TRANSACTIONS OF THE SAN DIEGO SOCIETY OF NATURAL HISTORY Volume 20 Number 4 pp. 69-79 24 June 1983 Two new idoteid isopods from Baja California and the Gulf of California (Mexico) and an analysis of the evolutionary history the genus Colidotea (Crustacea: Isopoda: Idoteidae) fARY Richard C. Brusca Department of Marine Invertebrates, San Diego Natural History Museum. San Diego, California 92112 iSA Abstract. Two new species of idoteine isopod crustaceans are described from Baja California, Colidotea wallersteini new species and Synidoteafrancesac new species (Crustacea: Val\ifera: Idoteidae: Idoteinae). The genus Colidotea is rediagnosed. a key to the known species presented, and its evolution and historical biogeography described. Both trans-oceanic dispersal and vicariance phenomona appear to have played roles in the establishment of modern distributional patterns of Colidotea. Introduction The idoteid isopod fauna of the northeast Pacific has. in the past 10 years, come to be quite well known (see Brusca and Wallerstein 1979b for an introduction to the literature). The present study adds 2 new species to this fauna, based on material collected by Dr. D. G. Lindquist (University of North Carolina) and some previously unsorted samples of microcrustaceans at the Allan Hancock Foundation (University of Southern California). The terminology used in this paper is standard for the idoteid isopod literature (see Menzies 1950 for a summary). The following abbrev iations arc used: AHF. Allan Hancock Foundation; USNM, National Museum of Natural History; SDNHM. San Diego Natural History Museum. Systematics Order Isopoda Suborder Valvifera Family Idoteidae Subfamily Idoteinae Genus Synidotca Harger, 1878 The systematics and biogeography of the genus Synidotca were reviewed by Men- zies and Miller (1972). who recognized 36 valid species and subspecies. 8 of which occur in California. Iverson (1972) described a ninth species from California {S. Dwdia). Brusca and Wallerstein (1979a) presented new distributional records for S. harfordl Benedict, 1897, which at that time was believed to be the southernmost ranging species of the genus in the northeastern Pacific. They noted its disjunct occurrence: central California to Magdalena Bay (SW Baja California), Mexico, reappearing again m the central Gulf of California. Mexico (2 known records). Brusca and Wallerstein (1979b) reviewed the distributions of the 7 known northeastern Pacific shallow-water Synidotca. noting that all but S. harfordi were entirely restricted to the cold-temperate waters of the Arctic. Aleutian and Oregonian Provinces. Brusca (in press) discusses phylogenetic 70 Figure 1. Synidotea francesae new species. Holotype, AHF 736. Female. relationships, evolutionary history and zoogeography of Synidotea. as well as the 21 other genera of Idoteinae. Synidotea francesae new species Figures 1, 2. 3 Types. — HoloXype: female. AHF 736; Allotype: male. AHF 736a. Paratypes: 1 female, SDNHM; 1 female, USNM. Locality. — AW specimens from single collection: Mexico, Gulf of California, So- nora. El Golfo dc Santa Clara (about 4 miles SE of town); found on sandy beach, "scavenging" on cast up tubes of Chaetopterus species (Polychaeta); air temperature 24°C; water temperature (surO 19°C; 17 April 1973; collected by D. G. Lindquist. Diagnosis. — CQp\\3.\or\ without horns or other projections; frontal margin convex; eyes bulge outward; body without tubercles or rugae; plcotclson wider than long; per- 71 FidiRF 2. Synlciotca francesac ncv,' species. Holotype. AHF 736. Female, a. antenna 1. b. antenna 2. c, left mandible, d, lacinia of right mandible, e, maxilla 1. f. maxilla 2. g. maxilliped. h. pereopod I. i. pereiopod IV. J. pereopod VII. k. uropod. 