Crymostygius thingvallensis, Kristjánsson & Svavarsson, 2004

Kristjánsson, B. K. & Svavarsson, J., 2004, Crymostygidae, a new family of subterranean freshwater gammaridean amphipods (Crustacea) recorded from subarctic Europe, Journal of Natural History 38 (15), pp. 1881-1894 : 1883-1892

publication ID	https://doi.org/ 10.1080/00222930310001597295
persistent identifier	https://treatment.plazi.org/id/116187A8-A039-FFE8-FE24-26FCFC27C9D4
treatment provided by	Carolina
scientific name	Crymostygius thingvallensis
status	sp. nov.

Treatment

Crymostygius thingvallensis View in CoL sp. nov.

( figures 1–6 View FIG View FIG View FIG View FIG View FIG View FIG )

HOLOTYPE: female, 18 mm, 7 June 1998, Vatnsvik (64‡14’46̎N, 21‡03’19̎W), Thingvallavatn, Iceland ( figure 7 View FIG ), groundwater inflow, electric fishing, coll. B. K. Kristjánsson, IMNH 2003.06 .17.1.

PARATYPES: female, 22 mm, 9 August 2000, Vatnsvik (64‡14’46̎N, 21‡03’19̎W), Thingvallavatn, Iceland, groundwater outflow, electric fishing, coll. B. K. Kristjánsson and G. Á. Ólafsdóttir, preserved in alcohol, IMNH 2003.06 . 17.2. Juvenile, 13 mm, 30 June 2003, Vatnsvik (64‡14’46̎N, 21‡03’19̎W), Thingvallavatn, Iceland, groundwater inflow, electric fishing, coll. B. K. Kristjánsson, IMNH 2003.07 .03.1.

Diagnosis. As for the genus.

Description. Adult body length 18–22 mm ( figure 1 View FIG ). Body long and slender, unpigmented. Indication of eye pigment. Pleonites with several fine setae on posterior margin. Uronites unfused, uronites 1 and 2 with posterodorsal clusters of differently sized setae, single posterodorsal seta in each setae cluster on uronites 1, 2 and on uronite 3 (female paratype only with spines in cluster on uronite 2). Interantennal lobe of head evenly rounded anteriorly, inferior antennal sinus moderately deep ( figure 1C View FIG ). Coxae shallow, contiguous, posterior margin of coxa 4 without excavation. Distoposterior corners of pleonal plates rounded.

Antenna 1 ( figure 2A View FIG ) 43–53% length of body, about 125% longer than antenna 2; peduncle segment 1 80% of combined length of segments 2 and 3; primary flagellum with about 30 segments; accessory flagellum three-segmented, terminal segment short.

Antenna 2 ( figure 2B View FIG ) with peduncular segment 5 subequal to segment 4, 46% of length of flagellum. Flagellum with 14 segments.

Upper lip ( figure 2C View FIG ) evenly rounded, fine setae on distal margin.

Mandible ( figure 2D View FIG ) well developed. Left lacina mobilis seven-dentate, incisor five-dentate, nine large spines and some small in spine row; molar pointed, truncated distally, one long seta subapically. Palp with three segments ( figure 2E View FIG ; segment 3 missing in left mandible of holotype, second segment regenerating), segment 2 with 15 plumose setae on lateral margin, 72% of length of segment 3; segment 3 with four or five long plumose E-setae, row of more than 35 short

plumose D-setae, pair of long B-setae.

Lower lip ( figure 2F View FIG , slightly damaged, inner lobes presumably missing) with outer lobes evenly rounded; fine setae on distal margin.

Maxilla 1 ( figure 2G View FIG ): inner plate ovate, medial row of six plumose setae, small setae apically. Outer plate apically with about 17 spines, medial margin of spines with 19–24 denticles. Palp two-segmented, segment 2 apically and subapically with short plumose setae and six simple setae, one longer plumose seta laterally.

Maxilla 2 ( figure 2H View FIG ): both plates with similar armature, larger setae on inner plate, outer plate with single group of distal setae.

Maxilliped ( figure 3A View FIG ): outer plate ( figure 3B View FIG ) with about six blade spines subapically; apically about six plumose setae distally, about 16 naked setae on inner margin. Inner plate ( figure 3C View FIG ) with five blade-like spines and six plumose setae on apical and subapical inner margin. Dactylus with fairly long, uncurved nail.

Gnathopod 1 ( figure 3D View FIG ) stout; coxal plate longer than wide, with several setae anteriorly and distally; posterior margin of basis with clusters of long setae; basis and merus posterodistally fringed with slender setae; ischium posteriorly with four rows of marginal setae; carpus evenly convex posterodistally, eight rows of marginal setae; propodus ovoid, much longer than carpus, palmar margin slightly oblique, no distinct angle; palmar margin with about 19 bifid spines ( figure 3F View FIG ) and rows with few setae; dactylus about 70% of propodus length; dactylus with row of blade-like processes on posterior margin ( figure 3E View FIG ); unguis about 33% of dactylus

length.

