Astacoides hobbsi Boyko, 2005

Boyko, Christopher B., Ravoahangimalala, Olga Ramilijaona, Randriamasimanana, Désiré & Razafindrazaka, Tony Harilala, 2005, Astacoides hobbsi, a new crayfish (Crustacea: Decapoda: Parastacidae) from Madagascar, Zootaxa 1091 (1), pp. 41-51 : 43-50

Astacoides hobbsi Boyko , new species ( Fig. 1 )

Material examined. Male holotype, 55.8 mm CL ( FMNH 9912 ) and 3 male paratypes of 46.6 mm CL ( UADBA 32130 ex FMNH 9911 ), 47.2 mm CL ( UADBA 31231 ex FMNH 9913 ) and 54.3 mm CL ( FMNH 9914 ), respectively. All collected from Andranofotsiorana effluent of the river Ranomadio, 20°19'S, 47°39'E, Madagascar, Sept 2000, leg. D. Randriamasimanana & O. Ramilijaona Ravoahangimalala. Measurements of all specimens given in Table 1 .

Diagnosis. Rostrum moderately long (11.1±2.7 percent of carapace length). Areola 3.6±0.2 times as long as wide, constituting 42.0±2.2 percent of carapace length and 47.2±2.2 percent of postorbital carapace length. Branchiostegites weakly to moderately tuberculate, never spiniform. Width of first abdominal segment in males equivalent to 40.9±1.6 percent of carapace length, that of second 51.6±3.3 percent. All abdominal pleura lacking spines, that of third through sixth tapering and rounded ventrally. Dorsal surface of telson and uropods always with spiniform tubercles. Antennal scale with acute spine laterally. Merus of third maxilliped usually with single large spine mesially, sometimes with an additional smaller spine, no spines laterally. Carpus of cheliped without low, polished tubercles dorsally, with row of 2 or 3 tubercles mesially; width of palm of chela 41.9±1.7 percent of length of propodus; lateral and mesial margins of propodus lacking tubercles; dorsal surface of dactyl lacking tubercles. Keel of sternite XIII lacking bullar lobes. Median keel of sternite XII inflated but relatively narrow, that of sternite XIII strongly inflated and broad. Vertical arms of paired sternopleural bridges of sternite XIV widely separated.

Description. Rostrum ( Fig. 1A ) 8.4–13.3 percent of carapace length, with slightly divergent lateral carinae, each bearing row of 3 or 4 submarginal corneous­tipped tubercles; anteromedian prominence short, with 1 or 2 strong corneous tubercles; dorsal surface deeply excavate. Postorbital ridge weak and terminating anteriorly in small tubercle. Suborbital angle truncate and bearing weak, rounded, postmarginal tubercle. Branchiostegal spine absent. Antennal, mandibular, and hepatic regions with anteriorly directed, rounded to acute tubercles, those on lower madibular region flanking cervical groove forming distinct mandibular arc with row of tubercles on crest; submarginal irregular row of well­developed tubercles extending from ventral base of suborbital angle to anterior extremity of cervical groove. Anteroventral branchiostegal region ( Fig. 1B ) with sparse, small tubercles; lateral surface of branchiostegites with few small tubercles anterolaterally, cervical spine small, acute. Areola 3.3–3.8 times as long as broad and constituting 39.1–44.6 percent of carapace length (45.1–50 percent of postorbital carapace length).

Basal podomere of antennular peduncle with strong spine on distal mesioventral margin. Antennal peduncle with relatively smooth coxa (renal aperture slit­shaped) and 1 strong spine on basis. Antennal scale ( Fig. 1C ) with mesial margin gently rounded, lateral surfaces with acute spine, and distolateral tip with single spine; ventral keel with 1 acute distal spine. Antennal flagellum reaching third to sixth abdominal tergum (smaller specimens with proportionally longer flagellum).

Epistome ( Fig. 1D ) with 6–8 small, rounded tubercles in each posterolateral area; deep anteromedian depression present and conspicuous, laterally with 1 or 2 very small rounded tubercles on margin and 1 small tubercle on each posterolateral corner, sagittiform, anteromedian lobe extending as far anteriorly as just beyond distal margin of ischium of antennule.

Sternal keel of segment XIII ( Fig. 1E ) lacking bullar lobes. Median keel of sternite XII inflated but relatively narrow; that of sternite XIII strongly inflated and broad, no constriction between anterior and middle segment. Lateral processes of sternites XI through XIII strongly splayed. Vertical arms of paired sternopleural bridges of sternite XIV widely separated. Phallic papillae of Astacoides ­ type ( Fig. 1F ).

Mandible with proximocephalic cusp of caudal molar process long, continuous with distoproximal cusp. Nodular cluster of 8 or 9 subacute tubercles between distoproximal and cephalodistal cusps.

