Exosphaeroma paydenae, Wall, Adam R., Bruce, Niel L. & Wetzer, Regina, 2015

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 : 19-24

Taxon classification Animalia Isopoda Sphaeromatidae

Exosphaeroma paydenae sp. n. Figures 5, 6, 7, 8, 22, 28

Exosphaeroma amplicauda . - Gurjanova 1936: 122, fig. 69. - Kussakin 1979: 399, Figs 254, 255.

Material examined.

HOLOTYPE: ♂ (7.8 mm): Alaska, Aleutian Islands, Kiska Harbor, ~ 52.00°N, ~ 177.31°E, ca. 1873, beach, low water, USNM 20474, 211(1025), coll. W.H. Dall [Specimen label reads "Alaska, Kyoka Harbor." per Marilyn Schotte, 15 Nov 2004 USNM 20474 reads "Aleutian Islands, Kiska Harbor" - maybe a transcription error on the label; specimens denoted as USNM 20474 are also possibly collected ca. 1873 similar to USNM 13312.] USNM 1251663.

PARATYPES: Allotype: ♀ (8.6 mm, whole animal figured): same locality as USNM 1251663, USNM 1251664. 1 ♂, 9 ♀, 2 juveniles, plus 1 ♂ and 1 ♀ prepared as SEM: all same locality as USNM 20474. 8 ♂ (8.0 mm), 1 ♂ broken: north coast of Amchitka, ~ 51.3°N, 179°E, 1 Jan 1873, USNM 13312, 284(1044), coll. W.H. Dall, USNM 1251665.

Description of male.

Body length 1.6 width; pereonites 5-7 each without ornamentation (Figures 5A, B; 22A, B). Pleon with 1 anterior weak tubercle on either side of longitudinal axis, 1 posterior weak tubercle on either side of longitudinal axis (Figures 5A, B; 22A). Pleotelson length 0.59 width, dorsal surface without ornamentation; ventrolateral ridge entire, with few setae (Figures 5A, B; 22A, D).

Antennula peduncle article 1 length 1.5 width, anterior medial margin with palm setae absent; article 2 length 1.1 width, inferior distal margin with palm setae absent; article 3 length 2.6 width; flagellum with 9 articles (Figure 6B). Antenna reaching posterior margin of pereonite 3, peduncle article 1 with fine, simple setae on superior margin; flagellum with 11 articles (Figure 6A).

Left mandible incisor with 3 cusps; lacinia mobilis with 2 cusps; lacinia mobilis spine row comprised of 6 curved, serrate spines (Figure 6F). Right mandible incisor with 3 cusps; spine row comprised of 7 curved, serrate spines; crushing surfaces strongly ridged (Figure 6E). Maxillula mesial lobe with 4 circumplumose RS, and 2 long, simple setae; lateral lobe with 7 long, curved, pectinate RS, gnathal surface with 1 curved, simple RS (Figure 6D). Maxilla mesial lobe with 1 long, straight RS, and 8 plumose RS on gnathal surface; middle lobe with 5 long, curved, pectinate RS; lateral lobe with 3 long, curved, pectinate RS (Figure 6C). Maxilliped endite distal surface with 8 plumose setae, and 1 simple RS; distomesial margin with 1 coupling hook; palp article 1 with 1 long, simple RS; article 2 distal apex with 12 long, simple RS; article 3 distal apex with 9 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 9 long, simple RS (Figure 6G).

Pereopod 1 (Figure 7A) basis superior margin without palm setae, inferior distal angle without long, simple setae, inferior medial margin setal patch absent; ischium length 1.9 width, superior margin with 2 long, simple setae, inferior distal angle without long, simple setae; merus 0.58 ischium length, superior distal angle with 3 long, simple setae; carpus inferior distal angle with 2 long, simple setae; propodus length 2.1 width, 0.83 ischium length, superior distal angle with 1 long, simple seta, inferior margin with 3 long, simple setae; dactylus length 1.1 width, length 0.3 propodus length, inferior margin covered with fine scales, distal margin with 2 simple setae (Figure 7A). Pereopod 3 (Figure 7B) basis superior margin without palm setae, inferior proximal margin with setal patch present; ischium length 2.6 width, superior margin with 3 long, simple RS, inferior distal angle with long, simple RS absent, and with setal patch absent; merus weakly lobate, length 1.4 width, 0.53 ischium length, superior distal angle with a cluster of 5 long, simple RS, inferior margin covered in setal mat; carpus length 0.88 merus length, 1.5 width, superior margin with 2 long, simple setae on distal angle, inferior margin with setal mat, and 1 long, simple seta; propodus weakly curved, length 2.9 width, 1.7 carpus length, superior distal margin without palm setae, inferior margin covered in setal mat; dactylus length 1.6 width, length 0.33 propodus length, inferior margin first 0.75 covered with scales, distal margin with 3 long, simple setae (Figure 7B). Pereopod 7 (Figure 7C) basis superior margin with palm setae absent, inferior proximal margin with setal patch, inferior distal angle with long, simple setae absent; ischium length 2.6 width, superior margin with 7 long, simple RS; merus lobate, merus length 1.6 width, merus length 0.56 ischium length, superior distal angle with 9 RS, inferior margin with setal mat, inferior distal angle with 2 biserrate setae; carpus length 1.8 width, carpus length 0.96 merus length, inferior margin with setal mat, superior distal angle with a cluster of 9 long, biserrate setae, superior distal angle with a cluster of 2 long, simple, RS, inferior distal angle with a cluster of 4 long, biserrate setae, inferior distal angle with 1 long, simple RS; propodus weakly curved, length 3.9 width, length 1.8 carpus length, inferior margin first 0.75 with setal mat, inferior distal margin with 2 long, simple setae, and with palm setae absent; dactylus length 2.0 width, dactylus length 0.26 propodus length, inferior margin with fine scales, distal margin with 4 simple setae (Figure 7C).