72 Figure 3. Synidotea francesae new species, a, pleopod I (holotype). b, pleopod 2 (holotype). c, appendix masculinum of pleopod 2. male (allotype), d, pleopod 5 (holotype). eonites V-VII manifestly shorter than I-IV; median dorsal pattern rounded, as in S. laticauda; dorsum with heavy pigmentation. Description. — hQxxgXh to at least 6 mm; body ovate and darkly pigmented: dorsum smooth. Cephalon: Lacking horns or other projections; frontal margin convex, although anterolateral angles somewhat expanded; eyes elevated, on distinct bulges. Antenna 1 with tri-articulate peduncle and uniarticulate flagellum; distal third of terminal article with simple setae and esthetascs. Antenna 2 with 5-articulate peduncle and 8-articulate flagellum; all articles with setae; articles 4 and 5 of peduncle each with distinct distal patch of chromatophores; flagellum quite short, extended only to pereonitc II. Max- illiped typical for the genus, with single coupling hook. Maxilla 1 typical for the genus; inner lobe with 2 stout plumose setae; outer lobe with 6 long simple setae and 4 short pectinate setae. Maxilla 2 typical for the genus, with plumose, simple and comb setae as figured. Mandible with 4-toothed incisor and large molar process, the latter smooth on outer margin and toothed on inner margin; lacinia mobilis of left mandible 3- toothcd; lacinia of right mandible 3-toothed but with additional large serrate spinelike process. Pereon; Manifestly elevated along middorsal line; entire dorsal surface with dark pigmentation, except along lateral margins. Pereonites I-IV large, long and without dorsal coxal plates; pereonites V-VII small, short, and with large dorsal coxal plates, visible in dorsal aspect by presence of faint suture lines just median of edge of chro- matophorc pattern; all pereopods form ventral coxal plates that meet in midline of sterna. Median dorsal pattern of pereonites II-IV {scusu Menzies and Miller 1972) with rounded posterior margins. Pereonites I V-VII slightly produced along posteromedial margin. Pereopod I with dactyl nearly as long as propodus. Picon; Posterior border with faint indentation, otherwise evenly convex. Pleon (=plcotelson) width equal to length, or up to 1.5 times wider than long. Plcopods 1-3 73 Table 1. Principal attributes distinguishing Colidotca and its sister-group. Synisoma. from each other and from all other genera of Idoteinae.* For comparable data on the other 20 genera of Idoteinae see Brusca (in press). with plumose marginal setae, decreasing posteriorward; pleopods 4-5 without plumose marginal setae. Uropod with 3 stout plumose setae at junction of protopod and lamella. Appendix masculinum of male simple, with weakly grooved inner margin and a few distal setae; penes entirely fused into large tongue-like flap. Ety}}iology\ — Synidotea fraucesae is named in honor of Frances Runyan: biological illustrator, horticulturist, and friend. Discussion.— Synidoicajrancesae is similar to S. laticaucia Benedict, 1897, and S. harfordi Benedict. 1897 (both known from California shoi"es), in having a smooth dorsum with a characteristic medial dorsal pattern, evenly convex lateral margins on the body somites, elevated (bulging) eyes, and notch at the apex of an otherwise evenly convex pleotelson. It differs most strikingly from these species in having a pleon as wide or wider than long, a barely perceptable notch at the pleotelson apex (rather than a deep notch), pereonites V-VII manifestly reduced in size, and a distinct dorsal chro- matophore pattern. It differs further from 5". laticauda in having an evenly convex tVontal margin, a 4-toothed incisor on the mandible, and shorter antennae. It differs further from S. harfordi in having rounded posterior margins on the medial dorsal pattern of pereonites II-IV, shorter antennae, and a coupling hook on the maxillipedal endite. Of the 18 species o^ Synidotea now known from the eastern Pacific, only S. fran- ccsac is a regular resident of warm waters (i.e., the Eastern Pacific Zoogeographic Region); all others are temperate or polar species. The genus is worldwide in distribution but notably absent from the New World tropics. Brusca and Wallerstein (1979b) and Wallerstein and Brusca (1982) hypothesized that this absence is due to the inability of Synidotea species to develop certain morphological (size; body spination) and life history (early reproduction; predator avoidance behaviors) adaptations that have al- lowed successful radiation in this region by other genera (e.g., Erichsoiwlla. Eusyni- nicriis, FarasyniDicrus). and that any species of Idoteidae that may be found successfully inhabiting the warm coastal waters of the tropical eastern Pacific would have had to evolve some of these adaptations. In the subtropical waters of the Gulf of California. S.francesae has evolved at least 1 (small size) if not more (e.g., early reproduction) of these attributes which presumably ha\e played a role in its ability to survive the predation-intense summers of this region. Menzies and Miller (1972) state that the mean length of the 8 Arctic species ol\Synidolca is 18.8 ± 2.6 mm, while the mean length of the 5 tropical species then known (all from the Old World) was 8.0 ± 2.2 mm. Temperate species fall between these two extremes. By comparison, the largest specimen oWSynidoteafrancesae examined is onh 6 mm in length. 