Jassa marmorata Holmes, 1905

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 : 46-53

Jassa marmorata Holmes, 1905

( Table 10 , Figs 15–21 )

Synonyms: see Conlan (1990).

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 short setae at the anterodistal junction of the propodus (setae <25% of anterior margin length andslightly lateral).

Gnathopod 2: basis witha row of closely spaced setae along the anterolateral margin (at least some 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: large individuals with plumose setae on the flagellum and peduncular article 5.

Gnathopod 2: propodus, palmar defining spines not produced on a ledge, present in small thumbed males but absent in 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 distally squared, longer relative to body length and on the proximal half of the propodus. The dactyl is expanded close to the junction with the propodus but is not centrally toothed.

Adult female:

Antenna 2: large animals with plumose setae on the flagellum and peduncular article 5.

Gnathopod 2: propodus, palm concave, palmar defining angle acute.

Remarks. Jassa marmorata has often been mis-identified as J. falcata in the past ( Conlan 1990). Sexton and Reid (1951) studied the development of J. falcata and their J. falcata “broad form” is in fact J. marmorata . The transformation of four males from non-thumbed to thumbed state in aquarium cultured specimens is reproduced in Fig. 18 from Sexton and Reid’s (1951) plates. This shows that some subadult males have a small “pre-thumb” in the palm of gnathopod 2 ( Figs 8a, b , 14 d, e and 18 ) while others do not ( Figs 9a , 10a and 18 ). The appearance of a pre-thumb appears to occur only in larger juveniles ( Fig. 16 ). Fig. 18 also shows that while the palmar defining spines are retained in small thumbed males, they are lost in large thumbed males.

Sexton and Reid (1951) produced intersexes with a short, narrow thumb and small, setose brood plates by inbreeding siblings generated by a pair collected in the wild. Although the intersexes mated with female siblings, the offspring did not survive to maturity. Two intersexes and an ovigerous female were also found in NMNH 148787, 3–38, taken in a dredge at 18–27 m over sandy, weedy bottom inside the northern point of entrance to Magdalena Bay, Lower California, on July 18, 1938. Both intersexes had all the distinguishing features of J. marmorata but short thumbs on the second gnathopods and a toothed dactyl similar to that in minor forms of J. falcata and J. staudei .

Jassa marmorata is morphologically similar to J. valida and the two overlap in distribution at the junction of their ranges in North Carolina, which is a biogeographic break for many species ( Pappalardo et al. 2015). Distributions listed in OBIS for J. marmorata for the coasts of the US south of North Carolina, including the Gulf of Mexico require confirmation because they may be for mis-identified J. valida . Asimilar southerly range into the Gulf of Mexico and on the coasts of Cuba and the Bahamas listed by Conlan (1990) may also be for J. valida , not J. marmorata . It is possible that some or all records of J. marmorata on the coasts of Uruguay and Argentina described by Alonso de Pina (2005) are unrecognized J. valida , since J. valida is already known from this coast. The most dependable character to distinguish the two species of any size is the lack of apical setae on the telson of J. marmorata and presence in J. valida . However, viewing this character requires moving the third uropods out of the way of the telson (this can be done by holding the animal on its side and bending the uropods downwards with a fine needle). It also requires that the usual pair of setae at the the telson knobs, which project dorso-distally, are not confused with the apical setae, which project distally. The other diagnostic characters of J. marmorata , which are easier to view, can be used for adult and subadult specimens.

Due to the availability of a large number of specimens from the neotype population (162 adult and juvenile males measured for Fig. 16 ), there were 10 major form and 17 minor form males that overlapped in body length (4.08–4.67 mm) for comparison of thumb length relative to body length. A Kruskal-Wallis test indicated that thumb lengthwassignificantly longerinthe major thanminorforms of thissizerange (HKW = 4.017, p <0.001; median thumb length 0.39 vs 0.22 mm, respectively). The thumbs also appeared wider in major than minor forms ( Fig. 17 ) although there were insufficient specimens with a common range of body length to test this. The second gnathopod propodus length was significantly greater in major form adult males (mean 1.812 ± 0.245 mm) than juvenile males (1.533 ± 0.200 mm) of the same body length range (4.08–5.83 mm) (t -test, t = 3.458, p = 0.001, n = 27 major forms and 12 juveniles) ( Fig. 17 ). Similarly, the juvenile males had a significantly longer propodus than the adult females of thesamebodylengthrange (3.25–5.33 mm) (HKW = 2.195, p <0.05, median 1.20 mmforjuvenile males, n = 15 and 0.88 mm for adult females, n = 8) ( Fig. 17 ).

The SEM image of the telson ( Fig. 20 ) shows paired short plumose setae to either side of the telson nubs and associated long, erect seta dorsal to each nub. The nub magnifications show that the nubs are actually cusped and the erect setae are ringed at their tips by rows of scales. Presumably, the erect setae have a sensory function, perhaps for position within the tube and the cusped nubs may assist with gaining a purchase within the tube. Possibly the plumose setae are mechanoreceptive as well (Kauffmann 1994).

