Hippolyte karenae Fransen & Grave 2019, sp. nov.

Hippolyte karenae sp. nov.

(Figs. 7–13)

http://zoobank.org/ 21E17642-C84D-44ED-BDAC-3C69E3728E3E

Material examined. St. Helena: holotype ovigerous female (pocl 1.5 mm), on Macrorhynchia filamentosa (Lamarck, 1816), 20.4m, Speery Island (-16.029 -5.753), leg. P. Wirtz & J. Brown, 16.i.2014, fcn 14016/6305 (RMNH.CRUS.D.57333); 17 paratype specimens (pocl 0.6–1.6 mm), same data (RMNH. CRUS.D.57334); ovigerous female paratype (pocl 1.3 mm) same data, fcn 140116 /63/02-03 (OUMNH. ZC.2018-04-009); 6 paratype specimens, including 2 ovigerous females (pocl 0.6–1.3 mm), on Plumapathes pennacea (Pallas, 1766), 15.0m, Long Ledge (-15.945 -5.753), leg. P. Wirtz & J. Brown, 14.i.2014, fcn 140114 /60/3-6-7 (OUMNH. ZC.2018-4- 010); 5 paratype specimens, including 3 ovigerous females (pocl 0.6–1.5 mm), on M. filamentosa, 20.5m, Windy Cove (-15.998 -5.786), leg. P. Wirtz & J. Brown, 29.i.2014, fcn 140119 /83/01 (preserved with host) (OUMNH. ZC.2018-04-011).

Description. Carapace stout. In females (Fig. 7 A–C), rostrum moderately narrow, shorter than carapace, slightly exceeding antennular peduncle, with 3 dorsal teeth on rostrum proper of which distalmost close to tip of rostrum; 2 ventral teeth, distal tooth subapical, proximal tooth in front of level of distalmost dorsal tooth. Rostrum in males (Fig. 7B) more slender and shorter than in females, with 1–3 dorsal teeth and usually one subdistal ventral tooth. Hepatic tooth robust, reaching anterior margin of carapace. Antennal tooth small, just below slightly protruding infraorbital angle. Pterygostomial angle slightly protruding.

Third pleonite of abdomen (Fig. 7A) dorsal outline in lateral view distinctly curved. Ratio between dorsal length and height of sixth pleonite: 2.7.

Telson (Fig. 12B) with proximal pair of dorsolateral cuspidate setae between proximal third and middle of telson length; distal pair of dorsolateral cuspidate setae usually between first pair and telson apex. Telson apex (Fig. 12C) with 6 strong terminal cuspidate setae (external distinctly shorter than intermediate and median ones); 2 short ones present between long median ones.

Unpigmented part of eyestalk (Fig. 7A, C) (measured dorsally from point where it begins to broaden to base of cornea) longer than broad and longer than cornea. Cornea not overreaching stylocerite.

Antennular peduncle (Fig. 7D) reaching 0.6 of scaphocerite in mature females. First joint of antennular peduncle with strong distal outer tooth. Stylocerite long, reaching 0.8–0.9 of first joint of antennular peduncle in mature females. Outer antennular flagellum about as long as inner antennular flagellum. Outer antennular flagellum with 8–9 joints in females: 5–6 thick proximal and 2–3 thin distal joints; first thick joint 1.6 times as long as wide, other thick joints about as long as broad. Inner antennular flagellum with about 10 joints. Outer antennular flagellum in males usually with sturdier joints than in females.

Scaphocerite of antenna (Fig. 7E) 2.7 times as long as wide. Distolateral tooth of scaphocerite far from reaching tip of blade. Distolateral tooth and blade separated by distinct notch. Basicerite with distinct ventrolateral tooth. Carpocerite short, falling short of distal margin of basal segment of antennular peduncle.

Mandible (Fig. 8A) with incisor and molar process, palp absent. Incisor process with 4 teeth. Molar process with several bristles of short and robust setae.

Maxillula (Fig. 8B) with upper lacinia broadly rectangular, medially with two rows of stout spines and few long plumose setae anteriorly and posteriorly. Lower lacinia slender, curled inward, distally with few serrulate setae. Palp distally with one long plumose seta.

Maxilla (Fig. 8C) with basal endite bilobed; distal lobe medially with slender serrulate setae and anteriorly with few long plumose setae; proximal lobe slightly larger than distal lobe, medially with serrulate setae. Coxal endite short, medially with row of long plumose setae. Scaphognathite well developed. Palp short, distally with one plumose seta.

First maxilliped (Fig. 8D) with coxal and basal endites partly fused, large and broad; basal endite medially with slender serrulate setae; coxal endite medially with long plumose setae. Exopod well-developed, distally with 4 plumose setae; caridean lobe narrow. Epipod small, faintly bilobed. Palp long and slender with plumose setae medially and distally.

Second maxilliped (Fig. 9A) with dactylar segment of endopod almost twice as broad as long, medially densely fringed with long serrulate setae. Propodal segment anteriorly with few long plumose setae. Carpal segment short, unarmed, triangular. Meral segment short, unarmed, triangular. Basal and ischial segment fused, slightly longer than broad, medially with row of long plumose setae; exopod about twice as long as endopod, with few plumose setae distally and proximally. Coxal segment partly fused with basal segment, laterally with bilobed epipod.