74 Genus Colidotea Richardson, 1905 The genus Colidotea was briefly reviewed by Brusca and Wallerstein (1979b). The genus now contains 4 species: C. wstrata (Benedict), southern California; C. findleyi Brusca and Wallerstein. Baja California; C. edniondsoni Miller. Hawaii; arfid C. wal- Icrsteifii new species. Baja California (Fig. 7). Brusca (in press) discusses the phylogeny, evolutionar\ history and zoogeography of Colidotea and its sister-group. Synisonia Leach. Both genera are restricted to warm-temperate and subtropical waters of the New World (Colidotea) and Old World {Synisoma). Table 1 summarizes the principal fea- tures that distinguish these 2 genera from one another and from all other genera of Idoteinac. A reexamination of the 4 known species of Colidotea warrants an expanded di- agnosis of the genus and a key to the species, as follows. Diag}iosis. — \doXQ'maQ with body compact, pereon merging smoothly with pleon. Cephalon with anterolateral angles produced; with or without a medial cephalic process or spine; eyes lateral. Second antennae with flagella comprised of a few. or a dozen or so articles, the number increasing somewhat with age (length). Maxillipedal palp of 4 free articles, apical article large and ovate; epipod present; endite with or without coupling hooks. Mandible with large lacinia mobilis. nearly as large, or as large as incisor process. Pereon with coxal plates present on segments II-VII; coxae may or may not be visible in dorsal aspect, or may be visible only on posteriormost perconites. Pleon comprised of single piece, with one pair of lateral incisions (=suture lines); pleon length less than '/i total body length; uropods uniramous. Appendix masculinum of male arising from base of pleopod 2 endopod. Uropods uniramous. Key to the Species of Colidotea 1. Cephalon with medial spine or process, which may or may not project over supra-antennal line 2 - Cephalon without medial spine or process 3 2. Cephalic process bifurcate (2-pronged); frontal process subacute (convex); pleo- telson with posterior margin angulate; bases of pereopods with dark chromato- phore band C edmondsoni - Cephalic process simple (single apex); frontal process notched (concave); pleo- telson with posterior margin evenly rounded; bases of pereopods without dark chromatophore band C. rostrata 3. Frontal process notched (concave); coxal plates hidden in dorsal aspect; pleo- telson posterior margin subacute; eyes large; maxilla 2 trilobate C findleyi - Frontal process not notched, but convex; coxal plates visible on pereonites IV- VII. in dorsal aspect; pleotelson posterior margin evenly rounded; eyes small; maxilla 2 bilobate C wallersteini new species Colidotea wallersteini new species Figures 4, 5 7y/7C'^. — Holotype: male, AHF452. Paratypes: AHF4925; SDNHM (1 specimen); USNM (1 specimen). Locality. — Known from only two localities. Holotype: Mexico. Baja California Norte (Pacific coast), Punta Clara, south Rio Santo Tomas, 1 8 December 1 945. collected by C. Hubbs (H45-217a). Paratypes: Mexico. Guadalupe Island, off' N coast of Baja California. Melpomene Cove, intertidal collections. 18 December 1949. collected by R. J. Menzies and D. Reish, I 'elero III (Allan Hancock Foundation), Station No. 1915- 49. Diagnosis. — Body straight-sided; coxal plates visible in dorsal aspect on perconites IV-VII. Cephalon with supra-antennal line forming 3 points. 1 medial and 2 submedial; frontal process distally convex; antenna 1 flagellum a single article; antenna 2 flagcllum with about 9 articles; lacinia mobili present on both right and left mandible; molar 75 K-:-- \-/ .;■ . FiGi'RF 4. Coliciotca wallcrsietiii new species. H(>loi\pc. AHF 452. Male. process simple, greatly reduced (smaller than lacinia); maxilliped with 2 coupling hooks on right. 