Dynoides elegans (Boone, 1923)

Wetzer, Regina & Mowery, Gracie, 2017, Redescription of Dynoideselegans (Boone, 1923) (Crustacea, Isopoda, Sphaeromatidae) from the north-eastern Pacific, ZooKeys 646, pp. 1-16 : 4-12

Dynoides elegans (Boone, 1923) Figures 1, 2, 3, 4, 5, 6, 7, 8

Clianella elegans Boone, 1923: 153; Kussakin and Malyutina 1993: 1174.

Dynoides elegans . Li 2000: 138.

Material examined.

HOLOTYPE ♂ (7.04 mm), California, San Diego County, La Jolla, Scripps Institution for Biological Research, ~ 32.27°N ~ 117.61°W, 23 Oct 1915, USNM 50421 [RW16.020] designated by Boone.

2 ♂ PARATYPES (6.03, 5.36 mm, smaller specimen dissected and figured), same data as holotype, USNM 1422085.

Non-type material: 1 ♂ (6.16 mm), California, Los Angeles County, White Point, San Pedro, ~ 33.715°N ~ 118.314°W, 18 May 1919. Coll. E.P. Chace, USNM 50422 [RW16.022].

2 ♂ (largest ♂ 5.36 mm, 2nd male used for SEM), plus 8 non-gravid females, subadults and juveniles, California, Los Angeles County, Palos Verdes Peninsula, Pt. Fermin, shore at Paseo del Mar, ~0.5 mi. W of Gaffey Street, 33.71°N 118.30°W, mid-low intertidal, chipping overhanging rock with hammer and Phragmatopoma tubes on under side of rock, 0.99 m. Fixed and preserved in 95% ethanol. 27 Mar 2004. Sta. #2. Coll. R. Wetzer, N.D. Pentcheff, and LMU students. RW04.030. LACM-MBPC 17829.

Additional material examined.

1 male (5.36 mm), 3?females/subadults, 13 juv., Pt. Fermin, shore at Paseo del Mar, ~0.5 mi. W of Gaffey Street, eastern end of beach, ~ 33.71°N ~ 118.3°W, mid intertidal, scraping live barnacles off deeply crenulated rock shelf, fixed and preserved in 95% ethanol. 13 Jun 2006. Coll. R. Wetzer. RW06.063. LACM-MBPC 17831.

1 male (5.35 mm), 5 subadults, 2 juv., Los Angeles County, Santa Catalina Island, Big Fisherman Cove, in front of USC Wrigley Institute, 33.44°N 118.48°W, algal scrapings, ca. 1-2 ft. below low water, fixed and preserved in 95% ethanol. 7 Apr 2006. Acc. No. F.P.2.2006-6. Coll. N.D. Pentcheff, N.L. Bruce, R.Wetzer. RW06.006. LACM-MBPC 17830.

2 subadult males (largest individual 5.4 mm), 2 juvenile specimens, and posterior half of a gravid female, Santa Catalina Island, Avalon Harbor, ~ 33.35°N ~ 118.33°W, either rock or artificial substrate, subtidal scrapings, 3.05 m. Probably fixed in formalin, stored in 95% ethanol. 1 May 2011. Sta. 406. Coll. LACSD, rcvd. from D. Cadien. RW12.212. LACM-MPBC 17832.

9 specimens (largest 7.37 mm), Santa Barbara County, Santa Cruz Island, Pelican Bay, ~ 34.035°N ~ 119.703°W, under Mytilus beds, 18 Jul 1939. Coll. W.G. Hewatt. RW16.019. USNM 86407, Acc. No. 154967.

1 male (6.83 mm), Pacific, Mexico, Baja California Norte, Cedros Island, South Bay, Sta. 288-34, 10 May 1934. RW16.028. USNM 252317, Acc. No. 128938.

2 specimens (3.9 mm and 4.0 mm) photographed live, Los Angeles County, San Pedro, White Point, 33.72°N 118.32°W, rocky intertidal, hand, preserved in 95% ethanol. 23 Jun 2016. Coll. A. Wall, J. Wall, K. Omura, N.D. Pentcheff, L. Harris. RW16.051. LACM-MBPC 16919.

Description of male.

Body length 2.4 × width; pereonites 1-5 smooth, pereonite 1 medially very slightly raised, pereonites 6-7 with very small tubercles; pleotelson covered with small tubercles; pleotelson length 1.2 × width, anterior of pleotelsonic sinus with prominent rounded tubercle barely overhanging base of sinus, sinus walls straight-sided, finely crenulate, and slightly raised. Coxal margins with setae appearing membranous, membrana cingula, (Figures 1A, B; 5B, C; 7A, B).