Third maxilliped (Fig. 9B) reaching about mid-length of scaphocerite when extended forward. Distal segment medially with few, rather short serrulate setae, with about 8 large conical teeth on apex and distal third of medial border (Fig. 9C). Penultimate segment 0.3 times length of distal segment. Antepenultimate segment almost as long as distal segment, without distolateral spine, with few plumose setae on mesial margin. Basal segment medially with row of plumose setae; exopod as long as basal segment, with row of few plumose setae in distal half. Coxal segment without epipod nor arthrobranch.

First pereiopod (Fig. 9D) short, compact. Fingers about as long as palm, spatulate, with serrate cutting edges. Carpus shorter than chela, tapering proximally, excavate distally, unarmed. Merus as long as chela, about twice as long as wide, mesially with row of long plumose setae. Ischium much shorter than merus, medially with several long plumose setae. Basal segment about as long as wide, medially with long plumose seta.

Second pereiopod (Fig. 9E) long and slender, reaching mid-length of scaphocerite when extended. Chela with fingers as long as palm, cutting edges entire. First joint of carpus about as long as third joint, second joint distinctly shorter; first joint 2.0 times as long as wide, second joint 1.1, third joint 1.6 respectively. Merus slender, slightly shorter than carpus. Ischium about half length of merus, unarmed, two-jointed. Basal segment short, half length of ischium, unarmed. Coxal segment medially with few long simple setae.

Ambulatory pereiopods rather long and robust. Third pereiopod (Fig. 10A) almost reaching or slightly overreaching distal margin of scaphocerite when extended forward. Merus in mature females about 5.3 times as long as wide, carpus of third pereiopod 2.3 times as long as wide, propodus 6.0 times as long as wide. Merus with 1–3 subdistal outer spines. Carpus with 1–2 proximal outer spines. Propodus with 2 single ventral spinules in proximal half and 3 pairs of ventral spinules in distal third; lateral one in each pair longest; one distolateral spinule. Dactylus (Fig. 11A) about 0.45 of propodus length, corpus slightly curved, tapering distally, flexor margin with row of 9 spinules increasing in size distally except for unguis which is slightly smaller than subdistal spinule.

Fourth pereiopod (Fig. 10B) similar to third. Merus with one subdistal outer spine, seldom absent. Carpus with one proximal outer spine. Propodus with 3 single ventral spinules in proximal 2/3 and 3 pairs of ventral spinules in distal third. Dactylus (Fig. 11B) as in third pereiopod.

Fifth pereiopod (Fig. 10C) similar to third and fourth. Merus without spines. Carpus without or with single proximal outer spine. Propodus with 2 single ventral spinules in proximal third, with 4 pairs of spinules in distal 2/ 3. Dactylus (Fig. 12A) as in third and fourth pereiopod, with 10 spinules on flexor margin, including unguis.

Eggs small (diameter variable, depending on their developmental stage).

First pleopod of male with endopod less than half length of exopod; medial margin of endopod with row of simple setae; lateral margin of endopod with row of long plumose setae.

Second pleopod of male with endopod slightly shorter than exopod; appendix masculina and appendix interna subequal; appendix masculina distally with 6 finely serrulate long setae.

Ambulatory pereiopods in males distoventrally broadened with series of paired ventral serrulate spinules.

Colour. Not known.

Measurements. Maximum pocl in ovigerous females 1.5 mm; maximum pocl. in males 1.3 mm.

Etymology. This species is named in honour of Karen van Dorp, who for more than

10 years was the exemplary collection manager of the crustacean collection of Naturalis Biodiversity Center in Leiden, the Netherlands.

Host. All known specimens were collected from the hydroid Macrorhynchia filamentosa (Lamarck, 1816) and the antipatharian Plumapathes pennacea (Pallas, 1766). It is not know at this stage whether these records represent obligate or facultative associations.

Distribution. Presently only known from St. Helena in the tropical South-Central Atlantic.

Systematic remarks. The new species differs from all previously described Atlantic species of the genus, except H. coerulescens and H. obliquimanus, by having a well-developed tooth on the outer angle of the first peduncular article of the antennula. Hippolyte karenae sp. nov. can be easily distinguished from H. coerulescens by the absence of a postero-dorsal tooth on the fifth pleonite (vs. present in H. coerulescens), as well as by the shape of the rostrum, dorsal outline of the third pleonite and the different armature of the dactyli of the ambulatory pereiopods. In general morphology, the new species is somewhat reminiscent of the western Atlantic H. obliquimanus, but can be distinguished from that species by having one tooth on the outer angle of the first peduncular article of the antennula in adults (vs. 2–3 in H. obliquimanus, but sometimes only 1 in juveniles, see d’Udekem d’Acoz 1997). A further clear difference between both species is the armature and shape of the dactyli of the ambulatory pereiopods, with the dactyl being robust in H. karenae sp. nov. (vs. gracile in H. obliquimanus), the much more stronger developed accessory spinules in H. karenae sp. nov., the presence of two secondary ungui in H. obliquimanus (vs. absent in H. karenae sp. nov., although with several distal accessory spinules strongly developed).