Jassa herdmani Walker 1893
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 herdmani

description: Jassaherdmani Walker, 1893
(Table 11, Figs 48–53)
Synonyms: see Conlan (1990).
Diagnosis.
Both sexes:
Mandibular palp: article 2, dorsal margin witha 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 very short setae; carpus without a single or small cluster of setae at the anterodistal junction of the propodus.
Gnathopod 2: basis with a few minute setae along the anterolateral margin but without long filter setae (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 underlying about 40% 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 absent except in small males. Thumb distally acute or squared in minor males and squared in major males. Dactyl centrally toothed in minor forms and shallowly expanded proximally in major forms.
Adult female:
Antenna 2: without plumose setae on the flagellum and peduncular article 5.
Gnathopod 2: propodus, palm concave, palmar defining angle acute, distal to but close to the defining spines.
Remarks. The neotype (Fig. 48), which was erected by Conlan (1990), is a minor form male with short thumb and toothed dactyl, corresponding with “The specimen originally described as P. herdmani, taken by Professor Herdman from a Compound Ascidian off the Island of Bute...” (Walker 1911, p. 71). Jassa herdmani naturally co-occurs with J. falcata and J. marmorata but the three species differ in microhabitat selection, life cycle, reproduction and temperature adaptation (Beermann & Franke 2012; Beermann & Purz 2013). The identity of the three species can be easily confused, especially when small (Sexton & Reid 1951; Conlan 1990). Conlan (1990) outlines how these can be distinguished on the basis of the antenna 2 plumosity, gnathopod 1 and 2 shape and setation and uropod 3 inner ramus spination.
Fig. 49 shows the thumb length relationships among specimens collected later by D.M. Reid from Plymouth Harbour on April 14, 1937. Although the collection was small, different morphologies of the minor and major form adult male are evident and the subadult male has a small pre-thumb before it molts into a (probably major form) thumbed male, judging by its large body length. Sexton and Reid (1951) called this pre-thumbed stage of the subadult male the “cut-across stage”. Reproductions of Sexton and Reid’s (1951) figures that are confirmed J. herdmani are shown in Figs 50 and 51. These specimens were collected in Plymouth Harbour at various dates between 1928 and 1930 and kept in aquaria, where changes in their morphologies were recorded as they molted. The transformation of the subadult male 13D to major form thumbed male 13E (their labels) is shown in Fig. 51. They mistook these specimens as J. falcata, calling them the ʺNarrow Form” of J. falcata. The females of the two species also differ subtly, with the palmar angle of the gnathopod 2 propodus more bulbous and farther from the defining spines in J. falcata (Fig. 44) than in J. herdmani (Figs 51, 52).
The dactyl toothing appears to vary with thumb length. In the minor form with short, distal thumb (Figs 48 and 49), the dactyl tooth is pronounced. In the major form with longer, more proximal thumb (Fig. 51, specimen 13E), the dactyl tooth is shallower and more proximal. In the large major form with a long, proximal thumb (Figs 48, 49 and 51, specimen 1), the dactyl is expanded proximally, rather than more centrally toothed. One of the key features for J. herdmani is the cluster of setae on the dorsal margin of the mandibular palp article 2. This is shown in Fig. 53.
One specimen noted in Lobo et al. (2017) as being Jassa sp. is J. herdmani (specimen examined 4 March 2019). This is likely the Jassa sp. in their Fig. 2 that matches other specimens of J. herdmani from the North Sea in their CO1-5P sequence.
The finding of a single juvenile female in coral rubble at Aqaba, Jordan by Lyons and Myers (1991) (identification confirmed) places the range of J. herdmani far outside the northeast Atlantic coast and western Mediterranean Sea where it has most often been collected (Fig. 9). This suggests that J. herdmani may have a propensity for exotic dispersal similar to J. marmorata, J. slatteryi and J. morinoi. It commonly fouls offshore structures in the North Sea (oil and gas platforms, wind turbines and shipwrecks) (Coolen et al. 2018; Luttikhuizen et al. 2019) which are thought to supply extended shallow, hard substrate and it has been collected on buoys (Sexton and Reid 1951) and boat bottoms as far back as 1890 (NHM 1925.9.8:1602). The Suez Canal is a transportation route for many exotic species, resulting in the eastern Mediterranean having many more introductions than the western Mediterranean (Galil et al. 2015). Lyons and Myers (1991) suggest that J. herdmani may be on the Atlantic coast of central Africa as well. This is based on literature reports that have not been confirmed by examination of specimens. Possibly these reports refer to J. marmorata or J. morinoi which are confirmed there (Figs 1, 2, 5 and 6).
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 87-92, DOI: 10.11646/zootaxa.4939.1.1, http://zenodo.org/record/4580622