Dynomene kroppi, Mclay, 2001

Mclay, Colin L., 2001, Dynomenidae and Dromiidae (Decapoda, Brachyura) from Guam, Philippine Islands, Tonga and Samoa, Zoosystema 23 (4), pp. 807-856 : 811-813

Dynomene kroppi n. sp.

( Figs 1 ; 3A )

TYPE MATERIAL. — Holotype 11.9 × 9.7 mm, from Piti Reef , Guam ( MNHN-B26474 ), paratype 9.5 × 7.5 mm, from GUM300 ( MNHN-B26475 ).

MATERIAL EXAMINED. — Guam. Piti Bay, 13°27’N, 144°47’E, 2 m, outer reef flat west of Camel Rock, rubble partially consolidated by sponge, 11. VI.1986, coll. R. Kropp, 1 8.6 × 7.7 mm ( GUM 245B). — Piti Reef, 2 m, among rocks, 24.VII.1993, 1 7.3 × 6.2 mm ( GUM 271). — Piti Reef, 0.5-2 m, among rocks, 4-18.VIII.1993, 1 (ovig.), 10.7 × 9.4 mm ( GUM 298). — Piti Reef, 1 m, among rocks, VIII.1993, 3 7.0 × 6.0, 8.8 × 7.6, 11.9 × 9.7 (holotype) mm, 1 9.5 × 7.5 mm (paratype) ( GUM 300). — Piti Reef, 1 m, 28.VII.1993, 1 6.3 × 5.5 mm ( GUM 301). — Piti Reef, 1 m, among rocks, 31.VII.1993, coll. H. T. Conley, 1 9.0 × 7.7 mm ( GUM 307).

ETYMOLOGY. — Named after Roy K. Kropp for his contribution to the knowledge of the Decapoda , especially Brachyura , of Guam.

SIZE. — Maximum size for females, 10.7 × 9.4 mm and males, 11.9 × 9.7 mm. The ovigerous female carried around 150 eggs, mean diameter = 0.47 mm (n = 5).

DEPTH AND HABITAT. — All specimens came from coral rubble and rocks in shallow water, 1- 2 m.

DISTRIBUTION. — Known only from Guam, North Pacific.

DESCRIPTION

Carapace wider than long, ratio cw/cl= 1.12- 1.26, shape sub-oval, frontal and posterior ends truncate, anterolateral margin gently rounded and posterolateral margins convergent. Posterior margin eroded at corners to accommodate last pair of pereopods and medially to accommodate first segment of abdomen. Carapace surface smooth, sparsely covered with short plumose setae, not bent at right angles, and scattered longer filiform setae (long setae five times length of short setae and 0.15 of cw). Setae denser on pereopods. Setae not arranged in clumps and not dense enough to obscure carapace surface.

Carapace surface smooth, frontal groove short, separating pair of low rounded swellings; carapace regions not defined, cervical grooves not marked in male holotype but evident in female paratype. Anterolateral carapace margin begins just below postorbital corner: bearing six teeth, first four small, blunt and near beginning, last two more distant, larger and more acute. Small blunt posterolateral tooth marks beginning of posterolateral margin.

Frontal margin continuous above orbits that are clearly exposed dorsally, no post-orbital notch; sub-orbital margin not projecting (just visible dorsally) and unarmed. Sub-hepatic area convex, minutely denticulated.

First article of antennule much longer than wide, becoming broader distally and fitting closely beside epistome; second article at almost right angles to first, fitting beneath frontal margin; remaining articles folded into orbital cavity. First article of antenna moveable, beaked medially enclosing urinal aperture; second article longer than wide, surface convex, produced distally at both corners, lateral lobe curves over base of eyestalk; third article longer than wide; fourth article as long as wide, attached at an angle and bearing flagella 0.65 × cw. Epistome triangular, surface flat, posterior margin eroded to accommodate edges of mxp3.

Subhepatic area convex and minutely granulated. The mxp3 operculiform, bases separated widely by sternum; palp (carpus, propodus, and dactyl) setose along medial margin, two-thirds length of ischium + merus; crista dentata has six very small teeth. Male sternal suture 4/5 complete, others incomplete; in female suture 4/5 faintly marked, complete, suture 7/8 carrying entrances to spermathecae, short, ending apart between bases of fourth pereopods.

Male chelipeds much longer than first pair of walking legs; merus trigonal, superior border armed with row of six small blunt tubercles, inferior border with several scattered tubercles; carpus unarmed except for blunt spur on inner superior border; propodus unarmed except for some very faint tubercles on superior border, fixed finger curved, edentate; moveable finger also curved, bearing single prominent tooth mid-way, fingers only touch at tips, widely gaping. Female chelipeds smaller, about as long as first walking legs; tooth on moveable finger absent.

