Untold diversity: the astonishing species richness of the Notodelphyidae (Copepoda: Cyclopoida), a family of symbiotic copepods associated with ascidians (Tunicata) Author Kim, Il-Hoi 0000-0002-7332-0043 Korea Institute of Coastal Ecology, Inc., 802 - ho, 302 - dong, 397 Seokcheon-ro, Ojeong-gu, Bucheon, Gyeonggi-do 14449, Republic of Korea ® ihkim @ gwnu. ac. kr; https: // orcid. org / 0000 - 0002 - 7332 - 0043 ihkim@gwnu.ac.kr Author Boxshall, Geoff A. 0000-0002-7332-0043 Korea Institute of Coastal Ecology, Inc., 802 - ho, 302 - dong, 397 Seokcheon-ro, Ojeong-gu, Bucheon, Gyeonggi-do 14449, Republic of Korea ® ihkim @ gwnu. ac. kr; https: // orcid. org / 0000 - 0002 - 7332 - 0043 ihkim@gwnu.ac.kr text Megataxa 2020 2020-12-24 4 1 1 6 http://zoobank.org/3fdd970e-62f1-4f67-8cce-10870bdb3c01 journal article 54097 10.11646/megataxa.4.1.1 7c9bc39d-9910-46f1-9558-c0647b9cbbdb 2703-3090 4591138 Diceratus unidentatus gen. et sp. nov. ( Figs. 334 , 335 ) Typematerial . Holotype (intact ♀ , MNHN-IU-2014- 21383 ) anddissectedparatype ( ♀ , figured) from Eudistoma hepaticum (Van Name, 1921) (MNHN-IT-2008-4067 = MNHNA 3/ EUD /18), westof Îleta Cochons, Guadeloupe , depth 1–5 m , 01 January 1981 . FIGURE 334. Diceratus unidentatus gen. et sp. nov. , female. A, habitus, right; B, cephalic horns; C, caudal rami, dorsal; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule; J, maxilla. Scale bars: A, 0.1 mm; B, 0.05 mm; C–I, 0.02 mm. FIGURE 335. Diceratus unidentatus gen. et sp. nov. , female. A, maxilliped; B, leg 1; C, leg 2; D, leg 3; E, leg 4; F, leg 5. Scale bars: 0.02 mm. Etymology . The specific name is a combination of the Latin uni (=one) and dentat (=toothed), referring to the single tooth on the coxal gnathobase of the mandible. Descriptionoffemale . Body ( Fig. 334A ) stout, strongly curved ventrally: body length 1.12 mm. Dorsal cephalic shield expanded ventrolaterally, with 2 pairs of horn-likeprocesses posterolaterally ( Fig. 334B ); ventral process smaller than dorsal. Metasome 4-segmented: fourth pedigerous somite inflated, as long as anterior part of prosome. Free urosome recurved ventrally, 5- segmented. Anal somite and caudal rami densely covered with ornamentation of thick setules. Caudal rami ( Fig. 334C ) originating close to each other, elongate, about 3.5 times longer than wide (80×23 μm): armed with 6 setae, but setae hardly discernible from setules; 2 proximal setae positioned at 36 and 50% of ramus length. Rostrum ( Fig. 334D ) large, longerthanwide (86×55 μm), gently tapering in proximal two-thirds and steeply tapering in distal third towards blunt apex, ornamented with many surface setules (or spinules). Antennule ( Fig. 334E ) stronglytapering, 7-segmented; armature formula 2, 16, 7, 3+aesthetasc, 3+aesthetasc, 1, and 10+2 aesthetascs; setae naked, crowded, and relatively short. Antenna ( Fig. 334F ) stout, 3-segmented; coxa and basis unarmed; endopod 41×15 μm, 0.67 times as long as basis, armed with 1 seta in middle and 3 setae distally plus weakly curved terminal claw, less than half length of endopod. Labrum ( Fig. 334G ) strongly tapering, with soft, setulose distal part. Mandible ( Fig. 334H ) with coxal gnathobaseforkedintostrongdistaltoothwidelyseparated from narrow proximal branch provided with pectinate distal margin: basiswith 1 setaonmedial margin: exopod with 4 or 5 setae (outermost seta present or absent, if present, only half as long as other 4 setae): endopod with 1 and 7 setae on first and second segments, respectively; setae on second segment unequal, outer margin seta very small, spinule-like, distalmost seta (fifth seta) much longerthan others. Maxillule ( Fig. 334I ) with 6 setaeon arthrite, 1 on epipodite, 2 on basis, 4 onexopodand 3 (middle seta longest) on endopod; coxal endite absent. Maxilla ( Fig. 334J ) 4-segmented; syncoxawith 3, 2, and 2 setae on first to third endites, respectively; basis with 2 small setae and large claw ornamented with large spinules along distal half of concave margin; endopod small with 1 and 3 setae on first and second segments, respectively. Maxilliped ( Fig. 335A ) small, unsegmented, armedwith 2 setae distally, ornamented with spinules mainly on outer surface. Leg 1 ( Fig. 335B ) with 3-segmented exopod and 2- segmented endopod; second endopodal segment armed with only 5 setae; inner and distal setae on third exopodal segment naked, all other setaeon both rami feebly pinnate. Legs 2–4 ( Fig. 335 C-E) with 3-segmented rami; endopods shorter than exopods. Inner coxal seta absentin legs 1–4. Outer seta on basis of legs 1–4 naked and uniformly sized. Basis of leg 1 with broad inner distal seta. Outer spine on first exopodal segment of leg 1 arched, large, 36 μm long, extending to base of second outer armature element of third segment. All setae on rami of legs 2–4 naked and bluntly tipped. Armature formula for legs 1–4 as follows: Leg 5 ( Fig. 335F ) positioned posteroventrally on somite, represented by outer digitiform protopodal process tipped with seta and inner, pointed exopodal process bearing smallseta on outer margin. Male . Unknown. Remarks . The differences between the type species Diceratus unidentatus gen. et sp. nov. and D . bispinosus (Ooishi, 1998) comb. nov . include: (1) the apex of the rostrum is blunt in the type species (vs. acutely pointed in D . bispinosus ); (2) the caudalramus is elongate, about 3.5 timeslongerthan wide in Diceratus unidentatus gen. et sp. nov. (vs. at most 3.0 timeslongerthan wide in D . bispinosus , measured from the original illustration); (3) the coxal gnathobase of the mandible bears only 1 major tooth (vs. 1 major and 1 or 2 subsidiary teeth in D . bispinosus ); (4) the maxillular arthrite bears 6 setae (vs. 4 or 5 setae in D . bispinosus ); (5) the endopod of leg 1 is 2-segmented (vs. 3-segmented in D . bispinosus ); and (6) the third endopodal segment of leg 2 is armed with 4 setae (vs. 3 setaein D . bispinosus ).