Stellatoniscus tentaculus, Oanh & Boyko, 2020

Oanh, Le Thi Kieu & Boyko, Christopher B., 2020, Cancrion khanhensis sp. nov. (Crustacea: Isopoda: Entoniscidae) infesting Monomia haanii (Stimpson, 1858) (Crustacea: Brachyura: Portunidae) from Nha Trang Bay, Khanh Hoa, Vietnam, with remarks on larval stages of entoniscids and description of a new family, genus and two new species of hyperparasites, Zootaxa 4894 (3), pp. 366-386 : 376-383

Stellatoniscus tentaculus sp. nov.

( Figs 5–7 , 8 D–F)

LSID urn:lsid:zoobank.org:act:96DD92CC-7A40-4F59-A6B1-002ADEC5048A

Type material. Holotype. Mature female (30 mm, longest tentaculum, stage IV), Nha Trang bay, Khanh Hoa province, Vietnam, from Ke Ga cape (12.301°N, 109.245°E) to Cu Hin cape (12.150°N, 109.233°E), ex mature female Cancrion khanhensis sp. nov. (32 mm, stage 12), ex male Monomia haanii (Stimpson, 1858) (89 mm CW), 8 Jan 2019, coll. L. T. K. Oanh ( NOMV-E.56948 ).

Allotype. Cryptoniscus larva (1.9 mm), same locality and collector data as holotype, ex mature female C. khanhensis sp. nov. (35 mm), ex female M. haanii (70 mm CW), 2 Jan 2019 ( NOMV-E.56946).

Paratypes. All same locality and collector data as holotype. January 2019. Cryptoniscus larvae (1.8 mm), ex mature female C. khanhensis sp. nov. (35 mm), ex female M. haanii (70 mm CW), 2 Jan 2019 ( CNVB 10040); Immature female (4.0 mm, stage I), ex mature female C. khanhensis sp. nov. (32 mm), ex male M. haanii (89 mm CW), 8 Jan 2019 ( NOMV-E.56947); Six cryptoniscus larvae (1.8–2.2 mm), two immature females (3.7–4.0 mm, stage I), mature female (21 mm longest tentaculum, stage IV), ex mature female C. khanhensis sp. nov. (32 mm), 8 Jan 2019 ( CNVB 10041).

February 2019. Three cryptoniscus larvae (1.8–2.2 mm), ex mature female C. khanhensis sp. nov. (26 mm), ex female M. haanii (69 mm CW), 23 Feb 2019 ( CNVB 10042); Five cryptoniscus larvae (1.8–2.2 mm), immature female (3.9 mm, stage I), mature female (29 mm longest tentaculum, stage IV), ex mature female C. khanhensis sp. nov. (31 mm), ex male M. haanii (65 mm CW), 28 Feb 2019 ( CNVB 10043); Cryptoniscus larva (1.8 mm), ex gill of male M. haanii (64 mm CW), 28 Feb 2019 ( CNVB 10044) Three cryptoniscus larvae (1.9–2.2 mm), two immature females (3.3–3.8 mm, stage I), mature female (27 mm longest tentaculum), ex mature female C. khanhensis sp. nov. (31 mm TL), ex immature male M. haanii (55 mm CW), 28 Feb 2019 ( CNVB 10045); Four cryptoniscus larvae (1.9–2.0 mm), immature female (3.3 mm, stage I), mature female (21 mm longest tentaculum, stage IV), ex mature female C. khanhensis sp. nov. (34 mm), ex male M. haanii (61 mm CW), 28 Feb 2019 ( CNVB 10045); Cryptoniscus larva (2.0 mm), ex mature female C. khanhensis sp. nov. (24 mm), ex male M. haanii (61 mm CW), 28 Feb 2019 ( CNVB 10047).

March 2019. Cryptoniscus larva (1.9 mm), four cryptoniscus larvae (2.0 – 2.1 mm), ex on gill and hepatopancreas, respectively, of female M. haanii (47 mm CW), 5 Mar 2019 ( CNVB 10048); Two cryptoniscus larvae (2.2 mm), ex mature female C. khanhensis sp. nov. (31 mm), one cryptoniscus larva (2.0 mm), ex female M. haanii (73 mm CW), 5 Mar 2019 ( CNVB 10049); Three cryptoniscus larvae (2.1–2.2 mm), one mature female (21 mm longest tentaculum, stage IV), ex mature female C. khanhensis sp. nov. (27 mm), ex female M. haanii (66 mm CW), 5 Mar 2019 ( CNVB 10050); Six cryptoniscus larvae (1.9–2.2 mm), 8 mature females (13–25 mm longest tentaculum, stage IV), ex mature female C. khanhensis sp. nov. (32 mm), ex female M. haanii (58 mm CW), 21 Mar 2019 ( CNVB 10051).

