Scoliosoma dimerosum, 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 : 563-565

Scoliosoma dimerosum gen. et sp. nov.

( Figs. 377 , 378 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21415 ) from a flat gall on the branchial wall of the ascidian Polycarpa rima Monniot F. & Monniot C., 1996 (Holotype MNHN-IT-2008-6761 = MNHN S1/POL.B/318), CRRFOCDN A3, Eastern Fields Atoll, Coral Sea, Papua New Guinea, depth 30 m, 22 October 1993.

Etymology. The specific name is derived from the Greek di (=two) and mer (=a part), referring to the twosegmented endopod of the maxilla in the new species.

Descriptionoffemale. Body ( Fig. 377A ) curved ventrally; body length 2.65 mm. Prosome tapering anteriorly, divided by 3 constrictions into cephalosome, first and second pedigerous somites, and fused third and fourthpedigerous somites; cephalosome ( Fig. 377B ) 364×382 μm, with weak lateral constriction near middle; dorsal cephalic shield extended ventrally. Fused third and fourth pedigerous somites forming swollen, globular brood pouch. Urosome ( Fig. 377C ) 6-segmented, tapering posteriorly; first urosomite not articulated from brood pouch. Genitalsomite (second urosomite) 160×377 μm; 4 abdominalsomites 227×340, 168×245, 154×168, and 105×123 μm, respectively. Caudalramus ( Fig. 377D ) small, 42×28 μm, incompletely articulated from anal somite, covered with minute spinules; armed with 3 small setae.

Rostrumshortandsemicircularasin D. haplomerosum gen. etsp. nov. Antennule ( Fig. 377E ) broad, leaf-like, about 1.3 times longer than wide, with several incomplete suture lines (or wrinkles) along posterior surface, armed with 11 smallsetae (grouped as 2, 3, and distal 6), and with minute spinules on anterior surface. Antenna ( Fig. 377F ) stout, 4-segmented; proximal 3 segments unarmed; terminal (secondendopodal) segment 50×18 μm; armed with 5 smallsetae (grouped as 1, 2, and 2) plus small, strongly curved terminal claw, about one-third as long as terminal segment.

Labrum ( Fig. 377G ) shortand broad, with patches of minute spinules posterolaterally. Mandible ( Fig. 377H ) with broad coxal gnathobase bearing numerous surface spinules; medial margin of gnathobase with pronounced distal tooth, 1 spiniform toothand 1 serrate projectionnear middle, and serrate proximal part: palp consisting of welldefined basis, exopod, and 2-segmented endopod; basis with weakly pinnate seta at mediodistal corner; exopod with 4 naked setae; first and second endopodal segments with 1 and 4 naked setae, respectively. Maxillule ( Fig. 377I ) bilobed distally; inner lobe (precoxal arthrite) with 5 pinnate setae on margin; smaller outer lobe (palp) bearing total of 5 setae, inner distal seta weakly pinnate, other 4 naked. Maxilla ( Fig. 377J ) 4-segmented; syncoxawith 2 endites and 2 and 1 setaeon first and second endites, respectively; basis with strong claw fringed with narrow membrane along concave margin; endopod small with 1 seta on first segment and 3 setae (1 large and 2 small) on second. Maxilliped ( Fig. 377K ) assmalllobe bearing 2 pinnate setae apically.

Legs 1–4 ( Fig. 378 A-D) rudimentary, lacking defined protopods. Legs 1–3 represented by lobate, blunt rami. Leg 4 as single small lobe (exopod). Both rami subequal in leg 1, but endopodal lobe markedly smaller than exopodal lobe in legs 2 and 3. Exopod of legs 1–4 with 1 small seta proximally on outer margin. Additional minute setae present: 2 distally on endopod of leg 2, and 4 each on inner margin of exopod of legs 3 and 4. Both rami of leg 1 and exopod of legs 2 and 3 ornamented with minute spinules. Leg 5 absent.

Male. Unknown.

Remarks. Scoliosoma dimerosum gen. et sp. nov. closely resembles the type species S. haplomerosum gen. et sp. nov. They share a similar body form, short caudal rami bearing 3 setae, broad, leaf-like antennules, an almost identically reduced maxillule, and very similar swimming legs. Nevertheless, thereare significantdifferences between them, including; the rami of the mandibular palp are not demarcated in S. haplomerosum gen. et sp. nov., unlike D. dimerosum gen. et sp. nov. in which the palp is clearly divided into the basis, exopod, and 2-segmented endopod, and the maxillary endopod is unsegmented in the type species but 2-segmented in S. dimerosum gen. et sp. nov.

Figures

FIGURE 377. Scoliosoma dimerosum gen. et sp. nov., female: A, habitus, right; B, cephalosome, dorsal; C, urosome, ventral; D, right caudal ramus, ventral; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule; J, maxilla; K, maxilliped. Scale bars: A, 0.2 mm; B, C, 0.1 mm; D–K, 0.02 mm.

FIGURE 378. Scoliosoma dimerosum gen. et sp. nov., female: A, leg 1; B, leg 2; C, leg 3; D, leg 4. Scale bars: A, 0.05 mm; B–D, 0.02 mm.