Sipadantonius roihani, Boonyanusith & Wongkamhaeng & Azman, 2024

Boonyanusith, Chaichat, Wongkamhaeng, Koraon & Azman, Abdul-Rahim, 2024, Sipadantonius roihani gen. et sp. nov., a new genus and species of Pseudocyclopidae Giesbrecht, 1893 (Copepoda, Calanoida) from the marine cave “ Turtle Tomb ” of Sipadan Island, Sabah, Malaysia, ZooKeys 1219, pp. 303-329 : 303-329

Sipadantonius roihani sp. nov.

Figs 2 , 3 , 4 , 5 , 6 (female); 6–8 (male )

Material examined.

Holotype • ♀ (adult), 0.95 mm long; 3 August 2023; coll. Azman, B. A. R.; light trap; UKMMZ -1631 . Allotype • ♂ (adult), 0.87 mm long, collection data for holotype; UKMMZ -1632 . Paratypes • 1 ♀ (adult) and 1 ♂ (adult); each was utterly dissected and mounted on a slide in glycerol and then sealed with nail varnish; the data was identical to that of the holotype; UKMMZ -1633 –1634 .

Additional material.

• 2 ♂♂ (adult); the data was identical to that of the holotype; preserved in 70 % ethanol, subsequently retained in collection of the Sabah Parks Zoological Collection in Semporna, Sabah .

Type locality.

The marine cave “Turtle Tomb” , Sipadan Island, Sabah, Malaysia; the entrance is located at 4°07'04.8"N, 118°37'41.0"E. Samples were collected in the cave at a depth of 22.0 meters below the sea surface, ~ 100 meters from the entrance.

Description of adult female.

Body (Fig. 2 A, B ) with a total length of 0.91–0.95 mm (measured from anterior margin of cephalosome to tip of furcal rami; mean: 0.93 mm; n = 3), slightly dorsoventrally flattened; integument covered with hair-like spinules. Prosome six-segmented, elliptical, ~ 70 % of body length and 2.2 × as long as urosome, ~ 2.3 × as long as wide, with greatest width at posterior margin of the first pedigerous somite (P 1 - bearing somite) (Fig. 2 A ). Cephalosome and all pedigerous somites free, with smooth hyaline frill on posterior margin of cephalosome and first four pedigerous somites (Fig. 2 A, B ); postero-lateral corners symmetrical and rounded (Fig. 2 B ). Naupliar eye not discernible. Urosome four-segmented, comprising genital double-somite, and three free abdominal somites; all somites with finely serrated hyaline frill on posterior margin (Fig. 2 C – F ). Genital double-somite barrel-shaped (Fig. 2 E ), ~ 27 % of urosome length, as long as wide, with greatest width at mid-length of double-somite, with lingual-shaped genital operculum ventromedially; two gonoporal plates triangular-shaped, partially hidden under genital operculum (Fig. 2 E ). Three free abdominal somites subequal in length. Anal somite with slightly developed anal operculum; posterior margin with serrated hyaline frill dorso-laterally (Fig. 2 F, G ); anal operculum with smooth free margin, ornamented with row of spinules (Fig. 2 F ).

Furcal rami (Fig. 2 F, G ) symmetrical, parallel, each ~ 3 × as long as wide, with serrated hyaline frill on distal margin and two cuticular pores laterally (Fig. 2 F, G ); furcal setae I and III absent; furcal seta II spiniform, with setulae along inner margin; seta IV shorter than seta V, with breaking planes and plumose; seta V longest, with breaking plane and plumose, sub-equal to urosome length, ~ 1.2 × as long as seta IV; seta VI plumose, ~ 0.8 × as long as seta V; seta VII very short and plumose, inserted beside seta VI (Fig. 3 A ). Length ratio of furcal setae II to ramus length ~ 0.5 and the ratio of setae to ramus length from seta IV to seta VII: 3.3: 3.9: 3.0: 0.2.

