Jassa kjetilanna Vader & Krapp 2005
Creators: name: Conlan, Kathleen E.
name: Desiderato, Andrea
name: Beermann, Jan
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Ischyroceridae
Jassa
Jassa kjetilanna

description: Jassakjetilanna Vader & Krapp, 2005
(Table 13, Figs 96–98)
Diagnosis.
Both sexes:
Mandibular palp: article 2, dorsal margin without a fringe of setae.
Maxilla 1: without a seta or setal cluster at the base of the palp article 1.
Gnathopod 1: basis, anterolateral margin with a few short setae along its length; carpus with a very short seta at the anterodistal junction of the propodus (seta about 10% of anterior margin length and slightly lateral).
Gnathopod 2: basis with a row of short setae along the anterolateral margin (setal lengths <10% of the basis width); carpus and propodus, setae on the anterior margin short and simple (setal length <basis width).
Pereopods 5–7: propodus not expanded anteriorly.
Uropod 1: ventral peduncular spinous process underlying about 1/3 of the longest ramus.
Uropod 3: inner ramus without spines mid-dorsally (with only the single apical spine).
Telson: tip without apical setae (only the usual short setae at each dorsolateral cusp).
Thumbed male:
Antenna 2: without plumose setae on the flagellum and peduncular article 5.
Gnathopod 2: propodus, palmar defining spines produced on a ledge in both small and large thumbed males. In minor males, the thumb is distally acute, short relative to body length and located on the distal half of the propodus. The dactyl is not centrally toothed. In major males, the thumb is also acute, relatively short, and on the proximal half of the propodus. The dactyl is shallowly expanded close to the junction with the propodus but is not centrally toothed.
Adult female:
Antenna 2: without plumose setae on the flagellum and peduncular article 5.
Gnathopod 2: propodus, palm sinuous; dactyl, inner margin evenly curved, tip fitting into depression between palmar angle and defining spines.
Remarks. Known only from the Falkland Islands, this species bears the characteristics of the genus Jassa (antennal setation, strong mandibular palp, gnathopod 2 palm defined by a cluster of spines, terminal male’s thumb produced distally to the spines; pereopod 3 and 4 merus anteriorly produced over the carpus).
Specimens collected on 29 October 2003 by A. and W. Vader from the lithodid crab Paralomis granulosa (Hombron & Jacquinot, 1846) at 20–30 m depth in Choiseul Sound, East Falkland, were borrowed from Tromsø Museum, Norway (TSV Cr 19054). The collection consisted of 3 major form thumbed males, 3 subadult (or near-subadult nonthumbed males), 5 adult females (2 ovigerous) and 14 juveniles. Representatives of each group were illustrated (Figs 96–98). Although Vader & Krapp (2005) thoroughly illustrated the types, which were also collected from Choiseul Sound, there was some minor disagreement between the types and the specimens examined, as follows.
Maxilla 2: The inner ramus is an extension of the base, not segmented as illustrated by Vader & Krapp (2005).
Gnathopod 1: The cluster of setae at the anterodistal junction of the carpus and propodus, stated as present in Vader & Krapp’s (2005) description but absent in the specimens they illustrated, are confirmed present in the specimens examined herein (single, slightly lateral seta in the specimens examined).
Gnathopod 2: Subadult males have a small ‘pre-thumb’ (Fig. 97), but the juvenile male gnathopod 2 illustrated by Vader & Krapp (2005) has too large a thumb to be subadult. Instead, it is likely a ‘minor form’ adult. The larger thumbed gnathopod 2 illustrated by Vader & Krapp (2005) is not ‘hyperadult’, but resembles that of a ‘major form’ adult male (Conlan 1990).
Uropod 1: The interramal spine that projects underneath the rami is not lateral as illustrated.
Uropod 3: The apparent lack of the characteristic pair of cusps proximal to the curved embedded spine at the tip of the outer ramus were present in the specimens examined herein.
No conclusions could be drawn on the variation of thumb size relative to body size as only three thumbed males were available for measurement. In comparison with other Southern Hemisphere species of Jassa, Vader & Krapp (2005) considered the relationship of J. kjetilanna to J. thurstoni and J. alonsoae due to their co-occurrence in the Falkland Islands. Jassa alonsoae has many morphological features that are not shared with J. kjetilanna, but J. thurstoni is more similar if intraspecific variation is taken into consideration. It requires the use of sex- and ageinvariant characters to differentiate species of Jassa because their morphology varies so much with age, size and sex. Using only key characters, J. kjetilanna and J. thurstoni are separable by the length of the seta or setal cluster on the carpus at the anterodistal junction of the propodus. This is minute in kjetilanna (length ~10% of the anterior margin of the carpus) and easily overlooked, but longer in J. thurstoni (~25% of the length of the carpus). This setal length is invariant in other species of Jassa, so the length difference between J. kjetilanna and J. thurstoni is considered significant enough to indicate that these species are morphologically distinct. There are also shape and size differences: slender, long antennae in J. thurstoni, shorter, stouter antennae in J. kjetilanna; anteriorly produced coxa 1 in J. thurstoni adult male and less produced coxa 1 in J. kjetilanna; differently shaped thumbs in the adult males with tendency to pronunciation of the defining spines in J. kjetilannna and loss in J. thurstoni; and similarly sized pereopods 5–7 in J. kjetilanna with relatively strong spines at the anterodistal end of the propodus compared to increasingly longer pereopods 5–7 in J. thurstoni with slender, seta-like spines anterodistally on the propodus.
description: Published as part of Conlan, Kathleen E., Desiderato, Andrea & Beermann, Jan, 2021, Jassa (Crustacea: Amphipoda): a new morphological and molecular assessment of the genus, pp. 1-191 in Zootaxa 4939 (1) on pages 148-152, DOI: 10.11646/zootaxa.4939.1.1, http://zenodo.org/record/4580622