Antennula peduncle article 1 length 3.6 × width, anterior medial margin with 2 palm setae; article 2 as long as wide, inferior distal margin with 1 palm seta, superior margin with 1 palm seta; article 3 length 2.2 × width, proximal margin with 1 simple seta; flagellum with 14 articles, 12 distalmost articles with aesthetascs (Figure 1C). Antenna reaching anterior margin of pereonite 3; article 5 length 2.2 × width, flagellum with 17 articles (Figure 1D). Clypeus and labrum as in Figure 5E, F.

Left mandible incisor with 3 cusps; lacinia mobilis with 3 cusps; lacinia mobilis spine row comprised of 2 serrate and 3 simple spines; crushing surfaces strongly ridged; mandibular palp article 1 with 2 minute setae; article 2 with 2 palm setae and 2 plumose setae; article 3 with long, plumose setae (Figure 2A). Maxillula mesial lobe with about 7 spines; lateral lobe with about 10 spines (Figure 2B). Maxilla mesial lobe with 2 simple setae and 3 plumose RS on gnathal surface; middle lobe with 2 simple setae and 2 pectinate RS; lateral lobe with 2 pectinate RS (Figure 2C). Maxilliped endite distal surface with 5 plumose setae; distomesial margin with 1 coupling hook; palp article 2 distal apex with 9 long, (some broken) simple RS; article 3 distal apex with 8 long, simple RS; article 4 distal apex with 6 long, simple RS, lateral distal angle with 1 long, simple RS; article 5 distal apex with 4 long, simple RS (Figures 2D; 5F).

Pereopods 1-7 (Figures 3 A–G; 5F) all with one strong secondary unguis on the dactyl, ambulatory, and similar; merus, carpus, and propodus inferior margins more setose than superior margins (as figured). Pereopod 1 basis length 2.3 × width; ischium length 2.8 × width. Pereopod 2 basis length 3.6 × width; ischium length 3.1 × width. Pereopod 1 more stout than pereopods 2-7. Pereopod 7 basis length 3.4 × width, ischium length 4.0 × width.

Penial process length 2.3 × basal width, basal third fused (Figure 5G).

Pleopod 1 peduncle length 2.3 × width with 2 coupling hooks (Figure 4A); PMS extending to posterior margin of pleonal cavity (Figure 5G). Pleopod 2 peduncle length 3.2 × width with 2 coupling hooks, appendix masculina proximally slightly swollen, distally narrowing, basal mesial margin with scales, distal third doubled back on proximal half (Figure 4B). Pleopod 3 peduncle length 2.0 × width with 2 coupling hooks (Figure 4C). Pleopods 1-3 exopods and endopods with PMS as figured (note: not all drawn, but indicated). Pleopod 4 endopod and exopod subequal, exopod with transverse suture (Figure 4D). Pleopod 5 endopod and exopod subequal, endopod length 1.4 × width with one distal scale patch and one smaller submedial scale patch, exopod length 1.6 × width (Figure 4E).

Uropod exopod proximolateral margin rolled, weakening distally; in the adult ♂ holotype (USNM 50421) and 2 adult ♂ paratypes (USNM 1422085) uropods extend well beyond posterior margin of pleotelson (as figured in Figure 1B), but do so otherwise only in the largest males (see Figures 5B; 7A, B).

Description of female.

Body length 2.2 × width; (Figures 6A, B, C). Dorsal ornamentation as in the male. Pleotelson length 1.2 × width. Uropodal endopod longer than exopod, endopod just barely extending to posterior margin of pleotelson (Figure 6D). Dorsally uropodal exopod proximolateral margin weekly rolled, tapering to an evenly rounded distal margin. Gravid female estimated with 8-12 mancas. Figure 6D is the posterior half of female broken open exposing 3 mancas.

Size. Largest ♂ to 7.37 mm, largest ♀ to 5.4 mm.

Color. When alive brightly colored, individuals highly varied (Figure 7A, B). When preserved in ethanol, specimens quickly become pale buff to whitish. Bright red coloration outlining pleotelsonic slit fades last.

Distribution.

California: San Diego to Santa Barbara Counties.

Molecular data.