Rostrum (Figs 2 B , 3 D ) well developed, single plate and V-shaped; base broad, completely fused to anterior margin of cephalic shield and tapering to rounded tip between bases of antennules, with two sensillae, lacking rostral filaments.

Antennules (Figs 2 A , 3 C, D ) symmetrical, representing 26 - segmented, reaching distal margin of urosomite 2; ancestral segments II and III completely fused, representing evident segment II; ancestral segments X – XI partly fused, with remnant of ancestral articulation; ultimate segments ~ 1 / 3 of the length of pre-ultimate segment. Armature formula as follows (Roman numerals correspond to ancestral segment): 1 + ae (I), 2 + ae (II – III), 1 + ae (IV), 2 + ae (V), 2 + ae (VI), 2 + ae (VII), 2 + ae (VIII), 2 + ae (IX), 2 + ae (X), 2 + ae (XI), 2 + ae (XII), 2 + ae (XIII), 2 + ae (XIV), 2 + ae (XV), 2 + ae (XVI), 2 + ae (XVII), 2 + ae (XVIII), 2 + ae (XIX), 2 + ae (XX), 2 + ae (XXI), 1 (XXII), 1 (XXIII), 2 (XXIV), 2 + ae (XXV), 2 (XXVI), 5 + ae (XXVII – XXVIII).

Antennae (Fig. 4 A ) biramous. Coxa short, bearing one seta on distomedial corner. Basis with two setae on distomedial corner. Exp nine-segmented, setal formula from proximal to distal segments: 1.1. 1.1. 1.1. 1.1. 3. Endp two-segmented; proximal segment bearing two setae inserted at the same place on medial margin; distal segment bilobed, bearing nine apical setae on medial lobe and seven apical setae on distal lobe, with curved row of spinules on outer margin.

Mandibles (Fig. 4 B ) with sclerotised gnathobase comprising nine cuspidate teeth and one small dorsal seta on cutting edge. Mandibular palp biramous; basis with four setae on inner margin. Exp five-segmented, setal formula from proximal to distal segments: 1.1. 1.1. 2. Endp two-segmented; proximal segment with four setae on distomedial corner; distal segment short, with ten apical setae.

Maxillulae (Fig. 4 C ) with praecoxal arthrite bearing nine spinulose and spiniform marginal setae and one smooth marginal seta, with one seta on anterior surface and four setae on posterior surface; proximalmost one on posterior surface longest, unipinnate. Coxal epipodite with nine apical setae; two proximal ones shortest; coxal endite with six apical setae. Basis fused to Endp, proximal and distal endites armed with four and five apical setae, respectively; basal exite knob-like appearance, unarmed. Exp with eleven setae along apical and outer margin. Endp two-segmented, proximal and middle segments completely fused, setal formula: 4.3. 7.

Maxillae (Fig. 4 D ) seven-segmented, comprising praecoxa, coxa, basis and four-segmented Endp. Proximal and distal praecoxal endites with five and three apical setae, respectively. Coxa with two endites, each armed with three apical setae, with long spinules near distal margin of endite. Basis with large basal endite, armed with four apical setae; one of which strong and spiniform. Endp with setal formula: 3.2.2.3.

Maxillipeds (Fig. 4 E ) eight-segmented, comprising syncoxa, basis, and six-segmented Endp. Syncoxa with four syncoxal endites, setal formula: 1.2.4.4; one seta on second and third endite ~ 2 × as long as seta arising nearby. Basis with three medial setae, with row of spinules on anterior surface. Endp with setal formula: 2.4. 4.3. 3 + 1.4; seta 4 on segment II of Endp spiniform, with feather-like tip (Fig. 4 G ).

