Synalpheus microneptunus, Hultgren, Kristin M., Iii, Kenneth S Macdonald & Duffy, Emmett, 2011

Hultgren, Kristin M., Iii, Kenneth S Macdonald & Duffy, Emmett, 2011, Sponge-dwelling snapping shrimps (Alpheidae: Synalpheus) of Barbados, West Indies, with a description of a new eusocial species, Zootaxa 2834, pp. 1-16 : 8-10

Synalpheus microneptunus n. sp.

( Figures 3–6 )

Synalpheus “ microneptunus ” in Hultgren & Duffy (2011)

Type material. Holotype: Ovigerous female, CL 2.73 mm ( USNM 1154070, original VIMS 08BR7001), Cement Factory (13°17'21.84"N, 59°39'27.72"W), from Xestospongia proxima , 21.X.2008. Paratypes: 1 non-ovigerous individuals, CL 2.16–2.49 mm ( USNM 1154071–1154082, original VIMS 08BR7002–1 to 7002–12), same collection data as holotype.

Additional material examined. 2 non-ovigerous individuals ( VIMS 08BR5103, 5703), Brandon’s Beach, no host recorded. 8 ovigerous females, 31 non-ovigerous individuals ( VIMS 08BR3601–3, 4103–4, 5201–3, 5302–3, 5401–2), Brandon’s Beach, from X. proxima . 1 non-ovigerous individual ( VIMS 08BR6301), Breach Reef, no host recorded. 1 ovigerous female, 3 non-ovigerous individuals ( VIMS 08BR6001–2, 6101), Breach Reef, from X. proxima . 1 non-ovigerous individual ( VIMS 08BR6710), Cement Factory, no host recorded. 1 ovigerous female, 11 non-ovigerous individuals ( VIMS 08BR301, 1701), Spawnee Reef, from X. proxima . 2 ovigerous females, 8 non-ovigerous individuals ( VIMS 08BR401, 2001–2, 2302), Spawnee Reef, from Xestospongia subtriangularis . Largest ovigerous female, CL 2.86 mm, largest non-ovigerous individual, CL 2.55 mm.

Description: Body subcylindrical; carapace smooth, sparsely setose, posterior margin with distinct cardiac notch. Rostrum longer and narrower than ocular hoods ( Fig 3 ), latter dorsally convex; blunt distally, separated from rostrum by adrostral sinus. Stylocerite acute, with blunt tip reaching beyond midpoint of first segment of antennular peduncle. Basicerite with blunt projection on dorsomesial corner, with longer ventrolateral spine, latter not reaching third segment of antennular peduncle and about 3/4 length of scaphocerite. Scaphocerite with short blade ranging from vestigial to <1/4 length of distolateral spine, latter robust, acute, reaching almost to distal end of third segment of antennular peduncle; lateral margin concave. Third maxilliped ( Fig. 3 ) with distal circlet of approximately seven spines on distal segment.

Major first pereopod ( Fig. 3 ) massive, with fingers clearly shorter than half-length of palm; fixed finger slightly shorter than dactyl. Palm of chela with distodorsal protuberance tapering to acute point, curved toward dactyl. Minor first pereopod ( Fig. 4 ) with palm less than two times longer than high; fingers clearly shorter than palm; dactyl with flexor margin concave, blade-like, with three distinct distal teeth, latter subequal in length; fixed finger with flexor margin excavate, trowel-like, and with single distal tooth.Second pereopod ( Fig. 4 ) with carpus foursegmented, subequal in length to merus; chela fingers distally filiform.Third pereopod ( Fig. 5 ) slender; dactyl biunguiculate, mesial margin of flexor unguis strongly convex; propodus with row of five movable spines on flexor margin and one pair of distal movable spines flanking base of dactyl; carpus with distal movable spine on flexor margin; merus almost four times longer than wide, without movable spines. Fourth pereopod ( Fig. 5 ) similar to third, slightly weaker, with four spines on flexor margin of propodus. Fifth pereopod ( Fig. 5 ) weaker than fourth; carpus without distal spine; propodus with one spine on flexor margin and five transverse combs of stout setae on ventral face.First pleura ( Fig. 6 ) of male with posterior corner slightly produced ventrally into rounded bulge; second pleura of non-ovigerous individuals broadly rounded; third to fifth pleura of male with rounded anterior corner and slightly obtuse posterior corner.

Telson ( Fig. 6 ) with convex marginal lobe on distal margin; posterior corners adjacent to spines obtuse. Dorsal spines large, clearly removed from lateral margins. Posterior margin with six setae between two sets of spines, lateral spines half-length of mesial. Distance between distal spines 35-50% width of telson distal margin. Width of distal margin of telson 40–45% width of base of telson. Uropods ( Fig. 6 ) with three fixed teeth on distolateral margin of exopod; two of these teeth are subequal in size, one located anterior to the movable spine, the second (the lateral tooth of the diaeresis) is posterior to the movable spine. The third tooth is reduced in size and located between the larger teeth, in line with the base of the movable spine.

Color. Color in life pale, non-descript, distal portions of extremities tending towards dull yellow-orange; ovaries and embryos green.

Etymology. The species name is derived from its small size and its affinity with species of the Synalpheus paraneptunus species complex.