Both 18S-rDNA and 16S-rDNA were generated from the same individual from Pt. Fermin (RW04.030), GenBank numbers JF699541, and KU248214, respectively. Locality information is provided above in Material Examined. This specimen came from the same lot from which the SEM specimen in Figure 4 was prepared.

Remarks.

Dynoides elegans is morphologically most similar to Dynoides saldanai and Dynoides crenulatus (Pacific, Mexico, Oaxaca). These three species are easily distinguished from Dynoides dentisinus . Adult male specimens of Dynoides dentisinus are more robust than those of Dynoides elegans and have a distinctive, prominent large process extending over the pleotelson (Figure 8A, B). The presence of a prominent pleonal process is polymorphic in Dynoides ( Li 2000). The presence of a slit, sinus, notch, or foramen is also variable in the genus ( Li 2000). A pleotelson slit of various shapes is present in all three eastern Pacific Dynoides and the north-western Pacific Dynoides brevicornis ( Kussakin and Malyutina 1987).

A generic description of the "penes fused along proximal half of length" ( Li 2000) is an easily recognizable character. In Dynoides elegans penes may be considered fused closer to proximal third of length (Figure 5G). Of all of the material available for examination, we had only a single broken gravid female (Figure 6D). Gravid females are clearly rare. This may be attributed to our poor sampling during brooding episodes, which remain unknown. No specimens collected during the months January/February, August/September, or November/December were available for examination.

Dynoides elegans is most similar to the Oaxacan species, Dynoides saldanai . They share pleonal characters which are known to change as individuals, especially males, mature. Penial processes, pleonal process, appendix masculina, pleotelson morphology and also pleotelson sinus morphology are characters that all change with age in males. A fully adult male (penes and appendix masculina developed) may not be at the final fully developed male stage, potentially with some further changes to the pleotelson morphology. We do know that in males the sinus will transition progressively from a simple slit to a quite complex structure. The body length of the Dynoides elegans type specimens range from 5.36 to 7.04 mm. The subtle changes in morphology are readily observed in Figure 7, represented by specimens from the same collecting event. Note uropodal development and progression of a simple pleotelsonic slit to a heart-shaped slit. The largest male examined was 7.37 mm (Santa Cruz Island), and its pleotelsonic slit approaches heart-shape. The largest Dynoides saldanai specimen is 4.45 mm in length and female 3.0 mm. The two male specimens in Figure 7A and 7B are 3.9 and 4.0 mm in length.

The figured male paratype (Figure 1A) has a body length 2.35 × width. We note that in all other specimens measured, adult male body length is closer to 2.2 × width. Non-empirical observations of this species and other Sphaeromatidae from the north-eastern Pacific indicate that sexually mature adult males reached larger body sizes in the past than they do today (RW pers. obser.). Specimens of Dynoides elegans collected before the 1940s are among the largest individuals in the examined collections, with the largest males exceeding 7 mm body length. The largest specimens come from the oldest collections (specimens collected between 1915-1939). It appears that fully developed males in the past attained larger body sizes than more recently collected individuals (e.g., 2004-2016). To quantify this, populations of individuals appropriate to determine statistical significance need to be evaluated.

Dynoides elegans is known from San Diego County to Santa Barbara County, with a single male specimen (USNM 252317) recorded from Cedros Island off the Pacific Baja California coast. The Cedros Island specimen is most similar to White Point and Pt. Fermin specimens (Los Angeles County). These localities are roughly 700 km apart. To definitively confirm that Cedros Island is the southernmost locality in the species range, additional specimens are needed. Appropriate material for molecular analysis would greatly contribute to our understanding of the morphological diversity within species (e.g., varying amounts of membrane-like setae on the coxal margins, refer to Figure 7), across populations, and allow us to determine whether Dynoides saldanai might be a junior synonym of Dynoides elegans . The Dynoides saldanai type series consists of 27 specimens: 2 adult males, 10 juvenile males, 11 females, and 4 undetermined junveniles. The male holotype (4.45 mm) and allotype were deposited at the Institute of Biology of the National Autonomous University of Mexico. The paratypes are alleged to be in the National Museum of Natural History in Paris (Carvacho and Hassmann 1984). Type numbers were not provided. When substantially more fresh material has been collected, it would be useful to clarify the status of Dynoides saldanai by comparisons with the type material and any other specimens attributed to Dynoides saldanai and Dynoides elegans . Not examining Dynoides saldanai types at this time does not effect the status of Dynoides elegans .