April 2019. Two cryptoniscus larvae (2.1–2.2 mm), mature female (25 mm LT), ex mature female C. khanhensis sp. nov. (26 mm), ex male M. haanii (74 mm CW), 5 Apr 2019 ( CNVB 10052); Two cryptoniscus larvae (2.1–2.2 mm), ex immature female C. khanhensis sp. nov. (21 mm), ex male M. haanii (82 mm CW), 25 Apr 2019 ( CNVB 10053).

May 2019. Three cryptoniscus larvae (2.1–2.2 mm), immature female (5.1 mm, stage II), mature female (31 mm longest tentaculum, stage IV), ex mature female C. khanhensis sp. nov. (29 mm TL), ex male M. haanii (65 mm CW), 5 May 2019 ( CNVB 10054); Two cryptoniscus larvae (2.2 mm), ex mature female C. khanhensis sp. nov. (24 mm), ex male M. haanii (59 mm CW), 5 May 2019 ( CNVB 10055); Three cryptoniscus larvae (2.1–2.2 mm), immature female (4.0 mm, stage I), two immature females (6.2–6.4 mm, stage III), ex mature female C. khanhensis sp. nov. (26 mm), ex male M. haanii (71 mm CW), 5 May 2019 ( CNVB 10056); Three cryptoniscus larvae (2.1–2.2 mm), mature female (30 mm longest tentaculum, stage IV), epicaridium larvae (ca. 0.4 mm), ex mature female C. khanhensis sp. nov. (30 mm), ex male M. haanii (71 mm CW), 5 May 2019 ( CNVB 10009); Two cryptoniscus larvae (2.0– 2.2 mm), ex mature female C. khanhensis sp. nov. (26 mm), ex female M. haanii (57 mm CW), 16 May 2019 ( CNVB 10057).

June 2019. Three cryptoniscus larvae (2.0– 2.1 mm), ex mature female C. khanhensis sp. nov. (28 mm), ex female M. haanii (66 mm CW), 9 Jun 2019 ( CNVB 10058); Two cryptoniscus larvae (2.0– 2.1 mm), two immature females (4.3–5.2 mm, stage II), ex mature female C. khanhensis sp. nov. (33 mm), ex male M. haanii (82 mm CW), 30 Jun 2019 ( CNVB 10059).

July 2019. Four cryptoniscus larvae (2.0– 2.2 mm), immature female (4.0, stage I), ex mature female C. khanhensis sp. nov. (26 mm), ex ovigerous female M. haanii (73 mm CW), 21 Jul 2019 ( CNVB 10060); Three cryptoniscus larvae (1.9–2.2 mm), mature female (26 mm longest tentaculum, stage IV), ex mature female C. khanhensis sp. nov. (32 mm), ex female M. haanii (71 mm CW), 21 Jul 2019 ( CNVB 10061).

August 2019. Six cryptoniscus larvae (1.9–2.0 mm), immature female (5.3, stage II), mature female (19 mm longest tentaculum, stage IV), ex mature female C. khanhensis sp. nov. (31 mm), ex female M. haanii (82 mm CW), 7 Aug 2019 ( CNVB 10062); Two cryptoniscus larvae (2.0 mm), two immature females (3.7–4.1 mm, stage I), ex mature female C. khanhensis sp. nov. (39 mm), ex male M. haanii (58 mm CW), 13 Aug 2019 ( CNVB 10063).

Etymology. The new species name is derived from the Latin tentaculum and is given due to the tentacle-like shape of the body extensions of the female.

Description. Female ( Fig. 5 ) immature stage I 3.7 mm with compact central body and 4 rounded broad lobes ( Fig. 5A ); immature stage II 5.1 mm with compact central body and 4 rounded broad lobes, distal tips of each lobe extending into thin nipple-like projections ( Fig. 5B ); immature stage III 6.0 mm, central body reduced in size, with 8 thin, tentacular extensions ( Figs 5C , 8F ); mature stage IV 30 mm, central body very reduced with 10 very long filamentous tentacular extensions filled with eggs ( Figs 5D , 8D, E ).