Variation. There is variation in the size of the scaphocerite blade: while the blade is extremely small and difficult to find in most individuals, it is more conspicuous in others, however, but never reaches 1/4 length of the lateral spine of scaphocerite.

Hosts and ecology. In Barbados, we have found S. microneptunus n. sp. commonly in sponges in the genus Xestospongia ( X. proxima and X. subtriangularis ), with only two individuals found associated with other sponges, possibly as “contaminants” that moved during field collection from adjacent or attached Xestospongia spp. (listed as no host recorded). In Barbados, S. microneptunus n. sp. appears to be a specialist in Xestospongia spp.

Distribution. The type locality is Cement Factory reef off the North-West coast of Barbados. Presently known only from Barbados.

Remarks. Anker and Tóth (2008) recently reviewed Synalpheus paraneptunus and separated five new species from S. paraneptunus sensu stricto. This complex can be distinguished from the remainder of the S. gambarelloides group by the reduced setal brush on the dactyl of the minor chela, and the excavate, trowel-shaped flexor surface of the fixed finger of the minor chela. Although clearly a member of this complex, S. microneptunus n. sp. can be distinguished from all of the other species therein by several morphological characters. The most important diagnostic character is the consistent presence of four carpal segments on the second pereopod in both juveniles and adults of the new species; compared with five segments in all other taxa in the S. paraneptunus complex. Synalpheus microneptunus n. sp. appears to be most similar to S. duffyi Anker & Tóth, 2008 and S. ríosi Anker & Tóth, 2008 in that all three species possess a blade on the scaphocerite. However, while all three species also have three teeth on the distolateral margin of the uropodal exopod, in S. microneptunus n. sp., the middle tooth is consistently reduced in size and located directly in line with the movable spine, whereas in both S. duffyi and S. riosi , the middle tooth is anterior to the moveable spine and subequal in size to the other teeth. Colonies of S. microneptunus n. sp. also appear to be consistently smaller than those of S. duffyi , often with typically fewer than 10 individuals per colony (maximum = 15) in Barbados; in contrast, S. duffyi was found in colonies of up to 81 individuals at its type locality in Isla Grande, Panama ( Anker & Tóth 2008), and typically had 50–60 individuals in Jamaica ( Macdonald et al. 2009), while S. riosi is known from only a single colony of 140 individuals from Dominica ( Anker & Tóth 2008). These differences in colony size may of course reflect the sizes of sponges occupied, but they appear nevertheless to be consistent across geographic regions. Synalpheus microneptunus n. sp. is also noticeably smaller than all other species of the S. paraneptunus complex. Finally, a new multi-locus phylogeny indicated that S. microneptunus n. sp. appears to be most closely related to S. duffyi and to another undescribed species in the S. paraneptunus complex ( Hultgren & Duffy 2011).

Figures

FIGURE 3. Synalpheus microneptunus n. sp. Holotype, ovigerous female, CL 2.72 mm (USNM 1154070, original VIMS BR 08 - 7001) from Xestospongia proxima, Cement Factory, Barbados: A, carapace, anterior region, and cephalic appendages, dorsal view; allotype, non-ovigerous individual, CL 2.44 mm (USNM 1154072, original VIMS BR 08 - 7002 - 2) from Xestospongia proxima, Cement Factory, Barbados: B, anterior carapace and cephalic appendages, dorsal view; C, chela of major first pereopod, ventral view; D, same, dorsal view; E, same, anterior region; F, third maxilliped. Scale bar = 1 mm for A, D; 1.33 mm for B, 1.5 mm for C, E; 0.4 mm for F.

FIGURE 4. Synalpheus microneptunus n. sp. Paratype, non-ovigerous individual, CL 2.44 mm (USNM 1154072, original VIMS BR 08 - 7002 - 2) from Xestospongia proxima, Cement Factory, Barbados: A, minor first pereopod; B, same, distal region of fingers; C, second pereopod, setae not drawn; D, same, distal region. Scale bar = 0.33 mm for A, 0.16 mm for B, 1 mm for C, 0.4 mm for D.

FIGURE 5. Synalpheus microneptunus n. sp. Paratype, non-ovigerous individual, CL 2.44 mm (USNM 1154072, original VIMS BR 08 - 7002 - 2) from Xestospongia proxima, Cement Factory, Barbados: A, third pereopod; B, same, distal region; C, fourth pereopod; D, same, distal region; E, fifth pereopod; F, same, distal region. Scale bar = 1 mm for A, C, E; 0.27 mm for B, D, F.

FIGURE 6. Synalpheus microneptunus n. sp. Paratype, non-ovigerous individual, CL 2.49 mm (USNM 1154071, original VIMS BR 08 - 7002 - 1) from Xestospongia proxima, Cement Factory, Barbados: A, abdomen, right side; paratype, non-ovigerous individual, CL 2.44 mm (USNM 1154072, original VIMS BR 08 - 7002 - 2) from Xestospongia proxima, Cement Factory, Barbados: B, telson, dorsal view; C, distolateral margin of left uropodal exopod, dorsal view; paratypes, non-ovigerous individual, CL 2.44 (USNM 1154073, original VIMS BR 08 - 7002 - 3) from Xestospongia proxima, Cement Factory, Barbados: D, distolateral margin of right uropodal exopod, dorsal view. Scale bar = 1 mm for A, 1.4 mm for B, 0.25 mm for C, D.