Jassamyersi Conlan, 1990

Conlan, Kathleen E., Desiderato, Andrea & Beermann, Jan, 2021, Jassa (Crustacea: Amphipoda): a new morphological and molecular assessment of the genus, Zootaxa 4939 (1), pp. 1-191 : 133-137

Jassamyersi Conlan, 1990

( Table 12 , Figs 85–87 )

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 single or small cluster of relatively long setae at the anterodistal junction of the propodus (setal length about 1/3 the length of the anterior margin length).

Gnathopod 2: basis with only a few short setae along the anterolateral margin (setal lengths <20% 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 very short, underlying about 6% 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 not produced on a ledge.

Adult female:

Antenna 2: without plumose setae on the flagellum and peduncular article 5.

Gnathopod 2: propodus, palm sinuous, palmar defining angle shallowly rounded and towards the centre of the palm (not close to the palmar defining spines).

Remarks. This is the only Northern Hemisphere species that has a sinuous palm on the propodus of gnathopod 2. It also has a variably fringed basis, leading to mixed interpretation of whether a fringe of setae is present or absent. It shares with J. borowskyae and J. shawi a reduced peduncular process underlying the rami of uropod 1. Among the 166 specimens available for study, there were only 8 thumbed males. These all had very short thumbs and palmar defining spines proximal to the base of the thumb. The thumbed males had shorter setae on the antenna 2 than the females ( Fig. 85 ) but none had plumose setae as develops in thumbed males of some other species of Jassa . This may signify that J. myersi does not develop plumose setae but the sample size is small. However, none had slenderized bases of pereopods 3–4 which is typical of large thumbed males. Conlan (1990) suggested, therefore, that these males were not at maximal size for the species. Aplot of gnathopod 2 propodus length relative to body length shows an apparent greater size for males than females ( Fig. 87 ). Analysis of variance on adult females (n = 4) and juvenile males (n = 6) that overlapped in body length (3.5–4.5 mm) found that the differences in mean propodus length was not sufficiently great to exclude the possibility that the difference was due to random sampling variability (F = 1.041 -15, p = 1.0).

Southern Hemispherespecies

Figures

FIGURE 85. Jassa myersi Conlan, 1990. Holotype, adult male, 5.8 mm, NHMLA 61-125.1; allotype, adult female, 4.4 mm, NHMLA 125.2; paratype, juvenile male, 3.7 mm, NHMLA 125.3. Coal Oil Point, Goleta, California, 2 July 1961, J. L. Barnard, coll., station 39-H-2, on rock surfaces in Phyllospadix zone, low intertidal zone. Adult male 1, 4.5 mm and subadult male, 5.1 mm, Coal Oil Point, Goleta, California, 2 July 1961, J. L Barnard, coll., station 39-K-1, on rock surfaces in Phyllospadix zone, low intertidal zone (NHMLA). Lateral views: whole body and uropods; dorsal view: telson; other views medial. Appendages are of the holotype unless noted otherwise. Scale 0.1 mm. Illustration after Conlan (1990).

FIGURE 86. Jassa myersi Conlan, 1990. Variation in gnathopod 2 propodus length relative to body length in males and females from a single population. Coal Oil Point, Goleta, California, 2 July 1961, J. L. Barnard, coll., stations 39-H-1, 39-H-2 and 39-K- 1, on rock surfaces in Phyllospadix zone, low intertidal zone (NHMLA). Linear regression assumptions failed for all plots.

FIGURE 87. Jassa myersi Conlan, 1990. Holotype, adult male, 5.8 mm, NHMLA 61-125.1. Coal Oil Point, Goleta, California, 2 July 1961, J. L. Barnard, coll., station 39-H-2, on rock surfaces in Phyllospadix zone, low intertidal zone (NHMLA). Mouthparts. All views medial. Scale 0.1 mm.