Epicaridium larva ( Fig. 6 ) approximately 400 µm long (anterior margin of cephalon to end of telson). Body tear-drop shaped; anterior margin of head rounded; eyespots lacking ( Fig. 6A ). Antennula of 2 rounded articles, article 1 thinner than but subequal in width to terminal article; terminal article with 5 long setae ( Fig. 6B, C ). Antenna elongated, approximately 3/4 as long as body ( Fig. 6A, D ); composed of 7 articles, 4 peduncular and 3 flagellar; article 1 thin, approximately 1/4 thickness of article 2; articles 2 and 3 subquadrate, subequal in size; article 3 with marginal spine; article 4 cylindrical, twice as long as article 3, flagellar article 1 approximately 1/3 length of distal peduncular article, terminal two flagellar articles smaller, distal article with 2 long setae and 1 short seta ( Fig. 6A, D ). Mandibles within oral cone; vestiges of maxilliped posterior to oral cone ( Fig. 6B ).

Pereon with 6 gnathopodal pereopods ( Fig. 6A ), subequal in size and shape, each with slender, recurved dactylus extending length of propodus; propodus, carpus distinct; propodus globular, ventral surface with two large, plate-like setae; carpus small, subtriangular; merus small, subrectangular, with distodorsal seta and smaller distoventral seta; ischium and basis cylindrical, ischium approximately half as long as basis ( Fig. 6E ).

Pleon with 5 pairs of biramous pleopods ( Fig. 6A, F ); cylindrical coxopodite, ovate exopodite bearing 2 long setae, cylindrical endopodite bearing 3 long setae. Uropods biramous, ovate peduncle rounded at distal end with one long seta on outer angle, distally with 2 slender rami, endopod and exopod subequal in length, both ending in 2 long, robust setae ( Fig. 6G ).

Cryptoniscus larva ( Fig. 7A ) body fusiform, strongly convex dorsally ( Fig. 7B ), length 1.8–2.2 mm, maximum width at pereomere 3, 0.5 mm. Cephalon anterior margin round; eyes positioned dorsolaterally. Body pigmentation lacking. Antennula ( Fig. 7C ) expanded distolaterally, mesially approximated, covering almost entire ventral cephalon; first segment flattened, broad, 7 distal, rounded projections with a further two ridges overlapping medial projection; proximomesial area with 5 longitudinal ridges; proximal margin with 4 spines and 1 short seta slightly distally; second segment cylindrical, projecting distolaterally, distodorsal region with few scales; exopodite short, cylindrical, endopodite longer, distally tapered, epipodite short, subtriangular, distally extended, all three segments with numerous long setae. Antenna with 4 peduncular and 5 flagellar articles ( Fig. 7D ), extending to posterior margin of pereomere 4; basal peduncular article with lineae, other articles smooth, second peduncular article with distoventral stout seta, third peduncular article with 3 distoventral short thin setae, fourth peduncular article with distoventral minute setae; distal 2 peduncular articles longer and more slender than proximal 2; first flagellar article slightly narrower than distal peduncular article; proximal four flagellar articles with 2 minute setae, distalmost article with two long terminal setae ( Fig. 7D ). Oral cone small, triangular, anteriorly directed, maxilliped not visible ( Fig. 7A ).

Pereon with rounded coxal plates on pereomeres 1–6 ( Fig. 7A ), lobes becoming progressively slenderer from pereomere 1 to 6; coxal plates 1–4 with scales on lobes ( Fig. 7E ); coxal plates 5 and 6 without scales; no coxal plates on pereomere 7. Pereopods 1, 2 and 3–7 dissimilar in size and shape ( Fig. 7A ). Pereopod 1 stout, dactylus short, approximately half propodus length, with scale-like spinules on outer surface, propodus rounded, carpus strongly convex ventrally, traversed by series of parallel rough ridges, merus small with ridges, ischium and basis smooth, cylindrical, ischium approximately half size of basis ( Fig. 7F ). Pereopod 2 ( Fig. 7G ) larger than 1, dactylus reaching to distal margin of merus, surface smooth; propodus smooth with 2 short spine-like setae on ventral margin; carpus with small scales and 1 distoventral spine-like seta; merus with faint ridges and 1 distoventral spine-like seta; ischium recurved, nearly smooth, slenderer than that of pereopod 1; basis smooth, distally tapered, slenderer than that of pereopod 1. Pereopods 3–7 ( Fig. 7A, H, I ) subequal in size and shape, much slenderer than 1 and 2; dactylus smooth, recurved, approximately half length of propodus, those of pereopod 7 with small setae on dorsal and ventral surface; propodus slender, slightly medially inflated, 2 stout spine-like setae on distoventral surface; carpus subtriangular with single distoventral spine-like seta; merus approximately twice as long as carpus, distally expanded with single distoventral seta; ischium and basis subequal in size and shape, dorsomedial surface expanded into broad lobe.

