Coxicerberus abbotti (Lang, 1961)

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Suggested Common Name: Pacific Beach-Cerberus
Etymology: after Dr. D. P. Abbott, a researcher at the Hopkins Marine Station. Common name refers to the geographical range of this species, with many similarly-ranged species also having "Pacific" in their common names
Taxonomic History: Microcerberus abbotti Lang, 1961; Coxicerberus abbotti Wägele, Voelz & Vaun McArthur, 1995
Size Range: to 1.2mm
Description: (modified from Lang, 1961 and Coineau & Deboutteville, 1968) Body lacking pigment, transparent, about 10.5x longer than wide. Head with 3 small simple lateral setae and a pair of minute anterolateral dorsal setae. Antenna 1 6-segmented, segments 1-2 much more robust than others, segment 1 with 1 simple distolateral seta, segment 2 with 1 long and 1 short spatulate or slender plumose proximolateral sensory setae along with 2 distomedial and 1 medial simple setae, segments 3-6 lateral margins smooth, segment 3 with 2 long and 1 minute simple setae, segment 4 with 1 minute seta, segment 5 with 1 long seta, segment 6 with 1 elongate apical seta 2x longer than others, 1 short spatulate seta and a long cylindrical aesthetasc. Antenna 2 peduncle 6-segmented, all with various-lengthed simple setae, segment 1 almost triangular with 1 simple distolateral seta, segments 2-3 with with proximomedial tooth, segment 2 dorsal surface with 1 distomedial seta, segment 6 longer than others with 1 short and 1 long spatulate plumose distolateral sensory setae; flagellum 6-7-segmented, segment 1 often indistinct. Labium with 2 distinct lobes, each with 4 apical spines, lobes not demarked by sutures. Mandible body with lobe at base of palp; incisor brownish, sclerotized, 4-cuspid; left lacinia brownish, sclerotized, 3-4-cuspid, right lacinia replaced by a finely ciliated seta; spine row consisting with 2-3 finely ciliated spines; molar long, slender, distal half finely ciliated and narrower than proximal half; palp 1-segmented with apical long seta. Maxilla 1 exopod with 8 unequal distal spines; endopod much smaller than exopod, with 2 short robust apical spines. Maxilla 2 protopod 2-segmented; rami each with 1 apical pectinate seta. Maxilliped basis with an distomedial lobe with 1 apical lobe; palp segment 1 lacking spines or setae, segments 2-3 with 2 minute spines and 1 long seta, segment 4 with 2 long setae, segment 5 with 3 elongate apical setae and 1 shorter lateral setae, ventral surface with row of 5 spines, dorsal surface with 1 spine. Pereonite 1 anteriorly as wide as head, tapering posteriorly; tergite shieldlike, as wide as sternite, frontal margin produced into acute ventrolateral projection, lateral margins with 1 small simple seta. Pereonite 1 subchelate; dactyl claw long with 2 adjacent elongate setae, ventral margin with dense row of minute setae and 2 robust bifid spines. propus almost 2x as long as combined carpus to basis, palm with 5 serrate spines, the 2 proximal spines closer and finely serrated; carpus with broad posterior lobe; merus distinctively shorter than ischium; basis as long as ischium dorsal margin with 1 simple seta and 1 tooth. Pereopods 2-7 directed posteriorly; dactyl short, subrectangular, 2-clawed, 1 shorter but more robust and curved than other; merus short with distinct dorsal lobe; basis longer than other segments with dorsal tooth. Pereopods 2-5 carpus with 1 distodorsal plumose setae. Pereonites 2-4 tergite plates indistinctively divided, anteriorly somewhat narrower than the sternites; medial lobes rounded (sometimes flattened), not defined by suture, each with small apical simple seta; lateral lobes defined by distinct suture, longer than medial lobes, acute, with 1(-few) distomedial teeth and 1 proximolateral seta. Pereopods 2-4 propus apical margin flat; carpus distinctively longer than propus. Pereopod 2 ischium as long as carpus; basis dorsal surface with 1 spatulate plumose and 1 simple setae. Pereopods 3-7 ischium shorter than carpus. Pereopod 3-5 basis with 2 spatulate plumose setae with 1 simple seta between them. Pereopods 4-7 basis with dorsodistal spatulate plumose seta. Pereonites 5-7 tergites much narrower and slightly shorter than sternites, distinctively divided into lateral plates, plates each with 1 simple dorsolateral seta; posterior margin with blunt triangular projection laterally cupping pereopod base.  Pereopods 5-7 propus with distodorsal setae, apical margin lobed; carpus as long as propus; ischium with 1-2 dorsal setae. Pereopod 6-7 basis dorsal surface with 1 spatulate plumose and 1 simple setae. Pereopod 6 carpus with 2 distodorsal plumose setae. Pereopod 7 carpus with 1 distodorsal plumose setae. ♂ pleopod 2 coxae fused, broad-rectangular, hyaline, margins strongly sclerotized; protopod rectangular, a bit longer than wide, distomedial corner produced into a small bifid lobe; exopod small, medially curved, with 1 small apical simple seta; endopod large, body bilobed, lateral lobe narrow, acute, medial lobe broad, weakly bifid, cannula large, entirely free and far surpassing endopod body, with proximal rows of dorsal setae, distally coiled (nominate) or sinuous (juani), tip narrow-acute with a pair of subapical distally-pointing teeth. Pleopod 3 endite medial margin with 4-5 large serrate teeth. Uropod protopod lateral margin with 1 medial setae, medial margin convex with marginal spines, dorsal surface with 1 distal seta; exopod minute, indistinctively defined, with 2 long simple apical setae; endopod long, curved medially, with 5 plumose distal setae.
Geographic Range: Common to abundant but extremely underreported in coarse-sand beaches from at least Newport Beach to Trinidad in California (ssp. abbotti), also known from the San Juan Islands in the Salish Sea (ssp. juani). The exact ecologies seem to differ between subspecies, see each subspecies account for more information.
Notes: This species is split into two geographic subspecies: the nominate abbotti in coastal California and juani in the San Juan Islands of Washington.  The only other species known from the Pacific coast of North America is C. mexicanus, a member of the mirabilis group, which is dramatically different in general morphologically (see that account for more information).