Ischium of third maxilliped ( Fig. 1G ) produced distolaterally in subacute prominence. Merus with 1 large spine (or 1 large and 1 small) on mesiodistal margin; distodorsal margin with weak step­like indentations but no spines; most of lateral surface with prominent punctations in 2 major rows and smaller punctations scattered on surface.

Cheliped ( Fig. 1H ) with ischium bearing no more than 1 prominent spine distomesially and 2 small tubercles proximal to it; merus with ventromesial row of 4–6 spines (becoming increasingly spine­like distally) and ventrolateral row of 4 or 5, dorsal surface devoid of spines; dorsodistal margin smooth, never crenulate. Carpus with mesial row of 2 or 3 tubercles, distalmost forming large spine, other small, posteriormost almost rudimentary; 1 or 2 small tubercles present ventrally, and lateral surface sparsely punctate lacking tubercles. Propodus with width 39.6–43.5 percent of length, bearing well­defined lateral costa flanked by prominent row of punctations, lacking row of small corneous tubercles, margins nearly smooth; mesial surface of palm with row of 4 or 5 very indistinct tubercles. Opposable margin of fixed finger with row of 8 or 9 tubercles, fifth from base largest; dorsal surface of finger with low submedian ridge flanked by rows of punctations. Dactyl with row of punctations mesially; opposable margin with row of 5 or 6 tubercles; linear band of denticles interspersed between members of longer row of tubercles, and distal segments of band conspicuously broader than those on fixed finger.

Width of first abdominal segment 39.6–43.1 percent of carapace length, that of second 48.5–56.2 percent. Pleuron of second abdominal segment ( Fig. 1I ) with row of 4–13 low tubercles subparallel to anteroventral and ventral margins (more in larger specimens) and 1 or 2 additional low tubercles slightly dorsally; that of third with 2 or 3 low tubercles near ventral margin.

Telson subequal in length and width and studded with small acute tubercles. Anterolateral margin of shallow sutures marking cephalic and caudal sections provided with fixed spine and faint suture reaching mesially approximately 1/3 of length on each side, median section not recognizable as division. Proximal podomere of uropod lacking spines and tubercles; dorsal surface of mesial ramus with 3–5 spines on median carina, and 4–6 others on lateral half; lateral spine well developed; lateral ramus lacking spines on carina, but as many as 8–10, often well­developed ones, present dorsolaterally, distolateral margin of proximal section of lateral ramus of uropod with row of 3 or 4 spiniform tubercles; 10–13 spines on proximal margin of diaresis.

Branchial formula as given in Table 2.

Type locality and range. Andranofotsiorana effluent of the river Ranomadio , 20°19'S, 47°39'E, Fianarantsoa province, Madagascar. Known only from the type locality .

Size. The largest specimen is a male having a carapace length of 55.8 mm, postorbital carapace length, 51.1 mm. Females are unknown.

Color. Pale white.

Etymology. Named for the preeminent astacologist Horton H. Hobbs, Jr. (1914–1994), whose work on crayfish fauna worldwide, including Madagascar, provided all of us with a better understanding of the biology and taxonomy of these fascinating and diverse crustaceans.

Remarks. The lack of bullar lobes on sternite XIII of individuals of the new species clearly distinguishes them from Astacoides crosnieri , A. petiti , A. granulimanus , and A. madagascariensis , all of which have more or less developed bullar lobes. The lateral processes on sternite XIII of the new species are of a rounded, laterally swept­forward shape and in this more closely resemble those of A. betsileoensis rather than the laterallydirected elongate ones of A. caldwelli . However, the shape of the lateral processes of sternite XIII are distinctly curved laterally and the processes of sternite XII are triangular and subacute in the new species, whereas the processes of sternite XIII are not curved laterally and those of sternite XII are broad in A. betsileoensis . The median keel between sternites XI and XII is much narrower in A. hobbsi n. sp. than in either A. caldwelli or A. betsileoensis . Astacoides hobbsi n. sp. differs from A. betsileoensis most obviously in the minimal development of anterior carapace spines whereas individuals of A. betsileoensis have extremely well developed spines. In overall carapace characters, the new species more closely resembles A. madagascariensis , but with a narrower, rounder rostrum, less produced anterolateral spines, and being overall less spinose; the posterior half of the cephalothorax is narrower than that of A. madagascariensis as well. The abdomen, in lateral view, resembles most that of A. caldwelli and, except for some minor differences in the shape of the posterior pleura, is almost indistinguishable from that species. The chelipeds of A. hobbsi n. sp. resemble those of both A. madagascariensis and A. caldwelli , but are less spinose in the area of the mesial margin posterior to the base of the fixed finger and the mesial margin of the carpus. Likewise, the overall shape of the merus and ischium of the third maxilliped of the new species is most similar to those of A. caldwelli and A. madagascariensis , but differ from both of those species in having a less spinose mesial margin on the merus and a more strongly produced anterolateral spine on the ischium. The shape of the antennal scale is different from all other species of Astacoides , while the dentition on the mandible is most similar to A. petiti .

