Jassa kjetilanna, Vader & Krapp, 2005

Vader, Wim & Krapp, Traudl, 2005, Crab-associated amphipods from the Falkland Islands (Crustacea, Peracarida), Journal of Natural History 39 (33), pp. 3075-3099 : 3076-3081

Jassa kjetilanna n. sp.

(Figures 1–3)

Type material

Holotype: adult male, 6 mm, in alcohol; East Falkland , Choiseul Sound, 30 m, from Paralomis granulosa , 20 October 2003, caught in baited traps. Deposited at TromsØ Museum no. 13842 . Paratypes: nine juveniles, one ovigerous female, 5 mm, from Paralomis

Figure 1. Jassa kjetilanna n. sp.: A1, A25antenna 1, 2 male (×10); A1, A 2 female (×10); Md5mandible, Mxp5maxilliped (×20); Mx1, Mx25maxilla 1, 2 (×40).

granulosa , in alcohol; two slides of male, one of female and one of juvenile. One ovigerous female, 5 mm and one juvenile from Eurypodius latreillei in alcohol. All East Falkland , Choiseul Sound (58– 59 ° S, 52 ° W), 30 m, 29 October 2003, A. and W. Vader leg., caught in baited traps. Deposited at TromsØ Museum no. 13843 .

Additional material

Three specimens, Lively Sound, East Falkland, March 2003, A. Vader, from Paralomis ; four specimens, Lively Sound , East Falkland, 15 April 2003, A. Vader, from Paralomis bins ; 15 specimens, Lively Sound , East Falkland, 3 May 2003, A. Vader, from ‘‘spider crabs’’, a few from bins ; 26 specimens, Choiseul Sound , East Falkland, 29 October 2003. A. and W. Vader, from crab bins ; five specimens, Choiseul Sound , East Falkland, 29 October 2003, A. and W. Vader, from Paralomis granulosa .

Type locality

East Falkland, Choiseul Sound.

Diagnosis

A Jassa species with robust antennae, unexpanded coxa 1, smooth basis on Gn2 and slightly subchelate peraeopods without anteroproximally expanded propodus.

Description Male. 6 mm. A1,A2. Antennae: A1 peduncle articles length 1,253, all with long ventral setae, longest distally. Flagellum five-articulate, article 1» the following; accessory flagellum two-articulate, ca half article 1 of flagellum. A2 more robust than A1; peduncle article 5.4, with simple setae only ventrally; flagellum four-articulate, all articles robust, quite setose; article 1 about 50% of flagellum.

Labium: rounded, epistome triangular, about the same length as labium. Mandible: palp broad, article 2 with facial and marginal rows of setae, but no fringe of setae on dorsal margin. Maxilla 1: palp without setae on article 1, article 2 with row of facial setae and six distal robust setae, outer plate with seven spinal teeth, inner plate short, without any setae. Maxilla 2 and maxilliped typical of the genus (see Figure 1).

Gnathopods: Gn1: coxa almost rhomboidal, not greatly expanded anteriorly, ventral margin straight; basis anterior margin with a few short setae on anterodistal margin, posterior margin smooth; merus as long as carpus; carpus with posterior lobe very weak, with anterodistal setae-cluster; propodus elongate, palm long (three-quarters length of posterior border), very oblique, weakly convex, delimited by single robust seta; dactyl long, adjoining palm. Gn2: coxa deeper than broad, ventral margin straight; basis short, anteroventral flange weak, with a few short setae; carpus short, cup-shaped with narrow, rounded, smooth lateral lobes; propodus very large, oval, palm long (80% of posterior margin), very oblique, with groups of plumose setae on hinge-tooth area, on thumb, and on palmar corner, the latter delimited by a few robust setae not on a protuberance; thumb short, blunt, gap between thumb and palm narrow; dactyl broad, inner margin crenulate, not clearly expanded near hinge-tooth area of palm.

Peraeopods: P3–4 much smaller than P5–7. P3: merus with large posterior lobe, distally with group of setae, and reaching about 80% along carpus; propodus elliptical, with groups of setae along anterior margin; dactyl falcate, ca three-quarters length of propodus. P5–7: basis expanded, merus with posteroventral lobe, propodus not markedly expanded anteriorly, but weakly subchelate, with strong robust setae distally on anteroventral margin; dactyl falcate, about one-third length of propodus.

Uropod 1: peduncle with interramal spine short, less than one-third length of outer ramus; both rami with evenly spaced marginal spines and a few distal spines. U2,U1, with interramal spine practically absent. U3: peduncle » rami, with two small distomedial and one anterodistal robust setae, outer ramus slightly bent, with one strong distal cusp, outer margin finely serrated; inner ramus with single apical spine. Telson short, entire, triangular, with one pair of lateral setae.

Female. Antennae similar to male. Gn1 basically similar to male. Gn2: basis with a row of short setae along anterior margin, anterodistal flange better developed than in male: propodus smaller than in male, similar in form, thumb absent, palm strongly convex, hingetooth area different in form.

Colour in life. The entire animal, including antennae and gnathopods, is covered by a pattern of reddish stripes and patches, rapidly fading in moribund or fixed specimens.

Etymology

The name ‘‘ kjetilanna ’’, a noun in apposition, is chosen in honour of Kjetil Slettnes and Anna Vader, without whom the present material would not have been collected.

Remarks

Conlan (1990) made a monographic revision of the genus Jassa ; no new species have been described since. In Conlan’s key the present material keys out to J. thurstoni Conlan, 1990 , a species described from the South Orkney Islands in the Antarctic, but also found at South Georgia. However, J. kjetilanna differs from J. thurstoni a.o. in the following characters: (1) J. kjetilanna has the robust antennae normal in the genus, while J. thurstoni has unusually slender antennae (especially A2) for a Jassa ; (2) in J. thurstoni coxa 1 is anteriorly expanded, in J. kjetilanna not at all; (3) in Gn2 of the male the thumb is less well developed and much more setose in J. kjetilanna ; (4) the posterior peraeopods are more robust in J. kjetilanna , with a clear tendency towards a subchelate condition; (5) J. thurstoni has well-developed interramal spines on U1 (50% of inner ramus) and U2 (16%), while in J. kjetilanna these spines are much reduced (U1 30%) or almost absent (U2).

From the other Jassa species J . kjetilanna can be distinguished by the characters of Conlan’s (1990) identification key. The northern J. pusilla (G. O. Sars, 1894) is closest, but that is also a very slender species with conspicuously thin antennae. One other Jassa species has been recorded from the Falkland Islands, i.e. J. alonsoae Conlan, 1990 . It differs from J. kjetilanna in many characters, such as the short A1, the short setation on A2 and the setose basis of Gn2.

This is not the first record of a Jassa species living in association with decapods. Jassa pusilla has several times been found together with slow-moving invertebrates (gastropods, hermit crabs), but this is at best a slight preference (cf. Vader and Myers 1996). Chilton (1912) mentioned the temporary association of what he called Jassa falcata with large crustaceans in New Zealand; it is unclear, however, which Jassa species he had at hand. Interestingly, Monod (1926) briefly described a female ‘‘ Jassa falcata ’’ found on the carapace of Eurypodius in the Magellan Channels; from his figures of Gn2 and U3 this was not J. kjetilanna , but probably J. alonsoae .