Actium vestigialis Caterino and Chandler

Caterino, Michael S. & Chandler, Donald S., 2010, A New Species of Actium Casey (Staphylinidae: Pselaphinae) Endemic to Santa Catalina Island, California, The Coleopterists Bulletin 64 (3), pp. 187-191 : 188-190

Actium vestigialis Caterino and Chandler , new species

( Figs. 1–15 )

Type Material. Holotype male (CBP0100939):

“ CA: Los Angeles Co., 33.3890°N, 118.3962°W ,

Santa Catalina Isl., nr. Blackjack Peak, i.31.2010, M.S. Caterino & K.J. Hopp, Quercus litter”, SBMN; Paratypes: 5 females, same data as type (CBP0100940, CBP0100941, CBP0100942, CBP0100943, CBP0100944), SBMN, CASC, LACM, DSC ; 1 female (CBP0099367): “ CA: Los Angeles Co., 33.3896°N, 118.3969°W, Santa Catalina Isl. , nr. Blackjack Peak, i.31.2010, M.S. Caterino & K.J. Hopp, Lyonothamnus litter”, SBMN ; 1 female (CBP0025404): “ CA: Los Angeles Co., 33.4540°N, 118.5178°W, Santa Catalina Isl. , west end, i.30.2010, M.S. Caterino & K.J. Hopp, Lyonothamnus litter”, SBMN .

Diagnosis. This species is highly distinctive in the genus Actium . The combination of reduced eyes ( Fig. 2 ), strongly basally narrowed pronotum ( Fig. 3 ) and anteriorly narrowed elytra ( Fig. 5 ) (both probably related to its brachyptery), elongate carinae of abdominal tergite 1 ( Fig. 6 ), and lack of male secondary abdominal modifications separate it from all other species.

Description. Total body length 1.4 mm; pronotal width 0.31 mm; elytral width 0.50 mm. Body light rufescent, shining, covered with short, appressed setae; head widest behind eyes, narrowed strongly to bases of antennae and mandibles; head with about 60 clubbed ventral setae ( Fig. 2 ); eye composed of 5–7 facets, same in both sexes; frons with deep foveae, about as widely separated as the antennal insertions across middle, connected anteriorly by shallow v-shaped depression ( Fig. 4 ); vertex shallowly depressed posterad, with small cervical denticle in depression; clypeus with prominent setae directed anteromesally in anterolateral corners; labrum with several setae anteromesally directed near each side, with only short fine setae between. Antennae ( Fig. 7 ) about 1.5 times head length, antennomeres 1 and 2 approximately equal, about 1.5 times as long as wide, antennomeres 3–7 approximately equal, rounded, slightly broader than long, antennomeres 8–10 progressively more asym- metrically broadened medially, antennomere 10 disk-like and approximately 4 times as wide as long; antennal club more or less symmetrical, equal in length to antennomeres 7–10. Prothorax ( Fig. 3 ) broadest in anterior third, strongly narrowed posterad, at base little more than half as wide as widest point; disk with deep lateral fovea on each side behind middle, connected by shallowly impressed transverse depression, a shallow median longitudinal depression present behind the transverse one; prothoracic sides rounded, unmargined and lacking lateral crenulations. Prosternum with deep, setose, lateral foveae, hypomera smooth. Elytra ( Fig. 5 ) strongly narrowed to base, with two basal foveae and deep subhumeral fovea; sutural stria complete, discal stria extending to about elytral midpoint; subhumeral stria extending length of elytron. Metathoracic wings vestigial. Mesosternum with small mesal and larger lateral foveae along anterior margin; mesepimeron glabrous. Metasternum with pair of small lateral metasternal foveae and larger lateral mesocoxal foveae; metasternum not noticeably shortened. Prothoracic femora with setose depression in basal two-thirds of anterior face; tibiae lacking modified spurs or apical projections. Base of first visible abdominal tergite ( Fig. 6 ) with paired carinae about two-thirds length of sclerite; other tergites unmodified. First visible abdominal sternite with deep, setose foveae in anterolateral corners.

Male. Secondary sexual characters of male limited to mesofemur and mesotrochanter: mesofemur ( Fig. 13 ) with bluntly triangular tooth in basal onefourth of posterior margin, margin otherwise weakly arcuate; mesotrochanter with small posterior tooth. Male abdomen unmodified, lacking processes or depressions of lateral portions of sterna; pregenital sterna not depressed at middle. Aedeagus ( Figs. 11, 12 ) basally bulbous, with ventral transverse flange approximately one-third from apex; apices of parameres projecting slightly beyond obliquely truncate apex of median lobe; median lobe and one paramere each bearing a single seta.

Female. Sternite IX ( Fig. 14 ) with curved, elevated projections originating near the base, directed apicad; sternite X apically divided.

Ecological Data. Two of the paratype specimens were sifted from litter of Lyonothamnus floribundus floribundus Gray , the Catalina Island ironwood ( Rosaceae ). This tree species has a relictual distribution on the Channel Islands, being known from the mainland from fossil records only. It is tempting to assign some significance to this association in terms of the beetle’ s endemicity. However, the largest series of the new species was taken from Quercus (live oak) litter on the northern face of a shaded hilltop, from around some small boulder outcrops ( Fig. 15 ).

Remarks. We name this species in recognition of its numerous morphological reductions, brachyptery, microphthalmy, and loss of male secondary abdominal modifications.

Figures

Figs. 1–4. Scanning electron micrographs of paratype female of Actium vestigialis. 1) Dorsal habitus; 2) Head, lateral view; 3) Prothorax, dorsal view; 4) Head, dorsofrontal view.

Figs. 5–10. Scanning electron micrographs of paratype female of Actium vestigialis. 5) Elytra, dorsal view; 6) First visible abdominal tergite, dorsal view; 7) Antenna; 8) Mesofemur and mesotibia; 9) Profemur and protibia; 10) Metafemur and metatibia.

Figs. 11–14. Diagnostic morphological features of Actium vestigialis. 11) Aedeagus,left lateral view;12) Apex of parameres and median lobe of aedeagus, dorsal view; 13) Male mesothoracic leg, anterior view; 14) Sternites IX and X of female, dorsal view.

Fig. 15. Map of Santa Catalina Island, showing location relative to the southern California coast (inset), and collection localities of type series: type locality (star), additional locality (dot).