1 on left: maxilla 2 bilobate. smaller lobe with 2-jointed apical process ter- minating in single large seta; posterior margin of pleotelson evenly convex. /)«c'/7/J//V'//. — Bod\ smooth, straight-sided, with coxal plates on pereonites II-VII 76 FiciURE 5. Colidotca wallcrsieini new species. Holotypc. AHF 452. Male. a. right maxilliped. b. maxilla c, maxilla 2. d, right mandible, e, uropod. f, pleopod 1. g, pleopod 2. h, pcrcopod IV. i. pcrcopod I. SYNISOMA RO ST RATA FINDLEYI 77 C. WALLERSTEINI yr rzj 12 ZJ 11 Figure 6. Cladistic relationships of the 4 known species of Colidotea and their sister-group. Synisoma. See Brusca (in press) for character polarity analysis and discussion of relationships outside this clade. Apomorphies indicated are as follow: 1, Reduction from a 5-jointed to a 4-jointed maxillipedal palp. 2. Lacinia mobilis of mandible enlarged, subequal to incisor process. 3. Pleon reduced to a single piece, with a pair of lateral incisions indicating partial fusion of 1 pleomere. 4, Pleon reduced to a single piece, with no remaining lateral incisions. 5. Pleon greatly elongated. '/? or more total body length. 6. Cephalon with an anteromedial process. 7. Anteromedial process of cephalon bifid. 8. Adoption of a symbiotic relationship with sea urchins of the genus Strongylocenlrotiis. and associated morphological adaptations (e.g.. elliptical body; purple pigmenta- tion). 9. Eyes enlarged. 10, Posterior margin of pleon acute. 11. Second maxillae with only 2 lobes. 12, Typical "spines" of first maxilla outer lobe reduced to 3 slender, stout, simple setae. (visible in dorsal aspect only on IV-VII). Length to at least 16.5 mm; length 4-5 times width. Cephalon: Without tubercles or elevations of any kind; broadly immersed in per- eonite I; frontal process distally convex. Eyes very small, set on extreme lateral margins. Antenna 1 comprised of 4 articles, fourth being the single flagellar article, with terminal esthetascs. Antenna 2 with 9-articulate flagellum. Mandible with 4-toothed incisor; lacinia with 3 teeth and 3 stout setae; molar process greatly reduced, simple. Maxilla 1 outer lobe with about 9 small apical setae (some of which arc comb setae) and 3 stout simple setae; inner lobe ending in single stout setose spine. Maxilla 2 bilobatc; larger lobe with 2 very large plumose setae and about 7 smaller setae, some ctenose; smaller lobe with 2-jointed apical process terminating in single large seta. Maxilliped typical for genus; enditc with several large apical setae; 2 coupling hooks on right. 1 on left. Pereon; Smooth, straight-sided, forming continuous line with pleon; pereonite I with anterolateral angles produced to level of eyes, engulhng cephalon. Pereonites gradually increasing in width posteriorly; II-VI subequal in length; I and VII somewhat shorter than others. Well-developed coxal plates present on II-VII. visible in dorsal aspect only on IV-VII. Pcrcopods I-VII slender and ambulatory, terminating in re- flexed, biungulate dactyl; sctation simple; ischium of percopod 1 groo\ cd to receive basis. Pleon; Posterior margin of pleotelson evenly convex. Uropods simple; with single large plumose seta at junction of protopod and lamella. Pleopods typical of genus; 1- 2 with abundant plumose marginal setae; 3-5 reduced, somewhat fleshy, and cither 78 35° Fici RE 7. Distributions (locality records) of the known species of Colidotea. Open circle = C. wallcislcim. Closed circle = C. findleyi. Triangles = C rostrata. C. edmondsoni is endemic to the Hawaiian Islands (not on map). naked or at most with a few scattered simple setae (as in C. findleyi). Appendix mas- culina large, extended beyond apex of pleopodal lamellae, with short apical spines; base of pleopod 2 endopod "■muscularized" just below junction of appendix maxulinum. Etymology. — Colidotea wallersteini is named in honor of Dr. Barry Wallerstein, in acknowledgment of his work on the systematics and ecology of the Idoteidae and 79 in recognition of his long-standing friendship: furthermore, the resemblance in form is striking. Discussion.— Oi' the 4 known species of Colidolea. 