Penial process length 3.2 basal width (Figure 22C, D).

Pleopod 1 peduncle length 0.46 width, with a cluster of 3 coupling hooks; endopod mesial margin entirely covered with fine, simple setae; exopod length 1.7 width, ventral surface without fine, simple setae (Figure 8A). Pleopod 2 appendix masculina straight, distally narrowing, distal apex acute, length 16.0 basal width (Figure 8B). Pleopod 3 peduncle with a cluster of 3 coupling hooks, distolateral angle with 2 long, simple setae (Figure 8C). Pleopod 4 peduncle distolateral angle with 1 long, palm seta; endopod distal apex without plumose setae; exopod distal margin with 2 simple setae (Figure 8D). Pleopod 5 exopod proximolateral margin with palm setae absent; exopod with transverse suture starting laterally moving mesially, incomplete; exopod with 2 scale patches (Figure 8E). Uropod exopod length 2.5 width; rolled proximolateral margin weakening moving toward lateral, medial margin; mesial margin without setae; endopod length 2.8 width, extends past exopod, mesial margin without setae (Figures 8F; 22A, B, D).

Description of female.

Body length 2.2 width; pereonites 1-7 without tubercles, pereonite 7 distomesial margin weakly convex (Figure 22E, F). Pleon with 1 posterior weak tubercle on either side of longitudinal axis (Figure 22E, F). Pleotelson length 1.8 width, dorsal surface with 2 tubercles on either side of longitudinal axis; posterior margin of pleotelson acuminate (Figure 22E, F). Uropod exopod proximolateral margin rolled weakly; endopod posterior margin tapering to an evenly rounded tip, length 2.9 width, extends past exopod (Figure 22E, F).

Size.

Largest ♂ 8.0 mm, largest ♀ 8.6 mm.

Color.

Without chromatophores. Preserved specimen pale cream.

Remarks.

Exosphaeroma paydenae sp. n., unlike other Exosphaeroma sp. in this 'species flock’, lacks strong sexual dimorphism. Males have overall larger pleotelson and uropods than females. Exosphaeroma paydenae sp. n. is morphologically most similar to Exosphaeroma russellhansoni sp. n. Exosphaeroma paydenae sp. n. can be identified by: pereonites 1-7 without tubercles; pleon with one anterior weak tubercle on either side of longitudinal axis, one posterior weak tubercle on either side of longitudinal axis; pleotelson dorsal surface without ornamentation (Figures 5A, B; 22A, B).

Exosphaeroma russellhansoni sp. n., in contrast to Exosphaeroma paydenae has only one weak tubercle on either side of longitudinal axis of its pleon; pleotelson dorsum, with 2 small anterior tubercles (Figures 9A, B; 23A, D). 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 5 and 22).

Kussakin (1979) provided new figures for what he considered to be specimens of Exosphaeroma amplicauda from Alaska. In his description he wrote "one sample (three specimens) from Alaska was examined from the collections of the Zoological Institute, Academy of Sciences of the USSR." We here recognize the Alaska specimens as Exosphaeroma paydenae sp. n., which does not overlap in occurrence with species from further south, all described herein.

Distribution.

Alaska, Aleutians.

Etymology.

This species is named to honor LACM Trustee and long supporter of science at the Natural History Museum of Los Angeles County, Joan Payden. She is thanked for her gracious philanthropy which in part supported ARW as an undergraduate student researcher. ARW’s research experience describing and redescribing the Exosphaeroma along our coast piqued his interest in marine isopods and launched his career in Crustacea at the LACM.