The gill formula for A. hobbsi n. sp. is the same as found for A. caldwelli and A. madagascariensis , therefore it must be recognized as a relatively primitive (sensu Hobbs 1987) member of the genus with a formula of 13 + epr + 5r.

The maximum size of 55.8 mm appears to be intermediate for the genus, with maximum size for males being smaller for A. crosnieri and A. petiti (53.6 and 54.0 mm, respectively) and larger for A. granulimanus (63.5 mm), A. caldwelli (79.1 mm), A. betsileoensis (81.5 mm), and A. madagascariensis (87.1 mm) ( Hobbs 1987).

Antsiranana Mahajanga Toamasina Antananarivo Fianarantsoa Toliara Astacoides madagascarensis (H. Milne Edwards & Audouin, 1839) X X

A. caldwelli ( Bate, 1865) X X A. betsileoensis Petit, 1923 X X X A. granulimanus Monod & Petit, 1929 X X X A. crosnieri Hobbs, 1987 X A. petiti Hobbs, 1987 X X A. hobbsi , n. sp. X

The specimens were obtained from under blocks of rock and dead wood, as well as in the holes along the bank of the river. The local name for these crayfish is “orapotsy”, meaning “white crayfish”. Additional specimens of A. betsileoensis , known by the local name of “oramena” (red crayfish) were also collected in the same localities as the new species. Dubois (1938) listed “oramena” as one of the vernacular names for Malagasy crayfish but Hobbs (1987) was unable to assign this to any of the species known. Some of these specimens of A. betsileoensis presented a greenish hue, and are then known locally as “oramaitso” (green crayfish), which underscores the difficulty of applying common names to Astacoides species. Hobbs (1987), in his summary of information on all Astacoides species , noted that additional common names for A. betsileoensis include “oranjatsy”, “pepeo”, “orambanonga”, and “orambato”.

Additional specimens of both A. granulimanus ( Fig. 2 ) and A. caldwelli ( Fig. 3 ) also were found in the same river as A. hobbsi , n. sp. Astacoides granulimanus is a greenish/ black color with a white underside and is the best known and most widely distributed of the Madagascan species, occurring between 18– 24°S and 46– 48°E ( Hobbs 1987) and its occurrence in this locality is not unexpected. Astacoides caldwelli is a less common, but more striking species of crayfish that ranges from 18– 21°N and 46– 48°E, with a distinctive red and black flame­like color pattern that can even be seen on specimens long in preservative. The adaptive value of this coloration is unknown and, interestingly, no similar pattern is seen in preserved specimens of other Astacoides species. The fact that four species of Astacoides coexist in the same river system suggests that there might be significant resource and/or habitat partitioning between them. Only a detailed study of their habits and feeding modes can shed light on this.

As with many Madagascan organisms, all species of Astacoides must be considered as threatened by habitat destruction and by over­collection (Raberisoa et al. 1996). Crayfishes are subjected to a heavy predation pressure from a number of introduced species (such as eels, rats, and trout) and more are collected for food by humans ( Hobbs 1987). Support for recognition of the strong human impact on Astacoides spp. comes from data showing that 67% of residents of Ranomafana National park (Fianarantsoa province) reported collecting crayfishes (species unknown, but based on the localities probably A. crosnieri , A. betsileoensis , and/or A. granulimanus ), and 16% of them reported selling them ( Ferraro 2002). Based on current data, A. hobbsi should be given special consideration for conservation effort, as it is the species of Astacoides known from the fewest specimens and may have a very restricted distribution.

Figures

FIGURE 1. Astacoides hobbsi, n. sp. (all from holotype, FMNH 9912): A, dorsal view of carapace (2x); B, lateral view of carapace (2x); C, dorsal (left) and lateral (right) views of right antennal scale (4x); D, epistome and basal podomeres of antennae (3x); E, sternal area of segments X–XIV and coxae of associated pereopods (2x); F, phallic papilla on coxa of right fifth pereopod (6.5x); G, distal part of basis, ischium, and merus of left third maxilliped (3x); H, dorsal view of dactylus, propodus, carpus, and merus of right cheliped (2x); I, lateral view of abdomen (2x).

FIGURE 2. Astacoides granulimanus, preserved adult specimens (AMNH 17821); female (left) and male (right) (photo, S. Thurston).

FIGURE 3. Astacoides caldwelli, preserved adult specimens (FMNH 5721); female (left) and male (right) (photo, S. Thurston).