2 {C. roslrata and C. edmond- soni) share a unique derived character, the large cephalic tubercle. In addition to this synapomorphy, they have more general characters in common with one another than either shares with C. findlcyi or C. nul/crstcini. No synapomorphies are recognizable to unite the latter 2 taxa as sister-species, so their cladistic relationship must be viewed as a trichotomy at this time. The character relationships of the known species of Colidotea are expressed in the cladogram in Fig. 6. Because Hawaii arose as an oceanic island. C. cdniondsoni most likely evolved there in isolation subsequent to a dispersal event from western North America. Its immediate ancestor was probably a free-living species that was also the parent taxon to the commensal C. rostraia. Colidotea findleyi and C. wallersteini can be derived from this same ancestral lineage. The latter is strictly a warm-temperate species, known only from northwestern Baja California and Guadalupe Island (Fig. 7). Colidotea fin- dlcyi is also a warm-temperate species, but exhibits considerable eurythermy in its ability to survive the warm summer months typical of the northern Gulf of California. The disjunct occurrence o{ C. findleyi on both the western coast of Baja California (and Guadalupe Island), as well as the restricted northern Gulf of California population, suggests that it may have entered the Gulf during a period of lowered oceanic paleo- isotherms (i.e.. Pleistocene glacial periods). Brusca and Wallerstein (1979b) and Wal- lerstein and Brusca (1982) have discussed the probability of such events, suggesting that the Pleistocene glacials and interglacials (and the associated latitudinal shifts in coastal isotherms) resulted in a series of vicariant events such that populations of temperate species were repeatedly trapped in the northern Gulf of California as lati- tudinal isotherms shifted from north to south and back. These events were probably responsible for the evolution of the various northern Gulf endemic species that have warm-temperate (Californian) sister-taxa. If this theory is correct, C findleyi can most simply be envisioned as a sister-species of C wallersteini, the 2 taxa being vicariant products of one of the earlier Pleistocene glacial episodes. Sympatry was later effected when a subsequent glacial event facilitated the escape of C findleyi from the Gulf. The present interglacial period and relatively high coastal isotherms maintain the current disjunct distribution of CJindleyi. Acknowledgments This study was funded by a grant from the National Science Foundation (DEB 80-17835). Appreciation is extended to Bill Cooke, George Schultz. and Tom Bowman for the loan of specimens of Colidotea cdniondsoni: to the British Museum (Natural History) for the loan of Synisoina specimens: and to Fred Schram and Greg Pregill for reviewing the manuscript. Frances Runyan executed the two dorsal views. Literature Cited Brusca. R. C. In press. Phylogeny, evolution and biogeography of the marine isopod subfamily Idoleinae (Crustacea: Isopoda: Idoteidac). San Diego Soc. Nat. Hist. Trans. . and B. R. Wallerstein. 1979a. The marine isopod crustaceans of the Gulf of California. II. Idoteidae. New genus, new species, new rec- ords and comments on the morphology, tax- onomy and evolution within the family. Proc. Biol. Soc. Wash. 92(2):253-271. 1979b. Zoogeographic patterns of idoteid isopods in the northeast Pacihc. with a review of shallow-water zoogeography for the region. Bull. Biol. Soc. Wash. 3:67-105. Iverson, E. W. 1972. A new subtidal Synidolea from central California (Crustacea: Isopoda). Proc. Biol. Soc. Wash. 85(47):54 1-548. Menzies. R. J. 1950. The ta.xonomy. ecology and distribution of northern California isopods of the genus Idothca with the description of a new species. Wasmann .1. Biol. 8(2): 1 55-195. , and M. A. Miller. 1972. Systematics and zoogeography of the genus Synic/owu (Crus- tacea: Isopoda) with an account of Californian species. Smithson. Contrib. Zool., No. 102:1- 33. Wallerstein. B. R.. and R. C. Brusca. 1982. Fish predation: a preliminary study of its role in the zoogeography and evolution of shallow-water idoteid isopods (Crustacea: Isopoda: Idotei- dae). J. Biogeogr. 9:135-150.