Subordinate taxa: Coxicerberus abbotti abbotti, Coxicerberus abbotti juani

Key to subspecies
1 a. Body on average slenderer, appendages generally smaller and slenderer; ♂ pleopod 2 cannula coiled, often approaching each other or even crossing over, subapical teeth closer to tip; pereonites 2-4 lateral lobes with medial tooth acute; left mandible lacinia 3-toothed, spine row with 2(-3) spines; pereopods 5-7 ischium with 1 dorsal seta, basis averaging wider; pleopod 3 endite medial margin with 4 serrate teeth (apical tooth frequently not serrate); California coast --> Coxicerberus abbotti abbotti
b. Body on average more robust, appendages generally larger and more robust; ♂ pleopod 2 cannula sinuate but not coiled, generally pointing laterally, subapical teeth further from tip; pereonites 2-4 lateral lobes with medial tooth blunt; left mandible lacinia 4-toothed, lateral tooth closely appresed to adjacent tooth, spine row with 3 spines; pereopods 5-7 ischium with 2 dorsal setae, basis averaging narrower; pleopod 3 endite margin with 5 serrate teeth; San Juan Islands --> Coxicerberus abbotti juani

Sources

Coineau, N., & Deboutteville, C. D. (1968). Étude des Microcerberides (Crustacea, Isopoda) de la côte pacifique des Etats-Unis. 1re partie, systématique. Bull. Mus. Nat. Hist. Nat., (2), 39(5):955-964.

Lang, K. (1961). Contributions to the knowledge of the genus Microcerberus Karaman (Crustacea, Isopoda) with a description of a new species from the central Californian coast. Arkiv fӧr Zoologi, 13:493-510.

Wägele, J. W., Voelz, N. J., & Vaun McArthur, J. (1995). Older than the Atlantic Ocean: discovery of a fresh-water Microcerberus (Isopoda) in North America and erection of Coxicerberus, new genus. Journal of Crustacean Biology, 15(4):733-745.

Published: Feb 15, 2023