Exosphaeroma amplicauda (Stimpson, 1857)

Wall, Adam R., Bruce, Niel L. & Wetzer, Regina, 2015, Status of Exosphaeromaamplicauda (Stimpson, 1857), E. aphrodita (Boone, 1923) and description of three new species (Crustacea, Isopoda, Sphaeromatidae) from the north-eastern Pacific, ZooKeys 504, pp. 11-58 : 16-19

Taxon classification Animalia Isopoda Sphaeromatidae

Exosphaeroma amplicauda (Stimpson, 1857) Figures 1, 2, 3, 4, 21, 27, 28

Sphaeroma amplicauda Stimpson, 1857: 510; Richardson 1899a: 835; 1899b: 179; 1900: 222.

Exosphaeroma amplicauda . - Richardson 1905: 288, 289, fig. 301, 302; Gurjanova 1936: 122, fig. 69; Schultz 1969: 131, fig. 190.

Sphaeroma octoncum Richardson 1905: 293.

Exosphaeroma octoncum . - Iverson 1974: 166. - Richardson 1905: 293, fig. 309, 310. - Schotte 2012: online.

Not Exosphaeroma amplicauda . - Gurjanova 1936: 122, fig. 69. - Kussakin 1979: 399, figs 254, 255 [= Exosphaeroma paydenae sp. n.].

Material examined.

NEOTYPE (here designated): ♂ (5.1 mm): California, Marin County, Tomales Bay, north end of bay across from Hog Island, boat launch parking lot, 38.201°N, 122.922°W, intertidal, from underside of rocks, fixed and preserved in 95% ethanol, 9 Jan 2009, coll. R. Wetzer & A. Wall. RW09.003.1, LACM CR-2014.1.

Non-type material. 2 ♂ (RW09.003.2, LACM CR-2014.1), 3 ♀ (RW09.003.3, LACM CR-2014.1) [used for SEM], 1 ♂, ~40 ♀ and juveniles: same locality as RW09.003, LACM CR-2014.1. 6 ♂ (8.1 mm), 4 ♀ (7.1 mm), 10 juveniles (RW09.004.1), plus 2 ♂ and 4 ♀ prepared as SEM (RW09.004.2): intertidal, from underside of rocks, "family group", coll. A. Wall. RW09.004, LACM CR-2014.2. 7 ♂ (5.8 mm), ~20 ♀ (6.8 mm) and juveniles, and 3 ♀ used for SEM: intertidal, from underside of rocks, "family group", coll. A. Wall. RW09.005, LACM CR-2014.3. 2 ♂ (8.4 mm), ~25 ♀ (7.4 mm), and juveniles: intertidal, from empty Balanus glandula shells, coll. N.D. Pentcheff, RW09.006.1, LACM CR-2014.4. 1 ♂ (7.7 mm), 2 ♀ (6.5 mm), and 2 juveniles: E. side in cove across from Hog Island ( Nick’s Cove), ~ 38.197°N, ~ 122.935°W, 1 Nov 1971, A.0030, coll. E.W. Iverson & J. Carlton. RW04.020.1, LACM CR-2014.5. California, Monterey County, Monterey Bay, 4 specimens (labeled Exosphaeroma octoncum ), all are ♀. Acc. No. 03472, USNM 22574 (part).

Description of male.

Body length 1.6 width; pereonites 5-6 each with 1 median weak tubercle, and 1 weak lateral tubercle; pereonite 7 with weak median process and paired lateral tubercles (Figures 1A, B; 21A, D). Pleon with 1 posterior strong tubercle on either side of longitudinal axis (Figures 1A, B; 21A, D). Pleotelson length 0.82 width, dorsal surface with 2 small anterior tubercles; ventrolateral ridge extending posteriorly 0.75 of total length, with long setae (Figures 1A, B; 21A, C, D).

Antennula peduncle article 1 length 1.7 width, anterior medial margin with 2 palm setae; article 2 length 1.4 width, inferior distal margin with 2 palm setae; article 3 length 3.2 width; flagellum with 9 articles (Figure 2B). Antenna reaching anterior margin of pereonite 2; flagellum with 14 articles (Figure 2A).