P 1 – P 4 (Figs 5 A – H , 6 A – D ) biramous, comprising coxa, basis, and three-segmented rami. Integument ornamented with numerous spinules and short hairs. Intercoxal sclerite sub-rectangular. Coxa with medial seta on distomedial corner. Basis of P 2 – P 4 with cuticular window representing remnant of armament on outer margin (Figs 5 G , 6 C, D ) but the remnant not discernible in P 1 (Fig. 6 B ). Outer spine of P 1 Exp setiform; those of Exp of P 2 – P 4 stronger and oar-shaped. Distolateral corner of P 1 Exp - 2 drawn out into mint leaf-like process; those of Exp- 1 and Exp - 2 of P 2 – P 4 slightly extended, with two acutely protrusions beside spine; inner protrusion larger and longer than outer one. Anterior surfaces of Exp- 1 and Exp - 2 with cuticular pores near insertion of outer spine; Exp - 2 with acutely minute process near distomedial corner in P 2 – P 4 but not discernible in P 1; Exp - 3 with cuticular pores near insertion of both proximalmost outer spine and outer apical one. Endp of all swimming legs with cuticular pores near distal margin of Endp- 1 and at distal ~ 1 / 4 of Endp - 3. Outer and outer apical spines of all swimming legs relatively short, oar-shaped; inner apical spine with serrated cuticular expansion on outer margin. Armature of swimming legs as presented in Table 1 . Some other characteristics of P 1 – P 4 as following described.

P 1 (Figs 5 A – C , 6 A, B ). Coxa trapezoidal; anterior surface with triangular expansion on proximomedial corner and oval integumental window near distomedial corner; integumental window surrounded by curved spinules. Basis bearing medial seta on distomedial corner but lacking either lateral seta or remnant of armament on outer margin; posterior surface with short curved hyaline process near insertion of Exp (Fig. 6 B ). Anterior surface of Exp- 1 with row of long spinules on distolateral corner. Endp- 1 with bifid indenture on distolateral corner and long spinules along posterior margin; Endp - 2 with an acute indenture on distolateral corner.

P 2 (Fig. 5 D, E ). Coxa rectangular. Posterior surface of Exp- 1 with circular integumental window near insertion of inner seta; Exp - 3 with two outer spines. Endp- 1 with an acute indenture on distolateral corner; that of Exp - 2 bifid.

P 3 (Figs 5 F, G , 6 C ) as that of P 2 but Exp- 1 lacking integumental window on posterior surfaces and Exp - 3 with three outer spines.

P 4 (Figs 5 H , 6 D ) Coxa sub-quadrate. Basis and rami as those of P 3.

P 5 (Figs 6 E , 7 A ) biramous, with both rami three-segmented; armament as in Table 1 . Integument and intercoxal sclerite as described for P 2 – P 4. Coxa rectangular, longer than wide; medial seta shorter than those of P 1 – P 4. Basis, Exp- 1 and Exp - 2 as in P 3 and P 4, but inner seta on Exp- 1 shorter than those of P 1 – P 4. Exp - 3 ~ 2.5 × as long as wide, offset on inner side at distal ~ 1 / 3 of segment. Endp- 1 and Endp - 2 with an acute indenture on distolateral corner each; Endp - 3 longer than length of Endp- 1 and Endp - 2 combined. Ornamentation as that of P 3 and P 4.

Description of adult male.

Body (Fig. 7 B ) with a total length of 0.87 and 0.89 mm (measured from anterior margin of cephalosome to tip of furcal rami; mean: 0.89 mm; n = 2). Habitus slightly smaller and slenderer than in female (Fig. 7 B, C ). Prosome six-segmented, elliptical, ~ 70 % of body length and 2.2 × as long as urosome, ~ 2.6 × as long as wide, with greatest width at posterior margin of the first pedigerous somite. Cephalosome and first three pedigerous somites similar to those in female. Naupliar eye not discernible. Urosome five-segmented; comprising genital somite and four free abdominal somites. Genital somite slightly asymmetrical; ventral surface with gonopore on proximal margin. All free abdominal somites similar in length, each with finely serrated hyaline frill on posterior margin. Anal somite identical to that of female (Fig. 7 B, D ).

Furcal rami (Fig. 7 D ) identical to that of female, ~ 3 × as long as wide. Armament and ornamentation identical to that of female.