Pleon ventrally smooth ( Fig. 7A ); five pairs of biramous subequal pleopods; sympod rounded, distomesial corner with two long setae; exopods and exopods short, subquadrate, each with 5 long terminal setae ( Fig. 7J ). Pleotelson rounded ( Fig. 7B ). Uropods ( Fig. 7K, L ) biramous, composed of subquadrate sympod with single long seta at distolateral corner and very robust seta at distal medioventral corner, expanding to distal end of endopodal setae ( Fig. 7K ), endopod nearly twice as long as exopod, endopod with 2 long distal setae, exopod with 2 long distal setae and pair of lateral short setae.

Distribution. Nha Trang bay, Khanh Hoa province, Vietnam.

Remarks. Differences between the cryptoniscus larva of S. tentaculus gen. nov., sp. nov. and S. shieldsi sp. nov., known only from this larval stage, are given below in the Remarks under S. shieldsi sp. nov.

The infestation of C. khanhensis sp. nov. by the hyperparasite limited the reproductive development of the entoniscid host (smaller ovaries, lower quantity of eggs and/or epicaridium larvae), however it did not cause castration because infested entoniscids still had mature ovaries as well as entoniscid eggs and/or epicaridium larvae in their marsupia.

Discussion. Parasitic position. Almost all of the hyperparasite females were found in the brood chamber of mature (stage 12) C. khanhensis sp. nov. females (n=36). 88% (50/57) of cryptoniscus larvae of Stellatoniscus tentaculus gen. nov., sp. nov. were found in the brood chamber of entoniscid females, 5% (3/57) were found on the gills of Monomi haanii hosts, and 7% (4/57) were found on the hepatopancreas of M. haanii individuals. Those larvae found outside the brood chambers had located the crab host ( M. haani ) but not yet the entoniscid within.

Prevalence and intensity. Out of a total of 366 M. haanii examined, there were 37 crabs infested with C. khanhensis sp. nov.; of these entoniscids, 47% (23/49) were infested with S. tentaculus gen. nov., sp. nov. The prevalence of hyperparasite infestation in M. haanii was therefore 6% (22/366). The greatest number of hyperparasite females found in a single entoniscid brood chamber was eight, and they were often of mixed developmental stages; the greatest number of all life history stages (cryptoniscus larvae plus females) in the brood chamber of an entoniscid was 14; the smallest number was one. The greatest number of cryptoniscus larvae found infesting a single female C. khanhensis sp. nov. was six.

Figures

FIGURE 5. Female of Stellatoniscus tentaculus gen. nov., sp. nov. A, immature female (stage I); B, immature female (stage II); C, immature female (stage III); D, mature female. Scale bars: A–C = 1 mm; D = 5 mm.

FIGURE 6. Epicaridium larva of Stellatoniscus tentaculus gen. nov., sp. nov. A, habitus, lateral view; B, cephalon and pereomere 1, ventral view; C, antennula; D, antenna; E, pereopod 3; F, pleopod 1; G, uropods. Scale bars: A = 100 µm; B, E = 20 µm; C = 10 µm; D, F, G = 50 µm.

FIGURE 7. Cryptoniscus larva of Stellatoniscus tentaculus gen. nov., sp. nov. A, habitus, ventral view; B, habitus, dorsolateral view; C, antennula; D, antenna; E, pereomere 1 coxal plate; F, pereopod 1; G, pereopod 2; H, pereopod 7; I, pereopod 4; J, pleopod 1; K, uropod, ventral view; L, uropod, dorsal view. Scale bars: A, B = 0.5 mm; C, D, H, J–L = 0.1 mm; E–G, I = 0.2 mm.

FIGURE 8. A, Cancrion khanhensis sp. nov. mature ovigerous female; B, C. khanhensis sp. nov. mature female showing dorsolateral ovarian processes (arrows); C, C. khanhensis sp. nov, immature female (stage 8); D, C. khanhensis sp. nov. mature female infested by Stellatoniscus tentaculus gen. nov., sp. nov. mature female; E, S. tentaculus gen. nov., sp. nov. immature females (stage III); F, S. tentaculus gen. nov., sp. nov. mature female (stage IV). Scale bars = 5 mm.