Only two specimens of the ~25,000 specimens of Jassa examined were found to be densely coated in epibionts ( Fig. 21 ). All other specimens appeared to be clean or with much smaller and sparser epibionts. However, specimens collected in Helgoland Harbour ( Germany) often were coated with epibionts. Both of the densely coated specimens were large, major form thumbed males and the epibionts were algal in appearance (green Enteromorpha -like algae or filamentous as in Fig. 21 ). The specimen bearing a green algal coat (found among algae on a floating dock in Adelaide, Australia) was so densely covered that it was barely recognizable. The specimen shown in Fig. 21 was from a fouling community on a natural gas platform in Morecambe Bay, UK In both specimens, the epibionts were concentrated on the anterior of the body, coating the dorsum and second gnathopods. This pattern suggests that the animals were partially tubicolous during the time of infestation. Movement within the tube may have prevented epibiont accumulation on the posterior part of the body. The cleaning action of the first gnathopods may have prevented epibiont growth on body parts within reach, such as the antennae. That epibiont growth was able to establish in such quantity on these males suggests that the males had not molted for some time, and that they were senescent and not able to prevent epibiont settlement.

There are four corrections to Conlan (1990): (1) Sexton and Reid (1951) Plate 12, 5a–5f should be added to p. 2053; (2) specimens from Crooke’s Point, New York (p. 2054) are from Staten Island, New York, not the Hudson River (S. Grabe, pers. comm., date not recorded); (3) J. marmorata is not yet known from Alaska; an Alaskan specimen attributed to J. marmorata in Conlan (1990) and repeated by Fofonoff et al. (2019) is actually the indigenous J. staudei (specimen re-examined May 23, 2018); (4) Conlan (1990) did not recognize that “ J. marmorata ” in the Gulf of Mexico and on the US Atlantic coast from Florida to North Carolina were more likely to be J. valida than J. marmorata , although the two species could overlap in range ( Figs 1 , 2 , 7 , 8 ). Therefore, the identification of specimens from these coasts are suspect. This has been rectified for collections at the Canadian Museum of Nature (CMN) but not elsewhere (see Remarks section for J. valida ). Similarly, “ J. marmorata ” found in the southwestern Gulf of Mexico with J. valida by Winfield et al. (2021) are possibly also J. valida as the specimens they reported were very small (2.36 ± 0.38 mm body length, n = 5) and therefore likely difficult to view the diagnostic terminal seta(e) on the telson that denotes the identification as J. valida (Supplementary Data File S1). It was not possible to borrow the specimens to confirm the identification as the museum collections were closed due to the COVID-19 pandemic.

Aloan that came after Conlan (1990) is a sample of J. marmorata in a collection taken at 13 m depth on a shellmuddy-sand substrate offshore of S„o Paulo, Brazil in 1963. This is the earliest known collection of J. marmorata on the Atlantic coast of South America (Table 3). It is possible that this sample was contaminated by J. marmorata fouling the ship. Ascraping of a small ship in 1985 in this area found J. marmorata on the hull.

Astudy of amphipods inhabiting the moderately polluted Newport Bay in 1954 (now part of Los Angeles) found “ J. falcata ” in small numbers compared to the large populations on pilings in Los Angeles Harbor ( Barnard and Reish 1959). Although not seen, these specimens may be J. marmorata , since it has been found exclusively on other human-modified habitats on the Pacific coast of North America (this study and Fofonoff 2019). Jassa marmorata has been collected in California as far back as 1931 (Table 3).

Figures

FIGURE 1. Progressive discovery of Jassa marmorata from 1850 to 1949. Red dot: identification confirmed by specimen examination; green triangle: literature record (Supplementary Table S1) with identification not confirmed but judged likely to be this species; blue x: suspected or known to be on the hull or interior of a boat or ship.

FIGURE 2. Progressive discovery of Jassa marmorata from 1850 to 2020. Red dot: identification confirmed by specimen examination; green triangle: literature record (Supplementary Table S1) with identification not confirmed but judged likely to be this species; blue x: suspected or known to be on the hull or interior of a boat or ship.

FIGURE 7. Progressive discovery of Jassa valida from 1850 to 1949. Red dot: identification confirmed by specimen examination or by identical haplotypes to examined specimens; green triangle: literature record (Supplementary Table S1) with identification not confirmed but judged likely to be this species; blue x: suspected or known to be on the hull or interior of a boat or ship.

FIGURE 8. Progressive discovery of Jassa valida from 1850 to 2020. Red dot: identification confirmed by specimen examination or by identical haplotypes to examined specimens; green triangle: literature record (Supplementary Table S1) with identification not confirmed but judged likely to be this species; blue x: suspected or known to be on the hull or interior of a boat or ship.

