Mudflat Snapping Shrimp

Alpheus californiensis Holmes, 1900

Alpheus californiensis Holmes, 1900:186, pl. 2: fig. 42; pl. 3: figs. 43, 44.—Rathbun, 1904:108.—Word and Charwat, 1976:44.—Wicksten, 1984:189.

Crangon californiensis.—Schmitt, 1921:76, fig. 52.—MacGinitie, 1937:1032. pl. 1: fig. 2.—Johnson et al., 1947:122–138.—MacGinitie and MacGinitie, 1949:473.—Ricketts and Calvin, 1962:251, pl. 23: fig 3.

MATERIAL EXAMINED.—2, 3; Los Angeles C., northeast shore of Catalina Harbor, Catalina Island, California; 14 Dec 1970.

MEASUREMENTS.—Males, cl 9.0–10.0 mm; females, cl 6.5–8.6 mm.

DESCRIPTION.—Rostrum (Figure 29a,b) sharply triangular, carinate posteriorly and reaching to middle of visible part of first antennular segment. Rostral carina narrowly raised dorsally to middle of eye, then widened as triangular shape far posterior to eye; lateral margin of triangular part slightly overhanging orbitorostral groove.

Ocular hood slightly inflated dorsally above level of middle part of rostral carina. Orbitorostral groove distinct and reaching far posterior to eye, well defined posteriorly. Anterior margin of ocular hood rounded and slightly concave near base of rostrum.

First antennular segment with triangular carina extending from ventral inner margin; ventral part acute (Figure 29c). Second segment about 2.3 times as long as broad, 1.9 times as long as visible part of first segment and 2.5 times as long as third segment. Stylocerite broad proximally, narrowing to sharp point at tip, scarcely reaching to distal margin of first segment.

Scaphocerite with lateral margin concave at middle. Distal spine overreaching distal end of antennular peduncle and falling slightly short of distal end of carpocerite. Inner blade regularly narrowing distally, not reaching to distal end of antennular peduncle. Cleft between inner blade and distal spine arising from distal 0.4 of scaphocerite.

Carpocerite overreaching distal end of antennular peduncle by length of third antennular segment. Basicerite with small, narrow lateral spine.

Ultimate segment of third maxilliped (Figure 29d) fairly elongate, about 2.6 times as long as penultimate and 5 times as long as broad at proximal end; distal margin roundly truncate, not much narrower than proximal end and bearing long setae. Penultimate segment about 1.5 times as long as broad. Exopod slightly overreaching distal end of antepenultimate segment. Precoxa with one arthrobranch near distal end and also with small supplementary arthrobranch near proximal end.

Major chela of first pereopods (Figure 29e,f) about 2.6 times as long as broad, bearing sparse setae on inner face. Fingers occupying distal of chela, clearly narrower than palm. Movable finger regularly arched throughout length of superior margin in profile, compressed laterally and acutely rounded at tip; tip slightly overreaching tip of immovable finger. Immovable finger with inferior margin very slightly sinuous. Superior transverse groove of palm deep, U-shaped with proximal shoulder perpendicular to or very slightly overhanging groove. Superior outer palmar depression well defined, narrowly quadrangular, extending to oblique suture. Superior inner palmar depression longitudinally elongated triangular; anterior region deeper than posterior region. Inferior transverse groove very shallow, barely forming angle with inferior margin of immovable finger; proximal shoulder rounded, not produced anteriorly. Inferior outer palmar depression narrow, extending upward to width of palm; margin not clearly delimited anteriorly. Inferior inner palmar depression broadly triangular, extending upward to half width of palm and connecting inferiorly to shallow longitudinal depression near bottom of palm; margin not clearly delimited anteriorly. Outer palmar face with shallow elongate depression between superior and inferior palmar depressions. Inner palmar face with elongate rounded depression between superior and inferior palmar depressions. Merus about 1.9 times as long as broad; inferior inner margin slightly tuberculate at distal and bearing very small spine at distal end.

Minor chela of first pereopods in male (Figure 29g,h) rather stout, about 3.3 times as long as broad, fingers occupying about distal 0.5. Palm with superior and inferior transverse notches. Outer palmar face with elongate depression spreading from superior transverse notch and with slight depression spreading from inferior notch. Inner palmar face with slight depressions near superior and inferior notches and bearing very blunt tooth flanking dactylar articulation. Both fingers with acute tips. Movable finger with superior margin broadened bilaterally, well-developed balaeniceps in male. Immovable finger with fringe of setae medially at both lateral faces. Minor chela of first pereopods in female covered with fairly dense setae; movable finger not balaeniceps and immovable finger with no fringe of setae. Merus about 2.5 times as long as broad; superior margin slightly convex distally and inferior inner margin slightly tuberculate at distal , bearing very small spine on distal end.

Second pereopod (Figure 29i) overreaching distal end of carpocerite beyond most part of first carpal segment. Fingers of chela about 1.2 times as long as palm. First segment of carpus about 2 times as long as second; second segment about 2 times as long as third; third segment subequal to fourth; fifth segment 1.5 times as long as fourth.

Dactylus of third pereopod (Figure 29j) simple and slender, about 0.4 times as long as propodus. Propodus about 1.2 times as long as carpus, bearing 7 movable spines and 5 irregular adjacent spines on inferior margin and pair at distal end; distalmost spine reaching to distal of dactylus. Merus rather slender, about 4.8 times as long as broad and 2 times as long as carpus. Ischium with movable spine.

Fourth pereopod almost same as third pereopod. Ischium with movable spine.

Fifth pereopod much narrower than third pereopod. Ischium with movable spine.

Pleura (Figure 29k) of first four abdominal somites broadly rounded in both sexes; pleuron of fifth somite subtriangular on posterior ventral margin. Abdominal sterinite with no spine at midline. Appendix masculina slightly overreaching distal end of Appendix interna.

Telson (Figure 29l) about 1.6 times as long as broad at anterior end, armed with two pairs of rather stout dorsal spines and with no longitudinal median depression on dorsal surface. Posterior margin regularly convex, bearing series of inconspicuous seta-like spines and armed with pair of spines at each lateral end; inner spine two times as long as outer one.

Uropodal endopod bearing inconspicuous seta-like spines on distal margin and with inner depression at anterior half fairly disinct. Uropodal exopod bearing rather slender movable spine flanked laterally by acute, small immovable tooth and internally by round lobe; movable spine not reaching to distal margin of uropodal exopod; transverse suture forming two very shallow convex lobes.

TYPE-LOCALITY.—San Pedro, California.

DISTRIBUTION.—San Pedro, California, to Magdalena Bay, Baja California.