Redescription of Dynoides elegans (Boone, 1923) (Crustacea, Isopoda, Sphaeromatidae) from the north-eastern Pacific

Abstract Dynoides elegans (Boone, 1923) from southern California is reviewed, redescribed, and figured. The original species description did not include figures, making it difficult to attribute individuals to the species. Dynoides saldanai Carvacho and Haasmann, 1984 and Dynoides crenulatus Carvacho & Haasman, 1984 from the Pacific Coast of Mexico and Dynoides brevicornis Kussakin & Malyutina, 1987, from Furugelm Island, Peter the Great Gulf in the Sea of Japan, appear morphologically more similar to each other than to western Pacific species. A large pleonal process is present in about half of the Dynoides species, but is absent in this north-eastern Pacific clade and the north-western Pacific Dynoides brevicornis and Dynoides brevispina. Dynoides dentisinus Shen, 1929 possess a large pleonal spine. It is known from China, Japan, and Korea and is introduced in San Francisco Bay; it can be easily distinguished from Dynoides elegans by the presence of a pleonal process in the former. A key to the Pacific West Coast Dynoides is provided.


Introduction
The genus Dynoides Barnard, 1914 was erected for D. serratisinus Barnard, 1914 from Natal and Mozambique (Kensley 1978) and currently has 20 accepted species (WoRMS, World Register of Marine Species, Bruce and Schotte 2013). A complete synonymy for the genus was provided by Li (2000). In the north-eastern Pacific three species are known: D. crenulatus Carvacho & Haasman, 1984, D. saldanai Carvacho & Haasmann, 1984, both from the Pacific Coast off the Oaxacan State of Mexico, and the species redescribed here, D. elegans (Boone, 1923). Additionally, D. dentisinus Shen, 1929 originally described from the coast of North China also occurs in San Francisco Bay. Kussakin and Malyutina (1987) described D. brevicornis from Furugelm Island, Peter the Great Gulf in the Sea of Japan, (north-eastern Pacific). Additional species occur in the western Pacific (Japan, Korea, China, Singapore, India, and Australia).
Pearl Lee Boone described several new isopod genera and species from the California coast in her 1923 paper, all without figures. She erected the new genus Clianella Boone, 1923 for C. elegans from La Jolla, California based on six specimens collected in 1915 "from bunches of mussels along the outer ledge of rocks north of Scripps Institution of Biological Research." Of these she designated a male holotype and two male paratypes which are part of the United States National Museum of Natural History collections (Cat. Nos. 50421 and 1422085) and which were examined here. The other three paratypes were donated to the Scripps Institution of Biological Research (SIO). The SIO specimens could not be found in the SIO collections in 2016 and are presumed lost (pers. comm. Collection Manager, Harim Cha). Additionally, Boone included a single adult male specimen collected from "Point White, San Pedro, California, May 18, 1919, by Mr. E.P. Chace and donated to the U. S. National Museum" (USNM Cat. No. 1422085).
The individual designated by Boone as the holotype has previously had pleopods 1-4 removed. Some pleopods were recovered floating in the vial containing the specimen. One paratype had several broken pereopods, and its dorsum is cracked. The second paratype was complete and in as good a condition as can be expected of a 97-yearold specimen. Permission was granted for dissection and this individual is figured here.
The composition of Dynoides and its relationship to Clianella was reviewed by Li (2000) and the generic name Clianella placed into junior synonymy. The genus Dynoides is distinguished by "presence of pleotelsonic slit that may or may not have an anterior lobe and internal teeth; a penial process basally fused for half its length and an appendix masculina elongate, twice as long as the endopod and strongly reflexed" (Li 2000). Species of the genus are known from intertidal habitats.

Abbreviations
LACM -Natural History Museum of Los Angeles County; LMU -Loyola Marymount University; MBPC -Marine Biodiversity Center; USC -University of Southern California; USNM -United States National Museum, Smithsonian Institution; RSrobust seta/e; PMS -plumose marginal setae; SEM -scanning electron microscopy. Latitudes and longitudes denoted with "~" are approximate and estimated from Google Earth.

Material and methods
Descriptions are based on the male paratype and additional material as noted. Specimens examined have USNM or LACM catalog numbers. Numbers preceded by "RW" are field station numbers. Collections so labelled are readily retrieved in the LACM collections. Setal terminology broadly follows Watling (1989). We provide images of additional material from White Point (Boone's "Point White") and Pt. Fermin. Both localities are on the Palos Verdes Peninsula less than 5 km apart. Additionally, we examined material from Santa Catalina, San Cruz Islands (California Channel Islands) and Cedros Island (Baja California Norte, Mexico).
Specimens are prepared for SEM as described in Wall et al. (2015). Drawings were made with the aid of a camera lucida and illustrations were electronically "inked" with Affinity Designer, Serif Labs. Whole body illustrations were made with a Wild M5D stereo dissecting scope. Appendages were illustrated by dissecting off the appendage and placing them in glycerol on a depression slide and then imaged using a Nikon Labophot-2 compound scope. Specimens were measured with a micrometer. The lengths given in the "Material Examined" are of the largest specimen of each species and sex. Not all specimens were measured. If a length is provided and multiple specimens were present in a lot, the length refers to the largest specimen. In all species mature males appear larger than females, but body lengths for mature adults are similar. Males have broader and longer uropods than females, which contributes to this illusion.
Molecular data were generated for this species according to the protocols described in Wetzer et al. (2013). Voucher specimens are held in the LACM collections.

Key to the north-eastern Pacific species of Dynoides of the North American West Coast
This key is based on adult ♂ characters. Also note that weak pereon tubercles are visible only with SEM and not necessarily evident with light microscopy.  Barnard, 1914 Type species. Dynoides serratisinus Barnard, 1914: 408; from South Africa by monotypy.

Remarks.
A diagnosis and comprehensive synonymy was provided by Li (2000). Readily recognizable characteristics include cephalon longer than broad, penes fused along proximal half of the length. Appendix masculina elongate, twice as long as endopod, strongly reflexed. Uropodal rami broad, lamellar, and subequal in length. The genus presently has ~20 species, is intertidal to shallow water, and is most speciose in the northern Pacific with twelve species. Additional species occur off Brazil, South Africa, Sri Lanka, and Australia (Li 2000). At present, the relationships between species remain unassessed.
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 D. saldanai and D. 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 D. 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 D. 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 D. 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, D. 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 D. 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 D. 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 northeastern Pacific indicate that sexually mature adult males reached larger body sizes in the past than they do today (RW pers. obser.). Specimens of D. 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 D. saldanai might be a junior synonym of D. elegans. The D. 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 D. saldanai by comparisons with the type material and any other specimens attributed to D. saldanai and D. elegans. Not examining D. saldanai types at this time does not effect the status of D. elegans.