpacoxa, which are characterised by the absence of a setular group on the rostrum, a five-segmented female antennule, the presence of geniculate setae on the distal armature of the antennary endopod, a one-segmented antennary exopod with three setae, a two-segmented mandibular palp, prehensile short P1 endopod, P1 exopod with stout spines and presence of a sexually-dimorphic apophysis on the distal endopodal segment of the male P3; and (3) Laophontisochra, Acuticoxa and Concilicoxa gen. nov., which are characterised by the absence of a setular group on the rostrum, a four-segmented female antennule with elongation of the first segment, the presence of geniculate setae on the distal armature of the antennary endopod, the atrophied condition of the antennary exopod (represented by a single seta or absent), a two-segmented mandibular endopod, prehensile long P1 endopod, setiform elements on the P1 exopod and absence of sexual dimorphism in the male P3 (A. terueae comb. nov.) or development of a stout spine in the male P3 endopod (C. hispida gen. et sp. nov.) (Table 1). Corgosinho (2012) suggested that the development of the coxal outer process and the reduction of both rami in P2-P4, along with the strengthening of the outer exopodal elements in Huntemannia, Rosacletodes, Laophontisochra, Acuticoxa and Talpacoxa are the results of adaptation to a burrowing interstitial lifestyle. He also suggested that the burrowing ability of Talpacoxa was conferred by the remarkably-developed process of the P1 coxa and both compact and well-ornamented rami of the P1. It is likely that the specialised morphology of the intercoxal sclerite of P1, which is broad, elongate and bearing a transversal groove, can facilitate the burrowing activity (Corgosinho 2012: figs 4A, 6A). However, the morphology of the P2-P4 is relatively unsuitable for burrowing activity due to its weak outer elements and absence of the intercoxal sclerite. By contrast, three genera, Laophontisochra, Acuticoxa and Concilicoxa gen. nov., exhibit prehensile P1 endopods, with a small coxal projection, which is distinctly smaller than coxa, does not seem designed for burrowing. Instead, these three genera may have acquired a burrowing lifestyle by the development of stout and well-developed exopodal elements and large, broad intercoxal sclerites in P2-P4. Our comparison of the detailed morphology of thoracopods indicates that the P1 may play a role in the burrowing activity in Talpacoxa, whereas the P2-P4 confers this ability in Laophontisochra, Acuticoxa and Concilicoxa gen. nov. This hypothesis supports the subdivision of the nannopodid clade into three groups. Table 1. Comparison of morphological characters among nannopodid copepods with modified thoracopods for burrowing ability (female only).  The original description by Wilson (1958) provided only its segmentation.
2 Exopods of the P2-P4 are one-segmented, but with a vestigial suture line between the two segments.
3 Segmentation and armature of the male antenna and mandible were referred because those of females were damaged. 4 Björnberg (2014) described the exopod bearing one seta on the first segment, and one lateral and three terminal setae on the second segment. However, the illustration of Björnberg (2014, fig. 11A) indicates an armature of 0.033.

5
The male has a one-segmented exopod.