Colomastix thomasi, LeCroy, 2009

LECROY, SARA E., 2009, Colomastigidae *, Zootaxa 2260 (1), pp. 348-372 : 367-371

Colomastix thomasi sp. nov.

( Figs 11 , 12 )

Type material. Holotype, male, 2.1 mm, AM P78989, south of Lizard Head , Lizard Island (14°41’S 145°27’E), coral rubble, 2 m, J.D. Thomas, 29 January 1989 ( JDT / LIZ 14 ) . Paratypes: 6 males, 1 female, AM P79272 , same data ; 1 male, AM P78990 , off southern tip of island, Lizard Island , coral rubble and algal turf on patch reef, 1 m, J.D. Thomas, 23 January 1989 ( JDT / LIZ 3 ) ; 5 males, AM P79273 , beach at Lizard Head , Lizard Island, coral rubble from rubble beach, J. D. Thomas, 31 January 1989 ( JDT / LIZ 15 ) ; 2 males, 1 female, AM P79274 , south-west of Lizard Head , Lizard Island, algae-covered rubble on carbonate pavement with varying amounts of carbonate sand, 1.5 m, J.D. Thomas, 2 February 1989 ( JDT / LIZ 17 ) ; 2 males, GCRL 2875 , off Lizard Head , Lizard Island, small pieces of coral rubble on sand bottom, J.D. Thomas, 2 February 1989 ( JDT / LIZ 19 ) .

Additional material examined. 3 juveniles, AM P78988 ( QLD 1 ) .

Type locality. South of Lizard Head , Lizard Island, Queensland, Australia (14°41’S 145°27’E) .

Etymology. Named for James D. Thomas, who collected and made available for study all of the adult material of this species.

Description. Based on holotype, male, 2.1 mm, AM P78989 and paratype series of 2 males, AM P79274.

Head. Head as long as deep, subequal in length to pereon segments 1 and 2 combined; rostrum narrowly rounded; interantennal plate with anterodorsal and anteroventral angles extending forward subequally, anterior margin straight to slightly concave, without serrations, without ventral teeth. Antennae 1–2 marginal robust setae short. Antenna 1 peduncle article 1, dorsomedial margin without robust setae. Antenna 2 peduncle articles 3–5, ventrolateral margin with small, triangular robust setae; peduncle article 3, distomedial angle with 2 robust setae, without slender setae or process, dorsomedial margin without robust setae, ventromedial surface without robust setae; peduncle article 5, dorsal margin without stubby robust setae. Mouthparts other than maxilliped greatly reduced or vestigial. Maxilliped inner plates completely fused, basal shell not expanded to form a ventral keel.

Pereon. Coxa 1 anterior margin convex, anteroventral angle rounded. Coxae 1–4 without small anteroventral cusp. Coxal gills 2–5 subequal in size, gill 6 subequal to gill 5. Gnathopod 1 vestigial, exact morphology individually variable; propodus without setae. Gnathopod 2 basis broadly expanded distally, anterior margin entire, without anterodistal notch, without anterodistal process; ischium with inner anterodistal lobe not expanded; carpus much shorter than propodus, inner ventral surface with patch of setae, setae short, very fine; propodus greatly enlarged, inner ventral surface without patch of setae, palm deeply excavate, with 3 dissimilar, unequally spaced processes, palmar angle with 1 elongate subtriangular process, apical margin of process entire, middle process very small, rounded, process at dactylar hinge broad, subtriangular; dactylus, insertion on propodus apical, with large process on posterior margin, tip lanceolate, subacute. Pereopods 3–4 basis not produced anterodistally. Pereopods 3–7 basis unexpanded. Pereopod 7 propodus, anterior margin without setae.