P2-p4 decreasing in length posteriorly; meri with row of five or six tiny tubercles along upper bor- der; carpi more densely covered with tubercles; propodi with few scattered tubercles; dactyli curved, inner margins armed with five to six tiny spines increasing in size distally. Length of p3 merus 2.3 × width and about three-quarters of cl. P5 reduced, more so in male: in males length is 26% of preceding limb (female 34%) reaching only 30% along merus of p4 (female 50%). Limb sub-chelate: in males dactylus tiny, claw-like and opposed to propodal extension; in females dactylus longer, flattened; fine structure of dactyl and propodal extension unavailable.

Surface of abdomen smooth, segments increasing in width posteriorly except in female where last segment narrower because uropods totally exclude penultimate abdominal segment from lateral margin (in males uropods make up 30% of lateral margin). Female abdomen totally covers sternum and bases of pereopods, extending anteriorly so that telson covers bases of mxp3. No abdominal locking mechanism and sternal tubercles absent in paratype female. Male abdomen smaller, covering most of sternum, but not bases of pereopods. Male has small sternal tubercles at bases of p2, lying beside uropods when abdomen closed, but no abdominal locking mechanism.

Five pairs of pleopods in both sexes. First pair of female pleopods uniramous, other four pairs biramous. Male first pleopods uniramous, forming semi-rolled tube, with apical sperm aperture beside curved apical lobe, surrounded by setae. Second pleopods, as long as first pair, biramous, exopod rudimentary, gonopod (i.e. endopod) consisting of calcified proximal half and horny, needle-like distal half. Shaft of needle armed with four distal, evenly spaced, inset acute subterminal spines, directed distally, spiraling around shaft over 90°, and ending with single terminal spine. Last three pairs of pleopods rudimentary, uniramous, decreasing in length posteriorly.

DISCUSSION

D. kroppi n. sp. can be distinguished from D. pugnatrix by having six anterolateral teeth

(vs five in D. pugnatrix ); the anterolateral teeth smaller and blunter; p2-p4 with small blunt tubercles on the superior borders (vs acute tubercles); long setae on carapace which are filiform (vs feathered setae); only five or six spines on inner margins of dactyli of walking legs (vs 10 spines).

Surface evidence of sternal sutures in male and female D. kroppi n. sp. are typical of those found in other species of Dynomene : only suture 4/5 is evident, but incomplete, in both sexes and sutures 7/8, which end apart, are marked in females. Only suture 3/4 is deeply incised and complete. A similar situation is found in Acanthodromia A. Milne-Edwards, 1880 , Hirsutodynomene McLay, 1999 , Metadynomene McLay, 1999 and Paradynomene Sakai, 1963 . In Metadynomene , suture 5/6 is not incised on the surface but is marked by an uncalcified, translucent band across the sternum. The sternal sutures in dynomenids represent a derived condition in that most are not evident on the surface.

In D. kroppi n. sp., the uropods are sexually dimorphic, with the female uropods filling all of the abdominal lateral margin and male uropods only about 30%. This is similar to D. hispida and D. praedator but less than D. pugnatrix where male uropods fill about 75% of the lateral margin. In all species of Dynomene and Hirsutodynomene the uropods are sexually dimorphic with female uropods always being larger. Dynomenids are also unusual in having sexually dimorphic fifth pereopods (see McLay 1999: 449-454, figs 8-10).

D. kroppi n. sp. probably falls into the group of dynomenids that do not grow larger than about 20 mm cw. These species have a brood size ranging from 30 to 900 eggs with a mean diameter of 0.46 mm ( McLay 1999: 550). The D. kroppi n. sp. ovigerous female carried around 150 eggs, of diameter 0.47 mm, and clearly conforms with this group of small species, which undoubtedly have a planktonic larval stage.

The structure of the second male gonopod of D. kroppi n. sp. most closely resembles that of D. guamensis n. sp. and only differs in having a greater number of sub-terminal spines. Unfortunately we do not have the microscopic details of the second gonopod of D. pugnatrix which has a similar gross morphology. Otherwise, the closest dynomenids are D. hispida and D. praedator , both of which have five sub-terminal spines, arranged sinuously around the shaft (see McLay 1999: 456-461). However, D. hispida and D. praedator have two and three terminal spines respectively, while D. kroppi n. sp. has only one. Amongst dynomenids, the species of Dynomene tend to have a smaller number of gonopod spines (4 to 15) than is found in other genera ( McLay 1999: table 1).

Figures

FIG. 1. — Dynomene kroppi n. sp., Guam, Piti Reef, 1 m, holotype 11.9 × 9.7 mm; A, dorsal view of right half of carapace; B, outer face of right cheliped; C, dorsal view of right cheliped (MNHN-B26474). Setae omitted. Scale bars: 2 mm.

FIG. 3. — A, Dynomene kroppi n. sp., Guam, Piti Reef, 1 m, holotype 11.9 × 9.7 mm (MNHN-B26474), dorsal view of whole crab, setae removed from right side of carapace, right third and left fourth leg not shown; B, Dynomene guamensis n. sp., Guam, Piti Lagoon, 1-3.5 m, holotype 11.0 × 9.7 mm (MNHN-B26476), dorsal view of whole crab, setae removed from right side of carapace, left second leg not shown. Scale bars: 4 mm.