Antennules asymmetrical. Left antennule non-geniculate, reaching distal margin of urosomite 2; articulation and setation identical to those of female. Right antennule geniculate, representing 22 - segmented (Fig. 8 A, B ); ancestral segments II – IV completely fused, representing evident segment II; ancestral segment XIV with hook-like transformed seta; ancestral segments XXI – XXIII and XXIV – XXV completely fused representing evident segment XIX and XX, respectively; ultimate segments ~ 1 / 3 of the length of pre-ultimate segment; armature formula as follows (Roman numerals correspond to ancestral segment): 1 + ae (I), 3 + 2 ae (II – IV), 2 + ae (V), 2 (VI), 2 + ae (VII), 2 + ae (VIII), 2 + ae (IX), 2 + ae (X), 2 + ae (XI), 2 + ae (XII), 2 + ae (XIII); 1 hooked seta + 1 + ae (XIV), 2 + ae (XV), 2 + ae (XVI), 2 + ae (XVII), 2 + ae (XVIII), 1 + ae (XIX), 1 (XX), 1 + ae (XXI – XXIII), 4 + ae (XXIV – XXV), 2 (XXVI), 5 + ae (XXVII – XXVIII).

Antenna, mandible, maxillula, maxilla, maxilliped, and P 1 - P 4 as those of female.

P 5 (Fig. 8 C-E ) biramous, asymmetrical. intercoxal sclerite as described for female P 3; coxa lacking medial seta. Left leg biramous; coxa and basis as shown; Exp and Endp three-segmented each. Exp- 1 lacking inner seta, with conical, smooth outer spine; Exp - 2 transformed, with claw-like extension on medial margin and conical, smooth outer spine; Exp - 3 with conical, smooth subapical spine and minute apical spine, with claw-like cuticular expansion at base (Fig. 8 C, D ); Endp inserted on medial socket of basis; Endp- 1 without inner seta, anterior surface longer than posterior one; Endp - 2 shorter than that of right leg, with inner seta; Endp - 3 with six marginal setae and cuticular pore on anterior surface. Right leg biramous; coxa and basis as shown; Exp and Endp three-segmented each; Exp- 1 and Exp - 2 elongate, each with one outer spine, but lacking inner seta each; Exp - 3 with apical spine fused to segment bearing it, with spine on both lateral and medial margin; Endp- 1 as that of right leg; Endp - 2 longer than that of left leg, with longitudinal groove on distolateral corner and inner seta; Endp - 3 as that of right leg.

Variability.

Based on three male specimens, including the allotype, the inner seta was absent from the right P 4 Exp- 1 in the allotype. There was no additional remarkable variation between the females and males.

Abnormality.

There was a curved suture on the right side of the ventral surface of the genital somite in one male (Fig. 7 D ).

Etymology.

The specific epithet was conferred in honour of Mr Roihan Han, a Malaysian deep dive record holder (at a depth of 164 m), who also led the Turtle Tomb exploration activity. Consequently, the name is a noun in the genitive singular.

Differential diagnosis and remarks.

The new taxon belonged to the superfamily Pseudocyclopoidea Giesbrecht, 1893 , indicated by the following diagnostic characteristics mentioned in Bradford-Grieve et al. (2014):

fully developed the arthrodial membrane between body somites and limb segments,

identical configuration of mouthparts in both sexes,

segments I-VIII of Exp of the antenna with one seta each,

segment V of Endp of maxilliped with outer seta,

right antennule of the male geniculate,

P 1 – P 5 with both three-segmented rami,

Exp- 3 of P 1 – P 5 with two, two, three, three, and three outer spines, respectively.

Epacteriscidae Fosshagen, 1973 and Pseudocyclopidae Giesbrecht, 1893 ( Bradford-Grieve et al. 2014) are two families of primitive calanoid fauna that have been recently accepted within it. Among these two taxa, Epacteriscidae is the basal calanoid fauna from a phylogenetic perspective ( Bradford-Grieve et al. 2010).

