Pentachaetus palauensis, Kim & Boxshall, 2020

Kim, Il-Hoi & Boxshall, Geoff A., 2020, Untold diversity: the astonishing species richness of the Notodelphyidae (Copepoda: Cyclopoida), a family of symbiotic copepods associated with ascidians (Tunicata), Megataxa 4 (1), pp. 1-6 : 498

Pentachaetus palauensis gen. et sp. nov.

( Figs. 330 , 331 )

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21380 ) anddissectedparatype (♀, figured) from Lissoclinum sp., marine lake, Ngeruktabel I., Palau (07°17.87 Ń, 134°26.82 É), 09 August 2005.

	Coxa	Basis	Exopod	Endopod
Leg 1	0-0	1-I	I-1; 0-1; 1, 1, 4	0-1; 0-1; 1, 2, 3
Leg 2	0-0	1-0	1-0; 1-0; 3, 1, 5	0-0; 0-0; 0, 3, 2
Leg 3	0-0	1-0	1-0; 1-0; 3, 1, 5	0-0; 0, 3, 2
Leg 4	0-0	1-0	1-0; 1-0; 3, 1, 4	0-0; 1, 2, 1

Etymology. The name of the type locality, Palau Island, provides the specific name for the new species.

Descriptionoffemale. Body ( Fig. 330A ) small and stout; bodylength 745 μm. Prosome 600 μmlong, expanding gradually posteriorly; dorsal cephalic shield bearing paired pointed horn-like process ( Fig. 330C ) posterolaterally. Metasome bearing 3 faint dorsal constrictions; fourth pedigerous somite expanded, longer than anterior part of prosome. Fifth pedigerous somite not discernible, fused with fourth. Free urosome ( Fig. 330B ) 5-segmented: genital and four abdominal somites 45×90, 34×79, 38×63, 28×55, and 34×51 μm, respectively. Caudal rami widely separated at base; each ramus ( Fig. 330D ) about 3.1 times longerthan wide (46×15 μm) and about 1.4 times longer than anal somite, narrowing distally: armed with 5 setae; largest seta 78 μm long, 1.7 times longer than ramus; 2 proximal setae located at 33 and 50% of ramus length.

Rostrum ( Fig. 330E ) semicircular, widerthan long. Antennule( Fig.330F )tapering,110μmlong,6-segmented; armatureformula 2, 8, 2, 2, 3, and 8+aesthetasc; all setae naked. Antenna ( Fig. 330G ) slender, 3-segmented; coxa and basis unarmed; endopod (third segment) 4.9 times longerthanwide (49×10 μm) and aslongas basis; armed with 4 setae plus small terminal claw, about 0.3 times as long as endopod.

Labrum weak, flexible. Mandible ( Fig. 330H ) with 5 teeth and 2 small setae on coxal gnathobase: basis with 1 seta on medial margin: exopod with 5 large setae of equal length; endopod 2-segmented; first segment bearing digitiform process medially tipped with 1 seta; second segment with 4 setae (distal 2 equal in length, both longer than 2 onmedial margin). Maxillule ( Fig. 330I ) with 9 setae on arthrite, 1 on each epipodite and basis, 4 on exopod, and 3 on endopod; coxal endite absent. Maxilla ( Fig. 330J ) 4-segmented, armedwith 4, 2, and 2 setaeon first to third endites of syncoxa, respectively, smooth claw plus 2 unequal setae on basis, and 1 and 3 setae on first and secondendopodal segments, respectively. Maxilliped ( Fig. 331A ) lobate, armed with 6 setae and ornamented with spinules on outer margin.

Legs 1 and 2 ( Fig. 331B, C ) with 3-segmented rami. Legs 3 and 4 ( Fig. 331D, E ) with 3-segmented exopods and 2-segmented endopods; secondendopodal segment of legs 3 and 4 elongate, more than 4 times longer than wide. Inner coxal seta absent in legs 1–4. Outer seta on basis moderately large and pinnate in leg 1, but small and naked in legs 2–4. Inner distal spine on basis of leg 1 small, 8 μm long. Outer spine on first exopodal segment of leg 1 smooth, elongate, 23 μm long, extending beyond base of first outer element of third exopodal segment. Second exopodal segment of leg 1 lacking outer element. Armature formula for legs 1–4 as follows:

Leg 5 ( Fig. 331F ) represented by elongate outer protopodal process tipped with seta, and inner, claw-like smaller process (representing exopod); exopodal seta positioned between outer and inner processes.

Male. Unknown.

Remarks. The combination of a semicircular rostrum (which is wider than long), the relatively long outer seta on the mandibular exopod (which is almost as long as the other 4 exopodal setae), the completely 3- segmented exopod of leg 1, and the large, unornamented outer spine on the first exopodal segment of leg 1 serves to differentiate P. palauensis gen. et sp. nov. from its congeners (see Table 11 ).

Figures

FIGURE 330. Pentachaetus palauensis gen. et sp. nov., female. A, habitus, right; B, leg 5 and urosome, ventral; C, cephalic horn; D, left caudal ramus, dorsal; E, rostrum; F, antennule; G, antenna; H, mandible; I, maxillule; J, maxilla. Scale bars: A, 0.1 mm; B, 0.05 mm; C–H, J, 0.02 mm; I, 0.01 mm.

FIGURE 331. Pentachaetus palauensis gen. et sp. nov., female. A, maxilliped; B, leg 1; C, leg 2; D, leg 3; E, leg 4; F, leg 5. Scale bars: A, 0.1 mm; B–F, 0.02 mm.