Jassa carltoni Conlan 1990
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 carltoni

description: Jassacarltoni Conlan, 1990
(Table 12, Figs 78–82)
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 (usually) single or a small cluster of long setae at the anterodistal junction of the propodus (setae 65-70% of anterior margin length andslightly medial).
Gnathopod 2: basis with a few moderately long setae on the anterodistal margin (most setal lengths <40% 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 peduncular article 5 and flagellum.
Gnathopod 2: propodus large and stout, palmar defining spines not produced on a ledge, spines lost in large thumbed males. Major form: thumb about 30% the length of the propodus and curved posterodistally, dactyl sinuous, expanded proximally. Minor form: thumb about 15% the length of the propodus, dactyl expanded more distally than in the major form, into the palmar incision between the thumb and the proximal tooth.
Adult female:
Antenna 2: without plumose setae on peduncular article 5 and flagellum.
Gnathopod 2: propodus, palm concave, palmar defining angle acute, palmar defining spines relatively widely spaced.
Remarks. Conlan (1990) first recognized Jassa carltoni as a new species in Californian collections described by Barnard (1969) as “ Jassa falcata ”. The largest specimens available were chosen as the type lot (Fig. 78). However, the holotype, a major form male, appears to have a damaged thumb, as the tip is short and apically indented compared to the major form paratype (Fig. 79). The minor form paratype (Fig. 79) has a similarly shaped but shorter thumb with the dactyl expanded into the palmar incision. Additional specimens from British Columbia are figured in order to show the morphology of an undamaged major form male as well as a subadult male that had an obvious thumb inside the cuticle. Plots of thumb and propodus length on gnathopod 2 for specimens from a single population show that the major form thumbed male has a substantially longer thumb and gnathopod 2 propodus length than the minor form thumbed male (Figs 79, 80). Propodus length of adult females is also much less than for major form males but more similar to minor form and subadult males. However there were insufficient specimens of similar body length for statistical comparison.
Jassa carltoni most resembles J. slatteryi, both of which occur on the Pacific coast of North America. Although both have a 4-articled flagellum on antenna 2, the flagellum is slenderer in Jassa carltoni than in J. slatteryi and unlike J. slatteryi, it does not become plumose in large thumbed males. The palm of gnathopod 1 is convex while in J. slatteryi it is straight or shallowly concave. Both males and females of J. carltoni have a sparser setation on the anterior margin of the basis and a wider propodus on gnathopod 2 (maximal width ~65% of maximal length) than for J. slatteryi (maximal width ~50% of maximal length). The thumb shape also differs: tip rounded and curved posteriorly in major form males of J. carltoni and tip acute and not curved posteriorly in major form males of J. slatteryi. In minor form males of J. carltoni, the thumb is shorter and more acute than in the major forms, and more closely resembles J. slatteryi. The shape differences in the gnathopod 1 palm still hold, though.
Many (but not all) of the locations for J. slatteryi noted by Conlan (1990) for British Columbia are actually for J. carltoni, as this latter species was not recognized at that time to occur outside of California. It was only through recent molecular analysis that J. carltoni was discovered to occur also in British Columbia. Subsequent re-examination of collections found J. carltoni also in Oregon. A “ J. slatteryi ” noted by Conlan (1990) from Alaska (University of Alaska loan, Latouche T1, M75, 5 Sept. 1975) may also be J. carltoni but this specimen was no longer available for study and so is omitted from the distribution map. Given the similarity in environmental conditions between southeastern Alaska and British Columbia, it is likely that J. carltoni ranges northwards at least into southeastern Alaska. Jassa carltoni has not been found outside of the Pacific coast of North America, however.
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 page 126, DOI: 10.11646/zootaxa.4939.1.1, http://zenodo.org/record/4580622