Following the recent morphological examination, the new species demonstrated a close affinity to the family Pseudocyclopidae through the presence of the following shared characteristics:

rostrum single plate with a rounded tip and without rostral filaments,

furcal ramus symmetrical and without modification of the left furcal seta VI,

mandibles with well-developed Endp forming the main axis of the mandibular palp,

maxillulae with marginal setae IX on coxal epipodite,

maxillipeds with normally developed endopod segments II-VI longer than coxa,

distolateral corner of Exp- 2 the female P 5 extended,

Exp- 2 of the female P 5 offset in oblique angle to the main axis of the rami.

Exp- 2 of the left leg of the male P 5 with the inner process.

It was noted that the new species exhibited an affinity to the family Epacteriscidae , characterised by the presence of aesthetasc on the ancestral segment IV of the antennule and the absence of inner process on Exp - 2 of the right leg of the male P 5. Furthermore, a combination of the presence of aesthetasc on the ancestral segment XIX of antennule in both sexes and the presence of aesthetasc on the ancestral segment XX of the female antennule, as identified in the new species, had been observed exclusively in Caiconectes Fosshagen & Iliffe, 2007 . Nevertheless, the new species could not be classified as a member of this family due to its lack of a bilobed rostrum, rostral filament, and raptorial-adaptive features of mouthparts. An example of the last characteristic was the enlargement of the ventral teeth (e. g., Fosshagen et al. 2001; Fosshagen and Iliffe 2007). In light of this, the presence of the aesthetasc on the ancestral segment XX of the female antennule was probably convergent among the new species and Caiconectes . The taxonomic placement of the latter genus remained uncertain, having been more recently classified as incerta sedis. The assumption that Caiconectes belonged to the Epacteriscidae phylogenetic lineage, whereas the new species belonged to the Pseudocyclopidae lineage, was supported by the differences observed in the following characteristics between the new species and Caiconectes : configuration of the rostrum, feeding mode adaptive feature of mouthparts, ornamentation of the distolateral corner of the P 1 Exp - 2.

Consequently, the placement of the new species within the superfamily Pseudocyclopoidea and the family Pseudocyclopidae was deemed justified. It was suggested that the presence of aesthetasc on ancestral segment IV of the female antennule and the absence of inner process on Exp - 2 of the right leg of the male P 5 constituted merely an occasional occurrence of the characteristic within the representatives of the justified family. Following the synonymisation of the families Boholinidae and Ridgewayiidae with the family Pseudocyclopidae , 14 calanoid genera were included. The genera Boholina , Exumella , Placocalanus , Pseudocyclops and Ridgewayia are polytypic; whereas the remaining genera are monotypic, represented by one species. Among these genera, the monotypic genus Pinkertonius is considered the basal taxon. The phylogenetic study indicated four characteristics that distinguished Pinkertonius from other genera: (1) the separation of ancestral segments II and III of the female antennule, (2) the presence of aesthetasc on the ancestral segment IV of the male antennule, (3) the presence of medial seta 4 on the female P 5 Exp - 3, and (4) the separation of Exp - 2 and Exp - 3 of both rami of the male P 5. Based on the aforementioned characteristics, the new species represented one of the phylogenetic transitional stages between the genus Pinkertonius and other genera, as the same conditions of characteristics (2), (3), and (4) were present in the new species with separated ancestral segments II and III of the female antennule. Other characteristics shared by the new species and Pinkertonius ambiguus Bradford-Grieve, Boxshall & Branco-Bercial, 2014 included (1) the shape and the armament of Exp - 3 and Endp of the right leg of the male P 5, (2) the absence of armature element of maxillular basal exite, and (3) the relative length of ancestral segment XXVII of antennule.