Left mandible incisor with 3 cusps; lacinia mobilis with 3 cusps; lacinia mobilis spine row comprised of 5 curved, serrate spines (Figures 2E, 27D). Right mandible incisor with 4 cusps; spine row comprised of 6 curved, serrate spines; crushing surfaces strongly ridged (Figures 2D, 27D). Maxillula mesial lobe with 4 circumplumose RS; lateral lobe with 6 long, curved, pectinate RS (Figures 2F; 27E, F, G). Maxilla mesial lobe with 6 plumose RS on gnathal surface; middle lobe with 4 long, curved, pectinate RS; lateral lobe with 4 long, curved, pectinate RS (Figures 2G; 27E, G). Maxilliped endite distal surface with 5 plumose setae, and 2 simple RS; distomesial margin with 1 coupling hook; palp article 2 distal apex with 9 long, simple RS; article 3 distal apex with 12 long, simple RS, lateral distal angle with 1 long, simple RS; article 4 distal apex with 9 long, simple RS, lateral distal angle with 1 long, simple RS; article 5 distal apex with 7 long, simple RS (Figures 2H; 27E, G).

Pereopod 1 (Figure 3A) basis superior margin without palm setae, inferior distal angle with 1 long, simple seta, inferior medial margin setal patch absent; ischium length 2.4 width, superior margin with 4 long, simple setae, inferior distal angle with 1 long, simple seta; merus 0.42 ischium length, superior distal angle with 2 long, simple setae; carpus inferior distal angle with 1 long, simple seta; propodus length 2.5 width, 0.82 ischium length, superior distal angle with 2 long, simple setae, inferior margin with 3 long, simple setae; dactylus length 1.7 width, length 0.33 propodus length, inferior margin covered with scales, distal margin with 4 simple setae (Figure 3A). Pereopod 3 (Figures 3B, 27A) basis superior margin without palm setae, inferior distal angle with 1 long simple seta, inferior proximal margin with setal patch present; ischium length 2.5 width, superior margin with 3 long, simple RS, inferior distal angle with 1 simple RS, and with setal patch absent; merus lobate, length 1.4 width, 0.57 ischium length, superior distal angle with cluster of 4 simple RS, inferior margin covered in setal mat; carpus length 0.71 merus length, 1.2 width, superior margin with 1 long, simple seta on distal angle, inferior margin with setal mat and 1 long, simple seta; propodus weakly curved, length 2.5 width, 2.3 carpus length, superior distal margin with 1 palm seta, inferior margin first 0.67 covered in setal mat; dactylus length 1.3 width, length 0.36 propodus length, inferior margin distal 0.75 covered with scales, distal margin with 3 long, simple setae (Figures 3B, 27A). Pereopod 7 (Figures 3C; 27B, C) basis superior margin with palm setae absent, inferior proximal margin with setal patch absent, inferior distal angle with long, simple setae absent; ischium length 2.9 width, superior margin with 3 long, simple RS; merus lobate, merus length 1.8 width, merus length 0.66 ischium length, superior distal angle with 4 RS, inferior margin with setal mat, inferior distal angle with biserrate setae absent; carpus length 2.5 width, carpus length 1.3 merus length, inferior margin with setal mat, superior distal angle with a cluster of 5 long, biserrate setae, superior distal angle with a cluster of 3 long, simple, RS, distomesial margin with a cluster of 3 long, biserrate setae, inferior distal angle with a cluster of 5 long, biserrate setae, 1 long, simple RS; propodus weakly curved, length 4.0 width, length 1.3 carpus length, inferior margin proximal 0.33 with setal mat, superior distal angle with 2 long, simple setae, inferior margin with 2 long, simple setae, with palm setae absent; dactylus length 1.8 width, dactylus length 0.28 propodus length, margin with scales, distal margin with 3 simple setae (Figures 3C; 27B, C).