Gnathopod 2 ( figure 3G View FIG , gills not shown) stout, longer than gnathopod 1; coxal plate longer than wide, with several setae anteriorly and distally; basis longer than basis of gnathopod 1, posterior margin of basis with seven clusters of long setae; basis and merus posterodistally fringed with slender setae; ischium posteriorly with two rows of marginal setae; carpus angular posterodistally, seven rows of marginal setae, posterodistally numerous setae; propodus longer than propodus of gnathopod 1; much longer than carpus, palmar margin slightly oblique, no distinct angle; palmar margin with about 16 bifid spines on distal part of margin; eight rows with several setae proximally, few setae on distal margin, medio-anteriorly five rows of setae; dactylus about 58% of propodus length; dactylus with row of blade-like processes on posterior margin; unguis about 31% of dactylus length.

Pereopods 3 and 4 ( figure 4A, B View FIG ) slender, subequal in length; coxal plate longer than wide, with several setae anteriorly and distally. Basis slender; anteriorly, posteriorly and medially fringed with slender setae; dactylus about 35% of propodus length, several fine setae on posterior margin of dactylus ( figure 4C View FIG ).

Pereopods 5–7 ( figures 4D View FIG , 5A, B View FIG ) longer than pereopods 3 and 4, increasing in length towards posterior end. Basis slender, several fine setae on posterior margin of dactylus, increasing in numbers on posterior pereopods ( figures 4E View FIG , 5C View FIG ).

Stalked, club-shaped coxal gills present on gnathopod 2 and pereopods 3–6. Pair of lateral sternal gills on pereonites 3–7. Brood-plates present on pereopods 2–5, long and slender ( figures 3 View FIG , 4 View FIG ).

Pleopods 1–3 similar, biramous, unmodified, peduncle bearing two coupling spines. Pleopod 1 ( figure 6A, B View FIG ) outer ramus with at least 16 free segments and few fused segments proximally, inner ramus with at least 13 segments and few fused segments proximally. Similar segmentation on posterior pleopods.

Uropod 1 ( figure 6C View FIG ) slender, with about 11 spines on dorsal surface. Inner ramus with five apical spines, seven spines on dorsal surface. Outer ramus with four apical spines and about nine spines on dorsal surface.

Uropod 2 ( figure 6D View FIG ) with two spines on dorsolateral margin, one seta dorsodistally, four setae on dorsomedial margin. Inner ramus slightly longer than outer ramus, about as long as peduncle, with five apical spines and four spines on dorsal surface. Outer ramus with four apical spines and six spines on dorsal surface.

Uropod 3 ( figure 6E, F, H View FIG ) approximately 11.6% of body length. Peduncle small, one spine ventrodistally. Inner ramus vestigial, about as long as penduncle, 10% of length of outer ramus ( figure 6F View FIG ). Inner ramus distally with four small setae. Outer ramus two-segmented, with several apical spines on first segment, clusters of spines on lateral and medial margins; second segment with fine setae apically ( figure 6H View FIG ).

Telson ( figure 6G View FIG ) longer than broad, apical margin truncated with indication of small notch, apparently two to three spines and setae on apical lobes (female paratype with two setae and single seta respectively on each apical lobe).

Etymology. The species is named after the place Thingvellir (Þingvellir in Icelandic). The name means meeting (þing) and fields (vellir) and the Vikings came to þingvalla (thingvalla). In 930–1262 the Viking-Age settlers of Iceland established a remarkable society with an annual national assembly, the Althingi, as its most important institution, which met at Thingvellir. The gender is masculine.

Remarks. Only the female is known of this species. The species was collected at a spring inlet in Thingvallavatn. The lake, its formation, geology and its limnic ecosystem have been extensively studied ( Jónasson, 1992). The lake is about 90% fed by groundwater ( Adalsteinsson et al., 1992). Around 20% of the groundwater inflow occurs at and nearby Vatnsvik.

In the Vatnsvik area the groundwater is characterized by stability in temperature around 3‡C ( Ólafsson, 1992). The groundwater originates mainly from the ice cap of glacier Langjökull ( figure 7 View FIG ) and flows from its origin under the glacier towards the springs in less than 10 years (see discussion in Sveinbjörnsdóttir and Johnsen, 1992). The water flows through Eldborgir lava which has been dated at the age of 9130¡260 years ( Kjartansson, 1964; Saemundsson, 1992).