Pleon. Pleopods 1–3 inner ramus with 3 articles, outer ramus with 4 articles. Pleopod 2 peduncle, anteromedial surface with 3 slender setae. Uropod 1 inner ramus modified, strongly falcate, not expanded proximally, dorsal margin with large, simple, subapical slender seta, tip narrowing abruptly distal to seta, pleated, subtruncate; outer ramus one half length of inner ramus, tip serrate, subtruncate. Uropod 2 both rami, ventral margin lacking setae. Uropod 3 peduncle twice as long as deep; inner ramus expanded proximally, approximately one-third longer than outer ramus. Telson broadly subtriangular, dorsal surface flat, tip constricted, narrowly rounded, without lobes or processes, with 2 subapical minute slender setae.

Female (sexually dimorphic characters). Based on paratype, female, AM P79274. Head subequal in length to pereon segment 1 and half of pereon segment 2 combined. Antenna 2 peduncle article 3, distomedial angle with 1 robust seta. Mouthparts other than maxilliped moderately reduced. Oostegite 2 narrowly subovate (length:width ratio 3:1 or greater), approximately one-third longer than basis of gnathopod 2. Gnathopod 1 elongate, slender; propodus with simple apical setae. Gnathopod 2 basis weakly expanded distally; carpus subequal to propodus in length, inner ventral surface with patch of setae, setae elongate, very fine; propodus unenlarged, inner ventral surface with patch of setae, setae elongate, very fine, palm not excavate, without teeth or processes; dactylus without process on posterior margin, tip pleated, subtruncate. Pleopod 2 peduncle, anteromedial surface without slender setae. Uropod 1 inner ramus unmodified, lanceolate; outer ramus three-fourths length of inner ramus, tip lanceolate, subacute. Uropod 3 inner ramus lanceolate, ventral margin lacking setae.

Adult body length. 1.5–2.1 mm. There appears to be little difference in size between males and females in this species.

Colour in life. Unknown.

Host. Unidentified sponge.

Habitat. Coral rubble and algal turf on patch reefs, often over sand bottoms.

Depth range. 1–18 m.

Remarks. Colomastix thomasi sp. nov. is a tiny, very distinctive species that has, thus far, only been found off Lizard Head and in Watsons Bay on Lizard Island. The morphology of the outer ramus of uropod 1 in the male of C. thomasi sp. nov., with its subtruncate, serrate tip, as well as the unique, complex apical morphology of the inner ramus of that appendage, distinguish this species from all other known species of the genus. The cheliform gnathopod 2 of the male is also unusual, resembling that of only three other species ( C. gibbosa , an Atlantic species, C. inaequicornis Ledoyer, 1979 from Madagascar and C. minuta Müller, 1992 from the Society Islands). All three of these species have the large process or "thumb" at the palmar angle of the propodus and the former two species also have the very large process on the posterior margin of the dactylus. However, C. gibbosa has a bulbous tip on the inner ramus of uropod 1, C. inaequicornis has an elongate, unreduced gnathopod 1 and C. minuta has a bifurcate telson tip.

The female of C. thomasi sp. nov. has a distinctive pleated tip on the dactylus of gnathopod 2, a feature which, as stated in the remarks for C. plumosa , it shares only with C. plumosa , C. semiplumosa , C. azumai and C. littoralis . It can be distinguished from the first two of these species by the lack of any densely setose rami on uropods 2 or 3 and from the latter two species by the broadly rounded anteroventral angle of coxa 2, the lack of setae on the anterior margins of the propodi on pereopods 5–7 (unknown for female C. azumai or C. littoralis , but setae are present in the males of these species and this is not usually a sexually dimorphic character in Colomastix ) and the unequal rami of uropod 3. It differs from all four of these species in having only 3 articles rather than 4 on the inner ramus of pleopods 1–3.

Distribution. Australia. Queensland: Lizard Island (current study).

Figures

FIGURE 11. Colomastix thomasi sp. nov., paratype, male, 2.1 mm, paratype, female, 1.6 mm, AM P79274, south-west of Lizard Head, Lizard Island, Great Barrier Reef.

FIGURE 12. Colomastix thomasi sp. nov., paratype, male, 2.1 mm, paratype, female, 1.6 mm, AM P79274, south-west of Lizard Head, Lizard Island, Great Barrier Reef.