Penial process length 2.5 basal width (Figure 21B, C).

Pleopod 1 peduncle length 0.48 width, with a cluster of 3 coupling hooks; endopod mesial margin heavily covered in fine, simple setae; exopod length 1.7 width, ventral surface without fine, simple setae (Figure 4A). Pleopod 2 appendix masculina proximally swollen, distally narrowing, distal end curving mesially, straightening at distal tip, length 15.4 basal width (Figure 4B). Pleopod 3 peduncle with a cluster of 3 coupling hooks, distolateral angle with 1 large, plumose seta (Figure 4C). Pleopod 4 peduncle length 0.48 width, distolateral angle with 1 large, plumose seta; endopod distal apex 1 large, plumose seta; exopod distal margin with 2 plumose setae (Figure 4D). Pleopod 5 exopod proximolateral margin with palm setae absent; exopod with transverse suture entire, endopod with 1 scale patch; exopod with 3 scale patches (Figure 4E). Uropod exopod length 2.3 width; rolled proximolateral margin weakening moving distally; mesial margin without setae; endopod length 2.5 width, extends past exopod, mesial margin without setae (Figures 4F; 21A, C, D).

Description of female.

Body length 2.7 width; pereonites 1-7 without tubercles, pereonite 7 distomesial margin convex (Figure 21E, F). Pleon with 1 posterior tubercle on either side of longitudinal axis (Figure 21E, F). Pleotelson length 2.6 width, dorsal surface with 2 medium tubercles on either side of longitudinal axis; posterior margin of pleotelson acuminate (Figure 21E, F). Uropod exopod proximolateral margin weakly rolled; endopod posterior margin tapering to evenly rounded tip, length 4.8 width, extends past exopod (Figure 21E, F).

Size. Largest ♂ to 8.4 mm, largest ♀ to 7.5 mm.

Color. Without chromatophores: preserved specimen pale buff, whitish.

Remarks.

Exosphaeroma amplicauda is most morphologically similar to Exosphaeroma russellhansoni sp. n. but can be distinguished by: pereonites 5 and 6 with one weak median tubercle, and one weak lateral tubercle; pereonite 7 with weak median process and paired lateral tubercles. (Figures 1A, B; 21A, D). Appendix masculina distal end curving mesially, straightening at distal tip, length 15.4 basal width (Figure 4B).

Exosphaeroma russellhansoni sp. n. is characterized by: pereonite 5-6 each without ornamentation, pereonite 7 with weak median process (Figures 9A, B; 23A, D). Appendix masculina distal end curving mesially, apex weakly hooked mesially, length 11.4 basal width (Figure 12B). Exosphaeroma amplicauda is strongly sexually dimorphic; females lack dorsal tubercles on pereonites 1-7. Overall for all species in this 'species flock’ the males have a larger pleotelson and uropods. Weak pereon tubercles are visible only with SEM and not necessarily evident with light microscopy. Tubercles visible with light microscopy are figured in the line drawings (compare Figures 1 and 21).

We searched all probable museum collections for Stimpson’s type specimens, but to no avail (see Acknowledgements). It is highly likely that the type specimens are lost. The original and subsequent description ( Stimpson 1857, 1858) do not allow for definitive identification of the species. There are five morphologically similar species in the northeast Pacific. A neotype is here designated to stabilize the use of the name Exosphaeroma amplicauda (Stimpson, 1857) and conserve Stimpson’s concept for the species.

We borrowed the types of Sphaeroma octonctum Richardson, 1899 (USNM Cat. No. 22574); Richardson (1899) noted that there were five specimens from the type locality, Monterey Bay). We received only four specimens–three had been previously dissected, some with pleopods removed, and only one specimen was entire. None of these specimens are adult males, and these specimens are indistinguishable from female Exosphaeroma amplicauda from Tomales Bay. We place Sphaeroma octonctum into junior synonymy with Exosphaeroma amplicauda .

Distribution.

California: Marin, Sonoma, and San Mateo Counties.