Tanidromites longinosa, Starzyk, 2016

Starzyk, N, 2016, Three new species of the genus Tanidromites (Decapoda: Brachyura: Tanidromitidae) from the Late Jurassic (Oxfordian) of Poland, Palaeontologia Electronica 19 (3), pp. 1-14 : 5-7

Tanidromites longinosa n. sp.

Figures 2 , 3

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Diagnosis. Small sized species (max. carapace length 8.28 mm). Carapace is widest across hepatic region. Outer orbital spine is absent. There are small spines on lateral border between augenrest and cervical groove. AtC distance (as defined in Figure 1 ) is short (0.21-0.25 of RtC). Rostrum is very long (R/RtC>0.3) with a blunt tip. Augenrest is as long as wide, with short spines on the upper and suborbital margin. Posterior section of orbital margin smoothly changes into lateral bor- der of the carapace. Cervical pits are rounded. Hepatic pits and hepatic tubercles are absent.

Comparison. The species is most similar to Tanidromites sculpta. It is also a small sized species; as T. sculpta, T. etalloni, and T. alexandrae . The length of the biggest specimen of T. longinosa n.sp. is 8.28 mm. The augenrest is flattened and as long as wide, as in T. etalloni and T. sculpta. The difference is visible in the posterior section of the orbital margin, which is distinct in T. sculpta and T. etalloni and smoothly changes into the lateral bor- der of the carapace in T. longinosa . n. sp. The rostrum of T. longinosa n. sp. is longer than in other species of the genus, the ratio of length from the tip of the rostrum to the anterior groove, and of the length from the tip of the rostrum to the cervical groove is larger than 0.3. Another difference is visible in the convexity of the carapace, which in T. longinosa n. sp. is slightly convex, while in T. sculpta and T. alexandrae it is flat and in other species is highly convex.

Etymology. The trivial name refers to the long rostrum of this species. It comes from the Latin words longus – long, nasus – nose.

Material

Type material. Holotype: I-F / MP/ 6307 /1599/12; type locality: Ogrodzieniec; age: Early-Middle Oxfordian.

Paratypes. I-F / MP/ 6239 /1588/11; locality: Ogrodzieniec; I-F / MP/ 1788 /1517/08; I-F / MP/ 2725 / 1530/08; locality: Bzów; age: Middle Oxfordian. Coll.: I.K. R. Borek.

Additional material. Specimens from Bzów: I-F / MP / 1849 /1517/08; I-F / MP / 1908 /1517/08; I-F / MP / 2053 /1517/08; I-F / MP / 2054 /1517/08. Specimens from Kroczyce: I-F / MP / 6238 /1588/11, I-F / MP / 6302 /1599/12. Specimens from Ogrodzieniec: I-F / MP / 474 /1497/08; I-F / MP / 530 /1497/08; I-F / MP / 642 / 1502/08; I-F / MP / 6235 /1588/11; I-F / MP / 6242 /1588/ 11. Coll.: I.K. R. Borek.

Total number of specimens. 34.

Full list of the specimens and localities is presented in the Appendix.

Dimensions ( Table 1). The length of the biggest specimen is 8.28 mm and the maximum width across the epibranchial region is 6.42 mm.

Description. The carapace is slightly convex ( Figure 3.7 ), widest across the hepatic region. Lateral borders are parallel or narrowing posteriorly, smooth without the outer orbital spine, except the border between the end of the augenrest and the cervical groove (AtC) – there are several small spines there ( Figure 3.4 ). The AtC distance is short (0.21-0.25 of the RtC distance) ( Figures 2 , 3.1, 3.2, 3.8 ).

The rostrum is long (R/RtC>0.3), downturned; the axial groove does not reach the blunt tip ( Figure 3.1, 3.8 ).

The augenrest is as long as wide. There are short spines on the upper and suborbital margin ( Figures 2 , 3.3, 3.4 ). The suborbital margin slightly projects beyond the upper orbital margin. The posterior part of the orbital margin smoothly changes into the lateral border of the carapace ( Figure 3.5, 3.6 ). This character is visible on every specimen with an augenrest preserved, which means it is not caused by preservation but it is a repetitive character.

Mesogastric region is distinctly bordered by grooves in the anterior and posterior part, weaker in the middle. Anterior (narrow) part of the region is a little shorter than the posterior (wide) part. Cervical pits are rounded ( Figures 2 , 3.1 ). There is an incision in the posterior margin of the mesogastric region. Mesogastric scars (corresponding to attachments of the gastric muscles) are elongated, weakly developed, positioned on both sides of this incision, and extend across the entire posterior border of the mesogastric region. Proximally they are accompanied by a parallel pair of smaller scars which are very faint.

Protogastric and hepatic regions are not differentiated. Hepatic pits and tubercles are absent.

Epigastric regions are elongated. There is a small tubercle on the urogastric region. Cardiac region is weakly divided; there are two tubercles in the anterior part and one in the posterior. Branchial region is much longer and almost as convex as the epibranchial one.

The cervical groove is deep. The branchio-cardiac groove is deep in lateral parts (parallel to the cervical groove); middle part of this groove disappears ( Figure 3.1, 3.2 ).

There is no ornamentation on the carapace. Internal mold and the cuticle are smooth ( Figure 3.1, 3.2, 3.8 ). There is no well-preserved cuticle on the augenrest and no spines on the upper and suborbital margin covered with the cuticle.

Figures

FIGURE 1. Analyzed measurements and a groundplan of the morphological structures in the species of Tanidromites on the example of T. alexandrae (after Starzyk, 2015a, figure 1). Further explanation in text (ag – anterior groove, hp – hepatic pit, ht – hepatic tubercle, cp – cervical pit). Abbreviations for the measurements are in the Material and Methods.

FIGURE 2. Anterior part of the carapace and the augenrest in Tanidromites spp. The area of augenrest is shaded.

FIGURE 3. Tanidromites longinosa n. sp. 1, paratype (#6239, Ogrodzieniec) (cp – cervical pit); 2, specimen (#6242, Ogrodzieniec); 3, 4, upper orbital margin (3 – #2725 Bzów; 4 – #1908, Bzów); 5, 6, augenrest, anterior view (5 – #6302, Kroczyce; 6 – #1908, Bzów); 7, lateral view (#6238, Kroczyce); 8, holotype (#6307, Ogrodzieniec). Scale bars equal 1 mm.