Nevertheless, the new species was unable to be classified as a member of the genus Pinkertonius and all genera of the family Pseudocyclopidae based on the combination of the following characteristics:

furcal rami lacking seta III,

furcal seta VII inserted beside seta VI rather than in front of the seta V or seta VI,

antennule with aesthetasc on ancestral segment IV in both sexes,

ancestral segments XIX-XXIII of the male antennule without modified setae

maxillulae with six setae on coxal endite,

seta 4 of the endopodal segment II of maxilliped transformed,

basis of P 1 - P 5 without lateral seta,

the male P 5 Endp- 1 lacking inner seta,

the right leg of the male P 5 lacks process on the inner margin of Exp- 2.

Consequently, the new generic rank Sipadantonius gen. nov. was established within the family Pseudocyclopidae , intended to accommodate the new calanoid species from the Turtle Tomb of Sipadan Island, Sabah, Malaysia. Furthermore, the female exhibited the most plesiomorphic characteristics of the family Pseudocyclopidae by having aesthetascs on the ancestral segments IV and XX of antennule and six setae on the maxillular coxal endite. The number of setae on the maxillular coxal endite in Calanoida exhibited variability; however, it was noted that there had never been more than five setae ( Boxshall and Halsey 2004). To date, the presence of six elements on the coxal endite was recorded in the order Misophrioida Gurney, 1933 , as well as the families Canuellidae Lang, 1944 and Longipediidae Boeck, 1865 ( Boxshall and Halsey 2004).

Figures

Figure 2. Sipadantonius roihani gen. et sp. nov. female: A habitus, dorsal view B habitus, lateral view C urosome, ventral view D urosome, lateral view E genital double-somite, ventral view F furcal rami, dorsal view G furcal rami, lateral view. Arrowheads indicate integumental pores. Scale bars: 200 μm (A, B); 100 μm (C, D); 50 μm (E-G).

Figure 3. Sipadantonius roihani gen. et sp. nov. female: A tip of furcal ramus, dorsal view B tip of furcal ramus, ventral view C antennule D rostrum and segments 1–17 of antennule E segments 18–22 of antennule F segments 23–26 of antennule. Roman numerals on antennule correspond to ancestral segments. Scale bars: 50 μm (A, B); 200 μm (C); 100 μm (D-F).

Figure 4. Sipadantonius roihani gen. et sp. nov. female: A antenna B mandible C maxillule, with picture of setae on posterior surface of praecoxal arthrite and enlarged picture of coxal endite D maxilla E maxilliped, with enlarged picture of transformed seta. Arrowhead indicates transformed seta on maxilliped. Scale bars: 50 μm.

Figure 5. Sipadantonius roihani gen. et sp. nov. female: A P 1 B basis of P 1, posterior surface C P 1 Exp - 2 D P 2 E P 2 Exp- 1, posterior surface F P 3 G lateral margin of basis of P 3 H P 4. Arrowheads indicate the important characteristic of the structure. Scale bars: 50 μm.

Figure 6. Sipadantonius roihani gen. et sp. nov. photographs of lateral surface of basis of swimming legs, female (A-E) and male (F): A posterior hyaline process on basis of P 1 (indicated by arrow) B P 1 C P 3 D P 4 E, F P 5. Arrowheads indicate cuticular windows on lateral margin of basis. Scale bars: 10 μm.

Figure 7. Sipadantonius roihani gen. et sp. nov. female (A) and male (B-D): A P 5 B habitus, dorsal view C habitus, lateral view D urosome, ventral view. Arrow indicates the ventral suture on genital somite. Scale bars: 50 μm (A, D); 200 μm (B, C).

Figure 8. Sipadantonius roihani gen. et sp. nov. male: A segments 1–15 of antennule, with picture of segment 12 that aesthetasc is removed B segments 16–22 of antennule C P 5 furcal view D Exp - 2 and Exp - 3 of right leg of P 5, lateral view E Endp- 1 and Endp - 2 of left leg of P 5, posterior surface. Arrowheads indicate the important characteristic of the structure and Roman numerals on antennule correspond to ancestral segments. Scale bars: 200 μm (A, B); 50 μm (C-E).