FIGURE 9. Records of Northern Hemisphere species of Jassa that were found in the eastern and/or western North Atlantic and seas, along with J. kimi in the western Pacific. Red dot: identification confirmed by specimen examination; green triangle: literature record (Supplementary Table S1) with identification not confirmed but judged likely to be this species; blue x: suspected or known to be on the hull or interior of a boat or ship.

FIGURE 10. Records of Northern Hemisphere species of Jassa that were found in the eastern and/or western North Pacific and seas. Red dot: identification confirmed by specimen examination; green triangle: literature record (Supplementary Table S1) with identification not confirmed but judged likely to be this species; blue x: suspected or known to be on the hull or interior of a boat or ship.

FIGURE 14. Combined average abundance of Jassa marmorata and J. slattery in four algal groups sampled randomly on three floating docks at West Beach, Adelaide,Australia from October 2009 to September 2010. Surface water temperature at the docks varied from 12 °C in austral winter to 25 °C in austral summer. Neither species was found at temperatures>21°C.

FIGURE 15. Jassa marmorata Holmes, 1905. Neotype, adult male, major form, 6.7 mm, NMCC 1987-1067; adult female, 5.3 mm. Barren Islands Marina, Jamaica Bay Wildlife Refuge, Brooklyn, New York (40°35ʹN, 73°55ʹW), early July 1984, B. Borowsky, coll., among hydroids and Ulva on submerged docks at the marina, IZ 1984-112 (CMN). Lateral views: whole body, pereopod 3 and uropod 3; dorsal view: telson; other views medial. Scale 0.1 mm. Illustration after Conlan (1990).

FIGURE 16. Jassa marmorata Holmes, 1905. Variation in thumb length relative to body length in males in a single population (Barren Islands Marina, Jamaica Bay Wildlife Refuge, Brooklyn, New York (40°35ʹN, 73°55ʹW), early July 1984, B. Borowsky, coll., among hydroids and Ulva on submerged docks at the marina, IZ 1984-112 (CMN). Arrows refer to the associated gnathopod illustrations. Setae omitted except for those around the thumb and spines in order to landmark position changes with growth. All views lateral. Scale 0.1 mm. Linear regression assumptions passed for the major form male. Linear regression statistics: Major form, thumb length = -0.652 + 0.248 body length, r2 = 0.765, n = 103. Illustration after Conlan (1990).

FIGURE 17. Jassa marmorata Holmes, 1905. Variation in thumb width and gnathopod 2 propodus length relative to body length in males and females in a single population (Barren Islands Marina, Jamaica Bay Wildlife Refuge, Brooklyn, New York (40°35ʹN, 73°55ʹW), early July 1984, B. Borowsky, coll., among hydroids and Ulva on submerged docks at the marina, IZ 1984- 112 (CMN). Linear regression assumptions failed for all plots.

FIGURE 18. Jassa marmorata Holmes, 1905. Transformation of the propodus and dactyl of gnathopod 2 of four males as they moulted from non-thumbed to the final thumbed morphology. Most setae are not shown in order to enhance clarity. Adaptation of illustrations in Sexton and Reid (1951) with their figure numbers. First row: Plate 16, Specimen 10, J.30 a, male F1 of Broad- Form female J.CCLXII, 1 July 1929, before (10 a) and after (10f) moulting. Second row: Plate 21, Specimen 14(2), male J.11, F1 of J.CXLI, moult Feb. 10, 1929 (14d), moult Feb. 23, 1929 (14e) and dead May 1, 1929 (14f). Third row: Plate 15, Specimen 9, male J.30a (b) F1 of Broad-Form female J.CCLXII, moult July 6, 1929 (9a) and dead August 24, 1929 (9d). Fourth row: Plates 13 and 14, Specimen 8, male J.17e, F1 of Broad-Form pair J.CLXXIV, moult May 18, 1929 (8a), moult June 1, 1929 (8b) and as it emerged from its moult on June 1, 1929 (8k).

FIGURE 19. Jassa marmorata Holmes, 1905. Neotype, adult male, major form, 6.7 mm, NMCC 1987-1067, Barren Islands Marina, New York, IZ 1984-112 (CMN). Mouthparts. Frontal view: upper lip; lateral view: maxilla 2; other views medial. Scale 0.1 mm.

FIGURE 20. Jassa marmorata Holmes, 1905. Adult male, 6.8 mm. Barren Islands Marina, New York, IZ 1984-112 (CMN). Telson. A, cusps and associated setae. B, tip of erect seta arising proximally to each cusp. x2000.

FIGURE 21. Jassa marmorata Holmes, 1905.Adult male, 6.6 mm, coated with epibionts. Morecambe Bay, Irish Sea, England, UK, 19 May, 1986, P. G. Moore, coll., fouling natural gas platform, level D, CPP1, IZ1986-092 (CMN).